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LTC2938/LTC2939 Configurable 4- and 6-Supply Monitors with Watchdog Timer FEATURES
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DESCRIPTION
The LTC(R)2938/LTC2939 are configurable supply monitors for systems with up to four or six supply voltages that need watchdog supervision. One of sixteen preset or adjustable voltage monitor combinations can be selected using an external resistive divider connected to the program input. The preset voltage thresholds are accurate to 1.5% over temperature. The LTC2938 and LTC2939 also feature adjustable inputs with a 0.5V nominal threshold. 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 80A supply current makes the LTC2938 and LTC2939 ideal for power conscious systems. The LTC2939 monitors up to six supplies and the LTC2938 monitors up to four supplies.
L, LT, LTC, LTM, Linear Technology and the Linear logo 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.
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Simultaneously Monitors Four (LTC2938) or Six Supplies (LTC2939) Sixteen User-Selectable Combinations of 5V, 3.3V, 2.5V, 1.8V, 1.5V, 1.2V and/or Adjustable Voltage Thresholds Guaranteed Threshold Accuracy: 1.5% Adjustable Reset and Watchdog Timeout Low Supply Current: 80A Typical Power Supply Glitch Immunity Guaranteed RST for VCC > 1V High Temperature Operation to 125C 12-Pin 4mm x 3mm DFN or 12-Lead MSOP (LTC2938) and 16-Lead MSOP Package (LTC2939)
APPLICATIONS
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Desktop and Notebook Computers Multivoltage Systems Telecom Equipment Network Servers Automotive Control Systems
TYPICAL APPLICATION
6-Supply Monitor 12V (ADJ), 5V, 3.3V, 2.5V, 1.8V, 1.2V (ADJ)
12V 5V 3.3V 2.5V 1.8V 1.2V 2150k 1% 124k 1% V1 V2 V3 V4 V5 V6 VREF
Voltage Configuration Table
V1 (V) V2 (V) 3.3 3.3 3.3 3.3 3.3 2.5 2.5 1.8 1.8 1.8 2.5 2.5 1.8 1.8 1.5 1.2 V3 (V) 2.5 2.5 1.8 ADJ ADJ 1.8 1.8 1.5 1.5 1.2 ADJ ADJ ADJ ADJ ADJ ADJ V4 (V) 1.8 ADJ ADJ ADJ
-ADJ
V5 (V) ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ
V6 (V) ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ
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SYSTEM LOGIC
0.1F 0.1F
WDI LTC2939 WDO RST tRST = 94ms tWD = 940ms CRT 47nF
293839 TA01
100k 1%
100k 1%
R1 59k 1% R2 40.2k 1%
VPG GND
CWT CWT 47nF
CRT
5 5 5 5 5 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3
1.5 ADJ 1.2 ADJ ADJ ADJ -ADJ ADJ -ADJ ADJ ADJ
1
LTC2938/LTC2939 ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2, 3)
V1, V2, V3, V4, V5, V6, VPG ......................... -0.3V to 7V RST .............................................................. -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 Currents ............................................10mA
Operating Temperature Range LTC2939C..................................................... 0C to 70C LTC2939I .................................................. -40C to 85C LTC2939H .............................................. -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering 10 sec) MS Package Only .............................................. 300C
PIN CONFIGURATION
LTC2938 V3 V1 CRT RST WDO WDI 1 2 3 4 5 6 13 TOP VIEW 12 V2 11 V4 10 VREF 9 8 7 VPG GND CWT MS PACKAGE 12-LEAD PLASTIC MSOP TJMAX = 125C, JA = 130C/W V3 V1 CRT RST WDO WDI 1 2 3 4 5 6 LTC2938 TOP VIEW 12 11 10 9 8 7 V2 V4 VREF VPG GND CWT V5 V3 V1 NC CRT RST WDO WDI 1 2 3 4 5 6 7 8 LTC2939 TOP VIEW 16 15 14 13 12 11 10 9 V6 V2 V4 NC VREF VPG GND CWT
DE PACKAGE 12-LEAD (4mm 3mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W EXPOSED PAD (PIN 13) PCB GND CONNECTION OPTIONAL
MS PACKAGE 16-LEAD PLASTIC MSOP TJMAX = 125C, JA = 110C/W
ORDER INFORMATION
LEAD FREE FINISH LTC2938CDE#PBF LTC2938IDE#PBF LTC2938HDE#PBF LTC2938CMS#PBF LTC2938IMS#PBF LTC2938HMS#PBF LTC2939CMS#PBF LTC2939IMS#PBF LTC2939HMS#PBF TAPE AND REEL LTC2938CDE#TRPBF LTC2938IDE#TRPBF LTC2938HDE#TRPBF LTC2938CMS#TRPBF LTC2938IMS#TRPBF LTC2938HMS#TRPBF LTC2939CMS#TRPBF LTC2939IMS#TRPBF LTC2939HMS#TRPBF PART MARKING* 2938 2938 2938 2938 2938 2938 2939 2939 2939 PACKAGE DESCRIPTION 12-Lead (4mm x 3mm) Plastic DFN 12-Lead (4mm x 3mm) Plastic DFN 12-Lead (4mm x 3mm) Plastic DFN 12-Lead Plastic MSOP 12-Lead Plastic MSOP 12-Lead Plastic MSOP 16-Lead Plastic MSOP 16-Lead Plastic MSOP 16-Lead Plastic MSOP TEMPERATURE RANGE 0C to 70C -40C to 85C -40C to 125C 0C to 70C -40C to 85C -40C to 125C 0C to 70C -40C to 85C -40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LTC2938/LTC2939 ELECTRICAL CHARACTERISTICS
SYMBOL VCC VCCMINP VRT50 VRT33 VRT25 VRT18 VRT15 VRT12 VRTA VRTAN VREF VPG IVPG IV1 IV2 IV3 IV4 PARAMETER Minimum Internal Operating Voltage Minimum Required for Configuration 5V, 5% Reset Threshold 3.3V, 5% Reset Threshold 2.5V, 5% Reset Threshold 1.8V, 5% Reset Threshold 1.5V, 5% Reset Threshold 1.2V, 5% Reset Threshold ADJ Reset Threshold -ADJ Reset Threshold Reference Voltage Configuration Voltage Range VPG Input Current V1 Input Current V2 Input Current V3 Input Current V4 Input Current
The l 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 in Correct Logic State VCC Rising V1 Input Threshold V1, V2 Input Threshold V2, V3 Input Threshold V2, V3, V4 Input Threshold V2, V3, V4 Input Threshold V2, V3, V4 Input Threshold V3, V4, V5, V6 Input Threshold V4 Input Threshold 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 VRTX by More Than 1% ISINK = 2.5mA; VCC = 3V ISINK = 100A; VCC = 1V ISINK = 2.5mA; VCC = 3.3V ISOURCE = -1A; V2 = 3.3V VCWT = GND VCWT = 1.3V CWT = 1500pF Logic Low Open Logic High
l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
MIN
TYP
MAX 1 2.6
UNITS V V V V V V V V mV mV V V nA A A A nA A nA nA nA A A ms s
4.600 3.036 2.300 1.656 1.380 1.104 492.5 -18 1.192 0
4.675 3.086 2.338 1.683 1.403 1.122 500 0 1.210
4.750 3.135 2.375 1.710 1.425 1.140 507.5 18 1.228 VREF 20
80 0.8 0.52 0.34
125 2 1.2 15 0.8 15 15 15 -2.6 30 4
IV5, IV6 ICRT(UP) ICRT(DN) tRST tUV VOL VOL VOH ICWT(UP) ICWT(DN) tWD VWDI
V5, V6 Input Current (LTC2939) CRT Pull-Up Current CRT Pull-Down Current Reset Timeout Period Vn Undervoltage Detect to RST Voltage Output Low RST Voltage Output Low WDO Voltage Output High RST, WDO (Note 5) CWT Pull-Up Current CWT Pull-Down Current Watchdog Timeout Period WDI Input Threshold (VCC = 3.3V to 5.5V)
-1.4 10 2
-2 20 3 150 0.15 0.05 0.15
0.4 0.3 0.4
V V V V
V2 - 1 -1.4 10 20 0.7 1.4 -2 20 30 0.9 -2.6 30 40 0.4 1.1
A A ms V V V
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LTC2938/LTC2939 ELECTRICAL CHARACTERISTICS
SYMBOL IWDI PARAMETER WDI Input Current
The l 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 VWDI = GND VWDI = 0.7V VWDI = 1.1V VWDI = 5V VCC = 3.3V or 5.5V
l l l l l
MIN -10 10 2
TYP
MAX -30 30
UNITS A A A A s
tWP
WDI Input Pulse Width
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 outputs RST and WDO 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. For V2 configured to monitor 1.2V, 1.5V, 1.8V and 2.5V supplies, external pull-up resistors are required to ensure that the output voltage, high, is above the VIH input threshold of the external circuit.
TYPICAL PERFORMANCE CHARACTERISTICS
Normalized Threshold Voltages vs Temperature
NORMALIZED THRESHOLD VOLTAGES (V/V) 1.015 1.010 1.005 1.000 0.995 0.990 0.985 -50 -25 THRESHOLD VOLTAGE, VRTAN (mV) 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
29389 G01
29389 G02
29389 G03
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LTC2938/LTC2939 TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
90 V1 = 5V V2 = 3.3V V3 = 2.5V V4 = 1.8V 85 V5 = V6 = 1V IV4 (A) -100 -10 -1 80 -100n -10n 75 -1n 70 -50 -25 -100p -300 25C 125C TYPICAL TRANSIENT DURATION (s)
I(V4) vs V4 in -ADJ mode
400 350 300 250 200 150 100 50 0 -250 -200 -150 -100 V4 (mV) -50 0
29389 G05
Transient Duration vs Comparator Overdrive
TA = 25C
SUPPLY CURRENT, IV1 (A)
85C
RESET OCCURS ABOVE CURVE
50 25 75 0 TEMPERATURE (C)
100
125
1 10 100 0.1 RESET COMPARATOR OVERDRIVE (% OF VRTX)
29389 G06
29389 G04
RST Pull-Up Current vs V2
18 15 RST OUTPUT VOLTAGE (V) PULL-UP CURRENT (A) 12 9 VRT33 6 VRT18 3 0 0.5 VRT15 VRT12 1 1.5 2 2.5 3 V2 (V) 3.5 4 4.5 5 VRT25 TA = 25C 6
RST Output Voltage vs V1, VPG = GND
WATCHDOG TIMEOUT PERIOD, tWD (ms) TA = 25C 10k PULL-UP FROM RST TO V1 5 V1 = V2 4 3 2 1 0 0 1 2 V1 (V)
29389 G07 29389 G08
Watchdog Timeout Period vs Temperature
36 34 32 30 28 26 24 -50 -25 CWT = 1500pF (SILVER MICA)
3
4
5
50 25 75 0 TEMPERATURE (C)
100
125
29389 G09
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 = 25C RESET TIMEOUT PERIOD tRST (s) 10 1 100m 10m 1m 100
Reset Timeout Period vs CRT
TA = 25C
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
29389 G11
10 10p
100p
1n 10n CRT (F)
100n
1
29389 G12
29389 G10
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LTC2938/LTC2939 TYPICAL PERFORMANCE CHARACTERISTICS
ISINK vs Supply Voltage (RST)
15 TA = 25C 500
Voltage Output Low vs Sink Current (RST, WDO)
V1 = 5V V2 = 3V WDI INPUT CURRENT, IWDI (A) 125C 85C VOL (mV) 300 25C 200 -40C 20 15 10 5 0 -5 -10 -15
WDI Input Current vs Temperature
VWDI = 5V VWDI = 1.1V
12 VOL = 0.4V ISINK (mA) 9 VOL = 0.2V 6
400
3
100
VWDI = 0V VWDI = 0.7V -25 50 25 0 75 TEMPERATURE (C) 100 125
0
0
1
3 2 V1 OR V2 (V)
4
5
29389 G13
0
0
2
6 4 ISINK (mA)
8
10
-20 -50
29389 G14
29389 G15
WDO Pull-Up Current vs V2
18 15 PULL-UP CURRENT (A) 12 9 6 3 0 1 2 3 V2 (V) 4 5
29389 G16
WDI Input Threshold vs Temperature
1.50 WDI INPUT THRESHOLD, VWDI (V)
TA = 25C WDO = GND
HIGH 1.25 OPEN (MAXIMUM)
1.00
0.75 LOW OPEN (MINIMUM) 0.50 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
29389 G17
PIN FUNCTIONS
CRT: Reset Timeout Capacitor. Attach an external capaci. tor (CRT) to GND to set a reset timeout of 2ms/nF A 47nF capacitor generates a 94ms reset delay time. Leaving CRT unconnected generates a minimum timeout period of approximately 20s which will vary depending on parasitic capacitance on the pin. CWT: Watchdog Timeout Capacitor. Attach a capacitor (CWT) between CWT and GND to set a watchdog timeout period of 20ms/nF A 47nF capacitor generates a 940ms watchdog . timeout period. Leaving CWT unconnected generates a minimum timeout period of approximately 200s which
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LTC2938/LTC2939 PIN FUNCTIONS
will vary depending on parasitic capacitance on the pin. Tie CWT to GND to disable the watchdog function. GND: Device Ground. NC: No Internal Connection. RST: 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 reset delay time after all voltage inputs are above threshold. When the watchdog timer is enabled but not serviced prior to the configured watchdog timeout period, RST pulls low for one reset delay time. May be pulled to greater than V2 using an external pull-up. For V2 configured to monitor 2.5V or below, connect an external pull-up resistor to the interface logic supply to ensure that the output high voltage is above the VIH of the external circuit. Leave open if unused. V1: Voltage Input 1. Select from 5V or 3.3V. See the Applications Information section for details. The greater of V1 or V2 is also VCC for the device. Bypass this input to ground with a 0.1F (or greater) capacitor. V2: Voltage Input 2. Select from 3.3V, 2.5V, 1.8V, 1.5V or 1.2V. See the Applications Information section for details. The greater of V1, V2 is also VCC for the device. Bypass this input to ground with a 0.1F (or greater) capacitor. All status outputs are weakly pulled up to V2. V3: Voltage Input 3. Select from 2.5V, 1.8V, 1.5V, 1.2V or ADJ. See the Applications Information section for details. Tie to V1 if unused. V4: Voltage Input 4. Select from 1.8V, 1.5V, 1.2V, ADJ or -ADJ. See the Applications Information section for details. Tie to V1 if unused and configured for positive voltage. V5: Adjustable Voltage Input 5 for LTC2939. High impedance comparator input with 0.5V typical threshold. Tie to V1 if unused. V6: Adjustable Voltage Input 6 for LTC2939. High impedance comparator input with 0.5V typical threshold. Tie to V1 if unused. VPG: Threshold Select Input. Connect to an external 1% resistive divider between VREF and GND to select one of sixteen combinations of voltage thresholds (see Table 1). Do not add capacitance to the VPG input. VREF : 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. WDI: Watchdog Input: A three-state input that controls the operation of the watchdog timer. Leaving the WDI pin unconnected disables the watchdog timer while tying it low or high enables it. While RST is high, a transition between low and high logic levels (rising or falling edge) within the watchdog timeout period is required to inhibit WDO from pulling low and a watchdog initiated reset. A capacitor attached to CWT sets the watchdog timeout period. A transition between the low and high logic levels on the WDI input clears the voltage on the CWT capacitor, preventing WDO from going low. Once WDO is latched low, WDI must transition between low and high logic levels to clear WDO Transitions between open and logic low or logic high do not clear WDO. WDO: Watchdog Output. Logic output with weak 6A pullup to V2. May be pulled greater than V2 using external pull-up. For V2 configured to monitor 2.5V or below, connect an external pull-up resistor to the interface logic supply to ensure that the output high voltage is above the VIH of the external circuit. The watchdog timer is enabled when RST is high. The watchdog output pulls low if the watchdog timer expires and the output remains low until set high by the next WDI transition or anytime an undervoltage condition occurs. A watchdog failure also triggers a reset event. Leave open if unused. Exposed Pad (DE12 package only): The Exposed Pad may be left open or connected to device ground.
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LTC2938/LTC2939 BLOCK DIAGRAM
BUFFER VREF BANDGAP REFERENCE V1 V2 POWER DETECT VCC
VPG
A/D
V1 V2 V2 V3 V4 RESISTIVE DIVIDERS 4 4
+ -
4 ADJUSTABLE RESET PULSE GENERATOR
6A
RST
V5
- +
WDFAIL
0.5V
LTC2939
+
V6
-
VCC
2A V2 22A 6A
CRT GND WDFAIL WDI UV TRANSITION DETECT 2A VCC CWT 22A WATCHDOG TIMER
WDO
293839 BD
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LTC2938/LTC2939 TIMING DIAGRAM
Vn Monitor Timing
Vn
VRT tUV tRST
RST
293839 TD01
Reset and Watchdog Timing
Vn
RST tRST tRST tWD tRST tWD tRST tRST tWD tRST tWD tRST
WDO WDI
293839 TD02
POWER-ON RESET FOLLOWED BY RESET CAUSED BY UNDERVOLTAGE EVENT. WATCHDOG OUTPUT SET HIGH, WATCHDOG INPUT = DON'T CARE
WATCHDOG INPUT NOT TOGGLED, WATCHDOG TIMER EXPIRES, WATCHDOG OUTPUT PULLS LOW. RESET OUTPUT PULLS LOW FOR ONE RESET TIMEOUT PERIOD. WATCHDOG INPUT REMAINS UNTOGGLED, WATCHDOG OUTPUT REMAINS LOW, RESET OUTPUT PULLS LOW AGAIN AFTER ONE WATCHDOG TIMEOUT PERIOD. WATCHDOG OUTPUT CLEARED BY UNDERVOLTAGE EVENT.
WATCHDOG INPUT NOT TOGGLED, WATCHDOG TIMER EXPIRES, WATCHDOG OUTPUT PULLS LOW. RESET OUTPUT PULLS LOW. WATCHDOG OUTPUT LOW TIME SHORTENED BY UNDERVOLTAGE EVENT DURING RESET TIMEOUT.
WATCHDOG INPUT NOT TOGGLED, WATCHDOG TIMER EXPIRES, WATCHDOG OUTPUT PULLS LOW. RESET OUTPUT PULLS LOW. WATCHDOG OUTPUT NOT CLEARED BY WATCHDOG INPUT DURING RESET TIMEOUT. AFTER RESET COMPLETED, WATCHDOG INPUT CLEARS WATCHDOG OUTPUT.
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LTC2938/LTC2939 APPLICATIONS INFORMATION
Supply Monitoring The LTC2938 and LTC2939 are low power, high accuracy configurable four (LTC2938) and six (LTC2939) supply monitoring circuits with reset output and watchdog functions. Both watchdog and reset timeouts are adjustable using external capacitors. Single-pin configuration selects one of sixteen input voltage monitor combinations. All four (LTC2938) or six (LTC2939) voltage inputs must be above predetermined thresholds for the reset not to be invoked. The LTC2938/LTC2939 assert the reset during power-up, power-down and brownout conditions on any one of the voltage inputs. Power-Up The greater of V1 or V2 serves as the internal supply voltage (VCC). On power-up, VCC powers the drive circuits for the RST output. This ensures that the RST output will be low as soon as V1 or V2 reaches 1V. The RST output remains low until the part is configured. After configuration, if any one of the supply monitor inputs is below its configured threshold, RST will be at logic low. Once all the monitor inputs rise above their thresholds, an internal timer is started and RST is released after the configured delay time.
5V SUPPLY TOLERANCE
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 subsequently explained). A perfectly accurate supervisor for this supply generates a reset at exactly 4.75V. However, no supervisor is perfect. The actual reset threshold of a supervisor varies over a specified band. The LTC2938/LTC2939 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 LTC2938 and LTC2939 have 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 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.
NOMINAL SUPPLY VOLTAGE
MINIMUM RELIABLE SYSTEM VOLTAGE
IDEAL SUPERVISOR THRESHOLD
4.75V 1.5% THRESHOLD BAND 4.675V
-5% -6.5%
4.6V REGION OF POTENTIAL MALFUNCTION
-8%
293839 F01
Figure 1. 1.5% Threshold Accuracy Improves System Reliability
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LTC2938/LTC2939 APPLICATIONS INFORMATION
A less accurate supervisor increases the required system voltage margin and increases the probability of system malfunction. The LTC2938 and LTC2939 1.5% specification improves the reliability of the system over supervisors with wider threshold tolerances. Monitor Configuration Select the LTC2938/LTC2939 input voltage combination by placing the recommended resistive divider from VREF to GND and connect the tap point to VPG, as shown in Figure 2. Table 1 offers recommended 1% resistor values for the various modes. The rightmost column in Table 1 specifies optimum VPG / VREF ratios (0.01), when configuring with a ratiometric DAC. Upon power-up, the LTC2938 or LTC2939 enters a configuration period of approximately 150s during which the voltage on the VPG input is sampled and the monitor is configured to the desired input combination. Do not add capacitance to the VPG input. Immediately after programming, the comparators are enabled and supply monitoring begins.
LTC2938/ LTC2939 VREF VPG GND
293839 F02
R1 1% R2 1%
Figure 2. Monitor Programming
Table 1. Voltage Threshold Modes
MODE 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 V1 (V) 5 5 3.3 3.3 3.3 5 5 3.3 3.3 3.3 3.3 3.3 3.3 3.3 5 3.3 V2 (V) 3.3 3.3 2.5 2.5 1.8 3.3 3.3 1.8 1.8 1.8 2.5 2.5 1.8 1.5 3.3 1.2 V3 (V) ADJ ADJ ADJ ADJ 1.5 2.5 2.5 1.5 1.2 ADJ 1.8 1.8 ADJ ADJ 1.8 ADJ V4 (V) ADJ -ADJ ADJ -ADJ ADJ ADJ 1.8 1.2 ADJ ADJ 1.5 ADJ -ADJ ADJ ADJ ADJ R1 (k) Open 93.1 86.6 78.7 71.5 66.5 59 53.6 47.5 40.2 34.8 28 22.1 16.2 9.53 Short R2 (k) Short 9.53 16.2 22.1 28 34.8 40.2 47.5 53.6 59 66.5 71.5 78.7 86.6 93.1 Open VPG/VREF 0 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
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LTC2938/LTC2939 APPLICATIONS INFORMATION
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 LTC2939 V5 and V6 comparators are always in positive adjustable mode with a 0.5V reference. The tap point on an external resistive divider, connected between the positive voltage being sensed and ground, is connected to the high impedance, adjustable inputs (V3, V4, V5 and V6). Calculate the trip voltage from: R3 VTRIP = 0 . 5V * 1 + R4
VTRIP R3 1% V3, V4, V5 OR V6 R4 1% LTC2938/LTC2939
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 . 210 V = 1 . 210 k 1mA Tables 2 and 3 offer suggested 1% resistor values for various adjustable applications assuming 5% monitor thresholds.
Table 2. Suggested 1% Resistor Values for the ADJ Inputs
VSUPPLY (V) 12 10 8 7.5 6 5 3.3 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
+ -
0.5V
3 2.5
293839 F03
1.8 1.5 1.2 1 0.9
Figure 3. Setting the Positive Adjustable Trip Point
In the negative adjustable mode, the high impedance, adjustable input on the V4 comparator is connected to ground (Figure 4). The tap point on an external resistive divider, connected between the negative voltage being sensed and the VREF output, 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 . 210 V No min al R4 REF
LTC2938/LTC2839 VREF R4 1% R3 1% VTRIP V4
Table 3. Suggested 1% Resistor Values for the Negative ADJ Inputs
VSUPPLY (V) -2 -5 -5.2 -10 -12 VTRIP (V) -1.87 -4.64 -4.87 -9.31 -11.30 R3 (k) 1.87 464 487 931 1130 R4 (k) 121 121 121 121 121
Although all of the 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 supply for the device. Filter capacitors on the V3, V4, V5 and V6 inputs are allowed.
293839 F04
Figure 4. Setting the Negative Adjustable Trip Point
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12
LTC2938/LTC2939 APPLICATIONS INFORMATION
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 LTC2938/LTC2939 will reconfigure when VCC rises above 2.4V (max). 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 CRT and ground. The value of this capacitor is determined by: t pF CRT = RST = 500 * t RST 2M ms Leaving CRT unconnected generates a minimum reset timeout period of approximately 20s. The maximum reset timeout period 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. Watchdog Timer The watchdog circuit typically monitors a microprocessor's activity. The microprocessor is required to change the logic state of the WDI input on a periodic basis in order to clear the watchdog timer. Whenever an undervoltage condition exists, the watchdog timer is cleared and WDO is set high. The watchdog timer starts when RST pulls high. Subsequent edges received on the WDI input clear the watchdog timer. If uncleared, the watchdog timer continues to run until it times out. Once it times out, internal circuitry brings the WDO and RST outputs low. WDO remains low for at least one reset timeout period and can then be cleared by a new edge on the WDI input or anytime an undervoltage condition occurs. The watchdog timer may be disabled in three ways. One method is to simply ground CWT. With CWT held at ground, any undervoltage event forces WDO high indefinitely. A second method is to leave the WDI input floating or in high impedance. The last method is to continuously drive WDI between the low and high thresholds. 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 CWT and ground. The value of this capacitor is determined by: pF t C WT = WD = 50 * t WD 20M ms Leaving CWT unconnected generates a minimum watchdog timeout period of approximately 200s. The maximum watchdog timeout period 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. Pull-Up Resistors for WDO and RST The WDO and RST pins provide weak pull-up currents to V2. This current is typically greater than 6A when V2 is greater than 3.3V. The magnitude of the pull-up current decreases as V2 decreases. For V2 configured to monitor 2.5V, 1.8V, 1.5V and 1.2V supplies, external pull-up resistors are required from both pins to the interface logic supply to ensure that the output high voltage is above the VOH input threshold of the external circuit. The WDO and RST pins can be pulled to voltages higher than V2 by external pull-up resistors. Watchdog Application Figure 5 shows a typical application for the LTC2938/ LTC2939. The CWT timing capacitor adjusts the watchdog timeout period for optimal software execution. If the software malfunctions and the state of the WDI pin is unchanged before the end of the watchdog timeout period (tWD), the LTC2938/LTC2939 WDO pin is latched to a low state. At the same time, RST is pulled low to reset the microprocessor. While RST is low, the WDI pin does not affect RST or WDO. The system therefore resets for at least tRST.
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13
LTC2938/LTC2939 APPLICATIONS INFORMATION
After RST returns high, the microprocessor can poll the state of the WDO pin to determine if the reset was caused by an undervoltage condition or by a watchdog timeout. WDO high means that the reset was caused by undervoltage since this condition also resets the WDO latch (and the watchdog timer). If the WDO pin is low, the system reset was caused by watchdog timeout. The microprocessor can then change the state of WDI to clear the WDO latch. If the microprocessor fails to do so, the LTC2938/ LTC2939 will alternate between tRST and tWD timeout and RST will be pulled low for tRST after every watchdog timeout. WDO remains low until the microprocessor flips the state of WDI. Some microprocessors force their I/O pins into high impedance during reset which in turn, floats the WDI
5V 3.3V 0.1F 2.5V 1.8V 12V 1.2V 124k 1% 2150k 1% 0.1F
pin. This affects the response of the LTC2938/LTC2939. When the WDI pin is floated, the watchdog timer is reset and CWT is discharged towards ground but WDO remains unchanged. Putting WDI in high impedance does not affect tRST. Once RST goes high again, and WDI is driven from high impedence to a high or low state, the watchdog timer starts a complete tWD timeout period. A high-to-low or low-to-high transition at WDI clears WDO if it was previously latched low. The RST and WDO pins should not be tied together to generate the master reset signal since a watchdog timeout forces RST low together with WDO and the master reset signal will remain low indefinitely.
V1 V2
V3 V4 V5 V6 R1 59k 1% 100k 1% 100k 1% R2 40.2k 1% VREF LTC2939 RST WDO WDI MICROPROCESSOR
VPG GND CRT CRT 47nF
CWT CWT 47nF tRST = 94ms tWD = 940ms
293839 F05
Figure 5. 6-Supply Monitor, 12V (ADJ), 5V, 3.3V, 2.5V, 1.8V, 1.2V (ADJ) with Watchdog Enabled
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14
LTC2938/LTC2939 TYPICAL APPLICATIONS
Quad-Supply Monitor (Mode 14) with Watchdog Disabled
5V 3.3V 0.1F 1.8V 12V VTRIP = 11.25V R3 2.15M 1% R1 9.53k 1% 0.1F
V1 V2 SYSTEM LOGIC
V3 V4 LTC2938
RST
VREF
WDO
R4 100k 1%
VPG R2 93.1k 1% GND CRT CRT 47nF
WDI CWT
293839 TA02
5V Supply Monitor (Mode 1) with Watchdog Disabled and Unused Inputs Tied High
5V 0.1F R3 464k 1% R4 121k 1%
V1 V2 V3 V4 LTC2938 RST SYSTEM LOGIC
-5V VTRIP = - 4.64V
VREF R1 93.1k 1% R2 9.53k 1% VPG GND CRT CRT 47nF
WDO
WDI CWT
293839 TA03
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15
LTC2938/LTC2939 TYPICAL APPLICATIONS
Supply and Temperature Monitor (Mode 1, 5V, 3.3V, 28V, -5.2V, 12V, 100C)
5V 3.3V 0.1F 12V 28V -5.2V 2150k 1% 5110k 1% 467k 1% RHYST 280k 1% RBIAS 93.1k 1% 121k 1% 0.1F
V1 V2 10k 1%
V3 V5 V4 LTC2939 RST SYSTEM LOGIC
VREF R1 93.1k 1% V6
WDO
WDI GND CRT CWT CRT 47nF
293839 TA04
RNTC* 470k 100k 1% 100k 1%
VPG R2 9.53k 1%
*PANASONIC ERTJOEV474J
Buffered VREF to Power High Current Circuits
5V 3.3V 0.1F 2.5V 1.8V 12V 1.2V 124k 1% 2150k 1% 0.1F
V1 V2 RST WDO V3 V4 V5 V6 VREF R1 59k 1% R2 40.2k 1% LTC2939 5V WDI MICROPROCESSOR
+
LT1809
VPG GND 100k 1% 100k 1% CRT CRT 47nF CWT CWT 47nF
293839 TAO5
-
1.210V 10mA
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16
LTC2938/LTC2939 PACKAGE DESCRIPTION
UE/DE Package 12-Lead Plastic DFN (4mm x 3mm)
(Reference LTC DWG # 05-08-1695)
0.70 0.05 3.30 0.05 1.70 0.05 PACKAGE OUTLINE
3.60 0.05 2.20 0.05
0.25
0.05 0.50 BSC 2.50 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 0.10 (2 SIDES) R = 0.05 TYP 3.30 0.10 PIN 1 TOP MARK (NOTE 6) 3.00 0.10 (2 SIDES) 1.70 0.10 PIN 1 NOTCH R = 0.20 OR 0.35 45 CHAMFER 0.75 0.05 6 0.25 1 0.05 0.50 BSC 2.50 REF 0.00 - 0.05 BOTTOM VIEW--EXPOSED PAD
(UE12/DE12) DFN 0806 REV D
7
R = 0.115 TYP
0.40 12
0.10
0.200 REF
NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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17
LTC2938/LTC2939 PACKAGE DESCRIPTION
MS Package 12-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1668 Rev O)
0.889 (.035
0.127 .005)
5.23 (.206) MIN
3.20 - 3.45 (.126 - .136)
0.42 0.038 (.0165 .0015) TYP
0.65 (.0256) BSC
4.039 0.102 (.159 .004) (NOTE 3) 12 11 10 9 8 7
RECOMMENDED SOLDER PAD LAYOUT
0.406 0.076 (.016 .003) REF
0.254 (.010) GAUGE PLANE
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE 4)
0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) SEATING PLANE
123456 1.10 (.043) MAX
0.86 (.034) REF
NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.22 - 0.38 (.009 - .015) TYP
0.650 (.0256) BSC
0.1016 (.004
0.0508 .002)
MSOP (MS12) 1107 REV O
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18
LTC2938/LTC2939 PACKAGE DESCRIPTION
MS Package 16-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1669 Rev O)
0.889 (.035
0.127 .005)
5.23 (.206) MIN
3.20 - 3.45 (.126 - .136)
0.305 0.038 (.0120 .0015) TYP
0.50 (.0197) BSC
4.039 0.102 (.159 .004) (NOTE 3) 16151413121110 9
RECOMMENDED SOLDER PAD LAYOUT
0.280 0.076 (.011 .003) REF
0.254 (.010) GAUGE PLANE
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE 4)
0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) SEATING PLANE
12345678 1.10 (.043) MAX
0.86 (.034) REF
NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.17 -0.27 (.007 - .011) TYP
0.50 (.0197) BSC
0.1016 (.004
0.0508 .002)
MSOP (MS16) 1107 REV O
293839ff
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.
19
LTC2938/LTC2939 TYPICAL APPLICATION
Quad-Supply Monitor (Mode 14) with Pushbutton Reset
1F 5V V1 1.8V V3 CRT RST CRT 47nF SYSTEM LOGIC WDO WDI VPG GND CWT
293839 TAO6
3.3V V2 V4 LTC2938 VREF
1F
R3 2.15M 1% 12V VTRIP = 11.25V R1 9.53k 1% 10k*
CWT 47nF
R2 93.1k 1%
R4 100k 1%
MANUAL RESET PUSHBUTTON
*OPTIONAL RESISTOR FOR ADDED ESD PROTECTION
RELATED PARTS
PART NUMBER LTC2900 LTC2901 LTC2902 LTC2908 LTC2930 LTC2931 LTC2932 DESCRIPTION Programmable Quad-Supply Monitor Programmable Quad-Supply Monitor Programmable Quad-Supply Monitor Precision 6-Supply Monitor (Four Fixed and Two Adjustable) Configurable 6-Supply Monitor with Adjustable Reset Timer, Manual Reset Configurable 6-Supply Monitor with Adjustable Reset and Watchdog Timers Configurable 6-Supply Monitor with Individual Comparator Outputs COMMENTS Adjustable Reset, 10-Lead MSOP and DFN Packages Adjustable Reset and Watchdog Timer Adjustable Reset and Tolerance 8-Lead TSOT-23 and DFN Packages H-Grade Temperature Range, 3mm x 3mm DFN-12 Package H-Grade Temperature Range, Individual Supply Comparator Outputs, TSSOP-20 Package Adjustable Reset Timer and Tolerance, Pin-Selectable Tolerance (5%, 7.5%, 10% or 12.5%), Reset Disable for Margining, TSSOP-20 Package
293839ff
20 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0709 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2009

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