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LTC2903-1 Precision Quad Supply Monitor in 6-Lead SOT-23
FEATURES

DESCRIPTIO

Ultralow Voltage Reset: VCC = 0.5V Guaranteed Monitor Four Inputs Simultaneously 3.3V, 2.5V, 1.8V, ADJ (LTC2903-A1) 5V, 3.3V, 2.5V, 1.8V (LTC2903-B1) 5V, 3.3V, 1.8V, -5.2V (LTC2903-C1) 3.3V, ADJ, ADJ, ADJ (LTC2903-D1) 5V, ADJ, ADJ, ADJ (LTC2903-E1) Guaranteed Threshold Accuracy: 1.5% of Monitored Voltage over Temperature 10% (A1, B1, C1) and 5% (D1, E1) Undervoltage Monitoring Low Supply Current: 20A Typical 200ms Reset Time Delay Active Low Open-Drain RST Output Power Supply Glitch Immunity Low Profile (1mm) SOT-23 (ThinSOTTM) Package
The LTC(R)2903-1 monitors up to four supply voltages. The common reset output remains low until all four inputs have been in compliance for 200ms. Voltage thresholds maintain 1.5% accuracy over temperature (with respect to the monitored voltage). The LTC2903-1 features an open-drain RST output with a weak internal pullup. Internal supply voltage (VCC) is generated from the greater voltage on the V1, V2 inputs. VCC = V1 for LTC2903-D1 and LTC2903-E1. The RST output is guaranteed to sink at least 5A (VOL = 0.15V) for VCC down to 0.5V and will typically conduct current down to 0V. Quiescent current is 20A typical, making the LTC2903-1 ideal for power conscious systems. The LTC2903-1 is available in a 6-lead low profile (1mm) SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.
APPLICATIO S

Multivoltage Systems Optical Networking Systems Cell Phone Base Stations Network Servers
TYPICAL APPLICATIO
5V
Low Voltage Reset Pull-Down Performance vs External Pull-Up Current and Input Supply Voltage
0.10 0.09
3.3V
RESET PIN VOLTAGE (V)
DC/DC 2.5V CONVERTER 1.8V LTC2903-B1 RST V1 GND V2 V4 V3
2903 TA01
SYSTEM LOGIC
0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 1A 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 VIN, INPUT SUPPLY VOLTAGE (V) 1 2A 5A 20A 10A
C1 0.1F C2 0.1F
U
VIN = V1 = V2 = V3 LTC2903-B1
2903 TA01b
U
U
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1
LTC2903-1
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2, 3)
PACKAGE/ORDER INFORMATION
TOP VIEW V1 1 GND 2 V2 3 6 RST 5 V4 4 V3
V1, V2 ...................................................... - 0.3V to 6.5V V3 ................................................. 2.7V or (VCC + 0.3V) V4 (LTC2903-A1, -B1, -D1, -E1) ...............- 0.3V to 6.5V V4 (LTC2903-C1) .................................... - 6.5V to 0.3V RST ........................................................ - 0.3V to 6.5V Operating Temperature Range LTC2903C-X1 .......................................... 0C to 70C LTC2903I-X1 ...................................... - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
S6 PACKAGE 6-LEAD PLASTIC TSOT-23
TJMAX = 125C, JA = 230C/W
ORDER PART NUMBER LTC2903CS6-A1 LTC2903CS6-B1 LTC2903CS6-C1 LTC2903CS6-D1 LTC2903CS6-E1 LTC2903IS6-A1 LTC2903IS6-B1 LTC2903IS6-C1 LTC2903IS6-D1 LTC2903IS6-E1
S6 PART MARKING LTAFV LTAJN LTAJQ LTBMX LTBMZ LTAFW LTAJP LTAJR LTBMY LTBNB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL VRT33 VRT25 VRT18 VRTA PARAMETER 3.3V, 10% Reset Threshold 2.5V, 10% Reset Threshold 1.8V, 10% Reset Threshold Adjustable Reset Threshold
(LTC2903-A1) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 3.3V unless otherwise noted.
CONDITIONS V1 Input Threshold V2 Input Threshold V3 Input Threshold V4 Input Threshold

MIN 2.871 2.175 1.566 0.492
TYP 2.921 2.213 1.593 0.500
MAX 2.970 2.250 1.620 0.508
UNITS V V V V
(LTC2903-B1) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V unless otherwise noted.
SYMBOL VRT50 VRT33 VRT25 VRT18 PARAMETER 5V, 10% Reset Threshold 3.3V, 10% Reset Threshold 2.5V, 10% Reset Threshold 1.8V, 10% Reset Threshold CONDITIONS V1 Input Threshold V2 Input Threshold V3 Input Threshold V4 Input Threshold

MIN 4.350 2.871 2.175 1.566
TYP 4.425 2.921 2.213 1.593
MAX 4.500 2.970 2.250 1.620
UNITS V V V V
(LTC2903-C1) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V unless otherwise noted.
SYMBOL VRT50 VRT33 VRT18 VRT52N PARAMETER 5V, 10% Reset Threshold 3.3V, 10% Reset Threshold 1.8V, 10% Reset Threshold -5.2V, 10% Reset Threshold CONDITIONS V1 Input Threshold V2 Input Threshold V3 Input Threshold V4 Input Threshold

MIN 4.350 2.871 1.566
TYP 4.425 2.921 1.593
MAX 4.500 2.970 1.620
UNITS V V V V
29031f a
-4.524 -4.602 -4.680
2
U
W
U
U
WW
W
LTC2903-1
ELECTRICAL CHARACTERISTICS
SYMBOL VRT33 VRTAV2 VRTAV3 VRTAV4 PARAMETER 3.3V, 5% Reset Threshold V2 Adjustable Threshold V3 Adjustable Threshold V4 Adjustable Threshold
(LTC2903-D1) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 3.3V unless otherwise noted.
CONDITIONS V1 Input Threshold V2 Input Threshold V3 Input Threshold V4 Input Threshold

MIN 3.036 0.492 0.492 0.492
TYP 3.086 0.500 0.500 0.500
MAX 3.135 0.508 0.508 0.508
UNITS V V V V
(LTC2903-E1) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V unless otherwise noted.
SYMBOL VRT50 VRTAV2 VRTAV3 VRTAV4 PARAMETER 5V, 5% Reset Threshold V2 Adjustable Threshold V3 Adjustable Threshold V4 Adjustable Threshold CONDITIONS V1 Input Threshold V2 Input Threshold V3 Input Threshold V4 Input Threshold

MIN 4.600 0.492 0.492 0.492
TYP 4.675 0.500 0.500 0.500
MAX 4.750 0.508 0.508 0.508
UNITS V V V V
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 3.3V unless otherwise noted.
SYMBOL IV1 PARAMETER V1 Input Current (Note 4) CONDITIONS V1 = 3.3V (LTC2903-A1, LTC2903-D1) V1 = 5V (LTC2903-B1, LTC2903-C1, LTC2903-E1)

MIN
TYP 20 25 8 10 8 10
MAX 80 80 30 30 30 30 30 30 30 4 -6 30 260
UNITS A A A A nA A A nA nA A A nA ms s V V
IV2
V2 Input Current (Note 4)
V2 = 2.5V (LTC2903-A1) V2 = 3.3V (LTC2903-B1, LTC2903-C1) V2 = 0.55V (LTC2903-D1, LTC2903-E1) V3 = 1.8V (LTC2903-A1, LTC2903-C1) V3 = 2.5V (LTC2903-B1) V3 = 0.55V (LTC2903-D1, LTC2903-E1) V4 = 0.55V (LTC2903-A1) V4 = 1.8V (LTC2903-B1) V4 = -5.2V (LTC2903-C1) V4 = 0.55V (LTC2903-D1, LTC2903-E1) VX Less Than Threshold VRTX by More Than 1% IRST(DN) = -1A (LTC2903-A1, LTC2903-B1, LTC2903-C1) (LTC2903-D1, LTC2903-E1) VCC = 0.2V, IRST = 0.1A VCC = 0.5V, IRST = 5A VCC = 1V, IRST = 200A VCC = 3V, IRST = 2500A

IV3
V3 Input Current
IV4
V4 Input Current
2 -3 140 200 150 V2 - 1 V1 - 1 5 10 25 100
tRST tUV VOH
Reset Time-Out Period VX Undervoltage Detect to RST Output Voltage High RST (LTC2903-1) (Note 5)
VOL
Output Voltage Low RST (Note 6)
60 150 300 300
mV mV mV mV
Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: All currents into pins are positive, all voltages are referenced to GND unless otherwise noted. Note 3: The internal supply voltage (VCC) is generated from the greater voltage on the V1 and V2 inputs. VCC = V1 for options D1 and E1. Note 4: Under typical operating conditions, quiescent current is drawn
from the V1 input. When V2 exceeds V1, V2 supplies the quiescent current. V1 only for options D1 and E1. Note 5: The RST output pin on the LTC2903-1 has an internal pull-up to V2 (for options A1, B1 and C1) of typically 10A. However, for faster rise times or for VOH voltages greater than V2, use an external pull-up resistor. The internal pull-up is connected to V1 for options D1 and E1. Note 6: For options A1, B1 and C1, the RST pulldown current is derived from V1, V2 and V3. For options D1 and E1, pulldown strength is derived from V1.
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LTC2903-1 TYPICAL PERFOR A CE CHARACTERISTICS
5V Threshold Voltage vs Temperature
4.500 2.975
THRESHOLD VOLTAGE, VRT50 (V)
THRESHOLD VOLTAGE, VRT33 (V)
4.475 4.450 4.425 4.400 4.375 4.350 -50
THRESHOLD VOLTAGE, VRT25 (V)
-25
0 25 50 TEMPERATURE (C)
1.8V Threshold Voltage vs Temperature
1.625 0.510
THRESHOLD VOLTAGE, VRTA (V)
1.615 1.605 1.595 1.585 1.575 1.565 -50
THRESHOLD VOLTAGE, VRT52N (V)
THRESHOLD VOLTAGE, VRT18 (V)
-25
0 25 50 TEMPERATURE (C)
Supply Currents vs Temperature (LTC2903-A1)
30 25 20 IVX (A) IVX (A) IV1 15 10 IV2 5 IV3 0 -50 -25 0 25 50 TEMPERATURE (C) 75 100 5 V1 = 3.3V V2 = 2.5V V3 = 1.8V 30 25 20 15 10
IVX (A)
4
UW
75 75
29031 G07
3.3V Threshold Voltage vs Temperature
2.250
2.5V Threshold Voltage vs Temperature
2.950
2.235
2.220
2.925
2.205
2.900
2.190
100
2.875 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2.175 -50
-25
0 25 50 TEMPERATURE (C)
75
100
29031 G01
29031 G02
29031 G03
ADJ Threshold Voltage vs Temperature
-4.530 -4.555 -4.580 -4.605 -4.630 -4.655
-5.2V Threshold Voltage vs Temperature
0.505
0.500
0.495
100
0.490 -50
-25
0 25 50 TEMPERATURE (C)
75
100
-4.680 -50
-25
0 25 50 TEMPERATURE (C)
75
100
29031 G04
29031 G05
29031 G06
Supply Currents vs Temperature (LTC2903-B1)
V1 = 5V V2 = 3.3V V3 = 2.5V V4 = 1.8V IV1
Supply Currents vs Temperature (LTC2903-C1)
30 25 20 IV1 15 10 IV2 5 V1 = 5V V2 = 3.3V V3 = 1.8V V4 = -5.2V
IV2 IV4 0 -50 -25
IV3
IV3 0 -5 -50 IV4 -25 50 25 0 TEMPERATURE (C) 75 100
29031 G09
0 25 50 TEMPERATURE (C)
75
100
29031 G08
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LTC2903-1 TYPICAL PERFOR A CE CHARACTERISTICS
Supply Currents vs Temperature
25 LTC2903-E1 20 LTC2903-D1 IV1 (A) 15
400
TYPICAL TRANSIENT DURATION (s)
350 300 250 200 150 100 50 0 1 10 100 0.1 RESET COMPARATOR OVERDRIVE (% OF VRTX)
29031 G10
RESET TIME-OUT PERIOD, tRST (ms)
10
5
0 -50
-25
0 25 50 TEMPERATURE (C)
RST Output Voltage with 10k Pull-Up to V1
5.0 4.5 V1 = V2 = V3 LTC2903-B1, -C1 0.30 0.25
RST OUTPUT VOLTAGE (V)
RST OUTPUT VOLTAGE (V)
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 0.5 1 1.5 2 2.5 3 V1 (V) 3.5 4 4.5 5
RESET PIN VOLTAGE (V)
RST Current Sink Capability vs VCC
15
1.5
12 VOL = 0.4V
IRST (mA)
VOL (V)
6
VOL = 0.2V
0.6
VOL (V)
9
3
0
0
0.5
1
1.5
2
2.5 3 VCC (V)
3.5
UW
75
29031 G20
29031 G12
Transient Duration vs Comparator Overdrive
260 240 220 200 180 160
Reset Time-Out Period vs Temperature
RESET OCCURS ABOVE CURVE
100
140 -50
-25
0 25 50 TEMPERATURE (C)
75
100
29301 G11
RST Output Voltage with 10k Pull-Up to V1
0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 V1 = V2 = V3 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 V1 (V)
29301 G13
Low Voltage Reset Pull-Down Performance vs External Pull-Up Current and Input Supply Voltage
VIN = V1 = V2 = V3
0.20 0.15 0.10 0.05 V1 ONLY
20A 10A
5A 2A 1A 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 VIN, INPUT SUPPLY VOLTAGE (V) 1
0.01 0
29031 G14
RST Voltage Output Low vs RST Sink Current
LTC2903-A1, -E1 V1 = 3.3V 1.5 85C 25C 1.2 -45C 0.9 0.9
RST Voltage Output Low vs RST Sink Current
LTC2903-B1, -C1, -D1 V1 = 5V 25C
1.2
85C
-45C
0.6
0.3
0.3
0
0 0 5 10 15 25 30 IRST (mA) 20 35 40 45 0 10 20 40 30 IRST (mA) 50 60
4
4.5
5
29031 G15
29031 G16
29031 G16
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5
LTC2903-1 TYPICAL PERFOR A CE CHARACTERISTICS
RST Pull-Up Current vs V2
-90 LTC2903-A1, -B1, -C1 -80 V1, V3, V4 ABOVE THRESHOLD -70 -60 IRST (A) -50 -40 -30 -20 -10 0 0 0.5 1 1.5 2 2.5 3 V2 (V) 3.5 4 4.5 5 VRT25 VRT33 -80
IRST (A)
RST Pull-Up Current vs External Pull-Down Voltage on RST
-40 -35 -30 LTC2903-B1, -C1
-80 -70 -60
IRST (A)
IRST (A)
-25 -20 -15 -10 -5 0 0 0.5 1 2 1.5 VRST (V) 2.5 3 3.5 LTC2903-A1
6
UW
RST Pull-Up Current vs V1
LTC2903-D1, -E1 -70 V2, V3, V4 ABOVE THRESHOLD -60 -50 -40 -30 -20 -10 0 LTC2903-E1 LTC2903-D1
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V1 (V)
29031 G21
29031 G18
RST Pull-Up Current vs External Pull-Down Voltage on RST
LTC2903-E1
-50 -40 -30 -20 -10 0 0 1 2 3 VRST (V) 4 5 6
29031 G22
LTC2903-D1
29031 G19
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LTC2903-1
PI FU CTIO S
V1 (Pin 1): Voltage Input 1. Internal VCC is generated from the greater voltage on the V1 and V2 inputs. VCC = V1 for options D1 and E1. Bypass this pin to ground with a 0.1F (or greater) capacitor. GND (Pin 2): Ground. V2 (Pin 3): Voltage Input 2. Internal VCC is generated from the greater voltage on the V1 and V2 inputs. VCC = V1 for options D1 and E1. For option A1, B1, C1 bypass this pin to ground with a 0.1F (or greater) capacitor. V2 is an adjustable input for options D1 and E1. See Table 1b for recommended ADJ resistor values. V3 (Pin 4): Voltage Input 3. This input assists the RST pulldown circuitry below 1V (for options A1, B1 and C1 only). V3 is an adjustable input for options D1 and E1. See Table 1b for recommended ADJ resistor values. V4 (Pin 5): Voltage Input 4. Table 1 lists the recommended ADJ resistor values for options A1, B1 and C1. See Table 1b for options D1 and E1. RST (Pin 6): Reset Logic Output. Pulls low when any voltage input is below reset threshold and held low for 200ms after all voltage inputs exceed threshold. The pin contains a weak pull-up to V2 (V1 for options D1 and E1). Use an external pull-up for faster rise times or output voltages greater than V2 (V1 for options D1 and E1).
TI I G DIAGRA
W
U
U
UW
U
VX
VRTX tUV tRST 1.5V
29031 TD
RST
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LTC2903-1
BLOCK DIAGRA S
V1 1
V2 3
V3 4
V4 5
GND 2
V1 1
V2 3
V3 4
V4 5
GND 2
8
+
+
+
+
-
-
-
-
+
+
+
+
-
-
-
-
W
(LTC2903-A1, LTC2903-B1)
V1 V2
POWER DETECT
VCC V2 10A
RESET DELAY GENERATOR 200ms DELAY
6 RST
V1 V2 V3
LOW VOLTAGE PULL-DOWN
MONITORED VOLTAGES A1 V1 V2 BANDGAP REFERENCE
29031 BD1
B1 5V 3.3V 2.5V 1.8V
3.3V 2.5V 1.8V ADJ
V3 V4
0.5V
(LTC2903-C1)
V1 V2
POWER DETECT
VCC V2 10A
RESET DELAY GENERATOR 200ms DELAY
6 RST
V1 V2 V3
LOW VOLTAGE PULL-DOWN
MONITORED VOLTAGES V1 V2 V3 BANDGAP REFERENCE
29031 BD3
5V 3.3V 1.8V -5.2V
V4
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LTC2903-1
BLOCK DIAGRA S
(LTC2903-D1, LTC2903-E1)
V1 1
V2 3
V3 4
V4 5
GND 2 0.5V
APPLICATIO S I FOR ATIO
Power-Up
The LTC2903-1 issues a logic low on the RST output when an input supply voltage resides below the prescribed threshold voltage. Ideally, the RST logic output would remain low with the input supply voltage down to zero volts. Most supervisors lack pull-down capability below 1V. The LTC2903-1 power supply supervisors incorporate a new low voltage pull-down circuit that can hold the RST line low with as little as 200mV of input supply voltage on V1, V2 or V3 (V1 only for options D1 and E1). The pull-down circuit helps maintain a low impedance path to ground, reducing the risk of floating the RST node to undetermined voltages. Such voltages may trigger external logic causing erroneous reset operation(s). Furthermore, a mid-scale voltage could cause external circuits to operate in the middle of their voltage transfer characteristic, consuming more quiescent current than normal. These conditions could cause serious system reliability problems.
IRST (A)
U
+
+
+
+
-
-
-
-
W
W
V1
POWER DETECT
VCC V1 10A
RESET DELAY GENERATOR 200ms DELAY
6 RST
V1
LOW VOLTAGE PULL-DOWN
MONITORED VOLTAGES D1 V1 V2 BANDGAP REFERENCE
29031 BD2
E1 5V ADJ ADJ ADJ
3.3V ADJ ADJ ADJ
V3 V4
UU
When V1, V2 and V3 are ramped simultaneously (for options A1, B1 and C1 only), the reset pull-down current increases up to three times the current that may be pulled with a single input. Figure 1 demonstrates the reset pin
10000 TA = 25C VRST = 0.3VCC
1000
100
V1 = V2 = V3
V1 ONLY
10
1 0 0.2 0.4 0.6 VCC (V) 0.8 1.0 1.2
29031 F01
Figure 1. RST Pull-Down Current vs VCC
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9
LTC2903-1
APPLICATIO S I FOR ATIO
current sinking ability for single supply and triple supplytracking applications. Figure 2 shows a detailed view of the reset pin voltage with a 10k pull-up resistor to V1. The LTC2903-1 supervisors derive their internal supply voltage (VCC) automatically from the greater voltage on the V1 and V2 inputs (VCC = V1 for options D1 and E1). With all supply inputs above threshold, the quiescent current drawn from VCC is 20A (typ). Supply Monitoring The LTC2903-1 accurately monitors four inputs in a small 6-lead SOT-23 package. The low voltage reset output includes an integrated 200ms reset delay timer. The reset line pulls high 200ms after all voltage inputs exceed their respective thresholds. The reset output remains low during power-up, power-down and brownout conditions on any of the voltage inputs.
0.7 0.6 TA = 25C
RST OUTPUT VOLTAGE (V)
0.5 0.4 0.3
COMPETITION PART
0.2 0.1 0
V1 ONLY V1 = V2 = V3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 V1 (V)
29031 F02
Figure 2. RST Output Voltage with a 10k Pull-Up to V1 (Enlarged Area of Detail)
10
U
Triple Adjustable Options (LTC2903-D1, LTC2903-E1) LTC2903-D1 and LTC2903-E1 provide 3 adjustable inputs: V2, V3 and V4. The V1 threshold is 3.086V (3.3V, 5%) for option D1 and 4.675 (5V, 5%) for option E1. For each supply monitored by an adjustable input, connect an external resistor divider (R1 and R2) between the positive voltage being sensed and ground. The tap point for each divider is then connected to each adjustable input. All adjustable inputs are compared to an internal 0.5V reference. Figure 3 shows how each adjustable input is configured. Calculate the trip voltage from: R1 VTRIP = 0.5V 1 + R2
VTRIP LTC2903-A1 R1 V4 R2
W
UU
- +
0.5V
+ -
29031 F03
Figure 3. Setting the Positive Adjustable Trip Point
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LTC2903-1
APPLICATIO S I FOR ATIO
Table 1a contains suggested 1% resistor values for the ADJ inputs to obtain nominal -11.5% thresholds. Connect unused supervisor inputs to the highest supply voltage available.
Table 1a. Suggested 1% Resistor Values for the -11.5% ADJ Inputs
VSUPPLY (V) 12 10 8 7.5 6 5 3.3 3 2.5 1.8 1.5 1.2 1 0.9 VTRIP (V) 10.75 8.95 7.15 6.7 5.38 4.435 2.935 2.66 2.2 1.605 1.325 1.065 0.884 0.795 R1 (k) 2050 1690 1330 1240 976 787 487 432 340 221 165 113 76.8 59 R2(k) 100 100 100 100 100 100 100 100 100 100 100 100 100 100
Table 1b contains suggested 1% resistor values for the ADJ inputs to obtain nominal -6.5% thresholds.
Table 1b. Suggested 1% Resistor Values for the -6.5% ADJ Inputs
VSUPPLY (V) 12 10 8 7.5 6 5 3.3 3 2.5 1.8 1.5 1.2 1.0 0.9 0.8 0.7 0.6 VTRIP (V) 11.25 9.4 7.5 7 5.6 4.725 3.055 2.82 2.325 1.685 1.410 1.120 0.933 0.840 0.750 0.655 0.561 R1 (k) 2150 1780 1400 1300 1020 845 511 464 365 237 182 124 86.6 68.1 49.9 30.9 12.1 R2(k) 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
TYPICAL THRESHOLD ACCURACY (%)
U
Implications of Threshold Accuracy Specifying system voltage margin for worst-case operation requires consideration of three factors: power supply tolerance, IC supply voltage tolerance and supervisor reset threshold accuracy. Highly accurate supervisors ease the design challenge by decreasing the overall voltage margin required for reliable system operation. Consider a 5V system with a 10% power supply tolerance band. System ICs powered by this supply must operate reliably within this band (and a little more, as explained below). The bottom of the supply tolerance band, at 4.5V (5V - 10%), is the exact voltage at which a perfectly accurate supervisor generates a reset. Such a perfectly accurate supervisor does not exist--the actual reset threshold may vary over a specified band (1.5% for the LTC2903-1 supervisors). Figure 4 shows the typical relative threshold accuracy for all four inputs, over temperature. With this variation of reset threshold in mind, the nominal reset threshold of the supervisor resides below the minimum supply voltage, just enough so that the reset threshold band and the power supply tolerance bands do not overlap. If the two bands overlap, the supervisor could generate a false or nuisance reset when the power supply remains within its specified tolerance band (say, at 4.6V). Adding half of the reset threshold accuracy spread (1.5%) to the ideal 10% thresholds puts the LTC2903-1 thresholds at 11.5% (typ) below the nominal input voltage. For example, the 5V typical threshold is 4.425V, or 75mV below the ideal threshold of 4.500V. The guaranteed threshold lies in the band between 4.500V and 4.350V over temperature.
1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -50 -25 50 25 0 TEMPERATURE (C) 75 100
29031 F04
W
UU
Figure 4. LTC2903 Typical Threshold Accuracy vs Temperature
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LTC2903-1
APPLICATIO S I FOR ATIO
The powered system must work reliably down to the lowest voltage in the threshold band or risk malfunction before the reset line falls. In the 5V example, using the 1.5% accurate supervisor, the system ICs must work down to 4.35V. System ICs working with a 2.5% accurate supervisor must operate down to 4.25V, increasing the required system voltage margin and the probability of system malfunction. In any supervisory application, supply noise riding on the monitored DC voltage can cause spurious resets, particularly when the monitored voltage approaches the reset threshold. A less than desirable but commonly used technique used to mitigate this problem adds hysteresis to the input comparator. The amount of added hysteresis, usually specified as a percentage of the trip threshold, effectively degrades the advertised accuracy of the part. To maintain high accuracy, the LTC2903-1 does not use hysteresis. To minimize spurious resets while maintaining threshold accuracy, the LTC2903-1 employs two forms of noise filtering. The first line of defense incorporates proprietary tailoring of the comparator transient response. Transient events receive electronic integration in the comparator and must exceed a certain magnitude and duration to cause the comparator to switch. Figure 5 illustrates the typical transient duration versus comparator overdrive (as a percentage of the trip threshold VRT) required to trip the comparators. Once any comparator is switched, the reset line pulls low. The reset time-out counter starts once
400 TA = 25C
TYPICAL TRANSIENT DURATION (s)
350 300 250 200 150 100 50 0 0.1 1 10 100 RESET COMPARATOR OVERDRIVE (% OF VRTX)
29031 F05
RESET OCCURS ABOVE CURVE
Figure 5. Typical Transient Duration vs Overdrive Required to Trip Comparator
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U
all inputs return above threshold. The nominal reset delay time is 200ms. The counter clears whenever any input drops back below threshold. This reset delay time effectively provides further filtering of the voltage inputs. A noisy input with frequency components of sufficient magnitude above f = 1/tRST = 5Hz holds the reset line low, preventing oscillatory behavior on the reset line. Although all four comparators have built-in glitch filtering, use bypass capacitors on the V1 and V2 inputs because the greater of V1 or V2 supplies the VCC (options A1, B1 and C1) for the part (a 0.1F ceramic capacitor satisfies most applications). Apply filter capacitors on the V3 and V4 inputs in extremely noisy situations. Options D1 and E1 require a bypass capacitor only on V1. Apply filter capacitors on V2, V3 and V4 adjustable inputs in extremely noisy situations. Reset Output Rise and Fall Time Estimation The reset output line contains a weak pull-up current source to the V2 supply (V1 for options D1 and E1). Use an external pull-up resistor when the output needs to pull to another voltage and/or when the reset output needs a faster rise time. The open-drain output allows for wiredOR connections when more than one signal needs to pull down on the reset line. Estimate output rise time for the open-drain output without an external pull-up using: tRISE 2.2 * RPU * CLOAD where RPU is the on-resistance of the pull-up transistor and CLOAD is the external load capacitance on the pin. At room temperature, the average RPU is approximately 50k. When externally pulling up to voltages higher than V2 (V1 for options D1 and E1), an internal network automatically protects the weak pull-up circuitry from reverse currents. The reset output has very strong pull-down capability. Estimate the output fall time using: tFALL 2.2 * RPD * CLOAD where RPD is the on-resistance of the pull-down transistor and CLOAD is the external load capacitance on the pin. At room temperature, the average RPD is approximately 40. With a 150pF load capacitance the reset line can pull down in about 13ns.
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W
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LTC2903-1
TYPICAL APPLICATIO S
Quad Supply Monitor with Adjustable Input
U
3.3V C1 0.1F
1
V1
RST
6 R1 76.8k R2 100k
SYSTEM RESET
LTC2903-A1 2 GND V4 5
C2 0.1F 2.5V 3 V2 V3 4
1V (VTRIP = 0.884V) 1.8V
2903 TA02
Fixed Quad Supply Monitor with LED Indication on RST
5V 1k LED 5V C1 0.1F 2 C2 0.1F 3.3V 3 V2 V3 4
2903 TA05
1
V1
RST
6
SYSTEM RESET
LTC2903-B1 GND V4 5 1.8V
2.5V
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LTC2903-1
TYPICAL APPLICATIO S
Quad Supply Monitor with Unused Input Pulled Above Threshold
1.8V (VTRIP = 1.685V)
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5V C1 0.1F
1
V1
RST
6
SYSTEM RESET
LTC2903-C1 2 GND V4 5 -5.2V
C2 0.1F 3.3V 3 V2 V3 4
2903 TA03
Quad Supply Monitor with 3 Adjustable Inputs Monitoring 5% Supplies
1 C1 0.1F 2 6
3.3V
V1
RST
SYSTEM RESET
LTC2903-D1 GND V4 5 100k 2150k 12V (VTRIP = 11.25V) 365k 100k 2.5V (VTRIP = 2.325V)
237k
3 100k
V2
V3
2903 TA06
4
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LTC2903-1
PACKAGE DESCRIPTIO U
S6 Package 6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE ID 0.95 BSC 0.30 - 0.45 6 PLCS (NOTE 3) 0.80 - 0.90 0.20 BSC 1.00 MAX DATUM `A' 0.01 - 0.10 0.09 - 0.20 (NOTE 3) 1.90 BSC
S6 TSOT-23 0302
0.62 MAX
0.95 REF
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.30 - 0.50 REF
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
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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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LTC2903-1
TYPICAL APPLICATIO U
Quad Supply Monitor with Manual Reset Button
3.3V R3 10k 3.3V C1 0.1F V1 RST 12V (VTRIP = 10.75V) SYSTEM RESET MANUAL RESET BUTTON R1 RESD* (NORMALLY OPEN) 2050k 10k LTC2903-A1 GND C2 0.1F 2.5V V2 V3
2903 TA04
V4 R2 100k 1.8V
*OPTIONAL RESISTOR RECOMMENDED TO EXTEND ESD TOLERANCE
RELATED PARTS
PART NUMBER LTC690 LTC694-3.3 LTC699 LTC1232 LTC1326 LTC1326-2.5 LTC1536 LTC1726-2.5 LTC1726-5 LTC1727-2.5/LTC1727-5 LTC1728-2.5/LTC1728-5 LTC1985-1.8 LTC2900 LTC2901 LTC2902 LTC2904/LTC2905/ LTC2906/LTC2907 LTC2908 LTC2920-1/LTC2920-2 LTC2921/LTC2922 LTC2923 DESCRIPTION 5V Supply Monitor, Watchdog Timer and Battery Backup 3.3V Supply Monitor, Watchdog Timer and Battery Backup 5V Supply Monitor and Watchdog Timer 5V Supply Monitor, Watchdog Timer and Pushbutton Reset Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ Precision Triple Supply Monitor for PCI Applications Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ Micropower Triple Supply Monitor for 5V, 3.3V and ADJ Micropower Triple Supply Monitors with Open-Drain Reset Micropower Triple Supply Monitors with Open-Drain Reset Micropower Triple Supply Monitor with Push-Pull Reset Output Quad Voltage Monitor in MSOP Quad Voltage Monitor with Watchdog Quad Voltage Monitor with RST Disable Precision Dual Supply Monitors Precision Six Supply Monitor Single/Dual Power Supply Margining Controller Power Supply Trackers with Input Monitors Power Supply Tracking Controller COMMENTS 4.65 Threshold 2.9V Threshold 4.65 Threshold 4.37V/4.62V Threshold 4.725V, 3.118V, 1V Thresholds (0.75%) Meets PCI tFAIL Timing Specifications Adjustable RESET and Watchdog Time Outs Adjustable RESET and Watchdog Time Outs Individual Monitor Outputs in MSOP 5-Lead SOT-23 Package 5-Lead SOT-23 Package 5-Lead SOT-23 Package 16 User Selectable Combinations, 1.5% Threshold Accuracy 16 User Selectable Combinations, Adjustable Timers 16 User Selectable Combinations, Adjustable Tolerance Pin Selectable Thresholds 8-Lead SOT-23 and DFN Packages <0.4% Margin Voltage Precision 3 (LTC2921) and 5 (LTC2922) Remote Sense Switches Tracks Up and Down, Supply Sequencing
Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and ADJ 2.363V, 3.118V, 1V Thresholds (0.75%)
LTC1728-1.8/LTC1728-3.3 Micropower Triple Supply Monitors with Open-Drain Reset
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT/TP 1004 1K * PRINTED IN THE USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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