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LTC2902 Programmable Quad Supply Monitor with Adjustable Reset Timer and Supply Tolerance DESCRIPTIO
The LTC(R)2902 is a programmable supply monitor for systems with up to four supply voltages. One of 16 preset or adjustable voltage monitor combinations can be selected using an external resistor divider connected to the program pin. The preset voltage thresholds are digitally programmable to 5%, 7.5%, 10% or 12.5% below the nominal operating voltage, and are accurate to 1.5% over temperature. All four voltage comparator outputs are connected to separate pins for individual supply monitoring. The reset delay time is adjustable using an external capacitor. Tight voltage threshold accuracy and glitch immunity ensure reliable reset operation without false triggering. The RST output is guaranteed to be in the correct state for VCC down to 1V and may be disabled during supply margin testing. The LTC2902-1 features an open-drain RST output, while the LTC2902-2 has a push-pull RST output. The 43A supply current makes the LTC2902 ideal for power conscious systems and the part may be configured to monitor less than four inputs. The LTC2902-1/LTC2902-2 are available in the 16-lead narrow SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
s s
s
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s s s s s s s s
Simultaneously Monitors Four Supplies 16 User Selectable Combinations of 5V, 3.3V, 3V, 2.5V, 1.8V, 1.5V and/or Adjustable Voltage Thresholds Guaranteed Threshold Accuracy: 1.5% of Monitored Voltage Over Temperature Selectable Supply Tolerance: 5%, 7.5%, 10%, 12.5% Below Monitored Voltage Low Supply Current: 43A Typ Adjustable Reset Time RESET Disable Pin for Margining Applications Open-Drain RST Output (LTC2902-1) Push-Pull RST Output (LTC2902-2) Individual Nondelayed Monitor Outputs for Each Supply Power Supply Glitch Immunity Guaranteed RESET for VCC 1V
APPLICATIO S
s s s s s
Desktop and Notebook Computers Multivoltage Systems Telecom Equipment Portable Battery-Powered Equipment Network Servers
TYPICAL APPLICATIO
Quad Supply Monitor with Adjustable Tolerance (5V, 3.3V, 2.5V, 1.8V)
5V 3.3V DC/DC CONVERTER 2.5V 1.8V 13 R3 POWER 10k V4 GOOD 2 V1 COMP1 16 COMP2 14 1 V2 COMP3 15 LTC2902-2 COMP4 6 12 VREF RST 8 RDIS MARGIN 7 T0 TOLERANCE = 5% 11 9 VPG T1 GND CRT tRST = 216ms 10 5 CRT 47nF 2902 TA01 4 V3 3 SYSTEM LOGIC
C1 0.1F
C2 0.1F R1 59k 1% R2 40.2k 1%
U
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2902f
1
LTC2902
ABSOLUTE
(Notes 1, 2, 3)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW COMP3 COMP1 V3 V1 CRT RST T0 RDIS 1 2 3 4 5 6 7 8 16 COMP2 15 COMP4 14 V2 13 V4 12 VREF 11 VPG 10 GND 9 T1
V1, V2, V3, V4, VPG ..................................... - 0.3V to 7V RST (LTC2902-1)........................................ - 0.3V to 7V RST (LTC2902-2).......................... - 0.3V to (V2 + 0.3V) COMPX, RDIS ............................................. - 0.3V to 7V T0, T1 .......................................... - 0.3V to (VCC + 0.3V) CRT ............................................. - 0.3V to (VCC + 0.3V) VREF ............................................. - 0.3V to (VCC + 0.3V) Reference Load Current (IVREF) ............................ 1mA V4 Input Current (- ADJ Mode) ............................ -1mA Operating Temperature Range LTC2902-1C/LTC2902-2C ....................... 0C to 70C LTC2902-1I/LTC2902-2I .................... -40C to 85C Storage Temperature Range .................. - 65C to 150C Lead Temperature (Soldering, 10 sec)................... 300C
ORDER PART NUMBER LTC2902-1CGN LTC2902-2CGN LTC2902-1IGN LTC2902-2IGN GN16 PART MARKING 29021 29022 29021I 29022I
GN PACKAGE 16-LEAD PLASTIC SSOP
TJMAX = 125C, JA = 130C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL VRT50 PARAMETER 5V, 5% Reset Threshold 5V, 7.5% Reset Threshold 5V, 10% Reset Threshold 5V, 12.5% Reset Threshold 3.3V, 5% Reset Threshold 3.3V, 7.5% Reset Threshold 3.3V, 10% Reset Threshold 3.3V, 12.5% Reset Threshold 3V, 5% Reset Threshold 3V, 7.5% Reset Threshold 3V, 10% Reset Threshold 3V, 12.5% Reset Threshold 2.5V, 5% Reset Threshold 2.5V, 7.5% Reset Threshold 2.5V, 10% Reset Threshold 2.5V, 12.5% Reset Threshold 1.8V, 5% Reset Threshold 1.8V, 7.5% Reset Threshold 1.8V, 10% Reset Threshold 1.8V, 12.5% Reset Threshold 1.5V, 5% Reset Threshold 1.5V, 7.5% Reset Threshold 1.5V, 10% Reset Threshold 1.5V, 12.5% Reset Threshold ADJ, 5% Reset Threshold ADJ, 7.5% Reset Threshold ADJ, 10% Reset Threshold ADJ, 12.5% Reset Threshold
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, unless otherwise noted. (Note 3)
CONDITIONS V1 Input Threshold
q q q q q q q q q q q q q q q q q q q q q q q q q q q q
MIN 4.600 4.475 4.350 4.225 3.036 2.954 2.871 2.789 2.760 2.685 2.610 2.535 2.300 2.238 2.175 2.113 1.656 1.611 1.566 1.521 1.380 1.343 1.305 1.268 0.492 0.479 0.466 0.453
TYP 4.675 4.550 4.425 4.300 3.086 3.003 2.921 2.838 2.805 2.730 2.655 2.580 2.338 2.275 2.213 2.150 1.683 1.638 1.593 1.548 1.403 1.365 1.328 1.290 0.500 0.487 0.473 0.460
MAX 4.750 4.625 4.500 4.375 3.135 3.053 2.970 2.888 2.850 2.775 2.700 2.625 2.375 2.313 2.250 2.188 1.710 1.665 1.620 1.575 1.425 1.388 1.350 1.313 0.508 0.494 0.481 0.467
UNITS V V V V V V V V V V V V V V V V V V V V V V V V V V V V
2902f
VRT33
V1, V2 Input Threshold
VRT30
V2 Input Threshold
VRT25
V2, V3 Input Threshold
VRT18
V3, V4 Input Threshold
VRT15
V3, V4 Input Threshold
VRTA
V3, V4 Input Threshold
2
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LTC2902
ELECTRICAL CHARACTERISTICS
SYMBOL VRTAN VCC VCCMINP VCCMINC VREF PARAMETER - ADJ Reset Threshold Minimum Internal Operating Voltage Minimum Required for Programming Minimum Required for Comparators Reference Voltage
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, unless otherwise noted. (Note 3)
CONDITIONS V4 Input Threshold RST, COMPX in Correct Logic State; VCC Rising Prior to Program VCC Rising VCC Falling VCC 2.3V, IVREF = 1mA, CREF 1000pF T0 Low, T1 Low T0 Low, T1 High T0 High, T1 Low T0 High, T1 High VCC VCCMINP VPG = VREF V1 = 5V, IVREF = 12A, (Note 4) V2 = 3.3V V3 = 2.5V V3 = 0.55V (ADJ Mode) V4 = 1.8V V4 = 0.55V (ADJ Mode) V4 = -0.05V (-ADJ Mode) VCRT = 0V VCRT = 1.3V CRT = 1500pF VX Less Than Reset Threshold VRTX by More Than 1% ISINK = 2.5mA; V1 = 3V, V2 = 3V; V3, V4 = 0V; VPG = 0V ISINK = 100A; V2 = 1V; V1, V3, V4 = 0V ISINK = 100A; V1 = 1V; V2, V3, V4 = 0V VOH VOH Output Voltage High RST, COMPX (Note 5) Output Voltage High RST (LTC2902-2) (Note 6) T0, T1 Low Level Input Voltage T0, T1 High Level Input Voltage T0, T1 Input Current RDIS Input Threshold Low RDIS Input Threshold High RDIS Pull-Up Current ISOURCE = 1A ISOURCE = 200A
q q q q q q q q q q q q q q q q q q
MIN - 18
TYP 0
MAX 18 1 2.42 2.32
UNITS mV V V V V V V V V nA A A A nA A nA nA A A ms s
1.192 1.160 1.128 1.096 0
1.210 1.178 1.146 1.113
1.228 1.195 1.163 1.130 VREF 20
VPG IVPG IV1 IV2 IV3 IV4
Programming Voltage Range VPG Input Current V1 Input Current V2 Input Current V3 Input Current V4 Input Current
43 0.8 0.52 -15 0.34 -15 -15 -1.4 10 5 -2 20 7 150 0.15 0.05 0.05 V2 - 1 0.8 * V2
75 2 1.2 15 0.8 15 15 -2.6 30 9
q q q q q q
ICRT(UP) ICRT(DN) tRST tUV VOL
CRT Pull-Up Current CRT Pull-Down Current Reset Time-Out Period VX Undervoltage Detect to RST or COMPX Output Voltage Low RST, COMPX
0.4 0.3 0.3
V V V V V
Digital Inputs T0, T1, RDIS VIL VIH IINTOL VIL VIH IRDIS VCC = 3.3V to 5.5V VCC = 3.3V to 5.5V T0 = 0V, T1 = VCC VCC = 3.3V to 5.5V VCC = 3.3V to 5.5V VRDIS = 0V
q q q q q
0.3VCC 0.7VCC 0.1 0.4 1.6 -10 1
V V A V V A
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All voltage values are with respect to GND. Note 3: The greater of V1, V2 is the internal supply voltage (VCC). Note 4: Under static no-fault conditions, V1 will necessarily supply quiescent current. If at any time V2 is larger than V1, V2 must be capable of supplying the quiescent current, programming (transient) current and reference load current.
Note 5: The output pins RST and COMPX have internal pull-ups to V2 of typically 6A. However, external pull-up resistors may be used when faster rise times are required or for VOH voltages greater than V2. Note 6: The push-pull RST output pin on the LTC2902-2 is actively pulled up to V2.
2902f
3
LTC2902
TEST CIRCUITS
V1 V2 V3 V4 RST LTC2902-1 OR COMPX ISOURCE 1A
LTC2902-1 V1 V2 V3 V4
2902 F02
RST OR COMPX
ISINK 2.5mA, 100A
V1 V2 V3 V4
LTC2902-2 RST ISOURCE 200A
2902 F01
2902 F03
Figure 1. RST, COMPX VOH Test
Figure 2. RST, COMPX VOL Test
Figure 3. Active Pull-Up RST VOH Test
TI I G DIAGRA
TYPICAL PERFOR A CE CHARACTERISTICS
5V Threshold Voltage vs Temperature
4.75 4.70 3.135 5% 3.100
THRESHOLD VOLTAGE, VRT33 (V)
THRESHOLD VOLTAGE, VRT50 (V)
4.65 4.60 4.55 4.50 4.45 4.40 4.35 4.30 4.25 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100 12.5% 10% 7.5%
3.065 3.030 2.995 2.960 2.925 2.890 2.855 2.820 2.785 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100 12.5% 10% 7.5%
THRESHOLD VOLTAGE, VRT30 (V)
4
UW
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VX Monitor Timing
VRTX tUV RST tRST 1.5V VX
2902 TD
UW
COMPX
3.3V Threshold Voltage vs Temperature
2.850 5% 2.815 2.780 2.745 2.710 2.675 2.640 2.605 2.570
3V Threshold Voltage vs Temperature
5%
7.5%
10%
12.5%
2.535 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
80
100
2902 G01
2902 G02
2902 G03
2902f
LTC2902 TYPICAL PERFOR A CE CHARACTERISTICS
2.5V Threshold Voltage vs Temperature
2.375 2.350 5% THRESHOLD VOLTAGE, VRT18 (V) 1.710 1.685 1.660 7.5% 1.635 1.610 1.585 1.560 1.535 1.510 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100 12.5% 10%
THRESHOLD VOLTAGE, VRT25 (V)
2.325 2.300 2.275 2.250 2.225 2.200 2.175 2.150 2.125 2.100 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100 12.5% 10% 7.5%
THRESHOLD VOLTAGE, VRT15 (V)
ADJ Threshold Voltage vs Temperature
0.508 0.503 5% THRESHOLD VOLTAGE, VRTAN (V) 0.012 0.006 0.018
THRESHOLD VOLTAGE, VRTA (V)
0.498 0.493 0.488 0.483 0.478 0.473 0.468 0.463 0.458 0.453 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100 12.5% 10% 7.5%
VREF (V)
IV1 vs Temperature
100 V1 = 5V 90 V2 = 3.3V V3 = 2.5V 80 V4 = 1.8V 70
IV2 (A)
IV1 (A)
50 40 30 20 10 0 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100
1.0 0.9 0.8 0.7 0.6 0.5 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100
IV3 (A)
60
UW
1.8V Threshold Voltage vs Temperature
1.425 5% 1.405 1.385 1.365 1.345
1.5V Threshold Voltage vs Temperature
5%
7.5%
10% 1.325 1.305 1.285 1.265 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100 12.5%
2902 G04
2902 G05
2902 G06
- ADJ Threshold Voltage vs Temperature
1.228 1.216 1.204 1.192 1.180 1.168 1.156 1.144 1.132 -0.012 -0.018 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 1.112 1.108 80 100
VREF vs Temperature
5%
7.5%
0 -0.006
10%
12.5%
1.096 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
80
100
2902 G07
2902 G08
2902 G09
IV2 vs Temperature
1.5 V1 = 5V 1.4 V2 = 3.3V V3 = 2.5V 1.3 V4 = 1.8V 1.2 1.1 1.1
IV3 vs Temperature
V1 = 5V 1.0 V2 = 3.3V V3 = 2.5V 0.9 V4 = 1.8V 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100
2902 G10
2902 G11
2902 G12
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5
LTC2902 TYPICAL PERFOR A CE CHARACTERISTICS
IV4 vs Temperature
TYPICAL TRANSIENT DURATION (s)
1.0 V1 = 5V 0.9 V2 = 3.3V V3 = 2.5V 0.8 V4 = 1.8V 0.7
TYPICAL TRANSIENT DURATION (s)
IV4 (A)
0.6 0.5 0.4 0.3 0.2 0.1 0 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100
RST Output Voltage vs V1, VPG = 0V
5
RESET TIME-OUT PERIOD, tRST (ms)
RESET TIME-OUT PERIOD, tRST (sec)
RST OUTPUT VOLTAGE (V)
4
V1 = V2 = V3 = V4 10k PULL-UP FROM RST TO V1 TA = 25C
3
2
1
0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 V1 (V)
2902 G15
RST, COMPX ISINK vs Supply Voltage
10 9 8 7 ISINK (mA) 6 5 4 3 2 1 0 0 1 2 3 4 V1 OR V2 (V) 5 6
2902 G18
TA = 25C
VOL = 0.4V 2.0
VOL (V)
1.5 1.0 0.5 0
VOH (V)
VOL = 0.2V
6
UW
2902 G13
Typical Transient Duration vs Comparator Overdrive (V1, V2)
450 400 350 300 250 200 150 100 50 0 0.1 1 10 100 RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
2902 G14
Typical Transient Duration vs Comparator Overdrive (V3, V4)
220 200 180 160 140 120 100 80 60 40 20 0 1 10 100 0.1 RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
2902 G25
TA = 25C
TA = 25C RESET OCCURS ABOVE CURVE
RESET OCCURS ABOVE CURVE
Reset Time-Out Period vs Temperature
8.9 CRT = 1500pF 8.4 (SILVER MICA) 7.9 7.4 6.9 6.4 5.9 5.4 4.9 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100
Reset Time-Out Period vs Capacitance
10
TA = 25C
1
100m
10m
1m
100 10p
100p
10n 1n CRT (FARAD)
100n
1
2902 G17
2902 G16
RST, COMPX Voltage Output Low vs Output Sink Current
3.0 V2 = 3V V1 = 5V 2.5 85C - 40C 2.5 2.0 25C 3.0 3.5
RST High Level Output Voltage vs Output Source Current (LTC2902-2)
V1 = 5V V2 = 3V V3 = 2.5V V4 = 1V
- 40C 1.5 1.0 85C 0.5 0 25C
0
10
20
30
50 60 ISINK (mA) 40
70
80
90
0
0.5
1 1.5 ISOURCE (mA)
2
2.5
2902 G20
2902 G19
2902f
LTC2902 TYPICAL PERFOR A CE CHARACTERISTICS
COMPX Pull-Up Current vs V2 (COMPX Held at 0V)
20 18 16
PULL-UP CURRENT (A)
TA = 25C COMPX PROPAGATION DELAY (s)
14 12 10 8 6 4 2 0 1 1.5 2 2.5 3 3.5 V2 (V) 4 4.5 5
RST Pull-Up Current vs V2 (LTC2902-1)
20 18
PULL-UP CURRENT (mA)
TA = 25C
16 PULL-UP CURRENT (A) 14 12 10 8 6 4 2 0 2 2.5 3 3.5 V2 (V) 4 4.5 5
2902 G23
VRT33 VRT30 VRT25
PI FU CTIO S
COMP3 (Pin 1): Comparator Output 3. Nondelayed, active high logic output with weak pull-up to V2. Pulls high when V3 is above reset threshold. May be pulled greater than V2 using external pull-up. COMP1 (Pin 2): Comparator Output 1. Nondelayed, active high logic output with weak pull-up to V2. Pulls high when V1 is above reset threshold. May be pulled greater than V2 using external pull-up. V3 (Pin 3): Voltage Input 3. Select from 2.5V, 1.8V, 1.5V or ADJ. See Table 1 for details. V1 (Pin 4): Voltage Input 1. Select from 5V or 3.3V. See Table 1 for details. The greater of (V1, V2) is also VCC for the chip. Bypass this pin to ground with a 0.1F (or greater) capacitor. CRT (Pin 5): Reset Delay Time Programming Pin. Attach an external capacitor (CRT) to GND to set a reset delay time of 4.6ms/nF. Leaving the pin open generates a minimum delay of approximately 50s. A 47nF capacitor will generate a 216ms reset delay time.
UW
COMPX Propagation Delay vs Input Overdrive Above Threshold
250 TA = 25C
200
150
100 V1, V2 50 V3, V4 0 1000 10 100 INPUT OVERDRIVE ABOVE THRESHOLD (mV)
2902 G22
2902 G21
RST Pull-Up Current vs V2 (LTC2902-2)
6 5 4 3 2 1 0 2 2.5 3 3.5 V2 (V) 4 4.5 5
2902 G24
TA = 25C
VRT33 VRT30 VRT25
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LTC2902
PI FU CTIO S
RST (Pin 6): Reset Logic Output. Active low with weak pull-up to V2 (LTC2902-1) or active pull-up to V2 (LTC2902-2). Pulls low when any voltage input is below the reset threshold and held low for programmed delay time after all voltage inputs are above threshold. May be pulled above V2 using an external pull-up (LTC2902-1 only). T0 (Pin 7): Digital Input for Supply Tolerance Selection (5%, 7.5%, 10% or 12.5%). Used in conjunction with T1 (Pin 9). See Applications Information for tolerance selection chart (Table 4). RDIS (Pin 8): Digital Input for RST Disable. A low input on this pin forces the RST output to V2 (or pull-up voltage). Useful for determining supply margins without issuing reset command to processor. A weak internal pull-up allows pin to be left floating for normal monitor operation. T1 (Pin 9): Digital Input for Supply Tolerance Selection (5%, 7.5%, 10% or 12.5%). Used in conjunction with T0 (Pin 7). See Applications Information for tolerance selection chart (Table 4). GND (Pin 10): Ground. VPG (Pin 11): Voltage Threshold Combination Select Input. Connect to an external 1% resistive divider between VREF and GND to select 1 of 16 combinations of preset and/or adjustable voltage thresholds (see Table 1). Do not add capacitance on the VPG pin. VREF (Pin 12): Buffered Reference Voltage. A 1.210V nominal reference used for programming voltage (VPG) and for the offset of negative adjustable applications. The buffered reference can source and sink up to 1mA. The reference can drive a bypass capacitor of up to 1000pF without oscillation. V4 (Pin 13): Voltage Input 4. Select from 1.8V, 1.5V, ADJ or - ADJ. See Table 1 for details. V2 (Pin 14): Voltage Input 2. Select from 3.3V, 3V or 2.5V. See Table 1 for details. The greater of (V1, V2) is also VCC for chip. Bypass this pin to ground with a 0.1F (or greater) capacitor. All logic outputs (COMP1, COMP2, COMP3, COMP4) are weakly pulled up to V2. RST is weakly pulled up to V2 in the LTC2902-1 and RST is actively pulled up to V2 in the LTC2902-2. COMP4 (Pin 15): Comparator Output 4. Nondelayed, active high logic output with weak pull-up to V2. Pulls high when V4 is above reset threshold. May be pulled greater than V2 using external pull-up. COMP2 (Pin 16): Comparator Output 2. Nondelayed, active high logic output with weak pull-up to V2. Pulls high when V2 is above reset threshold. May be pulled greater than V2 using external pull-up.
8
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2902f
LTC2902
BLOCK DIAGRA
V3 3 V4 13 GND 10
RESISTIVE DIVIDER MATRIX
VPG 11 A/D BUFFER VREF 12
BUFFER GAIN ADJUST
7 T0
9 T1
+
V2 14
+
+
-
V1 4
+
-
-
-
W
V1 V2 POWER DETECT VCC 6A COMP1 V2 2 V2 6A COMP2 16 V2 6A COMP3 1 V2 6A BANDGAP REFERENCE COMP4 15 ADJUSTABLE RESET PULSE GENERATOR VCC V2 LTC2902-1 2A 6A 22A 10A VCC RST 6 5 CRT CRT LTC2902-2 V2 RST 6 8 RDIS
2902 DB-1
2902f
9
LTC2902
APPLICATIO S I FOR ATIO
Power-Up
On power-up, the larger of V1 or V2 will power the drive circuits for the RST and the COMPX pins. This ensures that the RST and COMPX outputs will be low as soon as V1 or V2 reaches 1V. The RST and COMPX outputs will remain low until the part is programmed. After programming, if any one of the VX inputs is below its programmed threshold, RST will be a logic low. Once all the VX inputs rise above their thresholds, an internal timer is started and RST is released after the programmed delay time. If VCC < (V3 - 1) and VCC < 2.4V, the V3 input impedance will be low (1k typ). Monitor Programming The LTC2902 input voltage combination is selected by placing the recommended resistor divider from VREF to GND and connecting the tap point to VPG, as shown in Figure 4. Table 1 offers recommended 1% resistor values for the various modes. The last column in Table 1 specifies optimum VPG/VREF ratios (0.01) to be used when programming with a ratiometric DAC. During power-up, once V1 or V2 reaches 2.4V (max), the monitor enters a programming period of approximately 150s during which the voltage on the VPG pin is sampled and the monitor is configured to the desired input combination. Do not add capacitance to the VPG pin. Immediately after programming, the comparators are enabled and supply monitoring will begin. Supply Monitoring The LTC2902 is a low power, high accuracy programmable quad supply monitoring circuit with four nondelayed monitor outputs, a common reset output and selectable supply thresholds. Reset timing is adjustable using an external capacitor. Single pin programming selects 1 of 16 input voltage monitor combinations. Two digital inputs select one of four supply tolerances (5%, 7.5%, 10% or 12.5%). All four voltage inputs must be above predetermined thresholds for the reset not to be invoked. The LTC2902 will assert the reset and comparator outputs during power-up, power-down and brownout conditions on any one of the voltage inputs.
10
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LTC2902 12 VREF 11 VPG 10 GND R1 1% R2 1%
2902 F04
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Figure 4. Monitor Programming Table 1. Voltage Threshold Programming
MODE 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 V1 (V) V2 (V) V3 (V) V4 (V) R1 (k) R2 (k) 5.0 5.0 3.3 3.3 3.3 5.0 5.0 5.0 5.0 5.0 3.3 3.3 3.3 5.0 5.0 5.0 3.3 3.3 2.5 2.5 2.5 3.3 3.3 3.3 3.0 3.0 2.5 2.5 2.5 3.3 3.3 3.0 ADJ ADJ ADJ ADJ 1.5 2.5 2.5 2.5 2.5 ADJ 1.8 1.8 1.8 1.8 1.8 1.8 ADJ -ADJ ADJ -ADJ ADJ ADJ 1.8 1.5 ADJ ADJ 1.5 ADJ -ADJ -ADJ ADJ ADJ Open 93.1 86.6 78.7 71.5 66.5 59.0 53.6 47.5 40.2 34.8 28.0 22.1 16.2 9.53 Short Short 9.53 16.2 22.1 28.0 34.8 40.2 47.5 53.6 59.0 66.5 71.5 78.7 86.6 93.1 Open VPG VREF 0.000 0.094 0.156 0.219 0.281 0.344 0.406 0.469 0.531 0.594 0.656 0.719 0.781 0.844 0.906 1.000
The inverting inputs on the V3 and/or V4 comparators are set to 0.5V when the positive adjustable modes are selected and with T0 and T1 low (5% tolerance) (Figure 5). The tap point on an external resistive divider, connected between the positive voltage being sensed and ground, is connected to the high impedance noninverting inputs (V3, V4). The trip voltage is calculated from: R3 VTRIP = 0.5V 1 + R4 Once the resistor divider is set in the 5% tolerance mode, there is no need to change the divider for the other tolerance modes (7.5%, 10%, 12.5%) because the internal reference is scaled accordingly, moving the trip point in - 2.5% increments.
2902f
LTC2902
APPLICATIO S I FOR ATIO
VTRIP R3 1% V3 OR V4 R4 1% LTC2902
+ - + -
0.5V 5% TOLERANCE MODE
2902 F05
Figure 5. Setting the Positive Adjustable Trip Point
12 R4 1% R3 1% VTRIP VREF LTC2902
13 V4
- +
2902 F06
Figure 6. Setting the Negative Adjustable Trip Point
In the negative adjustable mode, the noninverting input on the V4 comparator is connected to ground (Figure 6). The tap point on an external resistive divider, connected between the negative voltage being sensed and the VREF pin, is connected to the high impedance inverting input (V4). VREF provides the necessary level shift required to operate at ground. The trip voltage is calculated from:
R3 VTRIP = - VREF ; VREF = 1.210 V R4 T0,T1 Low (5% Tolerance Mode)
Once the resistor divider is set in the 5% tolerance mode, there is no need to change the divider for the other tolerance modes (7.5%, 10%, 12.5%) because VREF is scaled accordingly, moving the trip point in - 2.5% increments. In a negative adjustable application, the minimum value for R4 is limited by the sourcing capability of VREF (1mA). With no other load on VREF, R4 (minimum) is: 1.21V / 1mA = 1.21k Tables 2 and 3 offer suggested 1% resistor values for various adjustable applications.
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Table 2. Suggested 1% Resistor Values for the 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) 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 R3 (k) 2150 1780 1400 1300 1020 845 511 464 365 237 182 124 86.6 68.1 R4 (k) 100 100 100 100 100 100 100 100 100 100 100 100 100 100
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Table 3. Suggested 1% Resistor Values for the -ADJ Input
VSUPPLY (V) -2 -5 -5.2 -10 -12 VTRIP (V) -1.87 -4.64 -4.87 -9.31 -11.30 R3 (k) 187 464 487 931 1130 R4 (k) 121 121 121 121 121
Although all four supply monitor comparators have built-in glitch immunity, bypass capacitors on V1 and V2 are recommended because the greater of V1 or V2 is also the VCC for the chip. Filter capacitors on the V3 and V4 inputs are allowed. Power-Down On power-down, once any of the VX inputs drop below their threshold, RST and COMPX are held at a logic low. A logic low of 0.4V is guaranteed until both V1 and V2 drop below 1V. If the bandgap reference becomes invalid (VCC < 2V typ), the part will reprogram once VCC rises above 2.4V (max). Monitor Output Rise and Fall Time Estimation All of the outputs (RST, COMPX) have strong pull-down capability. If the external load capacitance (CLOAD) for a
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LTC2902
APPLICATIO S I FOR ATIO
tFALL 2.2 * RPD * CLOAD
particular output is known, output fall time (10% to 90%) is estimated using: where RPD is the on-resistance of the internal pull-down transistor. The typical performance curve (VOL vs ISINK) demonstrates that the pull-down current is somewhat linear versus output voltage. Using the 25C curve, RPD is estimated to be approximately 40. Assuming a 150pF load capacitance, the fall time is about 13.2ns. Although the outputs are considered to be "open-drain," they do have a weak pull-up capability (see COMPX or RST Pull-Up Current vs V2 curve). Output rise time (10% to 90%) is estimated using: tRISE 2.2 * RPU * CLOAD where RPU is the on-resistance of the pull-up transistor. The on-resistance as a function of the V2 voltage at room temperature is estimated using:
RPU =
6 * 105 V2 - 1
with V2 = 3.3V, RPU is about 260k. Using 150pF for load capacitance, the rise time is 86s. If the output needs to pull up faster and/or to a higher voltage, a smaller external pull-up resistor may be used. Using a 10k pullup resistor, the rise time is reduced to 3.3s for a 150pF load capacitance. The LTC2902-2 has an active pull-up to V2 on the RST output. The typical performance curve (RST Pull-Up Current vs V2 curve) demonstrates that the pull-up current is somewhat linear versus the V2 voltage and RPU is estimated to be approximately 625. A 150pF load capacitance makes the rise time about 206ns. Selecting the Reset Timing Capacitor The reset time-out period is adjustable in order to accommodate a variety of microprocessor applications. The reset time-out period, tRST, is adjusted by connecting a capacitor, CRT, between the CRT pin and ground. The value of this capacitor is determined by: CRT = tRST * 217 * 10 -9
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with CRT in Farads and tRST in seconds. The CRT value per millisecond of delay can also be expressed as CRT/ms = 217 (pF/ms). Leaving the CRT pin unconnected will generate a minimum reset time-out of approximately 50s. Maximum reset time-out is limited by the largest available low leakage capacitor. The accuracy of the time-out period will be affected by capacitor leakage (the nominal charging current is 2A) and capacitor tolerance. A low leakage ceramic capacitor is recommended. Tolerance Programming and the RESET Disable Using the two digital inputs T0 and T1, the user can program the global supply tolerance for the LTC2902 (5%, 7.5%, 10%, 12.5%). The larger tolerances provide more headroom by lowering the trip thresholds.
Table 4. Tolerance Programming
T0 Low Low High High T1 Low High Low High TOLERANCE (%) 5 7.5 10 12.5 VREF (V) 1.210 1.178 1.146 1.113
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Under conventional operation, RST and COMPX will go low when VX is below its threshold. At any time, the RDIS pin can be pulled low, overriding the reset operation and forcing the RST pin high. This feature is useful when determining supply margins under processor control since the reset command will not be invoked. The RDIS pin is connected to a weak internal pull-up to VCC (10A typ), allowing the pin to be left floating if unused. Ensuring RST Valid for VCC Down to 0V (LTC2902-2) When VCC is below 1V the RST pull-down capability is drastically reduced. The RST pin may float to undetermined voltages when connected to high impedance (such as CMOS logic inputs). The addition of a pull-down resistor from RST to ground will provide a path for stray charge and/or leakage currents. The resistor value should be small enough to provide effective pull-down without excessively loading the pull-up circuitry. Too large a value may not pull down well enough. A 100k resistor from RST to ground is satisfactory for most applications.
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LTC2902
TYPICAL APPLICATIO S
Quad Supply Monitor, 5% Tolerance 5V, 3V, 1.8V, 12V (ADJ)
1 2 1.8V 5V SYSTEM RESET CRT 3 4 5 6 7 8 16 15 14 13 12 11 10 9 R4 100k 1% 3V R3 2.15M 1% 12V VTRIP = 11.25V
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COMP3 COMP1 V3
COMP2 COMP4 V2
V1 LTC2902 V4 CRT RST T0 RDIS VREF VPG GND T1
2902 TA02
5V, -5V Monitor with Unused V2, V3 Inputs Pulled Above Trip Thresholds (5% Tolerance)
1 2 3 5V SYSTEM RESET CRT 4 5 6 7 8
COMP3 COMP1 V3
COMP2 COMP4 V2
16 15 14 13 12 11 10 9 R1 R4 16.2k 121k 1% 1% R2 86.6k 1%
2902 TA03
R3 464k 1% -5V VTRIP = -4.64V
V1 LTC2902 V4 CRT RST T0 RDIS VREF VPG GND T1
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LTC2902
TYPICAL APPLICATIO S
Quad Supply Monitor with LED Undervoltage Indicators, 12.5% Tolerance, Reset Disabled 5V, 3.3V, 2.5V, 1.5V
5V
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RL1 1k LED
RL3 1k LED 1 2 COMP3 COMP1 V3 COMP2 COMP4 V2 16 15 14 13 12 11 10 9
RL2 1k LED
RL4 1k LED
2.5V
3 4 5 6 7
3.3V 1.5V R1 53.6k 1% R2 47.5k 1%
V1 LTC2902 V4 CRT RST T0 RDIS VREF VPG GND T1
CRT
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2902 TA04
2902f
LTC2902
PACKAGE DESCRIPTIO
.254 MIN
.0165 .0015
RECOMMENDED SOLDER PAD LAYOUT 1 .015 .004 x 45 (0.38 0.10) .007 - .0098 (0.178 - 0.249) .016 - .050 (0.406 - 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE *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 .053 - .068 (1.351 - 1.727) 23 4 56 7 8 .004 - .0098 (0.102 - 0.249)
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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GN Package 16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.045 .005 .189 - .196* (4.801 - 4.978) 16 15 14 13 12 11 10 9 .009 (0.229) REF .150 - .165 .229 - .244 (5.817 - 6.198) .150 - .157** (3.810 - 3.988) .0250 TYP .008 - .012 (0.203 - 0.305) .0250 (0.635) BSC
GN16 (SSOP) 0502
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LTC2902
TYPICAL APPLICATIO
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 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 Push-Button 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 Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Push-Pull Reset Output Programmable Quad Supply Monitor Programmable Quad Supply Monitor COMMENTS 4.65V Threshold 2.9V Threshold 4.65V 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 Adjustable RESET, 10-Lead MSOP Package Adjustable RESET and Watchdog Timer, 16-Lead SSOP Package
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 Monitor with Open-Drain Reset
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
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Quad Supply Monitor with Hysteresis 5% Tolerance (Supplies Rising) 12.5% Tolerance (After RST Goes High)
5V 4 3.3V 2.5V 1.8V 14 3 13 8 12 R1 59k 1% R2 40.2k 1% 11 10 LTC2902-1 2 COMP1 16 V2 COMP2 1 V3 COMP3 15 V4 COMP4 6 RDIS RST 7 VREF T0 9 T1 VPG 5 CRT GND V1 10k CRT
2902 TA05
2902f LT/TP 1002 2K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2002

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