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FEATURES

LTC2931 Configurable Six Supply Monitor with Adjustable Reset and Watchdog Timers DESCRIPTION
The LTC(R)2931 is a configurable supply monitor for systems with up to six supply voltages. One of 16 preset or adjustable voltage monitor combinations can be selected using an external resistive divider connected to the mode select pin. The preset voltage thresholds are accurate to 1.5% over temperature. The LTC2931 also features adjustable inputs with a 0.5V nominal threshold. All six open-drain voltage comparator outputs are connected to separate pins for individual supply monitoring. The reset and watchdog timeout periods 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. Each status output has a weak internal pull-up and may be externally pulled up to a user defined voltage. The 52A supply current makes the LTC2931 ideal for power conscious systems and it may be configured to monitor fewer than six inputs.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6967591, 7239251, 7119714.

Simultaneously Monitors Six Supplies 16 User Selectable Combinations of 5V, 3.3V, 3V, 2.5V, 1.8V, 1.5V and Adjustable Voltage Thresholds Guaranteed Threshold Accuracy: 1.5% Adjustable Reset and Watchdog Timeout Low Supply Current: 52A Comparator/Monitor Output for Each Supply Power Supply Glitch Immunity Guaranteed RST for VCC 1V High Temperature Operation to 125C 20-Lead TSSOP Package
APPLICATIONS

Desktop and Notebook Computers Multivoltage Systems Telecom Equipment Portable Battery-Powered Equipment Network Servers Automotive
TYPICAL APPLICATION
Six Supply Monitor 12V (ADJ), 5V, 3.3V, 2.5V, 1.8V, 1.2V (ADJ)
12V 5V 3.3V 2.5V 1.8V 1.2V 10k 2150k 1% 124k 1% COMP1 COMP2 COMP3 COMP4 COMP5 V1 V2 0.1F 0.1F 100k 1% 100k 1% R1 59k 1% R2 40.2k 1% V3 V4 V5 V6 VREF VPG GND CWT CWT 47nF CRT RST
2931 TA01
Voltage Threshold Configuration Table
V1 (V) V2 (V) V3 (V) V4 (V) V5 (V) V6 (V) 5.0 3.3 2.5 1.8 ADJ ADJ 5.0 3.3 2.5 1.5 ADJ ADJ 5.0 3.3 2.5 ADJ ADJ ADJ 5.0 3.3 1.8 ADJ ADJ ADJ 5.0 3.3 1.8 -ADJ ADJ ADJ 5.0 3.3 ADJ ADJ ADJ ADJ 5.0 3.3 ADJ -ADJ ADJ ADJ 5.0 3.0 2.5 ADJ ADJ ADJ 5.0 3.0 1.8 ADJ ADJ ADJ 5.0 3.0 ADJ ADJ ADJ ADJ 3.3 2.5 1.8 1.5 ADJ ADJ 3.3 2.5 1.8 ADJ ADJ ADJ 3.3 2.5 1.8 -ADJ ADJ ADJ 3.3 2.5 1.5 ADJ ADJ ADJ 3.3 2.5 ADJ ADJ ADJ ADJ 3.3 2.5 ADJ -ADJ ADJ ADJ
SYSTEM LOGIC
POWER GOOD COMP6 WDI LTC2931 WDO tRST = 94ms tWD = 940ms CRT 47nF
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LTC2931 ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2, 3)
PIN CONFIGURATION
TOP VIEW COMP5 V5 COMP3 COMP1 V3 V1 CRT RST WDO 1 2 3 4 5 6 7 8 9 20 COMP6 19 V6 18 COMP2 17 COMP4 16 V2 15 V4 14 VREF 13 VPG 12 GND 11 CWT
V1, V2, V3, V4, V5, V6, VPG ........................ -0.3V to 7V RST , COMP1-6............................................ -0.3V to 7V CWT, WDO .................................................... -0.3V to 7V CRT, VREF WDI .............................-0.3V to (VCC + 0.3V) , Reference Load Current (IVREF) ..............................1mA V4 Input Current (-ADJ Mode) ..............................-1mA RST , WDO, COMP1-6 Currents ...........................10mA Operating Temperature Range LTC2931C ................................................ 0C to 70C LTC2931I.............................................. -40C to 85C LTC2931H .......................................... -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C
WDI 10
F PACKAGE 20-LEAD PLASTIC TSSOP TJMAX = 130C, JA = 90C/W
ORDER INFORMATION
LEAD FREE FINISH LTC2931CF#PBF LTC2931IF#PBF LTC2931HF#PBF TAPE AND REEL LTC2931CF#TRPBF LTC2931IF#TRPBF LTC2931HF#TRPBF PART MARKING LTC2931F LTC2931F LTC2931F PACKAGE DESCRIPTION 20-Lead Plastic TSSOP 20-Lead Plastic TSSOP 20-Lead Plastic TSSOP TEMPERATURE RANGE 0C to 70C -40C to 85C -40C to 125C
Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ This product is only offered in trays. For more information go to: http://www.linear.com/packaging/
ELECTRICAL CHARACTERISTICS
SYMBOL VCC VCCMINP VCCMINC VRT50 VRT33 VRT30 VRT25 VRT18 VRT15 VRTA VRTAN PARAMETER Minimum Internal Operating Voltage Minimum Required for Mode Selection Minimum Required for Comparators 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
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, unless otherwise specified. (Note 3)
CONDITIONS RST, COMPn in Correct Logic State VCC Rising VCC Falling V1 Input Threshold V1, V2 Input Threshold V2 Input Threshold V2, V3 Input Threshold V3, V4 Input Threshold V3, V4 Input Threshold V3, V4, V5, V6 Input Threshold V4 Input Threshold

MIN
TYP
MAX 1 2.4 2.3
UNITS V V V V V V V V V mV mV
4.600 3.036 2.760 2.300 1.656 1.380 492.5 -18
4.675 3.086 2.805 2.338 1.683 1.403 500 0
4.750 3.135 2.850 2.375 1.710 1.425 507.5 18
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LTC2931 ELECTRICAL CHARACTERISTICS
SYMBOL VREF VPG IVPG IV1 IV2 IV3 IV4 PARAMETER Reference Voltage Mode Selection Voltage Range VPG Input Current V1 Input Current V2 Input Current V3 Input Current V4 Input Current
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, unless otherwise specified. (Note 3)
CONDITIONS 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 = -0.02V (-ADJ Mode) V5, V6 = 0.55V VCRT = GND VCRT = 1.3V CRT = 1500pF Vn Less Than Reset Threshold by More than 1% ISINK = 3mA, VCC = 3V ISINK = 100A, VCC = 1V VCOMPn = GND ISINK = 3mA

MIN 1.192 0
TYP 1.210
MAX 1.228 VREF 20
UNITS V V nA A A A nA A nA nA nA A A ms s
52 0.8 0.52 -15 0.34 -15 -15 -15 -1.4 10 2 -2 20 3 150 0.15 0.05 -2 V2-1 -1.4 10 20 1.6 -2 20 30 -6 0.15
75 2 1.2 15 0.8 15 15 15 -2.6 30 4
IV5, IV6 ICRT(UP) ICRT(DN) tRST tUV VOL ICOMPn VOL VOH ICWT(UP) ICWT(DN) tWD VIH VIL tWP IWDI
V5, V6 Input Current CRT Pull-Up Current CRT Pull-Down Current Reset Timeout Period Vn Undervoltage Detect to RST or COMPn Voltage Output Low RST, COMPn COMPn Pull-Up Current Voltage Output Low WDO
0.4 0.3 -12 0.4
V V A V V
Voltage Output High RST, WDO, COMPn ISOURCE = -1A (Note 5) CWT Pull-Up Current CWT Pull-Down Current Watchdog Timeout Period WDI Input Threshold High WDI Input Threshold Low WDI Input Pulse Width WDI Pull-Up Current VCWT = GND VCWT = 1.3V CWT = 1500pF VCC = 3.3V to 5.5V VCC = 3.3V to 5.5V VCC = 3.3V VWDI = 1V
-2.6 30 40 0.4
A A ms V V ns A
150 -4 -10 -16
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into pins are positive, all voltages are referenced to GND unless otherwise noted. 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 COMPn have diode protected 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.
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LTC2931 TIMING DIAGRAMS
Vn Monitor Timing
Vn
VRT tUV tRST
RST
2931 TD
COMPn
Watchdog Timing
tRST RST
WDI tWP t < tRST WDO tRST tWD tWD
2931 TD2
tRST
tWD
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LTC2931 TYPICAL PERFORMANCE CHARACTERISTICS
Normalized Threshold Voltages vs Temperature
NORMALIZED THRESHOLD VOLTAGES (V/V) 1.015 THRESHOLD VOLTAGE, VRTAN (mV) 1.010 1.005 1.000 0.995 0.990 0.985 -50 -25 18 12 6 0 -6 -12 -18 -50 -25 VREF (V)
-ADJ Threshold Voltage vs Temperature
1.228 1.222 1.216 1.210 1.204 1.198
VREF vs Temperature
50 25 75 0 TEMPERATURE (C)
100
125
50 25 75 0 TEMPERATURE ( C)
100
125
1.192 -50 -25
50 25 75 0 TEMPERATURE (C)
100
125
2931 G01
2931 G02
2931 G03
Supply Current vs Temperature
70 V1 = 5V V2 = 3.3V 65 V3 = 2.5V V4 = 1.8V V5 = V6 = 1V 60 IV4 (A) 55 50 45 40 -50 -25 -100 -10 -1 -100n -10n -1n
I(V4) vs V4 in Negative Adjust Mode
300 TYPICAL TRANSIENT DURATION ( s) 250 200
Transient Duration vs Comparator Overdrive (V1,V2)
TA = 25 C
SUPPLY CURRENT, IV1 ( A)
125C
RESET OCCURS ABOVE CURVE 150 100 50 0
90C
25C 50 25 75 0 TEMPERATURE ( C) 100 125 -100p -300 -250 -200 -150 -100 V4 (mV) -50 0
2931 G05 2931 G04
0.1 1 10 100 RESET COMPARATOR OVERDRIVE (% OF VRTX)
2931 G06
Transient Duration vs Comparator Overdrive (V3, V4, V5, V6)
450 TYPICAL TRANSIENT DURATION ( s) 375 300 RESET OCCURS ABOVE CURVE 225 150 75 0 RST OUTPUT VOLTAGE (V) TA = 25 C 6 5 4 3 2 1 0
RST Output Voltage vs V1, VPG = GND
WATCHDOG TIMEOUT PERIOD, tWD (ms) TA = 25 C 10k PULL-UP FROM RST TO V1 36 34 32 30 28 26
Watchdog Timeout Period vs Temperature
CWT = 1500pF (SILVER MICA)
0.1 1 10 100 RESET COMPARATOR OVERDRIVE (% OF VRTX)
2931 G07
0
1
2 V1 (V)
3
4
5
2931 G08
24 -50 -25
50 25 75 0 TEMPERATURE ( C)
100
125
2931 G09
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LTC2931 TYPICAL PERFORMANCE CHARACTERISTICS
Reset Timeout Period vs Temperature
5 RESET TIMEOUT PERIOD, tRST (ms) WATCHDOG TIMEOUT PERIOD tWD (s) CRT = 1500pF (SILVER MICA) 100 10 1
Watchdog Timeout Period vs CWT
TA = 25 C RESET TIMEOUT PERIOD tRST (s) 10 1 100m 10m 1m 100 10
Reset Timeout Period vs CRT
TA = 25 C
4
3
100m 10m 1m 100 10p
2
1 -50
-25
75 0 25 50 TEMPERATURE ( C)
100
125
100p
1n 10n CWT (F)
100n
1
2931 G11
10p
100p
1n 10n CRT (F)
100n
1
2931 G12
2931 G10
ISINK vs Supply Voltage (RST, WDO, COMPn)
15 TA = 25 C 500
Voltage Output Low vs Output Sink Current (RST, WDO, COMPn)
V1 = 5V V2 = 3V 18 125 C 85 C VOL (mV) 300 25 C 200 -40 C PULL-UP CURRENT ( A) 15 12 9 6 3 0
COMPn and WDO Pull-Up Current vs V2
TA = 25 C COMPn = WDO = GND
12 VOL = 0.4V ISINK (mA) 9 VOL = 0.2V
400
6
3
100
0
0
1
3 2 V1 OR V2 (V)
4
5
2931 G13
0
0
2
6 4 ISINK (mA)
8
10
2931 G14
1
2
3 V2 (V)
4
5
2931 G15
COMPn Propagation Delay vs Input Overdrive Above Threshold
250 COMPn PROPAGATION DELAY ( s) TA = 25 C 18 15 PULL-UP CURRENT ( A) 12 9 6
RST Pull-Up Current vs V2
TA = 25 C
200
150 V1, V2 100 V3, V4, V5, V6
50
VRT33 VRT30
3 VRT25 0
0
1000 10 100 INPUT OVERDRIVE ABOVE THRESHOLD (mV)
2931 G16
2.0
2.5
3.0
3.5 V2 (V)
4.0
4.5
5.0
2931 G17
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LTC2931 PIN FUNCTIONS
COMP5 (Pin 1): Comparator Output 5. Real-time logic output with weak 6A pull-up to V2. Pulls high when V5 is above reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. V5 (Pin 2): Adjustable Voltage Input 5. High impedance comparator input with 0.5V typical threshold. See Applications Information for details. Tie to V1 if unused. COMP3 (Pin 3): Comparator Output 3. Real-time logic output with weak 6A pull-up to V2. Pulls high when V3 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. COMP1 (Pin 4): Comparator Output 1. Real-time logic output with weak 6A pull-up to V2. Pulls high when V1 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. V3 (Pin 5): Voltage Input 3. Select from 2.5V, 1.8V, 1.5V, or ADJ. See Applications Information for details. Tie to V1 if unused. V1 (Pin 6): Voltage Input 1. Select from 5V or 3.3V. See Applications Information for details. The greater of V1 or V2 is also VCC for the device. Bypass this pin to ground with a 0.1F (or greater) capacitor. CRT (Pin 7): Reset Timeout Capacitor. Attach an external . capacitor (CRT) to GND to set a reset timeout of 2ms/nF Leaving the pin open generates a minimum delay of approximately 25s. A 47nF capacitor generates a 94ms reset delay time. RST (Pin 8): Reset Output. Logic output with weak 6A pull-up to V2. Pulls low when any voltage input is below the reset threshold and held low for the configured delay time after all voltage inputs are above threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. WDO (Pin 9): Watchdog Output. Logic output with weak 6A pull-up to V2. May be pulled greater than V2 using external pull-up. The watchdog timer is enabled when RST is high. The watchdog output pulls low if the watchdog timer times out and remains low for one reset timeout period. The watchdog output is cleared with a WDI transition or anytime RST is low.The output will toggle between high and low as long as the watchdog and reset timers are allowed to time out. Leave open if unused. WDI (Pin 10): 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 capacitor attached to the CWT pin sets the watchdog time-out period. A rising or falling edge on the WDI pin clears the voltage on the CWT capacitor, preventing WDO from going low. Tie WDI to V1 or GND if unused. Tie CWT to GND to disable the watchdog function. CWT (Pin 11): Watchdog Timeout Capacitor. 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 timeout of approximately 200s. A 47nF capacitor generates a 940ms watchdog time-out period. Tie CWT to GND to disable the watchdog function. GND (Pin 12): Ground. VPG (Pin 13): Threshold Select Input. Connect to an external 1% resistive divider between VREF and GND to select 1 of 16 combinations and/or adjustable voltage thresholds (See Table 1). Do not add capacitance on the VPG pin. VREF (Pin 14): Buffered Reference Voltage Output. A 1.210V nominal reference used for the mode selection 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 15): Voltage Input 4. Select from 1.8V, 1.5V, ADJ or -ADJ. See Applications Information for details. Tie to V1 if unused and configured for positive voltage. V2 (Pin 16): Voltage Input 2. Select from 3.3V, 3V or 2.5V. See Applications Information for details. The greater of V1, V2 is also VCC for the device. Bypass this pin to ground with a 0.1F (or greater) capacitor. All status outputs are weakly pulled up to V2. COMP4 (Pin 17): Comparator Output 4. Real-time logic output with weak 6A pull-up to V2. Pulls high when V4 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused.
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LTC2931 PIN FUNCTIONS
COMP2 (Pin 18): Comparator Output 2. Real-time logic output with weak 6A pull-up to V2. Pulls high when V2 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. V6 (Pin 19): Adjustable Voltage Input 6. High impedance comparator input with 0.5V typical threshold. See Applications Information for details. Tie to V1 if unused. COMP6 (Pin 20): Comparator Output 6. Real-time logic output with weak 6A pull-up to V2. Pulls high when V6 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused.
BLOCK DIAGRAM
BUFFER VREF 14 1.210V V2 V2 BANDGAP REFERENCE 6A V2 6A A/D 4 V2 6A COMP1 4 COMP2 18 6A COMP3 3 COMP4 17 6A V2 COMP5 1 6A COMP6 20 CMP5 V2 6A RST
VPG 13
V1 6 V2 16 V3 5 V4 15 V5 2 RESISTIVE DIVIDER MATRIX 4 V2 CMP1-4 4
0.5V
V6 19 CRT 7 CRT
-
VCC
GND 12 POWER DETECT VCC 22A V2 10 WDI
8
+ + - +
CMP6 2A 4 10A VCC V1
4
-
ADJUSTABLE RESET PULSE GENERATOR V2 22A 6A
8
WDO 9 TRANSITION DETECT WATCHDOG TIMER VCC 2A
11 CWT CWT
2931 BD
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LTC2931 APPLICATIONS INFORMATION
Supply Monitoring The LTC2931 is a low power, high accuracy configurable six supply monitoring circuit with six real-time monitor outputs, a common reset output and a watchdog timer. External capacitors set the reset and watchdog timeout periods. An external resistive divider between VREF VPG , and GND selects 1 of 16 possible input voltage monitor combinations. All six voltage inputs must be above their predetermined thresholds for the reset not to be activated. The LTC2931 asserts the reset and comparator outputs during power-up, power-down and brownout conditions on any one of the voltage inputs. Power-Up The greater of V1 and V2 serves as the internal supply voltage (VCC). On power-up, VCC powers the drive circuits for the RST pin. This ensures that the RST output will be low as soon as either V1 or V2 reaches 1V. The RST output remains low until the part is configured. Once voltage thresholds are set, if any of the supply monitor inputs is below its configured threshold, RST will be a logic low. Once all the monitor inputs rise above their thresholds, an internal timer is started and RST is released after the delay time. If VCC < (V3 - 1.0V) and VCC < 2.4V, the V3 input impedance will be low (10k typical). Threshold Accuracy Consider a 5V system with 5% tolerance. The 5V supply may vary between 4.75V to 5.25V. System ICs powered by this supply must operate reliably within this band (and a little more as explained below). A perfectly accurate supervisor for this supply generates a reset at exactly 4.75V, however no supervisor is this perfect. The actual reset threshold of a supervisor varies over a specified band; the LTC2931 varies 1.5% around its nominal threshold voltage (see Figure 1) over temperature. The reset threshold band and the power supply tolerance bands should not overlap. This prevents false or nuisance resets when the power supply is actually within its specified tolerance band. The LTC2931 has a 1.5% reset threshold accuracy, so a "5%" threshold is typically set to 6.5% below the nominal input voltage. Therefore, a typical 5V, "5%" threshold is
5V SUPPLY TOLERANCE MINIMUM RELIABLE SYSTEM VOLTAGE NOMINAL SUPPLY VOLTAGE
IDEAL SUPERVISOR THRESHOLD
4.75V 1.5% THRESHOLD BAND 4.675V 4.6V REGION OF POTENTIAL MALFUNCTION
-5% -6.5% -8%
Figure 1. 1.5% Threshold Accuracy Improves System Reliability
4.675V. The threshold is guaranteed to lie in the band between 4.750V and 4.600V over temperature. The powered system must work reliably down to the low end of the threshold band, or risk malfunction before a reset signal is properly issued. A less accurate supervisor increases the required system voltage margin and increases the probability of system malfunction. The LTC2931 1.5% specification improves the reliability of the system over supervisors with wider threshold tolerances. Monitor Configuration Select the LTC2931 input voltage combination by placing the recommended resistive divider from VREF to GND and connecting the tap point to VPG, as shown in Figure 2. Table 1 offers recommended 1% resistor values for each of the 16 modes. The last column in Table 1 specifies optimum VPG/VREF ratios ( 0.01), when configuring with a ratiometric DAC. At power-up, once V1 or V2 reaches 2.4V, the monitor enters a setup period of approximately 150s. During the setup time, the voltage on the VPG pin is sampled and the monitor is configured to the desired input combinaLTC2931 VREF VPG GND R1 1% R2 1%
2931 F02
Figure 2. Mode Selection
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LTC2931 APPLICATIONS INFORMATION
Table 1. Voltage Threshold Modes*
MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (k) R2 (k) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 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
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
Table 3. Suggested 1% Resistor Values for the -ADJ Inputs
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
*V5 and V6 are always adjustable (ADJ).
tion. The comparators are enabled and supply monitoring begins. Do not add capacitance to the VPG pin. Using The Adjustable Thresholds The reference inputs on the V3 and/or V4 comparators are set to 0.5V when the positive adjustable modes are selected (Figure 3). The reference inputs on the V5 and V6 comparators are always set to 0.5V. The tap point on an external resistive divider, connected between the positive voltage being sensed and ground, is connected to the high
VTRIP R3 1% V3, V4, V5 OR V6 R4 1% LTC2931
impedance, adjustable inputs (V3, V4, V5, V6). Calculate the trip voltage from: VTRIP = 0.5V * 1+ R3 R4
In the negative adjustable mode, the reference level on the V4 comparator is connected to ground (Figure 4). The tap point on an external resistive divider, connected between
VREF R4 1% R3 1% V4
LTC2931
+ -
0.5V
VTRIP
2931 F03
2931 F04
Figure 3. Setting the Positive Adjustable Trip Point
Figure 4. Setting the Negative Adjustable Trip Point
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LTC2931 APPLICATIONS INFORMATION
the negative voltage being sensed and the VREF pin, is connected to the high impedance adjustable input (V4). VREF provides the necessary level shift required to operate at ground. The negative trip voltage is calculated from: VTRIP = -VREF * R3 ; V = 1.210V Nominal R4 REF low as long as the watchdog and reset timers are allowed to time out repeatedly. To disable the watchdog timer, simply ground the CWT pin (Pin 11). With CWT held at ground, any reset event forces WDO high indefinitely. It is safe to leave the WDI pin unconnected because the weak internal pull-up (10A typical) pulls WDI high. Tying WDI to V1 or ground is also allowed, but grounding the WDI pin forces the pull-up current to be drawn continuously. Selecting the Reset Timing Capacitor The reset timeout period is adjustable in order to accommodate a variety of microprocessor applications. The reset timeout 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 = 500 pF / ms * tRST 2M
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: , 1.210V =1.210k 1mA Tables 2 and 3 offer suggested 1% resistor values for various positive and negative supply adjustable applications assuming 5% monitor thresholds. Although all six 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 device. Filter capacitors on the V3, V4, V5 and V6 inputs are allowed. Power-Down On power-down, once any of the monitor inputs drops below its threshold, RST is 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 typical), the LTC2931 will enter the 150s setup period when VCC rises above 2.4V max. Watchdog Timer The watchdog circuit monitors a microprocessor's (P) 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. Whenever RST is low, the watchdog timer is cleared and WDO is set high. The watchdog timer starts when RST goes high. Subsequent edges received on the WDI pin clear the watchdog timer. The watchdog timer continues to run until it times out. Once it times out, internal circuitry brings the WDO pin low. WDO remains low for one reset timeout period unless it is cleared by another edge on the WDI pin or RST goes low. WDO toggles between high and
Leaving the CRT pin unconnected generates a minimum reset timeout of approximately 25s. Maximum reset timeout is limited by the largest available low leakage capacitor. The accuracy of the timeout period is 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 timeout period is adjustable and can be optimized for software execution. The watchdog timeout period, tWD, is adjusted by connecting a capacitor, CWT, between the CWT pin and ground. The value of this capacitor is determined by: CWT = tWD = 50 pF / ms * tWD 20M
Leaving the CWT pin unconnected generates a minimum watchdog timeout of approximately 200s. Maximum watchdog timeout is limited by the largest available low leakage capacitor. The accuracy of the timeout period is affected by capacitor leakage (the nominal charging current is 2A) and capacitor tolerance. A low leakage ceramic capacitor is recommended.
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LTC2931 APPLICATIONS INFORMATION
Supply and Temperature Monitor Figure 5 illustrates how to configure the LTC2931 to monitor temperature. Temperature is sensed by a thermistor, RNTC, as part of a voltage divider driving adjustable input V6. Output COMP6 goes low when the temperature is higher than the trip point, and is fed back through RHYST to provide hysteresis. Assume a thermistor (RNTC) with values RHOT at the upper threshold and RCOLD at the lower threshold. Minimize errors arising from V6 input current (15nA maximum) by choosing RCOLD 100k, and to limit the loading on VREF choose RHOT 1k. RBIAS and RHYST are , calculated from: RBIAS = (RHOT/VRTA) * (VREF - VRTA) = 1.42 * RHOT RHYST = V1 (RCOLD * RHOT ) * VRTA (RCOLD-RHOT ) Five Supply Power-up Sequencer In Figure 6, the LTC2931's real-time COMP outputs are used to enable DC/DC converters sequentially. The system is powered by a 12V source. The system is started when the push-button is pressed and the LTC2950-1 brings the RUN pin of the LTM4600 high. Subsequently, the LTM4600 generates a 5V output which applies power to each of the 4 DC/DC converters. The LTC2931 is configured to mode 13 (see Table 1). When the threshold is reached on V1, COMP1 pulls high. COMP1 then enables the 3.3V converter first. When the threshold is reached on V2, COMP2 pulls high and enables the 1.8V converter next. When all the converters have been enabled and are good, COMP5 pulls high. RST pulls high 9.4ms after COMP5. Figure 7 shows the power-up sequence of the five supplies and the DONE and RST outputs. If the KILL input on the LTC2950-1 does not receive a logic high within 512ms of initial power-up, EN pulls low and the LTM4600 is powered down. In the event that the external 12V supply drops below 9.6V, COMP6 and RST will pull low. The LTC2950-1 then receives a logic low on the KILL input, which powers down the LTM4600 and the sequencing circuit.
V1 is the nominal operating voltage at input V1, VREF = 1.210V, VRTA = 0.5V, and RPU < RHYST. The closest 1% value was chosen for RHYST. In Figure 5, the trip points are 115C with RHOT = 11.1k (COMP6 goes low) and 100C with RCOLD = 18.5k (COMP6 goes high). A reset is generated in the event of an over-temperature condition. COMP6 (Temp Good) and COMP5 (Power Good) distinguish over-temperature and undervoltage faults.
5V 0.1F
10k LTC2931 V1 COMP1 COMP2 COMP3 COMP4 COMP5 COMP6 VREF RST WDO V6 VPG GND CRT WDI CWT CRT 47nF
RPU 10k
10k
3.3V 12V 28V -5.2V 2150k 1% 5110k 1% 467k 1% RHYST 280k 1% RBIAS 15.8k 1% 121k 1% R1 93.1k 1%
V2 V3 V5 V4
POWER GOOD TEMP GOOD SYSTEM LOGIC
*PANASONIC ERTJOEV474J **OPTIONAL FOR ESD PROTECTION
2931 F05
10k** MANUAL RESET PUSH BUTTON 100k 1% 100k 1% RNTC* 470k R2 9.53k 1%
CWT 47nF
tRST = 94ms tWD = 940ms
Figure 5. Supply and Temperature Monitor (5V, 3.3V, 28V, -5.2V, 12V, 115C)
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LTC2931 APPLICATIONS INFORMATION
12V (9.6V THRESHOLD) LTM4600 VIN VOUT RUN 10k 5V LT3028 VOUT 3.3V SHDN 10k 10k 5V
VIN
3.3V
EN LTC2950-1 VIN INT PB KILL 10k
VIN
LT3028 VOUT 1.8V SHDN
1.8V SYSTEM LOGIC
LTC3704 VOUT -5.2V VIN 10k RUN/UVLO
-5.2V
VIN 10k
LT3028 VOUT 2.5V SHDN
2.5V
DONE
12V SUPPLY STATUS
COMP1 COMP2 COMP3 COMP4 COMP5 COMP6
2931 F06
V1 10k 1820k 1% 0.1F 365k 1% 487k 1% V2 V3 V4 V5 V6 RST 100k 1% 100k 1% 121k 1% VREF R1 16.2k 1% R2 86.6k 1% VPG CRT 4.7nF tRST = 9.4ms WDI GND CWT LTC2931 WDO
Figure 6. Five Supply Power-Up Sequencer with Push Button (Watchdog Functions Disabled)
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LTC2931 APPLICATIONS INFORMATION
PB 5V
3.3V 2.5V 1.8V
2V/DIV
-5.2V
DONE
RST
10ms/DIV
2931 FO7
Figure 7. Five Supply Power-Up Sequencing (Based on Circuit in Figure 6)
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LTC2931 PACKAGE DESCRIPTION
F Package 20-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1650)
6.40 - 6.60* (.252 - .260) 1.05 0.10 20 19 18 17 16 15 14 13 12 11
6.60 0.10
4.50 0.10
6.40 (.252) BSC
0.45 0.05
0.65 BSC 1 2 3 4 5 6 7 8 9 10 1.10 (.0433) MAX
0 - 8
RECOMMENDED SOLDER PAD LAYOUT 4.30 - 4.50** (.169 - .177)
0.25 REF
0.09 - 0.20 (.0035 - .0079)
0.50 - 0.75 (.020 - .030)
0.65 (.0256) BSC
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE **DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
0.19 - 0.30 (.0075 - .0118) TYP
0.05 - 0.15 (.002 - .006)
F20 TSSOP 0204
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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.
15
LTC2931 TYPICAL APPLICATION
System Reset Generated by Watchdog Timing or Supply Voltage Failure
5V 0.1F LTC2931 V1 3.3V 2.5V 1.8V 182k 1% 1.5V 100k 1% R1 59k 1% V2 V3 V4 V5 V6 VREF COMP1 COMP2 COMP3 COMP4 COMP5 COMP6 RST WDO VPG CRT 4.7nF R2 40.2k 1% 4.7nF GND
2931 TA02
10k POWER GOOD
RESET
SYSTEM LOGIC
CWT
WDI
10 tWD = 94ms tRST = 9.4ms
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0508 REV B * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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