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LT1579 300mA Dual Input Smart Battery Backup Regulator
FEATURES
s s s s s s s s s s s s s
DESCRIPTION
The LT(R)1579 is a dual input, single output, low dropout regulator. This device is designed to provide an uninterruptible output voltage from two independent input voltage sources on a priority basis. All of the circuitry needed to switch smoothly and automatically between inputs is incorporated. The LT1579 can supply 300mA of output current from either input at a dropout voltage of 0.4V. Quiescent current is 50A, dropping to 7A in shutdown. Two comparators are included to monitor input voltage status. Two additional status flags indicate which input is supplying power and provide an early warning against loss of output regulation when both inputs are low. A secondary select pin is provided so that the user can force the device to switch from the primary input to the secondary input. Internal protection circuitry includes reverse-battery protection, current limiting, thermal limiting and reversecurrent protection. The device is available in fixed output voltages of 3V, 3.3V and 5V, and as an adjustable device with a 1.5V reference voltage. The LT1579 regulators are available in narrow 16-lead SO and 16-lead SSOP packages with all features, and in SO-8 with limited features.
Maintains Output Regulation with Dual Inputs Dropout Voltage: 0.4V Output Current: 300mA 50A Quiescent Current No Protection Diodes Needed Two Low-Battery Comparators Status Flags Aid Power Management Adjustable Output from 1.5V to 20V Fixed Output Voltages: 3V, 3.3V and 5V 7A Quiescent Current in Shutdown Reverse-Battery Protection Reverse Current Protection Remove, Recharge and Replace Batteries Without Daisy-Chained Control Outputs Loss of Regulation
APPLICATIONS
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Dual Battery Systems Battery Backup Systems Automatic Power Management for Battery-Operated Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
5V Dual Battery Supply
OUTPUT VOLTAGE (V) INPUT VOLTAGE (V)
Automatic Input Switching
+
5V 300mA 4.7F
12 10 8 6 4 2 0 5.05 5.00 4.95 0 2 4 6 8 10 12 14 16 18 20 TIME (ms)
1578 TA02
+
1F
IN1 2.7M LBI1 1M LT1579-5
OUT
VIN1
IIN1
SS
+
1F
IN2 2.7M LBI2 1M
SHDN LBO1 LB02 BACKUP DROPOUT BIASCOMP GND 0.01F
1579 TA01
TO POWER MANAGEMENT
U
U
U
SWITCHOVER POINT
VIN2 = 10V ILOAD = 50mA 80 IIN2 60 40 20 0
INPUT CURRENT (mA)
1
LT1579 ABSOLUTE MAXIMUM RATINGS
Power Input Pin Voltage ...................................... 20V* Output Pin Voltage Fixed Devices............................................. 6.5V, - 6V Adjustable Device ............................................ 20V* Output Pin Reverse Current .................................... 5mA ADJ Pin Voltage .............................................. 2V, - 0.6V ADJ Pin Current ...................................................... 5mA Control Input Pin Voltage ............................ 6.5V, - 0.6V Control Input Pin Current ....................................... 5mA BIASCOMP Pin Voltage ............................... 6.5V, - 0.6V BIASCOMP Pin Current .......................................... 5mA Logic Flag Output Voltage ............................ 6.5V, - 0.6V Logic Flag Input Current ......................................... 5mA Output Short-Circuit Duration .......................... Indefinite Storage Temperature Range ................. - 65C to 150C Operating Junction Temperature Range .... 0C to 125C Lead Temperature (Soldering, 10 sec).................. 300C
*For applications requiring input voltage ratings greater than 20V, consult factory.
PACKAGE/ORDER I FOR ATIO
TOP VIEW GND 1 POWER INPUTS VIN1 2 VIN2 3 SS 4 CONTROL SHDN 5 INPUTS LBI1 6 LBI2 7 GND 8 16 GND 15 OUT 14 BACKUP 13 DROPOUT 12 LBO1 11 LBO2 10 BIASCOMP 9 GND LOGIC OUTPUTS
ORDER PART NUMBER LT1579CGN-3 LT1579CGN-3.3 LT1579CGN-5 LT1579CS-3 LT1579CS-3.3 LT1579CS-5 GN PART MARKING 15793 157933 15795 ORDER PART NUMBER
8 7 6 5 OUT BACKUP DROPOUT BIASCOMP LOGIC OUTPUTS
GN PACKAGE S PACKAGE 16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SO
SEE APPLICATION INFORMATION SECTION TJMAX = 125C, JA = 95C/W (GN) TJMAX = 125C, JA = 68C/W (S)
TOP VIEW POWER INPUTS VIN1 1 VIN2 2
CONTROL SHDN 3 INPUT GND 4
LT1579CS8-3 LT1579CS8-3.3 LT1579CS8-5 S8 PART MARKING 15793 157933 15795
S8 PACKAGE 8-LEAD PLASTIC SO
SEE APPLICATION INFORMATION SECTION TJMAX = 125C, JA = 90C/W
Consult factory for Industrial and Military grade parts.
2
U
U
W
WW U
W
TOP VIEW GND 1 POWER INPUTS VIN1 2 VIN2 3 SS 4 CONTROL INPUTS SHDN 5 LBI1 6 LBI2 7 GND 8 16 GND 15 OUT 14 ADJ 13 BACKUP 12 LBO1 11 LBO2 10 BIASCOMP 9 GND LOGIC OUTPUTS
ORDER PART NUMBER LT1579CGN LT1579CS
GN PACKAGE S PACKAGE 16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SO
SEE APPLICATION INFORMATION SECTION TJMAX = 125C, JA = 95C/W (GN) TJMAX = 125C, JA = 68C/W (S)
GN PART MARKING 1579
TOP VIEW POWER INPUTS VIN1 1 VIN2 2 8 7 6 5 OUT ADJ LOGIC BACKUP OUTPUT BIASCOMP
ORDER PART NUMBER LT1579CS8
CONTROL SHDN 3 INPUT GND 4
S8 PACKAGE 8-LEAD PLASTIC SO
S8 PART MARKING 1579
SEE APPLICATION INFORMATION SECTION TJMAX = 125C, JA = 90C/W
LT1579
ELECTRICAL CHARACTERISTICS
PARAMETER Regulated Output Voltage (Note 1) CONDITIONS LT1579-3 VIN1 = VIN2 = 3.5V, ILOAD = 1mA, TJ = 25C 4V < VIN1 < 20V, 4V < VIN2 < 20V, 1mA < ILOAD < 300mA
q q q q q q q q q
MIN 2.950 2.900 3.250 3.200 4.925 4.850 1.475 1.450
TYP 3.000 3.000 3.300 3.300 5.000 5.000 1.500 1.500 1.5 1.5 1.5 1.5 3 3
MAX 3.050 3.100 3.350 3.400 5.075 5.150 1.525 1.550 10 10 10 10 12 25 12 25 15 35 10 20 0.28 0.39 0.35 0.45 0.47 0.60 0.60 0.75 100 400 200 500 1.5 4 12 7.0 7.0 2.8 5 12 12
UNITS V V V V V V V V mV mV mV mV mV mV mV mV mV mV mV mV V V V V V V V V A A A A mA mA mA A A V V A A A A
LT1579-3.3 VIN1 = VIN2 = 3.8V, ILOAD = 1mA, TJ = 25C 4.3V < VIN1 < 20V, 4.3V < VIN2 < 20V, 1mA < ILOAD < 300mA LT1579-5 Adjust Pin Voltage Line Regulation LT1579 LT1579-3 VIN1 = VIN2 = 5.5V, ILOAD = 1mA, TJ = 25C 6V < VIN1 < 20V, 6V < VIN2 < 20V, 1mA < ILOAD < 300mA VIN1 = VIN2 = 3.2V, ILOAD = 1mA, TJ = 25C (Note 2) 3.7V < VIN1 < 20V, 3.7V < VIN2 < 20V, 1mA < ILOAD < 300mA VIN1 = 3.5V to 20V, VIN2 = 3.5V to 20V, ILOAD = 1mA
LT1579-3.3 VIN1 = 3.8V to 20V, VIN2 = 3.8V to 20V, ILOAD = 1mA LT1579-5 VIN1 = 5.5V to 20V, VIN2 = 5.5V to 20V, ILOAD = 1mA LT1579 Load Regulation LT1579-3 VIN1 = 3.2V to 20V, VIN2 = 3.2V to 20V, ILOAD = 1mA (Note 2) VIN1 = VIN2 = 4V, ILOAD = 1mA to 300mA, TJ = 25C VIN1 = VIN2 = 4V, ILOAD = 1mA to 300mA
LT1579-3.3 VIN1 = VIN2 = 4.3V, ILOAD = 1mA to 300mA, TJ = 25C VIN1 = VIN2 = 4.3V, ILOAD = 1mA to 300mA LT1579-5 LT1579 Dropout Voltage (Notes 3, 4) VIN1 = VIN2 = VOUT(NOMINAL) VIN1 = VIN2 = 6V, ILOAD = 1mA to 300mA, TJ = 25C VIN1 = VIN2 = 6V, ILOAD = 1mA to 300mA VIN1 = VIN2 = 3.7V, ILOAD = 1mA to 300mA, TJ = 25C (Note 2) VIN1 = VIN2 = 3.7V, ILOAD = 1mA to 300mA
q
5
q
2
q
ILOAD = 10mA, TJ = 25C ILOAD = 10mA ILOAD = 50mA, TJ = 25C ILOAD = 50mA ILOAD = 150mA, TJ = 25C ILOAD = 150mA ILOAD = 300mA, TJ = 25C ILOAD = 300mA
0.10
q
0.18
q
0.25
q
0.34
q
Ground Pin Current (Note 5) VIN1 = VIN2 = VOUT(NOMINAL) + 1V
ILOAD = 0mA, TJ = 25C ILOAD = 0mA ILOAD = 1mA, TJ = 25C ILOAD = 1mA ILOAD = 50mA ILOAD = 150mA ILOAD = 300mA
50
q
100
q q q q q q q q q q q
0.7 2 5.8 3.3 2.0 0.25 0.9 0.75 1.3 5 5 3
Standby Current (Note 6) ILOAD = 0mA Shutdown Threshold Shutdown Pin Current (Note 7) Quiescent Current in Shutdown (Note 9)
IVIN2: VIN1 = 20V, VIN2 = VOUT(NOMINAL) + 0.5V, VSS = Open (HI) IVIN1: VIN1 = VOUT(NOMINAL) + 0.5V, VIN2 = 20V, VSS = 0V VOUT = Off to On VOUT = On to Off VSHDN = 0V IVIN1: VIN1 = 20V, VIN2 = 6V, VSHDN = 0V IVIN2: VIN1 = 6V, VIN2 = 20V, VSHDN = 0V ISRC: VIN1 = VIN2 = 20V, VSHDN = 0V
3
LT1579
ELECTRICAL CHARACTERISTICS
PARAMETER Adjust Pin Bias Current (Notes 2, 7) Minimum Input Voltage (Note 8) Minimum Load Current Secondary Select Threshold Secondary Select Pin Current (Note 7) Low-Battery Trip Threshold Low-Battery Comparator Hysteresis Low-Battery Comparator Bias Current (Notes 7, 10) Logic Flag Output Voltage Ripple Rejection Current Limit Input Reverse Leakage Current Reverse Output Current CONDITIONS TJ = 25C ILOAD = 0mA LT1579 VIN1 = VIN2 = 3.2V
q q q q q q q
MIN
TYP 6 2.7
MAX 30 3.2 3
UNITS nA V A V V A V mV nA V V dB mA
Switch from VIN2 to VIN1 Switch from VIN1 to VIN2 VSS = 0V VIN1 = VIN2 = VOUT(NOMINAL) + 1V, High-to-Low Transition VIN1 = VIN2 = 6V, ILBO = 20A (Note 11) VIN1 = VIN2 = 6V, VLBI = 1.4V, TJ = 25C ISINK = 20A ISINK = 5mA VIN1 - VOUT = VIN2 - VOUT = 1.2V (Avg), VRIPPLE = 0.5VP-P fRIPPLE = 120Hz, ILOAD = 150mA VIN1 = VIN2 = VOUT(NOMINAL) + 1V, VOUT = - 0.1V VIN1 = VIN2 = -20V, VOUT = 0V LT1579-3 VOUT = 3V, VIN1 = VIN2 = 0V LT1579-3.3 VOUT = 3.3V, VIN1 = VIN2 = 0V LT1579-5 VOUT = 5V, VIN1 = VIN2 = 0V
0.25
1.2 0.75 1
2.8 1.5 1.550 30 5 0.45 1.3
1.440
1.500 18 2
q q
0.17 0.97 55 70 400
q q
320
1.0 3 3 3 12 12 12
mA A A A
The q denotes specifications which apply over the full operating temperature range. Note 1: Operating conditions are limited by maximum junction temperature. The regulated output voltage specification will not apply for all possible combinations of input voltage and output current. When operating at maximum input voltage, output current must be limited. When operating at maximum output current, the input voltage range must be limited. Note 2: The LT1579 (adjustable version) is tested and specified with the adjust pin connected to the output pin and a 3A DC load. Note 3: Dropout voltage is the minimum input-to-output voltage differential required to maintain regulation at the specified output current. In dropout, the output voltage will be equal to VIN - VDROPOUT. Note 4: To meet the requirements for minimum input voltage, the LT1579 (adjustable version) is connected with an external resistor divider for a 3.3V output voltage (see curve of Minimum Input Voltage vs Temperature in the Typical Performance Characteristics). For this configuration, VOUT(NOMINAL) = 3.3V. Note 5: Ground pin current will rise at TJ > 75C. This is due to internal circuitry designed to compensate for leakage currents in the output transistor at high temperatures. This allows quiescent current to be minimized at lower temperatures, yet maintain output regulation at high temperatures with light loads. See the curve of Quiescent Current vs Temperature in the Typical Performance Characteristics.
Note 6: Standby current is the minimum quiescent current for a given input while the other input supplies the load and bias currents. Note 7: Current flow is out of the pin. Note 8: Minimum input voltage is the voltage required on either input to maintain the 1.5V reference for the error amplifier and low-battery comparators. Note 9: Total quiescent current in shutdown will be approximately equal to IVIN1 + IVIN2 - ISRC. Both IVIN1 and IVIN2 are specified for worst-case conditions. IVIN1 is specified under the condition that VIN1 > VIN2 and IVIN2 is specified under the condition that VIN2 > VIN1. ISRC is drawn from the highest input voltage only. For normal operating conditions, the quiescent current of the input with the lowest input voltage will be equal to the specified quiescent current minus ISRC. For example, if VIN1 = 20V, VIN2 = 6V then IVIN1 = 5A and IVIN2 = 5A - 3A = 2A. Note 10: The specification applies to both inputs independently (LBI1, LBI2). Note 11: Low-battery comparator hysteresis will change as a function of current in the low-battery comparator output. See the curve of Low-Battery Comparator Hysteresis vs Sink Current in the Typical Performance Characteristics.
4
LT1579 TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
0.8 0.7 = TEST POINTS TJ 125C
DROPOUT VOLTAGE (V)
DROPOUT VOLTAGE (V)
0.6 0.5 TJ = 25C 0.4 0.3 0.2 0.1 0 0 50 100 150 200 250 OUTPUT CURRENT (mA) 300
0.5 0.4 0.3 0.2 0.1
QUIESCENT CURRENT (A)
Quiescent Current in Shutdown
7 6 VIN1 = 20V VIN2 = 6V VSHDN = 0V
3.08 3.06
QUIESCENT CURRENT (A)
5 4 IVIN1 3 2 1 0 - 50 - 25 IVIN2
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
50 25 75 0 TEMPERATURE (C)
LT1579-5 Output Voltage
5.12 ILOAD = 1mA 5.09
ADJUST PIN VOLTAGE (V)
OUTPUT VOLTAGE (V)
INPUT CURRENT (A)
5.06 5.03 5.00 4.97 4.94 4.91 4.88 - 50 - 25 0 50 75 25 TEMPERATURE (C) 100 125
UW
1579 G35
Dropout Voltage
0.7 0.6
100
Quiescent Current
A
90 80 70 60 50 40 30 20 10 STANDBY QUIESCENT CURRENT 50 25 0 75 TEMPERATURE (C) 100 125 OPERATING QUIESCENT CURRENT VIN = 6V RL = (FIXED) RL = 500k (ADJUSTABLE)
A: ILOAD = 300mA B: ILOAD = 150mA C: ILOAD = 100mA D: ILOAD = 50mA E: ILOAD = 10mA F: ILOAD = 1mA
B C D E
F 0 - 50 - 25 50 25 75 0 TEMPERATURE (C) 100 125
0 - 50 -25
1579 G01
1579 G02
LT1579-3 Output Voltage
3.38
ILOAD = 1mA
LT1579-3.3 Output Voltage
ILOAD = 1mA 3.36 3.34 3.32 3.30 2.28 2.26 2.24
3.04 3.02 3.00 2.98 2.96 2.94
100
125
2.92 - 50 - 25
0
75 50 25 TEMPERATURE (C)
100
125
2.22 - 50 - 25
0
50 75 25 TEMPERATURE (C)
100
125
1579 G36
1579 G03
1579 G04
Adjust Pin Voltage
1.54 ILOAD = 1mA 1.53 1.52 1.51 1.50 1.49 1.48 1.47 1.46 - 50 - 25 0 50 75 25 TEMPERATURE (C) 100 125
Input Current
60 50 40 30 20 10 0 -0.2 -0.1 0 IIN2 IIN1 VOUT = 5V VIN2 = 6V ILOAD = 0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 VIN1 - VOUT (V)
1579 G07
1579 G05
1579 G05
5
LT1579 TYPICAL PERFORMANCE CHARACTERISTICS
Input and Ground Pin Current
1.2 1.0 IIN2 IIN1 VOUT = 5V VIN2 = 6V ILOAD = 1mA 300 250 200 150 IGND 100 50 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 VIN1 - VOUT (V)
1579 G08
INPUT CURRENT (mA)
0.8 0.6 0.4 0.2 0 -0.2 -0.1 0
INPUT CURRENT (mA)
Input and Ground Pin Current
60 IIN2 50 IIN1 1.0 0.8 VOUT = 5V VIN2 = 6V ILOAD = 50mA 0.6 0.4 0.2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 VIN1 - VOUT (V)
1579 G10
INPUT CURRENT (mA)
40 30 20 10 0 -0.2 -0.1 0
INPUT CURRENT (mA)
Input and Ground Pin Current
160 140 IIN2 IIN1 4.0 3.5
350 300
INPUT CURRENT (mA)
INPUT CURRENT (mA)
120 100 80 60 40 20 0 -0.2 -0.1 0 IGND VOUT = 5V VIN2 = 6V ILOAD = 150mA
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 VIN1 - VOUT (V)
1579 G12
6
UW
IGND
Input and Ground Pin Current
12 IIN2 10 8 6 4 2 0 -0.2 -0.1 0 IGND IIN1 VOUT = 5V VIN2 = 6V ILOAD = 10mA 500 400 300 200 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 VIN1 - VOUT (V)
1579 G09
600
GROUND PIN CURRENT (A) GROUND PIN CURRENT (mA) GROUND PIN CURRENT (mA)
GROUND PIN CURRENT (A)
Input and Ground Pin Current
1.2 120 100 80 60 40 20 0 -0.2 -0.1 0 IIN2 IIN1 VOUT = 5V VIN2 = 6V ILOAD = 100mA IGND 3.0 2.5 2.0 1.5 1.0 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 VIN1 - VOUT (V)
1579 G11
GROUND PIN CURRENT (mA)
Input and Ground Pin Current
14 IIN2 IIN1 12
GROUND PIN CURRENT (mA)
3.0 2.5 2.0 1.5 1.0 0.5
250 200 150 100 50 0 -0.2 -0.1 0 VOUT = 5V VIN2 = 6V ILOAD = 300mA IGND
10 8 6 4 2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 VIN1 - VOUT (V)
1579 G13
LT1579 TYPICAL PERFORMANCE CHARACTERISTICS
Ground Pin Current
8 7
VIN1 = VIN2 = VOUT(NOMINAL) + 1V
SHUTDOWN PIN THRESHOLD (V)
MINIMUM INPUT VOLTAGE (V)
GROUND PIN CURRENT (mA)
6 5 4 3 2 1 0 0 50 200 250 150 OUTPUT CURRENT (mA) 100 300
1579 G37
Shutdown Pin Current
2.5
SECONDARY SELECT PIN THRESHOLD (V)
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
SECONDARY SELECT PIN THRESHOLD (V)
VSHDN = 0V
SHUTDOWN PIN CURRENT (A)
2.0
1.5
1.0
0.5
0 - 50 - 25
50 0 75 25 TEMPERATURE (C)
Secondary Select Pin Current
1.0
SECONDARY SELECT PIN CURRENT (A)
LOGIC FLAG OUTPUT VOLTAGE (V)
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
VSS = 0V
LOGIC FLAG OUTPUT VOLTAGE (V)
0 - 50 -25
50 25 0 75 TEMPERATURE (C)
UW
100
1579 G16
Minimum Input Voltage
3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 - 50 -25 50 25 0 75 TEMPERATURE (C) 100 125 0.8 1.0
Shutdown Pin Threshold
ILOAD = 1mA
0.6
0.4
0.2
0 - 50 - 25
50 0 75 25 TEMPERATURE (C)
100
125
1579 G14
1579 G15
Secondary Select Threshold (Switch to VIN2)
2.0 ILOAD = 1mA 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
Secondary Select Threshold (Switch to VIN1)
ILOAD = 300mA
ILOAD = 1mA
125
0 - 50 -25
50 25 0 75 TEMPERATURE (C)
100
125
0 - 50 -25
50 25 0 75 TEMPERATURE (C)
100
125
1579 G17
1579 G18
Logic Flag Output Voltage (Output Low)
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
1.2 1.0
Logic Flag Output Voltage (Output Low)
ISINK = 5mA 0.8 0.6 0.4 0.2 0 - 50 - 25 ISINK = 20A
100
125
0 1A
10A 100A 1mA LOGIC FLAG SINK CURRENT
10mA
1579 G20
50 25 75 0 TEMPERATURE (C)
100
125
1579 G19
1579 G21
7
LT1579 TYPICAL PERFORMANCE CHARACTERISTICS
Logic Flag Input Current (Output High)
25 25
CONTROL PIN INPUT CURRENT (mA)
LOGIC FLAG INPUT CURRENT (mA)
20
20
COMPARATOR HYSTERESIS (mV)
15
10
5
0 0 1 7 3 2 5 6 4 LOGIC FLAG VOLTAGE (V) 8 9
Low-Battery Comparator Hysteresis
25 ILBO(SINK) = 50A
20
REVERSE OUTPUT CURRENT (A)
REVERSE OUTPUT CURRENT (A)
COMPARATOR HYSTERESIS (mV)
15
10
5
0 - 50 - 25
50 0 75 25 TEMPERATURE (C)
Adjust Pin Input Current
1.0 ADJUST PIN INPUT CURRENT (mA) 0.9 0.8
CURRENT LIMIT (A)
TJ = 25C VIN1 = VIN2 = 0V
0.4 0.3 0.2 0.1 0
0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 ADJUST PIN VOLTAGE (V)
1579 G28
CURRENT LIMIT (A)
0.7
8
UW
1579 G22
Control Pin Input Current
20
Low-Battery Comparator Hysteresis
15
15
10
10
5
5
0 0 1 7 3 2 5 6 4 CONTROL PIN VOLTAGE (V) 8 9
0
0
10
30 40 20 ILBO SINK CURRENT (A)
50
1579 G24
1579 G23
Reverse Output Current
25
20
Reverse Output Current
18 16 14 12 10 8 6 4 2 VIN1 = VIN2 = 0V VOUT = 3V (LT1579-3) VOUT = 3.3V (LT1579-3.3) VOUT = 5V (LT1579-5)
20
TJ = 25C VIN1 = VIN2 = 0V CURRENT FLOWS INTO OUTPUT PIN
15
10
LT1579-3.3 LT1579-3
5 LT1579-5
100
125
0 0 1 2 7 3 5 6 4 OUTPUT VOLTAGE (V) 8 9
0 - 50 -25
50 25 0 75 TEMPERATURE (C)
100
125
1579 G25
1579 G26
1579 G27
Current Limit
0.6 0.5 VOUT = 0V 0.7 0.6 0.5 0.4
Current Limit
VIN1 = VIN2 = VOUT(NOMINAL) + 1V VOUT = - 0.1V TYPICAL
GUARANTEED 0.3 0.2 0.1 0 - 50 - 25
0
1
4 3 5 2 INPUT VOLTAGE (V)
6
7
50 25 75 0 TEMPERATURE (C)
100
125
1579 G29
1579 G38
LT1579 TYPICAL PERFORMANCE CHARACTERISTICS
Ripple Rejection
100 90 80 ILOAD = 150mA VIN = 6V + 50mVRMS RIPPLE
LOAD REGULATION (mV)
RIPPLE REJECTION (dB)
70 60 50 40 30 20 10 0 10 100
COUT = 47F SOLID TANTALUM
COUT = 4.7F SOLID TANTALUM
1k 10k FREQUENCY (Hz)
LT1579-5 Transient Response
OUTPUT VOLTAGE DEVIATION (mV) OUTPUT VOLTAGE DEVIATION (mV)
100 50 0 - 50 -100 100 75 50 25 0 0 50 100 150 200 250 300 350 400 450 500 TIME (s)
1579 G33
VIN = 6V CIN = 1F CERAMIC COUT = 4.7F TANTALUM
LOAD CURRENT (mA)
LOAD CURRENT (mA)
PIN FUNCTIONS
VIN1: The primary power source is connected to VIN1. A bypass capacitor is required on this pin if the device is more than six inches away from the main input filter capacitor. In general, the output impedance of a battery rises with frequency, so it is advisable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 1F to 10F is sufficient. VIN2: The secondary power source is connected to VIN2. A bypass capacitor is required on this pin if the device is more than six inches away from the main input filter capacitor. In general, the output impedance of a battery rises with frequency, so it is advisable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 1F to 10F is sufficient. OUT: The output supplies power to the load. A minimum output capacitor of 4.7F is required to prevent oscillations. Larger output capacitors will be required for applications with large transient loads to limit peak voltage transients. ADJ: For the adjustable LT1579, this is the input to the error amplifier. This pin is internally clamped to 7V and - 0.6V (one VBE). It has a bias current of 6nA which flows
UW
100k
1579 G30
Load Regulation
0 LT1579 -2 -4 -6 -8 -10 -12 -14 1M -16 - 50 - 25 0 50 75 25 TEMPERATURE (C) 100 125 LT1579-3.3 VOUT 50mV/DIV LT1579-5 ILOAD = 1mA TO 300mA LT1579-3 VIN1 5V 6V
LT1579-5 "Hot" Plugging and Unplugging Transient Response
UNPLUG VIN1
REPLACE VIN1
1579 G40
LT1579-5 Transient Response
100 50 0 - 50 -100 VIN = 6V CIN = 1F CERAMIC COUT = 22F TANTALUM
300 200 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1,0 TIME (ms)
1579 G34
U
U
U
9
LT1579
PIN FUNCTIONS
out of the pin (see curve of Adjust Pin Bias Current vs Temperature in the Typical Performance Characteristics). A DC load of 3A is needed on the output of the adjustable part to maintain regulation. The adjust pin voltage is 1.5V referenced to ground and the output voltage range is 1.5V to 20V. SHDN: The shutdown pin is used to put the LT1579 into a low power shutdown state. All functions are disabled if the shutdown pin is pulled low. The output will be off, all logic outputs will be high impedance and the voltage comparators will be off when the shutdown pin is pulled low. The shutdown pin is internally clamped to 7V and - 0.6V (one VBE), allowing the shutdown pin to be driven either by 5V logic or open collector logic with a pull-up resistor. The pull-up resistor is only required to supply the pull-up current of the open collector gate, normally several microamperes. If unused, the shutdown pin can be left open circuit. The device is active if the shutdown pin is not connected. SS: The secondary select pin forces the LT1579 to switch power draw to the secondary input (VIN2). This pin is active low. The current drawn out of VIN1 is reduced to 3A when this pin is pulled low. The secondary select pin is internally clamped to 7V and - 0.6V (one VBE), allowing the pin to be driven directly by either 5V logic or open collector logic with a pull-up resistor. The pull-up resistor is required only to supply the leakage current of the open collector gate, normally several microamperes. If secondary select is not used, it can be left open circuit. The LT1579 draws power from the primary first if the secondary select pin is not connected. BACKUP: The backup flag is an open collector output which pulls low when the LT1579 starts drawing power from the secondary input (VIN2). The BACKUP output voltage is 1V when sinking 5mA, dropping to under 200mV at 20A (see curve of Logic Flag Voltage vs Current in the Typical Performance Characteristics). This makes the BACKUP pin equally useful in driving both bipolar and CMOS logic inputs with the addition of an external pull-up resistor. It is also capable of driving higher current devices, such as LEDs. This pin is internally clamped to 7V and - 0.6V (one VBE). If unused, this pin can be left open circuit. Device operation is unaffected if this pin is not connected. DROPOUT: The dropout flag is an open collector output which pulls low when both input voltages drop sufficiently for the LT1579 to enter the dropout region. This signals that the output is beginning to go unregulated. The DROPOUT output voltage is 1V when sinking 5mA, dropping to under 200mV at 20A (see curve of Logic Flag Voltage vs Current in the Typical Performance Characteristics). This makes the DROPOUT pin equally useful in driving both bipolar and CMOS logic inputs with the addition of an external pull-up resistor. It is also capable of driving higher current devices, such as LEDs. This pin is internally clamped to 7V and - 0.6V (one VBE). If unused, this pin can be left open circuit. Device operation is unaffected if this pin is not connected. BIASCOMP: This is a compensation point for the internal bias circuitry. It must be bypassed with a 0.01F capacitor for stability during the switch from VIN1 to VIN2. LBI1: This is the noninvering input to low-battery comparator LB1 which is used to detect a low input/battery condition. The inverting input is connected to a 1.5V reference. The low-battery comparator input has 18mV of hysteresis with more than 20A of sink current on the output (see Applications Information section). This pin is internally clamped to 7V and - 0.6 (one VBE). If not used, this pin can be left open circuit, with no effect on normal circuit operation. If unconnected, the pin will float to 1.5V and the logic output of LB1 will be high impedance. LBI2: This is the noninverting input to low-battery comparator LB2 which is used to detect a low input/battery condition. The inverting input is connected to a 1.5V reference. The low-battery comparator input has 18mV of hysteresis with more than 20A of sink current on the output (see Applications Information section). This pin is internally clamped to 7V and - 0.6V (one VBE). If not used, this pin can be left open circuit, with no effect on normal circuit operation. If unconnected, the pin will float to 1.5V and the logic output of LB2 will be high impedance.
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LT1579
PIN FUNCTIONS
LBO1: This is the open collector output of the low-battery comparator LB1. This output pulls low when the comparator input drops below the threshold voltage. The LBO1 output voltage is 1V when sinking 5mA, dropping to under 200mV at 20A (see curve of Logic Flag Voltage vs Current in the Typical Performance Characteristics). This makes the LBO1 pin equally useful in driving both bipolar and CMOS logic inputs with the addition of an external pull-up resistor. It is also capable of driving higher current devices, such as LEDs. This pin is internally clamped to 7V and - 0.6V (one VBE). If unused, this pin can be left open circuit. Device operation is unaffected if this pin is not connected. LBO2: This is the open collector output of the low-battery comparator LB2. This output pulls low when the comparator input drops below the threshold voltage. The LBO2 output voltage is 1V when sinking 5mA, dropping to under 200mV at 20A (see curve of Logic Flag Voltage vs Current in the Typical Performance Characteristics). This makes the LBO2 pin equally useful in driving both bipolar and CMOS logic inputs with the addition of an external pull-up resistor. It is also capable of driving higher current devices, such as LEDs. This pin is internally clamped to 7V and - 0.6V (one VBE). If unused, this pin can be left open circuit. Device operation is unaffected if this pin is not connected.
BLOCK DIAGRAM
VIN1 VIN2
SHDN
SS
BIASCOMP 1.5V REFERENCE
LBI1
LBI2
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VOUT DROPOUT DETECT BIAS CURRENT CONTROL INTERNAL RESISTOR DIVIDER FOR FIXED VOLTAGE DEVICES ONLY
-
OUTPUT DRIVER CONTROL E/A
ADJ
+
WARNING FLAGS LB1 BACKUP DROPOUT LBO1
+ - +
LB2
LBO2
-
1579 * BD
11
LT1579
APPLICATIONS INFORMATION
Device Overview The LT1579 is a dual input, single output, low dropout linear regulator. The device is designed to provide an uninterruptible output voltage from two independent input voltage sources on a priority basis. All of the circuitry needed to switch smoothly and automatically between inputs is incorporated in the device. All power supplied to the load is drawn from the primary input (VIN1) until the device senses that the primary input is failing. At this point the LT1579 smoothly switches from the primary input to the secondary input (VIN2) to maintain output regulation. The device is capable of providing 300mA from either input at a dropout voltage of 0.4V. Total quiescent current when operating from the primary input is 50A, which is 45A from the primary input, 2A from the secondary and a minimum input current of 3A which will be drawn from the higher of the two input voltages. A single error amplifier controls both output stages so regulation remains tight regardless of which input is providing power. Threshold levels for the error amplifier and low-battery detectors are set by the internal 1.5V reference. Output voltage is set by an internal resistor divider for fixed voltage parts and an external divider for adjustable parts. Internal bias circuitry powers the reference, error amplifier, output driver controls, logic flags and low-battery comparators. The LT1579 aids power management with the use of two independent low-battery comparators and two status flags. The low-battery comparators can be used to monitor the input voltage levels. The BACKUP flag signals when any power is being drawn from the secondary input and the DROPOUT flag provides indication that both input voltages are critically low and the output is unregulated. Additionally, the switch to the secondary input from the primary can be forced externally through the use of the secondary select pin (SS). This active low logic pin, when pulled below the threshold, will cause power draw to switch from the primary input to the secondary input. Current flowing in the primary input is reduced to only a few microamperes, while all power draw (load current and bias currents) switches to the secondary. The LT1579 has a low power shutdown state which shuts off all bias currents and logic functions. In shutdown, quiescent currents are 2A from the primary input, 2A from the secondary input and an additional 3A which is drawn from the higher of the two input voltages. Adjustable Operation The adjustable version of the LT1579 has an output voltage range of 1.5V to 20V. The output voltage is set by the ratio of two external resistors as shown in Figure 1. The device servos the output to maintain the voltage at the adjust pin at 1.5V. The current in R1 is then equal to 1.5V/ R1 and the current in R2 is the current in R1 minus the adjust pin bias current. The adjust pin bias current, 6nA at 25C, flows out of the adjust pin through R1 to ground. The output voltage can now be calculated using the formula:
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R2 VOUT = 1.5V 1 + - (IADJ )(R2) R1
The value of R1 should be less than 500k to minimize the error in the output voltage caused by adjust pin bias current. With 500k resistors for both R1 and R2, the error induced by adjust pin bias current at 25C is 3mV or 0.1% of the total output voltage. With appropriate value and tolerance resistors, the error due to adjust pin bias current may often be ignored. Note that in shutdown, the output is turned off and the divider current is zero. The parallel combination of R1 and R2 should be greater than 20k to allow the error amplifier to start. In applications where the minimum parallel resistance requirement cannot be met, a 20k resistor may be placed in series with the adjust pin. This introduces an error in the reference point for the resistor divider equal to (IADJ)(20k).
OUT R2 ADJ GND R1 CFB
+
VOUT COUT
1579 * F01
Figure 1. Adjustable Operation
LT1579
APPLICATIONS INFORMATION
A small capacitor placed in parallel with the top resistor (R2) of the output divider is necessary for stability and transient performance of the adjustable LT1579. The impedance of CFB at 10kHz should be less than the value of R1. The adjustable LT1579 is tested and specified with the output pin tied to the adjust pin and a 3A load (unless otherwise noted) for an output voltage of 1.5V. Specifications for output voltages greater than 1.5V are proportional to the ratio of the desired output voltage to 1.5V; (VOUT/1.5V). For example, load regulation for an output current change of 1mA to 300mA is - 2mV typical at VOUT = 1.5V. At VOUT = 12V, load regulation is:
12 V -2mV = -16mV 1.5 V
(
)
Output Capacitance and Transient Response The LT1579 is designed to be stable with a wide range of output capacitors. The ESR of the output capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 4.7F with an ESR of 3 or less is recommended to prevent oscillations. Smaller value capacitors may be used, but capacitors which have a low ESR (i.e. ceramics) may need a small series resistor added to bring the ESR into the range suggested in Table 1. The LT1579 is a micropower device and output transient response is a function of output capacitance. Larger values of output capacitance decrease the peak deviations and provide improved output transient response for larger load current changes. Bypass capacitors, used to decouple individual components powered by the LT1579, will increase the effective output capacitor value.
Table 1. Suggested ESR Range
OUTPUT CAPACITANCE 1.5F 2.2F 3.3F 4.7F SUGGESTED ESR RANGE 1 to 3 0.5 to 3 0.2 to 3 0 to 3
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BIASCOMP Pin Compensation The BIASCOMP pin is a connection to a compensation point for the internal bias circuitry. It must be bypassed with a 0.01F capacitor for stability during the switch from VIN1 to VIN2. "Hot" Plugging and Unplugging of Inputs The LT1579 is designed to maintain regulation even if one of the outputs is instantaneously removed. If the primary input is supplying load current, removal and insertion of the secondary input creates no noticeable transient at the output. In this case, the LT1579 continues to supply current from the primary; no switching is required. However, when load current is being supplied from the primary input and it is removed, load current must be switched from the primary to the secondary input. In this case, the LT1579 sees the input capacitor as a rapidly discharging battery. If it discharges too quickly, the LT1579 does not have ample time to switch over without a large transient occurring at the output. The input capacitor must be large enough to supply load current during the transition from primary to secondary input. Replacement of the primary creates a smaller transient on the output because both inputs are present during the transition. For a 100mA load, input and output capacitors of 10F will limit peak output deviations to less than 50mV. See the "Hot" Plugging and Unplugging Transient Response in the Typical Performance Characteristics. Proportionally larger values for input and output capacitors are needed to limit peak deviations on the output when delivering larger load currents. Standby Mode "Standby" mode is where one input draws a minimum quiescent current when the other input is delivering all bias and load currents . In this mode, the standby current is the quiescent current drawn from the standby input. The secondary input will be in standby mode, when the primary input is delivering all load and bias currents. When the secondary input is in standby mode the current drawn from the secondary input will be 3A if VIN1 > VIN2 and 5A
13
LT1579
APPLICATIONS INFORMATION
if VIN2 >VIN1, so typically only 3A. The primary input will automatically go into standby mode as the primary input drops below the output voltage. The primary input can also be forced into standby mode by asserting the SS pin. In either case, the current drawn from the primary input is reduced to a maximum of 7A. Shutdown The LT1579 has a low power shutdown state where all functions of the device are shut off. The device is put into shutdown mode when the shutdown pin is pulled below 0.7V. The quiescent current in shutdown has three components: 2A drawn from the primary, 2A drawn from the secondary and 3A which is drawn from the higher of the two inputs. Protecting Batteries Using Secondary Select (SS) Some batteries, such as lithium-ion cells, are sensitive to deep discharge conditions. Discharging these batteries below a certain threshold severely shortens battery life. To prevent deep discharge of the primary cells, the LT1579 secondary select (SS) pin can be used to switch power draw from the primary input to the secondary. When this pin is pulled low, current out of the primary is reduced to 2A. A low-battery detector with the trip point set at the critical discharge point can signal the low battery condition and force the switchover to the secondary as shown in Figure 2. The second low-battery comparator can be used to set a latch to shutdown the LT1579 (see the Typical Applications).
VCC
RP LBO
SS GND
1579 F02
Figure 2. Connecting SS to Low-Battery Detector Output to Prevent Damage to Batteries
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Low-Battery Comparators There are two independent low-battery comparators in the LT1579. This allows for individual monitoring of each input. The inverting inputs of both comparators are connected to an internal 1.5V reference. The low-battery comparator trip point is set by an external resistor divider as shown in Figure 3. The current in R1 at the trip point is 1.5V/R1. The current in R2 is equal to the current in R1. The low-battery comparator input bias current, 2nA flowing out of the pin, is negligible and may be ignored. The value of R1 should be less than 1.5M in order to minimize errors in the trip point. The value of R2 for a given trip point is calculated using the formulas in Figure 3. The low-battery comparators have a small amount of hysteresis built-in. The amount of hysteresis is dependent upon the output sink current (ISINK) when the comparator is tripped low. At no load, comparator hysteresis is zero, increasing to a maximum of 18mV for sink currents above 20A. See the curve of Low-Battery Comparator Hysteresis in the Typical Performance Characteristics. If larger amounts of hysteresis are desired, R3 and D1 can be added. D1 can be any small diode, typically a 1N4148. Calculating VLBO can be done using a load line on the curve of Logic Flag Output Voltage vs Sink Current in the Typical Performance Characteristics.
VTRIP R2 LBI VOUT R4 LBO ISINK
+ -
R1 1.5V
R3
D1
R2 = (VTRIP - 1.5V)
HYSTERESIS = VHYST 1 +
() ()
R1 1.5V R2 R1
LTC1579 * F02
R3 =
FOR ADDED HYSTERESIS (1.5V + VHYST - 0.6V - VLBO)(R2) VHYST(ADDED)
FOR ISINK 20A, VHYST = 18mV, FOR ISINK < 20A, SEE THE TYPICAL PERFORMANCE CHARACTERISTICS
Figure 3. Low-Battery Comparator Operation
LT1579
APPLICATIONS INFORMATION
Example: The low-battery detector must be tripped at a terminal voltage of 5.5V. There is a 100k pull-up resistor to 5V on the output of the comparator and 200mV of hysteresis is needed to prevent chatter. With a 1M resistor for R1, what other resistor values are needed? Using the formulas in Figure 3,
R2 =
(5.5V - 1.5V)(1M) = 2.67M
1.5V
Use a standard value of 2.7M. With the 100k pull-up resistor, this gives a sink current and logic flag voltage of approximately 45A at 0.4V. The hysteresis in this case will be:
2.7M Hysteresis = 18mV 1 + = 67mV 1M
An additional 133mV of hysteresis is needed, so a resistor and diode must be added. The value of R3 will be:
R3 =
(1.5V + 18mV - 0.6V - 0.4V)(2.7M) = 10.5M
133mV
A standard value of 10M can be used. The additional current flowing through R3 into the comparator output is negligible and can usually be ignored Logic Flags The low-battery comparator outputs and the status flags of the LT1579 are open collector outputs capable of sinking up to 5mA. See the curve of Logic Flag Output Voltage vs. Current in the Typical Performance Characteristics. There are two status flags on the LT1579. The BACKUP flag and the DROPOUT flag provide information on which input is supplying power to the load and give early warning of loss of output regulation. The BACKUP flag goes low when the secondary input begins supplying power to the load. The DROPOUT flag signals the dropout condition on both inputs, warning of an impending drop in output voltage. The conditions that set either status flag are determined by input to output voltage differentials and
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current supplied to the load from each input. Normal output deviation during transient load conditions (with sufficient input voltages) will not set the status flags. Timing Diagram The timing diagram for the 5V dual battery supply is shown in Figure 4. The schematic is the same as the 5V Dual Battery Supply on the front of the data sheet. All logic flag outputs have 100k pull-up resistors added. Note that there is no time scale for the timing diagram. The timing diagram is meant as a tool to help in understanding basic operation of the LT1579. Actual discharge rates will be a function of the load current and the type of batteries used. The load current used in the example was 100mA DC.
A 6V VIN1 5V 6V VIN2 5V VOUT 5V 4.8V 100mA IIN1 0 100mA IIN2 0 1 LB01 BACKUP LB02 DROPOUT 0 1 0 1 0 1 0
LTC1579 * F03
B
C
D
E
Figure 4. Basic Dual Battery Timing Diagram
15
LT1579
APPLICATIONS INFORMATION
Five milestones are noted on the timing diagram. Time A is where the primary input voltage drops enough to trip the low-battery detector LB1. The trip threshold for LB1 is set at set at 5.5V, slightly above the dropout voltage of the primary input. At time B, the BACKUP flag goes low, signaling the beginning of the transition from the primary source to the secondary source. Between times B and C, the input current makes a smooth transition from VIN1 to VIN2. By time C, the primary battery has dropped below the point where it can deliver useful current to the output. The primary input will still deliver a small amount of current to the load, diminishing as the primary input voltage drops. By time D, the secondary battery has dropped to a low enough voltage to trip the second low-battery detector, LB2. The trip threshold for LB2 is also set at 5.5V, slightly above where the secondary input reaches dropout. At time E, both inputs are low enough to cause the LT1579 to enter dropout, with the DROPOUT flag signaling the impending loss of output regulation. After time E, the output voltage drops out of regulation. Some interesting things can be noted on the timing diagram. The amount of current available from a given input is determined by the input/output voltage differential. As the differential voltage drops, the amount of current drawn from the input also drops, which slows the discharge of the battery. Dropout detection circuitry will maintain the maximum current draw from the input for the given input/output voltage differential. In the case shown, this causes the current drawn from the primary input to approach zero, though never actually dropping to zero. Note that the primary begins to supply significant current again when the output drops out of regulation. This occurs because the input/output voltage differential of the primary input increases as the output voltage drops. The LT1579 will automatically maximize the power drawn from the inputs to maintain the highest possible output voltage. Thermal Considerations The power handling capability of the LT1579 is limited by the maximum rated junction temperature (125C). Power dissipated is made up of two components: 1. The output current from each input multiplied by the respective input to output voltage differential: (IOUT)(VIN - VOUT) and 2. Ground pin current from the associated inputs multiplied by the respective input voltage: (IGND)(VIN). If the primary input is not in dropout, all significant power dissipation is from the primary input. Conversely, if SS has been asserted to minimize power draw from the primary, all significant power dissipation will be from the secondary. When the primary input enters dropout, calculation of power dissipation requires consideration of power dissipation from both inputs. Worst-case power dissipation is found using the worst-case input voltage from either input and the worst-case load current. Ground pin current is found by examining the Ground Pin Current curves in the Typical Performance Characteristics. Power dissipation will be equal to the sum of the two components above for the input supplying power to the load. Power dissipation from the other input is negligible. The LT1579 has internal thermal limiting designed to protect the device during overload conditions. For continuous normal load conditions, the maximum junction temperature rating of 125C must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional heat sources nearby must also be considered. Heating sinking for the device is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Copper board stiffeners and plated throughholes can also be used to spread the heat. All ground pins on the LT1579 are fused to the die paddle for improved heat spreading capabilities. The following tables list thermal resistances for each package. Measured values of thermal resistance for several different board sizes and copper areas are listed for each package. All measurements were taken in still air on 3/32" FR-4 board with one ounce copper. All ground leads were connected to the ground plane. All packages for the LT1579 have all ground leads fused to the die attach paddle to lower thermal resistance. Typical thermal
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LT1579
APPLICATIONS INFORMATION
resistance from the junction to a ground lead is 40C/W for 16-lead SSOP, 32C/W for 16-lead SO and 35C/W for 8-lead S0.
Table 2. 8-Lead SO Package (S8)
COPPER AREA TOPSIDE* BACKSIDE 2500 sq mm 2500 sq mm 1000 sq mm 2500 sq mm 225 sq mm 2500 sq mm 100 sq mm 2500 sq mm
*Device is mounted on topside.
THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq mm 2500 sq mm 2500 sq mm 2500 sq mm 73C/W 75C/W 80C/W 90C/W
Table 3. 16-Lead SO Package (S)
COPPER AREA TOPSIDE* BACKSIDE 2500 sq mm 2500 sq mm 1000 sq mm 2500 sq mm 225 sq mm 2500 sq mm 100 sq mm 2500 sq mm
*Device is mounted on topside.
THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq mm 2500 sq mm 2500 sq mm 2500 sq mm 55C/W 58C/W 60C/W 68C/W
Table 4. 16-Lead SSOP Package (GN)
COPPER AREA TOPSIDE* BACKSIDE 2500 sq mm 2500 sq mm 1000 sq mm 2500 sq mm 225 sq mm 2500 sq mm 100 sq mm 2500 sq mm
*Device is mounted on topside.
THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq mm 2500 sq mm 2500 sq mm 2500 sq mm 70C/W 75C/W 80C/W 95C/W
Calculating Junction Temperature Example: Given an output voltage of 5V, an input voltage range of 5V to 7V for VIN1 and 8V to 10V for VIN2, with an output current range of 10mA to 150mA and a maximum ambient temperature of 50C, what will the maximum junction temperature be? When run from the primary input, current drawn from the secondary input is negligible and worst-case power dissipation will be: (IOUT(MAX))(VIN1(MAX) - VOUT) + (IGND)(VIN1(MAX)) Where: IOUT(MAX) = 150mA VIN1(MAX) = 7V IGND at (IOUT = 150mA, VIN1 = 7V) = 2mA
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Therefore, P = (150mA)(7V - 5V) + (2mA)(7V) = 0.31W When switched to the secondary input, current from the primary input is negligible and worst-case power dissipation will be: (IOUT(MAX))(VIN2(MAX) - VOUT) + (IGND)(VIN2(MAX)) Where: IOUT(MAX) = 150mA VIN2(MAX) = 10V IGND at (IOUT = 150mA, VIN2 = 10V) = 2mA Therefore, P = (150mA)(10V - 5V) + (2mA)(10V) = 0.77W Using a 16-lead SO package, the thermal resistance will be in the range of 55C/W to 68C/W dependent upon the copper area. So the junction temperature rise above ambient will be approximately equal to: (0.77W)(65C/W) = 50.1C The maximum junction temperature will then be equal to the maximum temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 50.1C + 50C = 100.1C Protection Features The LT1579 incorporates several protection features that make it ideal for use in battery-powered circuits. In addition to the normal protection features associated with monolithic regulators, such as current limiting and thermal limiting, the device is protected against reverse input voltages, reverse output voltages and reverse voltages from output to input. Current limit protection and thermal overload protection are intended to protect the device against current overload conditions at the output of the device. For normal operation, the junction temperature should not exceed 125C. Current limit protection is designed to protect the device if the output is shorted to ground. With the output shorted to ground, current will be drawn from the primary input until it is discharged. The current drawn from VIN2 will not increase until the primary input is discharged. This prevents a short-circuit on the output from discharging both inputs simultaneously.
17
LT1579
APPLICATIONS INFORMATION
The inputs of the device can withstand reverse voltages up to 20V. Current flow into the device will be limited to less than 1mA (typically less than 100A) and no negative voltage will appear at the output. The device will protect both itself and the load. This provides protection against batteries which can be plugged in backwards. Internal protection circuitry isolates the inputs to prevent current flow from one input to the other. Even with one input supplying all bias currents and the other being plugged in backwards (a maximum total differential of 40V), current flow from one input to another will be limited to less than 1mA. Output voltage will be unaffected. In the case of reverse inputs, no reverse voltages will appear at the load. Pulling the SS pin low will cause all load currents to come from the secondary input. If the secondary input is not present, the output will be turned off. If the part is put into current limit with the SS pin pulled low, current limit will be drawn from the secondary input until it is discharged, at which point the current limit will drop to zero.
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
GN Package 16-Lead Plastic SSOP (Narrow 0.150)
(LTC DWG # 05-08-1641)
0.189 - 0.196* (4.801 - 4.978) 16 15 14 13 12 11 10 9
0.015 0.004 x 45 (0.38 0.10) 0.007 - 0.0098 (0.178 - 0.249) 0.016 - 0.050 (0.406 - 1.270)
* DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0 - 8 TYP
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0.229 - 0.244 (5.817 - 6.198)
0.150 - 0.157** (3.810 - 3.988)
1
23
4
56
7
8
0.053 - 0.068 (1.351 - 1.727)
0.004 - 0.0098 (0.102 - 0.249)
0.008 - 0.012 (0.203 - 0.305)
0.025 (0.635) BSC
GN16 (SSOP) 1197
LT1579
PACKAGE DESCRIPTION
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.016 - 0.050 0.406 - 1.270
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0 - 8 TYP
0.016 - 0.050 0.406 - 1.270 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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Dimensions in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1 0.053 - 0.069 (1.346 - 1.752)
2
3
4
0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
SO8 0996
S Package 16-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.386 - 0.394* (9.804 - 10.008) 16 15 14 13 12 11 10 9
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1 0.053 - 0.069 (1.346 - 1.752)
2
3
4
5
6
7
8
0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
S16 0695
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LT1579
TYPICAL APPLICATION
Additional Logic Forces LT1579 Into Shutdown to Protect Input Batteries
IN1
C1 1F R1 1M
D2 D1 TO D3: 1N4148
IN2 D3 R8 330k D4 5.1V 1N751A C5 0.1F
RESET R9 1.5M 1/4 74C02
RELATED PARTS
PART NUMBER LT1175 LTC(R)1421 LTC1422 LTC1473 LTC1479 DESCRIPTION 500mA Negative Low Dropout Micropower Regulator Hot SwapTM Controller Hot Swap Controller Dual PowerPathTM Switch Driver PowerPath Controller for Dual Battery Systems COMMENTS Adjustable Current Limit, Shutdown Control Controls Multiple Supplies, 24-Lead SSOP Package Controls Single Supply, 8-Lead SO Package Power Path Management for Systems with Multiple Inputs Complete Power Path Management for Two Batteries, DC Power Source, Charger and Backup 12A IQ, Reverse Battery Protection
LT1521 300mA Low Dropout Micropower Regulator with Shutdown Hot Swap and PowerPath are trademarks of Linear Technology Corporation.
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
U
IN1 R2 2.7M LBI1 D1 R4 10M R3 1M LBO1 SS IN2 C2 1F R5 1M R6 2.7M LBI2 R7 1M LT1579-5
OUT R10 1M MAIN GOOD C3 4.7F
VOUT 5V/300mA
BACKUP
DROPOUT
NC
VCC 1/4 74C02 1/4 74C02
LBO2
BIASCOMP C4 0.01F
SHDN GND GND
1579 TA03
1579f LT/TP 0398 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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