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FEATURES
LTC2917/LTC2918 Low Voltage Supervisor with 27 Selectable Thresholds and Watchdog Timer DESCRIPTION
The LTC(R)2917-A/LTC2917-B and LTC2918-A/LTC2918-B are low voltage single-supply monitors with selectable thresholds and an adjustable watchdog timer. The parts operate from 1.5V to 5.5V and consume a quiescent current of only 30A. Two three state inputs select one of nine internally programmed thresholds without the need for external resistors. For the LTC2917, an additional three state input determines the tolerance (-5%, -10%, -15%). The tolerance for the LTC2918 is fixed at -5%. Threshold accuracy is guaranteed at 1.5% over the entire operating temperature range. Glitch filtering ensures reliable reset operation without false triggering. The reset timeout and the watchdog timeout may be set with no external components, or adjusted using an external capacitor. A windowed watchdog feature is available for high-reliability applications (B1 versions). A separate manual reset input on the LTC2918-A/LTC2918-B allows a simple push button interface. Operation to 125C makes the LTC2917-A/LTC2917-B and LTC2918-A/LTC2918-B suitable for automotive applications.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

9 Selectable Supply Voltages 12V, 5V, 3.3V, 2.5V, 1.8V 1.5V, 1.2V, 1V, +ADJ (0.5V) 3 Selectable Tolerances -5%, -10%, -15% (LTC2917) Manual Reset Input (LTC2918) 1.5V to 5.5V Supply Operation Adjustable Watchdog Timeout Windowed Watchdog Timeout for Higher Reliability Applications (LTC2917-B, LTC2918-B) 6.2V Shunt Regulator for High Voltage Operation Guaranteed to 125C Guaranteed Threshold Accuracy: 1.5% Low Quiescent Current: 30A Typical Power Supply Glitch Immunity Guaranteed RST for VCC 0.8V 10-Lead MSOP Packages and (3mm x 2mm) DFN Packages
APPLICATIONS

Handheld Devices Cell Phone Base Stations Automotive Control Systems Network Servers Optical Networking Systems
TYPICAL APPLICATION
1.8V Supply Monitor with Manual Reset and Internal Timers Selected
1.8V
Monitor Selection Table
NOMINAL VOLTAGE SEL1 VCC VCC VCC Open Open Open GND GND GND SEL2 VCC Open GND VCC Open GND VCC Open GND
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0.1F
10k
12V 5V 3.3V
P RST I/O
29178 TA01
VCC LTC2918-A VM RT WT MR GND tWDU = 1.6s tRST = 200ms RST WDI SEL1 SEL2
2.5V 1.8V 1.5V 1.2V 1V ADJ (0.5V)
1
LTC2917/LTC2918 ABSOLUTE MAXIMUM RATINGS
(Note 1, 2)
Terminal Voltages VCC (Note 3).......................................... -0.3V to 5.7V SEL1, SEL2, TOL, WDI, MR, RST ......... -0.3V to 7.5V VM ......................................................... -0.3V to 15V RT, WT ......................................-0.3V to (VCC + 0.3)V Terminal Currents VCC (Note 3).......................................................5mA
Operating Temperature Range LTC2917C/LTC2918C ............................... 0C to 70C LTC2917I/LTC2918I ............................. -40C to 85C LTC2917H/LTC2918H ........................ -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) MSOP-10 .......................................................... 300C
PIN CONFIGURATION
TOP VIEW TOP VIEW GND TOL SEL2 SEL1 VM 1 2 3 4 5 10 9 8 7 6 RST RT WT WDI VCC GND 1 TOL 2 SEL2 3 SEL1 4 VM 5 11 10 RST 9 8 7 6 RT WT WDI VCC
MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125C, JA = 200C/W LTC2917
DDB PACKAGE 10-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W EXPOSED PAD (PIN 11) PCB GND CONNECTION OPTIONAL LTC2917 TOP VIEW
TOP VIEW GND MR SEL2 SEL1 VM 1 2 3 4 5 10 9 8 7 6 RST RT WT WDI VCC
GND 1 MR 2 SEL2 3 SEL1 4 VM 5 11
10 RST 9 8 7 6 RT WT WDI VCC
MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125C, JA = 200C/W LTC2918
DDB PACKAGE 10-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W EXPOSED PAD (PIN 11) PCB GND CONNECTION OPTIONAL LTC2918
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LTC2917/LTC2918 ORDER INFORMATION
LEAD FREE FINISH LTC2917CMS-B1#PBF LTC2917IMS-B1#PBF LTC2917HMS-B1#PBF LTC2917CMS-A1#PBF LTC2917IMS-A1#PBF LTC2917HMS-A1#PBF LTC2918CMS-B1#PBF LTC2918IMS-B1#PBF LTC2918HMS-B1#PBF LTC2918CMS-A1#PBF LTC2918IMS-A1#PBF LTC2918HMS-A1#PBF TAPE AND REEL (MINI) LTC2917CDDB-B1#TRMPBF LTC2917IDDB-B1#TRMPBF LTC2917HDDB-B1#TRMPBF LTC2917CDDB-A1#TRMPBF LTC2917IDDB-A1#TRMPBF LTC2917HDDB-A1#TRMPBF LTC2918CDDB-B1#TRMPBF LTC2918IDDB-B1#TRMPBF LTC2918HDDB-B1#TRMPBF LTC2918CDDB-A1#TRMPBF LTC2918IDDB-A1#TRMPBF LTC2918HDDB-A1#TRMPBF TAPE AND REEL LTC2917CMS-B1#TRPBF LTC2917IMS-B1#TRPBF LTC2917HMS-B1#TRPBF LTC2917CMS-A1#TRPBF LTC2917IMS-A1#TRPBF LTC2917HMS-A1#TRPBF LTC2918CMS-B1#TRPBF LTC2918IMS-B1#TRPBF LTC2918HMS-B1#TRPBF LTC2918CMS-A1#TRPBF LTC2918IMS-A1#TRPBF LTC2918HMS-A1#TRPBF TAPE AND REEL LTC2917CDDB-B1#TRPBF LTC2917IDDB-B1#TRPBF LTC2917HDDB-B1#TRPBF LTC2917CDDB-A1#TRPBF LTC2917IDDB-A1#TRPBF LTC2917HDDB-A1#TRPBF LTC2918CDDB-B1#TRPBF LTC2918IDDB-B1#TRPBF LTC2918HDDB-B1#TRPBF LTC2918CDDB-A1#TRPBF LTC2918IDDB-A1#TRPBF LTC2918HDDB-A1#TRPBF PART MARKING* LTCQP LTCQP LTCQP LTDGD LTDGD LTDGD LTDCT LTDCT LTDCT LTDGG LTDGG LTDGG PART MARKING* LCQR LCQR LCQR LDGF LDGF LDGF LDCV LDCV LDCV LDGH LDGH LDGH PACKAGE DESCRIPTION 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP PACKAGE DESCRIPTION 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 10-Lead (3mm x 2mm) Plastic DFN 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 0C to 70C -40C to 85C -40C to 125C 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 0C to 70C -40C to 85C -40C to 125C
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. 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/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LTC2917/LTC2918 ELECTRICAL CHARACTERISTICS
SYMBOL VCC(MIN) VCC(UVLO) VCC(SHUNT) ICC PARAMETER Minimum Supply Voltage Supply Undervoltage Lockout Shunt Regulation Voltage VCC Pin Current IVCC = 0.5mA SEL1, SEL2, TOL, MR = Open SEL1, SEL2, TOL = GND (LTC2917) MR = VCC (LTC2918)
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 2.5V, unless otherwise noted. (Note 2)
CONDITIONS RST in Correct Logic State

MIN 0.8
TYP
MAX 1.5
UNITS V V V A A
5.7
6.2 30 45
7.0 50 80
Monitor Input (VM) VMT120 12V, 5% Reset Threshold 12V, 10% Reset Threshold 12V, 15% Reset Threshold 5V, 5% Reset Threshold 5V, 10% Reset Threshold 5V, 15% Reset Threshold 3.3V, 5% Reset Threshold 3.3V, 10% Reset Threshold 3.3V, 15% Reset Threshold 2.5V, 5% Reset Threshold 2.5V, 10% Reset Threshold 2.5V, 15% Reset Threshold 1.8V, 5% Reset Threshold 1.8V, 10% Reset Threshold 1.8V, 15% Reset Threshold 1.5V, 5% Reset Threshold 1.5V, 10% Reset Threshold 1.5V, 15% Reset Threshold 1.2V, 5% Reset Threshold 1.2V, 10% Reset Threshold 1.2V, 15% Reset Threshold 1V, 5% Reset Threshold 1V, 10% Reset Threshold 1V, 15% Reset Threshold ADJ (0.5V), 5% Reset Threshold ADJ (0.5V), 10% Reset Threshold ADJ (0.5V), 15% Reset Threshold VM Input Impedance (Note 4) ADJ Input Current Low Level Input Voltage High Level Input Voltage Pin Voltage when Open Allowable Leakage in Open State Pin Input Current RT Pull Up Current RT Pull Down Current Internal RT VCC Detect Current RT Internal Timer Threshold VTPIN = 0V, VCC VRT = 0.25V VRT = 1.1V VRT = VCC VRT Rising, Referenced to VCC I = 0A

11.04 10.44 9.84 4.600 4.350 4.100 3.036 2.871 2.706 2.300 2.175 2.050 1.656 1.566 1.476 1.380 1.305 1.230 1.104 1.044 0.984 0.920 0.870 0.820 460.0 435.0 410.0 0.5
11.22 10.62 10.02 4.675 4.425 4.175 3.086 2.921 2.756 2.338 2.213 2.088 1.683 1.593 1.503 1.403 1.328 1.253 1.122 1.062 1.002 0.935 0.885 0.835 467.5 442.5 417.5
11.40 10.80 10.20 4.750 4.500 4.250 3.135 2.970 2.805 2.375 2.250 2.125 1.710 1.620 1.530 1.425 1.350 1.275 1.140 1.080 1.020 0.950 0.900 0.850 475.0 450.0 425.0 8 15 0.5
V V V V V V V V V V V V V V V V V V V V V V V V mV mV mV M nA V V V
VMT50
VMT33
VMT25
VMT18
VMT15
VMT12
VMT10
VMTADJ
RVM IVM(ADJ) VTPIN, LOW VTPIN, HIGH VTPIN, Z ITPIN, Z ITPIN, H/L IRT(UP) IRT(DOWN) IRT(INT) VRT(INT, LH)
Fixed Threshold Modes VM = 0.5V

Three-State Inputs (SEL1, SEL2), (TOL, LTC2917)

1.4 0.9 5 20 -2 2 -100 -3 3 1 -160 -4 4 8 -300
A A A A A mV
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Reset Timer Control (RT)

4
LTC2917/LTC2918 ELECTRICAL CHARACTERISTICS
SYMBOL Reset Output (RST) tRST(INT) tRST(EXT) tUV VOL Internal Reset Timeout Period Adjustable Reset Timeout Period VM Undervoltage Detect to RST Asserted Output Voltage Low RST VRT = VCC CRT = 2.2nF VM Less Than Reset Threshold VMTX by More Than 5% VCC = 3.3V, IRST = 2.5mA VCC = 1V, IRST = 100A VCC = 0.8V, IRST = 15A RST = VCC VWT = 0.25V VWT = 1.1V VWT Rising, Referenced to VCC VWT = VCC VWT = 0V VWT = VCC B Versions, VWT = VCC CWT = 2.2nF B Versions, CWT = 2.2nF

The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 2.5V, unless otherwise noted. (Note 2)
PARAMETER CONDITIONS MIN 150 16 10 TYP 200 20 80 0.15 0.15 0.05 MAX 260 25 150 0.4 0.3 0.2 1 -2 2 -100 -3 3 -160 1 -3.5 1.3 37.5 130 1.6 50 160 tWDU(EXT)/32 0.4 1.1 400 1 0.2 * VCC 0.8 * VCC 50 250 100 150 2 62.5 200 -4 4 -300 8 UNITS ms ms s V V V A A A mV A A s ms ms ms V V ns A V V k ns
IOH(RST) IWT(UP) IWT(DOWN) VWT(INT, LH) IWT(INT) IWT(DIS) tWDU(INT) tWDL(INT) tWDU(EXT) tWDL(EXT) VIL(WDI) VIH(WDI) tPW(WDI)
RST Output Voltage High Leakage WT Pull Up Current WT Pull Down Current WT Internal Timer Threshold Internal WT VCC Detect Current Watchdog Disable Hold Current Internal Watchdog Upper Boundary Internal Watchdog Lower Boundary (Note 5) External Watchdog Upper Boundary External Watchdog Lower Boundary (Note 5) Input Low Voltage Input High Voltage Input Pulsewidth WDI Leakage Current
Watchdog Timer Control (WT)

Watchdog Input (WDI)
Manual Reset Input (LTC2918) VIL(MR) VIH(MR) RPU tPW(MR) Input Low Voltage Input High Voltage Pull Up Resistance Pulsewidth

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: VCC maximum pin voltage is limited by input current. Since the VCC pin has an internal 6.2V shunt regulator, a low impedance supply which exceeds 5.7V may exceed the rated terminal current. Operation
from higher voltage supplies requires a series dropping resistor. See Applications Information. Note 4: Input impedance is dependent on the configuration of the SEL pins. Note 5: In the LTC2917-B/LTC2918-B, edges must occur on WDI with a period between the lower and upper boundary or RST is invoked. For the LTC2917-A/LTC2918-A, the edges must simply occur before the upper boundary. See Applications Information.
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LTC2917/LTC2918 TYPICAL PERFORMANCE CHARACTERISTICS
Threshold Voltage vs Temperature
1.5 QUIESCENT SUPPLY CURRENT, ICC (A) 1.0 NORMALIZED VMTnn (%) 0.5 0 -0.5 -1.0 -1.5 -50 -25 VMT120 40
Quiescent Supply Current vs Temperature
MAXIMUM ALLOWABLE GLITCH DURATION (s) SEL1 = 0V SEL2 = 2.5V TOL = OPEN VCC = 5.5V 30 VCC = 2.5V VCC = 1.5V 25 300 250 200 150 100 50 0
Allowable Glitch Duration vs Magnitude
35
VMTADJ
RESET OCCURS ABOVE CURVE
VMT25
50 25 75 0 TEMPERATURE (C)
100
125
20 -50
-25
75 0 25 50 TEMPERATURE (C)
100
125
1 10 100 0.1 GLITCH PERCENTAGE PAST THRESHOLD (%)
29178 G03
29178 G01
29178 G02
Reset Timeout Period vs RT Capacitance
10000 RESET TIMEOUT PERIOD, tRST(EXT) (ms) RESET TIMEOUT PERIOD, tRST(INT) (ms) 250
Internal Reset Timeout Period vs Temperature
RT = VCC WATCHDOG TIMEOUT PERIOD, tWDU(INT) (ms) 2.0
Internal Watchdog Timeout Period vs Temperature
WT = VCC
1000
230
1.8
100
210
1.6
10
190
1.4
1
170
1.2
0.1 0.001
0.01 0.1 1 10 100 RT PIN CAPACITANCE, CRT (nF)
1000
150 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
1.0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
29178 G04
29178 G05
29178 G06
Watchdog Timeout Period vs Capacitance
SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V) WATCHDOG TIMEOUT PERIOD, tWDU(EXT) (ms) 10000 6.4
Shunt Regulation Voltage vs Temperature
ICC = 5mA SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V) 7.0
Shunt Regulation Voltage vs Supply Current
6.8
1000
6.3 ICC = 1mA
6.6
100
6.2
ICC = 100A
6.4
10
6.2
1 0.001
0.01 0.1 1 10 WT PIN CAPACITANCE, CWT (nF)
100
29178 G07
6.1 -50
-25
75 0 25 50 TEMPERATURE (C)
100
125
6.0 0.01
1 0.1 10 SUPPLY CURRENT, ICC (mA)
100
29178 G09
29178 G08
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LTC2917/LTC2918 TYPICAL PERFORMANCE CHARACTERISTICS
RST Output Voltage vs VCC
6 PULL-DOWN CURRENT, IRST (mA) 10k PULL-UP R TO VCC SEL1 = SEL2 = TOL = 0V 5 VM = 0.5V RST VOLTAGE (V) 4 3 2 1 0 0 1 2 3 4 SUPPLY VOLTAGE, VCC (V) 5
29178 G10
RST Pull-Down Current vs VCC
6 5 4 RST AT 150mV 3 2 1 0 0 1 2 3 4 SUPPLY VOLTAGE, VCC (V) 5
29178 G11
RST VOL vs IRST
1.0 NO PULL-UP R VCC = 2.5V
0.8 RST VOLTAGE (V) TA = 125C 0.6 TA = 25C 0.4
RST AT 50mV
0.2
TA = -40C
0
0
2
6 4 IRST (mA)
8
10
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PIN FUNCTIONS
GND: Device Ground. MR (LTC2918 only): Manual Reset Input (Active Low). A low level on the MR input causes the part to issue a reset, which is released one reset timeout after the input goes high. The pin has an internal 100k pull-up to VCC, and thus may interface directly to a momentary pushbutton. Leave open if unused. RST: Open Drain RST Output. Asserts low when VM is below the threshold selected by SEL1, SEL2 and TOL input pins. Held low for an adjustable timeout after VM input is above threshold. RT: Reset Timeout Control Pin. Attach an external capacitor (CRT) to GND to set a reset timeout of 9ms/nF. Leave RT open to generate a reset timeout of approximately 400s. Tie RT to VCC to generate a reset timeout of approximately 200ms. SEL1, SEL2: Monitor Voltage Select Three-State Input. SEL1, and SEL2 control the nominal threshold voltage that VM is set to monitor. Connect to VCC, GND or leave unconnected in open state. (See Table 1). TOL (LTC2917 only): Three-State Input for Supply Tolerance Selection (-5%, -10% or -15%). Controls the tolerance band at which the VM supply is monitored. Connect to VCC, GND, or leave unconnected in open state. (See Table 2) VCC: Power Supply input. Bypass this pin to ground with a 0.1F ceramic capacitor. A minimum of 1.5V on VCC ensures that the part is out of under voltage lockout and that the voltage thresholds are accurate. Operates as a direct supply input for voltages up to 5.5V. Operates as a shunt regulator for supply voltages greater than 5.7V and should have a resistor between this pin and the supply to limit VCC input current to no greater than 5mA. When used without a current-limiting resistor, pin voltage must not exceed 5.7V. VM: Voltage Monitor Input to RST comparator. SEL1, SEL2 and TOL inputs select the exact threshold that asserts the RST output. WDI: Watchdog Input. This pin must be driven to change state within a time less than the watchdog upper boundary time, or RST will be asserted low. On the LTC2917-B, LTC2918-B, the period must also be greater than the watchdog lower boundary time, and only falling edges are considered. Tie WT and WDI to GND to disable the watchdog timer. WT: Watchdog Timer Control Pin. Attach an external capacitor (CWT) to GND to set a watchdog upper boundary timeout time of 72ms/nF. Tie WT to VCC to generate a timeout of approximately 1.6s. Leave WT open to generate a timeout of approximately 3.2ms. Tie WT and WDI to GND to disable the watchdog timer. Exposed Pad (DFN Only): Exposed pad may be left open or connected to device ground.
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LTC2917/LTC2918 BLOCK DIAGRAM
LTC2917 SEL1 3 STATE DECODE SEL2 TOL LTC2918 MR VCC 100k RT VCC DETECT VCC VCC 6.2V
VM
+ -
0.5V
REFERENCE DIVIDER MATRIX
TIMING DIAGRAM
VM VMTx tUV RST 1V
29178 TD01
WDI
RST tWDU tRST
29178 TD01
Watchdog Timing (LTC2917-A, LTC2918-A)
WDI
RST t > tWDL t < tWDL tRST tWDU tRST
29178 TD03
Watchdog Timing (LTC2917-B, LTC2918-B)
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+ -
ADJUSTABLE RESET TIMER INTERNAL 1.6 SECOND TIMER ADJUSTABLE WATCHDOG TIMER VCC DETECT WT tRST
MONITOR DIVIDER MATRIX
INTERNAL 200ms TIMER RESET DRIVER LOGIC
RST
GND
WATCHDOG LOGIC
WDI
29178 BD
Monitor Input Timing
LTC2917/LTC2918 APPLICATIONS INFORMATION
Supply Monitoring The LTC2917/LTC2918 are low voltage single supply monitors with selectable thresholds. Two three-state inputs select one of nine internally programmed thresholds. For the LTC2917, a third three-state input selects the tolerance at which the supply connected to the VM pin is monitored (-5%, -10%, -15%). The tolerance for the LTC2918 is fixed at -5%. Threshold accuracy is guaranteed at 1.5% over the entire operating temperature range. The LTC2917/LTC2918 asserts the RST output low when VM is below the programmed threshold, and for a reset timeout period (tRST) after VM goes above the threshold. The reset timeout can be configured to use one of two internal timers with no external components, or an adjusted timer programmed by placing an external capacitor from RT to ground. Glitch filtering ensures reliable reset operation without false triggering. Power-Up VCC powers the drive circuits for the RST pin. Therefore, as soon as VCC reaches 0.8V during power up, the RST output asserts low. Until VCC reaches the undervoltage lockout threshold (guaranteed less than 1.5V), RST is held low regardless of the state of VM. Once VCC is above the undervoltage lockout threshold and VM is above the programmed threshold, the reset timer is started. After the reset timeout, the open drain pull-down releases RST and the external pull-up resistor pulls high. Power-Down On power-down, once VM drops below its threshold or VCC drops below the undervoltage lockout, RST asserts logic low. Monitor Threshold Control The monitor threshold on the VM pin is controlled by the SEL1, SEL2 and TOL three-state pins. The SEL1 and SEL2 pins select one of nine preset nominal voltages (including one externally adjustable threshold) as shown in Table 1. The SEL1 and SEL2 three-state input pins should be connected to GND, VCC or left unconnected during normal operation. Note that when left unconnected, the maximum leakage allowable from the pin to either GND or VCC is 5A. The tolerance at which the monitored supply is measured is set by the TOL pin (LTC2917 only) as shown in Table 2. If desired (e.g. for margining purposes), the TOL pin may be driven by a three-state buffer. That three-state buffer must have a VOL and VOH which meet the VIL and VIH of the TOL pin specified in the Electrical Characteristics, and maintain less than 5A of leakage in the open state.
Table 1. Voltage Threshold Settings
NOMINAL VOLTAGE 12V 5V 3.3V 2.5V 1.8V *1.5V *1.2V *1V *ADJ (0.5V)
*Require a separate supply for VCC
SEL1 VCC VCC VCC Open Open Open GND GND GND
SEL2 VCC Open GND VCC Open GND VCC Open GND
Table 2. System Voltage Tolerance Settings
TOLERANCE -5% -10% -15% TOL VCC Open GND
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LTC2917/LTC2918 APPLICATIONS INFORMATION
Threshold Accuracy The trip threshold for the supplies monitored is selected by configuring the three-state input pins. When using the adjustable input, a external resistive divider sets the trip threshold, allowing the user complete control over the trip point. Selection of this trip voltage is crucial to the reliability of the system. Any power supply has some tolerance band within which it is expected to operate (e.g. 5V10%). It is generally undesirable that a supervisor issue a reset when the power supply is inside this tolerance band. Such a "nuisance" reset reduces reliability by preventing the system from functioning under normal conditions. To prevent nuisance resets, the supervisor threshold must be guaranteed to lie outside the power supply tolerance band. To ensure that the threshold lies outside the power supply tolerance range, the nominal threshold must lie outside that range by the monitor's accuracy specification. All 27 of the selectable thresholds have the same relative threshold accuracy of 1.5% of the programmed nominal input voltage (over the full operating temperature range). Consider the example of monitoring a 5V supply with a 10% tolerance. The nominal threshold internal to the LTC2917 is 11.5% below the 5V input at 4.425V. With 1.5% accuracy, the trip threshold range is 4.425V75mV over temperature (i.e. 10% to 13% below 5V). The monitored system must thus operate reliably down to 4.35V or 13% below 5V over temperature. Glitch Immunity The above discussion is concerned only with the DC value of the monitored supply. Real supplies also have relatively high-frequency variation, from sources such as load transients, noise, and pickup. These variations should not be considered by the monitor in determining whether a supply voltage is valid or not. The variations may cause spurious outputs at RST, particularly if the supply voltage is near its trip threshold. Two techniques are used to combat spurious reset without sacrificing threshold accuracy. First, the timeout period helps prevent high-frequency variation whose frequency is above 1/ tRST from appearing at the RST output. When the voltage at VM goes below the threshold, the RST pin asserts low. When the supply recovers past the threshold, the reset timer starts (assuming it is not disabled), and RST does not go high until it finishes. If the supply becomes invalid any time during the timeout period, the timer resets and starts a fresh when the supply next becomes valid. While the reset timeout is useful at preventing toggling of the reset output in most cases, it is not effective at preventing nuisance resets due to short glitches (due to load transients or other effects) on a valid supply. To reduce sensitivity to these short glitches, the comparator has additional anti-glitch circuitry. Any transient at the input of the comparator needs to be of sufficient magnitude and duration tUV before it can change the monitor state. The combination of the reset timeout and anti-glitch circuitry prevents spurious changes in output state without sacrificing threshold accuracy. Adjustable Input When the monitor threshold is configured as ADJ, the internal comparator input is connected to the pin without a resistive divider, and the pin is high-impedance. Thus, any desired threshold may be chosen by attaching VM to a tap point on an external resistive divider between the monitored supply and ground, as shown in Figure 1.
VMON R2
R1
+ -
0.5V
Figure 1. Setting the Trip Point Using the Adjustable Threshold.
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+
29178 F01
-
VM
LTC2917/LTC2918 APPLICATIONS INFORMATION
RESET TIMEOUT PERIOD, tRST (EXT) (ms)
The reference input of the comparator is controlled by the tolerance pin. The external resistive divider should make the voltage at VM = 0.5V when the supply is at nominal value. The actual threshold of VM accounts for the supply tolerance of 1.5% guaranteed over the full operating temperature range. The resulting tolerances are -6.5%, -11.5%, -16.5% which correspond to 0.468V, 0.443V, 0.418V respectively. Typically, the user will pick a value of R1 based on acceptable current draw. Current used by the resistor divider will be approximately: 0.5V R1= I Recommended range of R1 is 1k--1M. Higher values of resistance exacerbate the degradation of threshold accuracy due to leakage currents. If the nominal value of the supply being monitored is VNOM, then R2 = R1(2VNOM - 1) Resistor tolerances must be taken into account when determining the overall accuracy. Selecting the Reset Timing Capacitor The reset timeout period can be set to one of two fixed internal timers or set with a capacitor in order to accommodate a variety of applications. Connecting a capacitor, CRT, between the RT pin and ground sets the reset timeout period, tRST. The following formula approximates the value of capacitor needed for a particular timeout: CRT = tRST * 110 [pF/ms] For example, using a standard capacitor value of 2.2nF would give a 20ms timeout. Figure 2 shows the desired reset timeout period as a function of the value of the timer capacitor. Leaving RT open with no external capacitor generates a reset timeout of approximately 400s. Shorting RT to VCC generates a reset timeout of approximately 200ms.
10000
1000
100
10
1
0.1 0.001
0.01 0.1 1 10 100 RT PIN CAPACITANCE, CRT (nF)
1000
29178 F02
Figure 2. Reset Timeout Period vs RT Capacitance RST Output Characteristics The DC characteristics of the RST pull-down strength are shown in the Typical Performance Characteristics section. RST is an open-drain pin and thus requires an external pull-up resistor to the logic supply. RST may be pulled above VCC, providing the voltage limits of the pin are observed. The open-drain of the RST pin allows for wired-OR connection of several LTC2917/LTC2918's. Watchdog LTC2917-A/LTC2918-A A standard watchdog function is used to ensure that the system is in a valid state by continuously monitoring the microprocessor's activity. The microprocessor must toggle the logic state of the WDI pin periodically (within upper boundary) in order to clear the watchdog timer. If timeout occurs, the LTC2917-A/LTC2918-A asserts RST low for the reset timeout period, issuing a system reset. Once the reset timeout completes, RST is released to go high and the watchdog timer starts again. During power-up, the watchdog timer remains cleared while RST is asserted low. As soon as the reset timer times out, RST goes high and the watchdog timer is started.
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LTC2917/LTC2918 APPLICATIONS INFORMATION
LTC2917-B/LTC2918-B For applications in which reliability is even more critical, the LTC2917-B/LTC2918-B implements a windowed watchdog function by adding a lower boundary condition to the standard watchdog function. If the WDI input receives a falling edge prior to the watchdog lower boundary, the part considers this a watchdog failure, and asserts RST low (releasing again after the reset timeout period as described above). The LTC2917-B/LTC2918-B WDI input only responds to falling edges. Setting the Watchdog Timeout Period The watchdog timeout period is adjustable and can be optimized for software execution. The watchdog timeout period is adjusted by connecting a capacitor between WT and ground. Given a specified watchdog timeout period, the capacitor is determined by: CWT = tWD * 13.8 [nF/s] For example, using a standard capacitor value of 0.047F would give a 3.4s watchdog timeout period. Leaving WT open with no external capacitor generates a timeout of approximately 3.2ms. Shorting WT to VCC generates a timeout of approximately 1.6s. Connecting WT to GND disables the watchdog function.
(VTRIP = 10.64V) 12V R2 1.15M RCC 11k CBYPASS 0.1F 3.3V RPU 10k
Manual Reset (LTC2918 Only) The LTC2918 includes the MR pin for applications where a manual reset is desired. MR is internally pulled up, making it ready to interface with a push button with no external components required. Asserting MR low when RST is high initiates a reset, resulting in RST being asserted low for the reset timeout time. Shunt Regulator The LTC2917 and LTC2918 contain an internal 6.2V shunt regulator on the VCC pin to allow operation from a high voltage supply. To operate the part from a supply higher than 5.7V, the VCC pin must have a series resistor, RCC, to the supply. See Figure 3. This resistor should be sized according to the following equation: VS(MAX ) - 5.7 V VS(MIN) - 7 V RCC 5mA 250A where VS(MIN) and VS(MAX) are the operating minimum and maximum of the supply. As an example, consider operation from an automobile battery which might dip as low as 10V or spike to 60V. We must then pick a resistance between 10.86k and 12k.
VCC LTC2917 VM SEL1 R1 49.9k SEL2 TOL GND WT CWT RT CRT RST WDI
VCC P RST I/O GND
29178 F03
Figure 3. 12V Supply Monitor Powered From 12V, Utilizing the Internal Shunt Regulator with 3.3V Logic Out
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LTC2917/LTC2918 TYPICAL APPLICATIONS
1V Supply Monitor with Windowed Watchdog Timeout and Internal Timers Selected
3.3V CBYPASS 0.1F RPU 10k
12V Supply Monitor with 20ms Reset Timeout and 3.4s Watchdog Timeout, with 3.3V Logic Out
3.3V CBYPASS 0.1F RPU 10k
VCC LTC2917-B 1V VM SEL1 SEL2 TOL GND WT RT 3.3V tWDU = 1.6s tWDL = 50ms tRST = 200ms RST WDI RST I/O
VCC P 12V GND
29178 TA02
VCC LTC2917-A VM SEL1 SEL2 TOL GND WT CWT 0.047F RT CRT 0.0022F RST WDI RST I/O
VCC P GND
29178 TA03
9V, -15% Tolerance Supply Monitor with 1.8V Logic Out
1.8V 9V CBYPASS 0.1F RPU 10k
R2 866k
VCC LTC2917-A VM SEL1 SEL2 TOL GND WT CWT RT CRT RST WDI RST I/O
VCC P GND
29178 TA04
R1 51.1k
29178f
13
LTC2917/LTC2918 TYPICAL APPLICATIONS
3.3V, -10% Tolerance Supply Monitor with Disabled Watchdog
3.3V CBYPASS 0.1F RPU 10k
1.8V, -5% Supply Monitor with Manual Reset
1.8V CBYPASS 0.1F RPU 10k
VCC LTC2917 VM SEL1 SEL2 TOL GND WT RT CRT RST WDI RST
VCC P VM GND
29178 TA06
VCC LTC2918 RST WDI RST I/O SEL1 SEL2 MR 10k* MANUAL RESET PUSH BUTTON GND WT RT
VCC P GND
29178 TA07
CWT
CRT
*OPTIONAL RESISTOR RECOMMENDED TO EXTEND ESD TOLERANCE
1.5V Supply Monitor with Tolerance Control for Margining, -5% Operation with -15% Margining
3.3V CBYPASS 0.1F RPU 10k
VCC LTC2917 1.5V VM SEL1 SEL2 GND WT CWT RST WDI TOL -15% -5% RT CRT RST I/O I/O
VCC P
GND
29178 TA08
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LTC2917/LTC2918 PACKAGE DESCRIPTION
MS Package 10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
3.00 0.102 (.118 .004) (NOTE 3) 10 9 8 7 6 0.497 0.076 (.0196 .003) REF
0.889 0.127 (.035 .005) GAUGE PLANE
0.254 (.010)
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE 4)
12345 5.23 (.206) MIN 3.20 - 3.45 (.126 - .136) 0.18 (.007) 0.53 0.152 (.021 .006) DETAIL "A" 1.10 (.043) MAX 0.86 (.034) REF
0.50 0.305 0.038 (.0197) (.0120 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
SEATING PLANE
0.17 - 0.27 (.007 - .011) TYP
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
0.50 (.0197) BSC
0.1016 0.0508 (.004 .002)
MSOP (MS) 0307 REV E
DDB Package 10-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1722 Rev O)
0.64 0.05 (2 SIDES) 0.70 0.05 2.55 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.39 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) 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 PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 0.10 (2 SIDES) 0.64 0.05 (2 SIDES) 5 0.25 0.05 2.39 0.05 (2 SIDES) BOTTOM VIEW--EXPOSED PAD PIN 1 R = 0.20 OR 0.25 x 45 CHAMFER
(DDB10) DFN 0905 REV O
3.00 0.10 (2 SIDES)
R = 0.05 TYP
R = 0.115 TYP 6
0.40 0.10 10
1
0.200 REF
0.75 0.05
0.50 BSC
0 - 0.05
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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
LTC2917/LTC2918 TYPICAL APPLICATION
Dual Supply Monitor (1.8V and 12V) with Manual Reset
1.8V CBYPASS 0.1F C1 0.1F RPU 10k
VCC LTC2916 VM SEL1 SEL2 MR MANUAL RESET PUSH BUTTON GND RT 1.8V RST 12V
VCC LTC2917-B VM SEL1 SEL2 TOL GND WT RT 1.8V RST WDI RST I/O
VCC P GND
29178 TA10
RELATED PARTS
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29178f LT 0907 * PRINTED IN USA
Micro Power Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Adjustable RESET and Watchdog Time-Outs
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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