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AS2975
180 mA Low Dropout Voltage Regulators
FEATURES
* 5V Fixed & at 180mA Output * Very Low Quiescent Current * Low Dropout Voltage * Extremely Tight Load And Line Regulation * Very Low Temperature Coefficient * Needs Only 1F For Stability * Current & Thermal Limiting * Unregulated DC Input Can Withstand -20V Reverse Battery And +60V Positive Transients * Similar Replacement For LP2950/LP2951 Sockets
APPLICATIONS
* Battery Powered Systems * Cordless Telephones * Radio Control Systems * Portable/Palm Top/Notebook Computers * Portable Consumer Equipment * Portable Instrumentation * Avionics * Automotive Electronics * SMPS Post-Regulator * Voltage Reference
AS2975 SO-8 versions only
* Error Flag Warns Of Output Dropout * Logic- Controlled Electronic Shutdown * Output Programmable from 1.24 to 29V
PRODUCT DESCRIPTION
The AS2975 is a low power voltage regulator. This device is an excellent choice for use in battery-powered applications such as cordless telephones, radio control systems, and portable computers. The AS2975 features very low quiescent current and very low dropout voltage (Typ. 50mV at light load and 380 mV at 180 mA). This includes a tight initial tolerance of 0.5% typ., extremely good load and line regulation 0.05% typ. and very low output temperature coefficient, making the AS2975 useful as a low-power voltage reference. Other additional key features include higher output current (150mA), positive transient protection up to 60V (Load dump), and the ability to survive an unregulated input voltage transient of -20V below ground (reverse battery). The error flag output feature is used as power-on reset for warning of a low output voltage, due to falling voltage input of batteries. Another feature is the logic-compatible shutdown input which enables the regulator to be switched on and off. The AS2975 is offered in a 3-pin TO-92 package compatible with other 5V regulators. The AS2975 is available in 8-pin plastic, SO-8 packages.
ORDERING INFORMATION
TO-92 3-PIN
AS2975YCN-X AS2975CN-X AS2975YCPX AS2975CP-X
X= 3.0V, 3.3V, OR 5.0V
PIN CONNECTIONS
OPER. TEMP. RANGE
PLASTIC SOIC 8-PIN
-40C to +125C -40C to +125C -40C to +125C -40C to +125C
8-Pin Surface Mount (S)
VOUT SENSE SHUTDOWN GND 1 2 3 4 8 7 VIN FEEDBACK 5V TAP ERROR VIN 1
TO-92 (N)
2 3
AS2975
Y= Output Tolerance (A = 0.5%, Blank = 1%)
6 5
GND
VOUT
Top View
Bottom View
Rev. 10/6/00
AS2975
ABSOLUTE MAXIMUM RATINGS
Power Dissipation..........................................Internally Limited Lead Temp. (Soldering, 5 Seconds) ................................ 260C Storage Temperature Range ............................ -65 to +150C Operating Junction Temperature Range (Note 10) AS2975 ..................................................... -55 to +150C AS2975AC/AS2975C............................... -40 to +125C Input Supply Voltage (Survival) ......................-20V to +60V Feedback Input Voltage ..................................-1.5V to +30V Shutdown Input Voltage..................................-0.3V to +30V Error Comparator Output ................................-0.3V to +30V ESD Rating ............................................................. 2KV Min
ELECTRICAL CHARACTERISTICS at VS=15V, TA=25C, unless otherwise specified.
temperature range.
Boldface apply over the full operating
PARAMETER
3.3 V Versions Output Voltage
CONDITIONS
(Note 2) TJ = 25C -25C TJ 85C -40C TJ +125C 100 A IL 180 mA TJ TJMAX TJ = 25C -25C TJ 85C -40C TJ +125C 100 A IL 180 mA TJ TJMAX Min 3.2835 3.2604 3.2505
AS2975
Typ 3.3 Max 3.3165 3.3396 3.3495 Min
AS2975AC
Typ 3.3 Max 3.3165 3.333 3.3396 3.3495 Min 3.267 3.2505 3.2604 3.201 3.2835 3.267 3.2608 3.2505
AS2975C
Typ 3.3 Max 3.333 3.695 3.3396 3.399
UNITS V
Output Voltage 5 V Versions Output Voltage
3.3
3.3
3.3
V
4.975 4.94 4.925
5.0
5.025 5.06 5.075
Output Voltage All Voltage Options Output Voltage Temperature Coefficient Line Regulation (Note 3) Load Regulation (Note 3) Dropout Voltage (Note 5)
5.0
4.975 4.95 4.94 4.925
5.0 5.0 5.0 5.0
5.025 5.050 5.06 5.075
4.95 4.925 4.90 4.85
5.0 5.0 5.0 5.0
5.05 5.075 5.10 5.15
V
V
20 (Note 1) 6V VIN 30V (Note 4) 100 A IL 180 mA IL = 100 A IL = 100 mA IL = 180 mA IL = 100 A IL = 100 mA IL = 180 mA VOUT = 0 CL = 1F CL = 200 F CL = 13.3 F (Bypass = 0.01 F pins 7 to 1(AS2975)) 1.22 Over Temperature ( Note 6) (Note 7) 1.19 40 20 0.03 0.04 50 380 450 150 8 18 130 0.05 430 160 100
120 0.1 0.1 80 450 500 170 12 22 200 0.2
20 0.03 0.04 50 380 450 150 8 18 130 0.05 430 160 100 0.1 0.1 80 450 500 170 12 22 200 0.2
50 0.04 0.1 50 380 450 150 8 18 130 0.05 430 160 100 0.2 0.2 80 450 500 170 12 22 200 0.2
ppm/C % % mV
Ground Current
Current Limit Thermal Regulation Output Noise, 10Hz to 100kHz
A mA mA mA %/W V rms
8-Pin Versions Only Reference Voltage Reference Voltage Feedback Pin Bias Current Reference Voltage Temperature Coefficient Feedback Pin Bias Current Temperature Coefficient Error Comparator Output Leakage Current Output Low Voltage Upper Threshold Voltage Lower Threshold Voltage
AS2975 1.235
1.25 1.27 60
1.22 1.19
AS2975AC 1.235 1.25 1.27 40 20 60
1.21 1.18
AS2975C 1.23
1.26 1.28
V V nA ppm/C
40 50
60
0.1
0.1
0.1
nA/C
VOH = 30V VIN = 4.5V IOL = 400A (Note 8) (Note 8)
0.01 150 40 60 75
1 250 40 95
0.01 150 60 75
1 250 40 95
0.01 150 60 75
1 250
A mV mV
95
mV
Rev. 10/6/00
Hysteresis
(Note 8)
15
15
15
mV
Rev. 10/6/00
AS2975
PARAMETER
8-Pin Version only (Continued) Shutdown Input Input Logic Voltage Shut Down Pin Input Current Low (Regulator ON) High (Regulator OFF) VS = 2.4V VS = 30V (Note 9) 1.3 2 30 675 3 50 800 10 0.6 2 30 675 3 50 800 10 1.3 0.7 2 30 675 3 50 800 10 A 1.3 0.7 V
CONDITIONS
(Note 2) Min
AS2975
Typ Max
AS2975AC
Min Typ Max Min
AS2975C
Typ Max
UNITS
Regulator Output Current in A Shutdown Note 1: Output or reference voltage temperature coefficients defined as the worst case voltage change divided by the total temperature range. Note 2: Unless otherwise specified all limits guaranteed for TJ = 25C, VIN = 6V, IL = 100A and CL = 1 F. Additional conditions for the 8-pin versions are feedback tied to 5V tap and output tied to output sense (VOUT = 5V) and VSHUTDOWN 0.8V. Note 3: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are covered under the specification for thermal regulation. Note 4: Line regulation for the AS2975 is tested at 150C for IL = 1mA. For IL = 100A and TJ = 125C, line regulation is guaranteed by design to 0.2%. See typical performance characteristics for line regulation versus temperature and load current. Note 5: Dropout voltage is defined as the input to output differential at which the output voltage drops 100mV below its nominal value measured at 1V differential at very low values of programmed output voltage, the minimum input supply voltage of 2V ( 2.3V over temperature) must be taken into account. Note 6: VREF VOUT (VIN - 1V), 2.3 VIN30V, 100AIL 100 mA, TJ TJMAX. Note 7: Comparator thresholds are expressed in terms of a voltage differential at the feedback terminal below the nominal reference voltage measured at 6V input. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = VOUT/VREF = (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the error output is guaranteed to go low when the output drops by 95mV x 5V/1.235 = 384mV. Thresholds remain constant as a percent of VOUT as VOUT is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed. Note 8: VSHUTDOWN 2V, VIN 30V, VOUT =0, Feedback pin tied to 5V Tap. Note 9: All typical values are not guaranteed. The value could vary from lot to lot. Note 10: The junction -to-ambient thermal resistance of the TO-92 package is 180C/ W with 0.4" leads and 160C/ W with 0.25" leads to a PC board. The thermal resistance of the 8-Pin DIP package is 105C/W junction-to-ambient when soldered directly to a PC board. Junction-to-ambient thermal resistance for the SOIC (S) package is 160C/W.
BLOCK DIAGRAM
UNREGULATED DC
+
7
FEEDBACK
8
INPUT
1
OUTPUT
5V @ 180mA MAX
2
SENSE
+ _
FROM CMOS OR TTL
180k .. 6
ERROR AMPLIFIER 5V TAP
3
SHUTDOWN
330k .. + 1 F ..
60k ..
+
60 mV
5
______ ERROR
+ _
ERROR DETECTION COMPARATOR
+ 1.23V
REFERENCE
TO CMOS OR TTL
4
GROUND
AS2975 Block Diagram
Rev. 10/6/00
AS2975
APPLICATION HINTS
EXTERNAL CAPACITORS
The stability of the AS2975 requires a 1.0F or greater capacitor between output and ground. Oscillation could occur without this capacitor. Most types of tantalum or aluminum electrolytic works fine here. For operations below -25C solid tantalum is recommended since the many aluminum types have electrolytes that freeze at about -30C. The ESR of about 5 or less and resonant frequency above 500kHz are the most important parameters in the value of the capacitor. The capacitors value may be increased without limit. At lower values of output current, less output capacitance is required for stability. For the currents below 10mA the value of the capacitor can be reduced to 0.33F and 0.1F for 1mA. More output capacitance is needed for the 8-pin version at voltages below 5V since it runs the error amplifier at lower gain. At worst case 3.3F or greater must be used for the condition of 10mA load at 1.23V output. The AS2975, unlike other low dropout regulators will remain stable and in regulation with no load in addition to the internal voltage divider. This feature is especially important in applications like CMOS RAM keep-alive. When setting the output voltage of the AS2975, a minimum load of 1A is recommended If there is more than 10 inches of wire between the input and the AC filter capacitor or if a battery is used as the input then a 1A tantalum or aluminum electrolytic capacitor should be placed from the input to the ground. Instability can occur if there is stray capacitance to the AS2975 feedback terminal (pin 7). This could cause more problems when using a higher value of external resistors to set the output voltage. This problem can be fixed by adding a 100 pF capacitor between output and feedback and increasing the output capacitor to at least 3.3F. The error comparator has an open-collector output which requires an external pull-up resistor. Depending on the system requirements the resistor may be returned to 5V output or other supply voltage. In determining the value of this resistor, note that the output is rated to sink 400A, this value adds to battery drain in a low battery condition. Suggested values range from 100K to 1M. If the output is unused this resistor is not required.
PROGRAMMING THE OUTPUT VOLTAGE OF AS2975
The AS2975 may be pin-strapped for 5V using its internal voltage divider by tying Pin 1 (output) to Pin 2 (sense) and Pin 7 (feedback) to Pin 6 (5V Tap). Also, it may be programmed for any output voltage between its 1.235V reference and its 30V maximum rating . As seen in Figure 2, an external pair of resistors is required. Refer to the below equation for the programming of the output voltage: VOUT = VREF x (1 + R1\ R2)+ IFBR1 The Vref is 1.235 and IFB is the feedback bias current, nominally -20nA. The minimum recommended load current of 1A forces an upper limit of 1.2 M on value of R2. If no load is presented the IFB produces an error of typically 2% in VOUT which may be eliminated at room temperature by trimming R1. To improve the accuracy choose the value of R2 = 100k this reduces the error by 0.17% and increases the resistor program current by 12A. Since the AS2975 typically draws 60A at no load with Pin 2 open-circuited this is a small price to pay
REDUCING OUTPUT NOISE
It may be an advantage to reduce the AC noise present at the output. One way is to reduce the regulator bandwidth by increasing the size of the output capacitor. This is the only way that noise can be reduced on the 3 lead AS2975 but is relatively inefficient, as increasing the capacitor from 1F to 220F only decreases the noise from 430V to 160V rms for a 100kHz bandwidth at 5V output. Noise could also be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick CBYPASS 1 / 2R1 x 200 Hz or choose 0.01F. When doing this, the output capacitor must be increased to 3.3F to maintain stability. These changes reduce the output noise from 430V to 100VRMS for a 100kHz bandwidth at 5V output. With the bypass capacitor added, noise no longer scales with output voltage so that improvements are more dramatic at higher output voltages.
ERROR DETECTION COMPARATOR OUTPUT
The Comparator produces a logic low output whenever the AS2975 output falls out of regulation by more than around 5%. This is around 60mV offset divided by the 1.235 reference voltage. This trip level remains 5% below normal regardless of the programmed output voltage of the regulator. Figure 1 shows the timing diagram depicting the ERROR signal and the regulator output voltage as the AS2975 input is ramped up and down. The ERROR signal becomes low at around 1.3V input, and goes high around 5V input (input voltage at which Vout = 4.75 ). Since the AS2975 dropout voltage is load dependent, the input voltage trip point (around 5V) will vary with the load current. The output voltage trip point (approx. 4.75V) does not vary with load.
Rev. 10/6/00
AS2975
TYPICAL PERFORMANCE CHARACTERISTICS
Rev. 10/6/00
AS2975
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Rev. 10/6/00
AS2975
TYPICAL APPLICATIONS
4.75V OUTPUT VOLTAGE _______ ERROR*
ERROR OUTPUT 100K
5
+VIN
8
______ ERROR
+VIN VOUT
1
1.2 to30V
AS2975
SHUTDOWN
3
+5.0V
INPUT VOLTAGE
+1.3V
+ +
INPUT
SD GND
4
R1 FB
7
+
3.3uF .01uF
1.23V
VREF
R2
* See Application Info.
_______ Figure 1. ERROR Output Timing
Figure 2. Adjustable Regulator
+VIN
+VIN
470K ..
5
8
470K ..
______ ERROR
+VIN VOUT
1
VOUT
ERROR OUTPUT
5
8
______ ERROR
+VIN VOUT
1
*VOUT= VIN
AS2975
+ 3
AS2975
R1 1F
SHUTDOWN INPUT
3
SD GND
4
FB
7
SD GND
4
FB
7
R2
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 4mV TO 400 CURRENT LIMIT IS TYPICALLY DEPENDING ON LOAD CURRENT.V 160 A
Latch Off When Error Flag Occurs
Wide Input Voltage Range Current Limiter
Rev. 10/6/00
AS2975
TYPICAL APPLICATIONS (continued)
+
6V SEALED LEADACID BATTERY SOURCE
120K FB
1.5K 1N457 8 +VIN 1
MAIN V-
AS385
VOUT
AS2975
FOR 5.5 V
400K 3 100K SD GND 4
SENSE
MEMORY V+
2
+
1F
20K
NI-CAD BACKUP BATTERY
Low Battery Disconnect
8
39k
RESET C4 +
2 SENSE VOUT 1
+VIN 5 ______ ERROR
+VOUT = 5V
+ 1F
AS2975
3
SD FB
7
39k
GND 4
TAP 6
1%
100k
C1 +
100k <5.8V**
6V LEAD1% ACID BATTERY
1k
C2 +
100k <6.0V**
1%
1k
C3 +
100 <6.2V**
R3
10k
* OPTIONAL LATCH OFF WHEN DROPOUT OCCURS. ADJUST R3 FOR C2 SWITCHING WHEN VIN IS 6.0V
1%
20k
** OUTPUTS GO LOW WHEN VIN DROPS BELOW DESIGNATED THRESHOLDS
Regulator with State-of-Charge indicator
Rev. 10/6/00
AS2975
TYPICAL APPLICATIONS (continued)
+VIN
8 AUX SHUTDOWN
OFF ON
3
+VIN SD
10K
_______ 5 ERROR 5 DEGREE SHUTDOWN FLAG
AS2975
VOUT GND
+
1
FB
7
4
TEMP SENSOR
AS35 8.2K
EXTERNAL CIRCUIT PROTECTED FROM TEMPERATURE OVER (V+ GOES OFF WHEN > 125) TEMP
OR
RELAY
System Over Temperature Protection Circuit
+5V 4 20mA 8 +V IN VOUT 1N4001 1
5
4.7mA UNREGULATED INPUT OUTPUT 330K .. 27K
2 +
IN VOUT
1
2N5432
AS2975
FB GND 4 1N457 MIN VOLTAGE = 4V 7 2
3
AS2975
VTAP FB
7
..
5V OUTPUT 4.7uF LOAD 50mA TO 300 mA
0.1uF
360K
..
SENSE GND
4
Open Circuit Detector for 4mA to 20mA Current Loop
300 mA Regulator with 0.75 Dropout
Rev. 10/6/00

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