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Final Electrical Specifications
LTC2901 Programmable Quad Supply Monitor with Adjustable Reset and Watchdog Timers
June 2002
FEATURES
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DESCRIPTIO
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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 Low Supply Current: 43A Typ Adjustable Reset Time Adjustable Watchdog Time Open-Drain RST Output (LTC2901-1) Push-Pull RST Output (LTC2901-2) Individual Nondelayed Monitor Output for Each Supply Power Supply Glitch Immunity Guaranteed RST for VCC 1V
The LTC(R)2901 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 accurate to 1.5% over temperature. All four voltage comparator outputs are connected to separate pins for individual supply monitoring. The reset and watchdog delay times are adjustable using external capacitors. 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. The LTC2901-1 features an open-drain RST output, while the LTC2901-2 has a push-pull RST output. The 43A supply current makes the LTC2901 ideal for power conscious systems and it may be configured to monitor less than four inputs. The parts are available in the 16-lead narrow SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Desktop and Notebook Computers Multivoltage Systems Telecom Equipment Portable Battery-Powered Equipment Network Servers
TYPICAL APPLICATIO
Quadruple Supply Monitor (5V, 3.3V, 2.5V, 1.8V)
5V 3.3V DC/DC CONVERTER 2.5V 1.8V 3 4 V3 V1 13 V4 COMP1 2 R3 10k POWER GOOD SYSTEM LOGIC
14 C1 0.1F C2 0.1F
V2
12
VREF
R1 59k 1% R2 40.2k 1%
11
VPG 10
16 COMP2 LTC2901-2 1 COMP3 15 COMP4 8 WDI 7 WDO 6 RST CWT CRT 47nF 9 CWT 47nF 5
GND CRT
tRST = 216ms tWD = 940ms
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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2901 TA01
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1
LTC2901
ABSOLUTE
(Notes 1, 2, 3)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW COMP3 COMP1 V3 V1 CRT RST WDO WDI 1 2 3 4 5 6 7 8 16 COMP2 15 COMP4 14 V2 13 V4 12 VREF 11 VPG 10 GND 9 CWT
V1, V2, V3, V4, VPG ..................................... - 0.3V to 7V RST (LTC2901-1)........................................ - 0.3V to 7V RST (LTC2901-2).......................... - 0.3V to (V2 + 0.3V) COMPX ....................................................... - 0.3V to 7V CWT, WDO .................................................. - 0.3V to 7V VREF, CRT, WDI ............................ - 0.3V to (VCC + 0.3V) Reference Load Current (IVREF) ............................ 1mA V4 Input Current (-ADJ Mode) ............................. -1mA Operating Temperature Range LTC2901-1C/LTC2901-2C ....................... 0C to 70C LTC2901-1I/LTC2901-2I .................... -40C to 85C Storage Temperature Range .................. - 65C to 150C Lead Temperature (Soldering, 10 sec)................... 300C
ORDER PART NUMBER LTC2901-1CGN LTC2901-2CGN LTC2901-1IGN LTC2901-2IGN GN16 PART MARKING 29011 29012 29011I 29012I
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 VRT33 VRT30 VRT25 VRT18 VRT15 VRTA VRTAN VCC VCCMINP VCCMINC VREF VPG IVPG IV1 IV2 IV3 IV4 PARAMETER 5V, 5% Reset Threshold 3.3V, 5% Reset Threshold 3V, 5% Reset Threshold 2.5V, 5% Reset Threshold 1.8V, 5% Reset Threshold 1.5V, 5% Reset Threshold ADJ Reset Threshold - ADJ Reset Threshold Minimum Internal Operating Voltage Minimum Required for Programming Minimum Required for Comparators Reference Voltage Programming Voltage Range VPG Input Current V1 Input Current V2 Input Current V3 Input Current V4 Input Current
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 V1, V2 Input Threshold V2 Input Threshold V2, V3 Input Threshold V3, V4 Input Threshold V3, V4 Input Threshold V3, V4 Input Threshold 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 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
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 3.036 2.760 2.300 1.656 1.380 0.492 - 18
TYP 4.675 3.086 2.805 2.338 1.683 1.403 0.500 0
MAX 4.750 3.135 2.850 2.375 1.710 1.425 0.508 18 1 2.42 2.32
UNITS V V V V V V V mV V V V V V nA A A A nA A nA A A ms
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1.192 0
1.210
1.228 VREF 20
43 0.8 0.52 -15 0.34 -15 -15 -1.4 10 4.9 -2 20 6.9
75 2 1.2 15 0.8 15 15 -2.6 30 8.9
ICRT(UP) ICRT(DN) tRST
CRT Pull-Up Current CRT Pull-Down Current Reset Time-Out Period
2
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W
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WW
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LTC2901
ELECTRICAL CHARACTERISTICS
SYMBOL tUV VOL PARAMETER VX Undervoltage Detect to RST or COMPX Output Voltage Low RST, COMPX
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 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 VOL VOH ICWT(UP) ICWT(DN) tWD VIH VIL tWP IWDI Output Voltage High RST, WDO, COMPX (Note 5) Output Voltage Low WDO Output Voltage High RST (LTC2901-2) (Note 6) CWT Pull-Up Current CWT Pull-Down Current Watchdog Time-Out Period WDI Input Threshold High WDI Input Threshold Low WDI Input Pulse Width WDI Pull-Up Current ISOURCE = 1A ISINK = 2.5mA; V1 = 5V, V2 = 3.3V; V3, V4 = 1V; VPG = 0V ISOURCE = 200A VCWT = 0V VCWT = 1.3V CWT = 1500pF VCC = 3.3V to 5.5V VCC = 3.3V to 5.5V VCC = 3.3V VWDI = 0V
q q q q q q q q q q q q
MIN
TYP 150 0.15 0.05 0.05
MAX
UNITS s
0.4 0.3 0.3
V V V V
V2 - 1 0.15 0.8 * V2 -1.4 10 20 0.4 150 -10 -2 20 30 -2.6 30 40 1.6 0.4
V V A A ms V V ns 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, WDO 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 LTC2901-2 is actively pulled up to V2.
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LTC2901
TEST CIRCUITS
V1 V2 V3 V4 RST, WDO LTC2901-1 OR COMPX ISOURCE 1A
LTC2901-1 V1 V2 V3 V4
2901 F02
RST, WDO OR COMPX
ISINK 2.5mA, 100A
V1 V2 V3 V4
LTC2901-2 RST ISOURCE 200A
2901 F01
2901 F03
Figure 1. RST, WDO, COMPX VOH Test
Figure 2. RST, WDO, COMPX VOL Test
Figure 3. Active Pull-Up RST VOH Test
TI I G DIAGRA S
VX Monitor Timing
RST
WDI tWP WDO tWD tWD
2901 TD2
4
W
UW
VX
VRTX tUV tRST 1.5V
RST
2901 TD
COMPX
Watchdog Timing
tRST
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LTC2901 TYPICAL PERFOR A CE CHARACTERISTICS
5V Threshold Voltage vs Temperature
4.750 THRESHOLD VOLTAGE, VRT33 (V)
THESHOLD VOLTAGE, VRT50 (V)
4.725 4.700 4.675 4.650 4.625 4.600 20 40 60 -60 -40 -20 0 TEMPERATURE (C)
3.115 3.105 3.095 3.085 3.075 3.065 3.055 3.045
THRESHOLD VOLTAGE, VRT30 (V)
2.5V Threshold Voltage vs Temperature
2.3750 2.3675
THRESHOLD VOLTAGE, VRT25 (V) THRESHOLD VOLTAGE, VRT18 (V)
1.710 1.705 1.700 1.695 1.690 1.685 1.680 1.675 1.670 1.665 1.660
2.3600 2.3525 2.3450 2.3375 2.3300 2.3225 2.3150 2.3075 2.3000 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100
THRESHOLD VOLTAGE, VRT15 (V)
ADJ Threshold Voltage vs Temperature
0.508 0.018 0.506 0.504 0.502 0.500 0.498 0.496 0.494 0.492 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100
THRESHOLD VOLTAGE, VRTAN (V)
THRESHOLD VOLTAGE, VRTA (V)
0 -0.006 -0.012 -0.018 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
VREF (V)
UW
3.3V Threshold Voltage vs Temperature
3.135 3.125 2.850 2.840 2.830 2.820 2.810 2.800 2.790 2.780 2.770 80 100
3V Threshold Voltage vs Temperature
80 100
2901 G01
3.035 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
2.760 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
80
100
2901 G02
2901 G03
1.8V Threshold Voltage vs Temperature
1.425 1.420 1.415 1.410 1.405 1.400 1.395 1.390 1.385
80 100
1.5V Threshold Voltage vs Temperature
1.655 -60 -40 -20 0 20 40 60 TEMPERATURE (C)
1.380 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
80
100
2901 G04
2901 G05
2901 G06
- ADJ Threshold Voltage vs Temperature
1.228 1.222 1.216 1.210 1.204 1.198
VREF vs Temperature
0.012 0.006
80
100
1.192 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
80
100
2901 G07
2901 G08
2901 G23
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LTC2901 TYPICAL PERFOR A CE CHARACTERISTICS
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
IV4 vs Temperature
TYPICAL TRANSIENT DURATION (s)
TYPICAL TRANSIENT DURATION (s)
1.0 V1 = 5V 0.9 V2 = 3.3V V3 = 2.5V 0.8 V4 = 1.8V 0.7
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
WATCHDOG TIME-OUT PERIOD, tWD (ms)
RST OUTPUT VOLTAGE (V)
4
RESET TIME-OUT PERIOD, tRST (ms)
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)
2901 G14
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UW
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
2901 G09
2901 G10
2901 G11
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)
2901 G13
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)
2901 G22
TA = 25C
TA = 25C RESET OCCURS ABOVE CURVE
RESET OCCURS ABOVE CURVE
2901 G12
Watchdog Time-Out Period vs Temperature
38 CWT = 1500pF 36 (SILVER MICA) 34 32 30 28 26 24 22 20 40 60 -60 -40 -20 0 TEMPERATURE (C) 80 100 8.9
Reset Time-Out Period vs Temperature
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
2901 G15
2901 G16
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LTC2901 TYPICAL PERFOR A CE CHARACTERISTICS
Watchdog Time-Out Period vs Capacitance
100 WATCHDOG TIME-OUT PERIOD, tWD (sec)
TA = 25C
10
RESET TIME-OUT PERIOD, tRST (sec)
ISINK (mA)
1
100m
10m
1m 10p
100p
10n 1n CWT (FARAD)
RST, WDO, COMPX Voltage Output Low vs Output Sink Current
3.0 V2 = 3V V1 = 5V 2.5 85C 2.0 - 40C 25C
2.5 VOH (V) 2.0 - 40C 1.5 1.0 85C 0.5 0
0 10 20 30 50 60 ISINK (mA) 40 70 80 90
PULL-UP CURRENT (A)
VOL (V)
1.5 1.0 0.5 0
COMPX Propagation Delay vs Input Overdrive Above Threshold
250
COMPX PROPAGATION DELAY (s)
14 12 10 8 6 4 VRT33 VRT30 VRT25
PULL-UP CURRENT (mA)
200
PULL-UP CURRENT (A)
150
100 V1, V2 50 V3, V4 0 1000 10 100 INPUT OVERDRIVE ABOVE THRESHOLD (mV)
2901 G25
UW
100n
2901 G17
2901 G20
Reset Time-Out Period vs Capacitance
10
TA = 25C
RST, WDO, COMPX ISINK vs Supply Voltage
10 9 TA = 25C
1
8 7 6 5 4 3
VOL = 0.4V
100m
10m
VOL = 0.2V
1m
2 1
1
100 10p
100p
10n 1n CRT (FARAD)
100n
1
2901 G18
0 0 1 2 3 4 V1 OR V2 (V) 5 6
2901 G19
RST High Level Output Voltage vs Output Source Current (LTC2901-2)
3.5 3.0
20
COMPX and WDO Pull-Up Current vs V2 (COMPX and WDO Held at 0V)
18 16 14 12 10 8 6 4 2 0 TA = 25C
V1 = 5V V2 = 3V V3 = 2.5V V4 = 1V
25C
0
0.5
1.5 ISOURCE (mA)
1
2
2.5
2901 G21
1
1.5
2
2.5
3 3.5 V2 (V)
4
4.5
5
2901 G24
RST Pull-Up Current vs V2 (LTC2901-1)
20 18 16 5 4 3 2 1 0 2 2.5 3 3.5 V2 (V) 4 4.5 5
2901 G26
RST Pull-Up Current vs V2 (LTC2901-2)
6 TA = 25C
TA = 25C
TA = 25C
VRT33 VRT30 VRT25
2 0 2 2.5 3 3.5 V2 (V) 4 4.5 5
2901 G27
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LTC2901
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. RST (Pin 6): Reset Logic Output. Active low with weak pull-up to V2 (LTC2901-1) or active pull-up to V2 (LTC2901-2). 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 (LTC2901-1 only). WDO (Pin 7): Watchdog Output. Active low logic output with weak pull-up to V2. May be pulled greater than V2 using external pull-up. The watchdog output pulls low if the watchdog timer is allowed to time out and remains low until set high by the next WDI transistion or anytime RST is low. The watchdog timer is enabled when RST is high. WDI (Pin 8): Watchdog Input. A logic input whose rising or falling edge must occur on this pin (while RST is high) within the selected watchdog time-out period, prohibiting a high-to-low transition on the WDO pin. The watchdog time-out period is set by the value of the capacitor that is attached to the CWT pin. A rising or falling edge on the WDI pin clears the voltage on the CWT capacitor, preventing WDO from going low. When disabling the watchdog function, tie CWT to GND. CWT (Pin 9): Watchdog Time-Out Programming Pin. Attach a capacitor (CWT) between CWT and GND to set a watchdog time-out period of 20ms/nF. Leaving the pin open generates a minimum time-out of approximately 200s. A 47nF capacitor will generate a 940ms watchdog time-out period. 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, RST, WDO) are weakly pulled up to V2 (LTC2901-1). RST is actively pulled up to V2 in the LTC2901-2. 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.
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LTC2901
BLOCK DIAGRA
V3 3 V4 13 GND 10
RESISTIVE DIVIDER MATRIX
VPG 11 A/D BUFFER VREF 12
+
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 2A 22A V2 LTC2901-1 6A RST 6 10A VCC TRANSITION DETECT WATCHDOG TIMER VCC 2A 22A 5 CRT CRT 8 WDI 9 CWT CWT
2901 DB-1
LTC2901-2 V2
RST 6 V2 6A WDO 7
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LTC2901
APPLICATIO S I FOR ATIO
Power-Up
The greater of V1, V2 is the internal supply voltage (VCC). On power-up, VCC 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 LTC2901 input voltage combination is selected by placing the recommended resistive 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
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
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LTC2901 12 VREF 11 VPG 10 GND R1 1% R2 1%
2901 F04
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Figure 4. Monitor Programming
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 LTC2901 is a low power, high accuracy programmable quad supply monitoring circuit with four nondelayed monitor outputs, a common reset output and a watchdog timer. Watchdog and reset timing are both adjustable using external capacitors. Single pin programming selects 1 of 16 input voltage monitor combinations. All four voltage inputs must be above predetermined thresholds for the reset not to be invoked. The LTC2901 will assert the reset and comparator outputs during power-up, powerdown and brownout conditions on any one of the voltage inputs. The inverting inputs on the V3 and/or V4 comparators are set to 0.5V when the positive adjustable modes are selected (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 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 No min al R4
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LTC2901
APPLICATIO S I FOR ATIO
VTRIP R3 1% V3 OR V4 R4 1% LTC2901
+ - + -
0.5V
2901 F05
Figure 5. Setting the Positive Adjustable Trip Point
12 R4 1% R3 1% VTRIP
VREF
LTC2901
13 V4
- +
2901 F06
Figure 6. Setting the Negative Adjustable Trip Point
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. Although all four supply monitor comparators have builtin 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.
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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
Monitor Output Rise and Fall Time Estimation All of the outputs (RST, COMPX, WDO) have strong pulldown capability. If the external load capacitance (CLOAD) for a particular output is known, output fall time (10% to 90%) is estimated using: tFALL 2.2 * RPD * CLOAD 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
2901is sn2901
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LTC2901
APPLICATIO S I FOR ATIO
tRISE 2.2 * RPU * CLOAD
Pull-Up Current vs V2 curve). Output rise time (10% to 90%) is estimated using: 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:
6 * 105 RPU = 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 LTC2901-2 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. Watchdog Timer The watchdog circuit typically monitors a P's activity. The P is required to change the logic state of the WDI pin on a periodic basis in order to clear the watchdog timer and prevent the WDO pin from going low. Whenever RST is low, the watchdog timer is cleared and WDO is set high. The watchdog timer is started when RST pulls high. Subsequent edges received on the WDI pin will clear the watchdog timer. The timer will continue to run until the watchdog timer times out. Once the watchdog timer times out, internal circuitry will bring the WDO pin low. WDO will remain low and the watchdog timer will remain cleared until the next edge is received on the WDI pin or until RST goes low. To disable the watchdog timer, simply ground the CWT pin (Pin 9). With CWT held at ground, any reset event will force WDO high indefinitely. It is safe to leave the WDI pin (Pin 8) unconnected because the weak internal pull-up (10A typ) will pull WDI high. Tying WDI to V1 or ground is also allowed, but grounding the WDI pin will force the pull-up current to be drawn continuously.
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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 * 217.4 * 10 -9 with CRT in Farads and tRST in seconds. The CRT value per millisecond of delay can also be expressed as CRT/ms = 217.4 (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. Selecting the Watchdog Timing Capacitor The watchdog time-out period is adjustable and can be optimized for software execution. The watchdog time-out period, tWD, is adjusted by connecting a capacitor, CWT, between the CWT pin and ground. Given a specified watchdog time-out period, the capacitor is determined by: CWT = tWD * 50 * 10-9 with CWT in Farads and tWD in seconds. The CWT value per millisecond of delay can also be expressed as CWT/ms = 50 (pF/ms). Leaving the CWT pin unconnected will generate a minimum watchdog time-out of approximately 200s. Maximum 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. Monitoring Power Supply Controller Activity Figure 7 demonstrates how the LTC2901 can be used to monitor switcher activity. The monitor is configured to supervise 3.3V, 2.5V, 1.8V and one adjustable input.
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LTC2901
APPLICATIO S I FOR ATIO
Because 2.5V does not exist in this application, the V2 input is tied to the V1 (3.3V) input. The feedback voltage on the LTC1772 (0.8V typ) is monitored with the adjustable input (V4). The RST pin will go high 216ms (CRT = 47nF) after the 3.3V and 1.8V supplies and the feedback voltage are above threshold. Individual input status is available at the COMPX pins. While the voltage monitors can detect low voltage or shorted inputs, the watchdog circuit can be used to detect an open circuit to the primary load. With the CWT pin
R5 0.15 LTC1772 6 ITH PGATE 2 5 VIN GND 3 4 VFB SENSE - 1 R6 10k C3 220pF L1 10H C1 10F 10V
M1
D1
C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T C2: SANYO POSCAP 6TPA47M D1: MOTOROLA MBRM120T3 L1: COILTRONICS UP1B-100 M1: Si3443DV R5: DALE 0.25W
Figure 7. Monitor Input, Output, Feedback Voltage and Low Load Conditions on DC/DC Controller
TYPICAL APPLICATIO S
Quad Supply Monitor with Watchdog Timer Disabled 5V, 3V, 1.8V, 12V (ADJ)
1.8V 5V SYSTEM RESET CRT
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unconnected, the watchdog time-out is approximately 200s. At low load currents on the 1.8V supply, the LTC1772 will go into Burst Mode(R) operation. With an open-ciruit load, the duty cycle at the gate of M1 will drop, and the pulse spacing will exceed the watchdog time-out period. The WDO pin will go low indicating the low load condition. The WDO pin will return high on the next pulse to the gate of M1. The WDO pin will remain high if the load is restored.
Burst Mode is a registered trademark of Linear Technology Corporation. VIN 3.3V 4 14 3 VOUT 1.8V 0.5A R1 28k 1% R2 71.5k 1% 13 8 12 11 10
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C2 47F 6V
R3 100k
R4 80.6k
LTC2901-2 2 V1 COMP1 16 V2 COMP2 1 V3 COMP3 15 V4 COMP4 6 WDI RST 7 VREF WDO 5 CRT VPG 9 CWT GND
3.3V MONITOR
1.8V MONITOR FEEDBACK MONITOR COMMON RESET OUT LOW LOAD INDICATOR
CRT 47nF
2901 F07
1 2 3 4 5 6 7 8
COMP3 COMP1 V3
COMP2 COMP4 V2
16 15 14 13 12 11 10 9 R4 100k 1% 3V R3 2.15M 1% 12V VTRIP = 11.25V
V1 LTC2901 V4 CRT RST WDO WDI VREF VPG GND CWT
2901 TA02
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LTC2901
TYPICAL APPLICATIO S
5V, -5V Monitor with Watchdog Timer Disabled and Unused V2, V3 Inputs Pulled Above Trip Thresholds
5V
WATCHDOG STATUS WDI CRT
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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% R3 464k 1% -5V VTRIP = -4.64V
V1 LTC2901 V4 CRT RST WDO WDI VREF VPG GND CWT
2901 TA03
Quad Supply Monitor with LED Undervoltage Indicators 5V, 3.3V, 2.5V, 1.5V
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
3.3V 1.5V R1 53.6k 1% R2 47.5k 1%
V1 LTC2901 V4 CRT RST WDO WDI VREF VPG GND CWT CWT
SYSTEM RESET
6 7 8
2901 TA04
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LTC2901
PACKAGE DESCRIPTIO
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
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GN Package 16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
0.189 - 0.196* (4.801 - 4.978) 16 15 14 13 12 11 10 9 0.009 (0.229) REF 0.229 - 0.244 (5.817 - 6.198) 0.150 - 0.157** (3.810 - 3.988) 1 0.015 0.004 x 45 (0.38 0.10) 0 - 8 TYP 0.053 - 0.068 (1.351 - 1.727) 23 4 56 7 8 0.004 - 0.0098 (0.102 - 0.249) 0.008 - 0.012 (0.203 - 0.305) 0.0250 (0.635) BSC
GN16 (SSOP) 1098
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LTC2901
TYPICAL APPLICATIO
Monitor Seven Supplies (12V, 5V, 3.3V, 2.5V, 1.8V, -2V, -5.2V) with Sequenced Reset and AC Present Indication
5V AC/DC DC/DC CONVERTERS 12V 5V 3.3V 2.5V 1.8V -2V -5.2V 10k 4 3.3V 1.8V 14 3 13 8 120V AC LOW VOLTAGE SECONDARY 121k 16.2k 1% 1% 487k 86.6k 1% 1% -5.2V 100k 1N4148 1N4148 Q1 2N3904 tRST1 + tRST2 = 432ms tWD = 13.6ms 12 11 10 LTC2901-1 2 V1 COMP1 16 V2 COMP2 1 V3 COMP3 15 V4 COMP4 6 WDI RST 7 VREF WDO 5 CRT VPG 9 CWT GND 5V MONITOR 3.3V MONITOR 1.8V MONITOR -5.2V MONITOR 12V 2.15M 1% CRT1 47nF 100k 100k 1% 121k 78.7k 1% 1% 187k 22.1k 1% 1% -2V 2.5V 4 14 3 13 8 12 11 10 LTC2901-1 2 V1 COMP1 16 V2 COMP2 1 V3 COMP3 15 V4 COMP4 6 WDI RST 7 VREF WDO 5 CRT VPG 9 CWT GND 10k
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 LTC1728-1.8/LTC1728-3.3 LTC1728-2.5/LTC1728-5 LTC1985-1.8 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 Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and AJD 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 Monitor with Open-Drain Reset Micropower Triple Supply Monitors with Open-Drain Reset Micropower Triple Supply Monitor with Push-Pull Reset Output COMMENTS 4.65V Threshold 2.9V Threshold 4.65V Threshold 4.37V/4.62V Threshold 4.725V, 3.118V, 1V Thresholds (0.75%) 2.363V, 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
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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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2.5V MONITOR 12V MONITOR -2V MONITOR COMMON RESET OUT AC PRESENT CWT 680pF
2901 TA05
CRT2 47nF
2901is sn2901 LT/TP 0602 1.5K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2002

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