LTC2917/LTC2918 Low Voltage Supervisor with 27 Selectable Thresholds and Watchdog Timer DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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 125˚C Guaranteed Threshold Accuracy: ±1.5% Low Quiescent Current: 30μA Typical Power Supply Glitch Immunity Guaranteed ⎯R⎯S⎯T for VCC ≥ 0.8V 10-Lead MSOP Packages and (3mm × 2mm) DFN Packages APPLICATIONS ■ ■ ■ ■ ■ Handheld Devices Cell Phone Base Stations Automotive Control Systems Network Servers Optical Networking Systems The LTC®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 30μA. 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 125°C 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. TYPICAL APPLICATION 1.8V Supply Monitor with Manual Reset and Internal Timers Selected Monitor Selection Table 1.8V 0.1μF 10k VCC μP LTC2918-A VM RST RST RT WDI I/O WT SEL1 MR SEL2 29178 TA01 GND tWDU = 1.6s tRST = 200ms NOMINAL VOLTAGE SEL1 SEL2 12V VCC VCC 5V VCC Open 3.3V VCC GND 2.5V Open VCC 1.8V Open Open 1.5V Open GND 1.2V GND VCC 1V GND Open ADJ (0.5V) GND GND 29178f 1 LTC2917/LTC2918 ABSOLUTE MAXIMUM RATINGS (Note 1, 2) Terminal Voltages VCC (Note 3).......................................... –0.3V to 5.7V SEL1, SEL2, TOL, WDI, ⎯M⎯R, ⎯R⎯S⎯T ......... –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 ............................... 0°C to 70°C LTC2917I/LTC2918I ............................. –40°C to 85°C LTC2917H/LTC2918H ........................ –40°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) MSOP-10 .......................................................... 300°C PIN CONFIGURATION TOP VIEW GND 1 TOP VIEW GND TOL SEL2 SEL1 VM 10 9 8 7 6 1 2 3 4 5 RST RT WT WDI VCC MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 200°C/W LTC2917 10 RST TOL 2 9 RT 8 WT SEL1 4 7 WDI VM 5 6 VCC SEL2 3 11 DDB PACKAGE 10-LEAD (3mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 11) PCB GND CONNECTION OPTIONAL LTC2917 TOP VIEW GND 1 TOP VIEW GND MR SEL2 SEL1 VM 1 2 3 4 5 10 9 8 7 6 MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 200°C/W LTC2918 RST RT WT WDI VCC 10 RST MR 2 9 RT 8 WT SEL1 4 7 WDI VM 5 6 VCC SEL2 3 11 DDB PACKAGE 10-LEAD (3mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 11) PCB GND CONNECTION OPTIONAL LTC2918 29178f 2 LTC2917/LTC2918 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2917CMS-B1#PBF LTC2917CMS-B1#TRPBF LTCQP 10-Lead Plastic MSOP 0°C to 70°C LTC2917IMS-B1#PBF LTC2917IMS-B1#TRPBF LTCQP 10-Lead Plastic MSOP –40°C to 85°C LTC2917HMS-B1#PBF LTC2917HMS-B1#TRPBF LTCQP 10-Lead Plastic MSOP –40°C to 125°C LTC2917CMS-A1#PBF LTC2917CMS-A1#TRPBF LTDGD 10-Lead Plastic MSOP 0°C to 70°C LTC2917IMS-A1#PBF LTC2917IMS-A1#TRPBF LTDGD 10-Lead Plastic MSOP –40°C to 85°C LTC2917HMS-A1#PBF LTC2917HMS-A1#TRPBF LTDGD 10-Lead Plastic MSOP –40°C to 125°C LTC2918CMS-B1#PBF LTC2918CMS-B1#TRPBF LTDCT 10-Lead Plastic MSOP 0°C to 70°C LTC2918IMS-B1#PBF LTC2918IMS-B1#TRPBF LTDCT 10-Lead Plastic MSOP –40°C to 85°C LTC2918HMS-B1#PBF LTC2918HMS-B1#TRPBF LTDCT 10-Lead Plastic MSOP –40°C to 125°C LTC2918CMS-A1#PBF LTC2918CMS-A1#TRPBF LTDGG 10-Lead Plastic MSOP 0°C to 70°C LTC2918IMS-A1#PBF LTC2918IMS-A1#TRPBF LTDGG 10-Lead Plastic MSOP –40°C to 85°C LTC2918HMS-A1#PBF LTC2918HMS-A1#TRPBF LTDGG 10-Lead Plastic MSOP –40°C to 125°C TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2917CDDB-B1#TRMPBF LTC2917CDDB-B1#TRPBF LCQR 10-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C LTC2917IDDB-B1#TRMPBF LTC2917IDDB-B1#TRPBF LCQR 10-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C LTC2917HDDB-B1#TRMPBF LTC2917HDDB-B1#TRPBF LCQR 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C LTC2917CDDB-A1#TRMPBF LTC2917CDDB-A1#TRPBF LDGF 10-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C LTC2917IDDB-A1#TRMPBF LTC2917IDDB-A1#TRPBF LDGF 10-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C LTC2917HDDB-A1#TRMPBF LTC2917HDDB-A1#TRPBF LDGF 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C LTC2918CDDB-B1#TRMPBF LTC2918CDDB-B1#TRPBF LDCV 10-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C LTC2918IDDB-B1#TRMPBF LTC2918IDDB-B1#TRPBF LDCV 10-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C LTC2918HDDB-B1#TRMPBF LTC2918HDDB-B1#TRPBF LDCV 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C LTC2918CDDB-A1#TRMPBF LTC2918CDDB-A1#TRPBF LDGH 10-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C LTC2918IDDB-A1#TRMPBF LTC2918IDDB-A1#TRPBF LDGH 10-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C LTC2918HDDB-A1#TRMPBF LTC2918HDDB-A1#TRPBF LDGH 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C 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/ 29178f 3 LTC2917/LTC2918 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 2.5V, unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS VCC(MIN) Minimum Supply Voltage ⎯R⎯S⎯T in Correct Logic State MIN VCC(UVLO) Supply Undervoltage Lockout VCC(SHUNT) Shunt Regulation Voltage IVCC = 0.5mA ● ICC VCC Pin Current SEL1, SEL2, TOL, ⎯M⎯R = Open SEL1, SEL2, TOL = GND (LTC2917) ⎯M⎯R = VCC (LTC2918) ● ● ● TYP MAX 0.8 V ● 5.7 UNITS 1.5 V 6.2 7.0 V 30 45 50 80 μA μA Monitor Input (VM) VMT120 12V, 5% Reset Threshold 12V, 10% Reset Threshold 12V, 15% Reset Threshold ● ● ● 11.04 10.44 9.84 11.22 10.62 10.02 11.40 10.80 10.20 V V V VMT50 5V, 5% Reset Threshold 5V, 10% Reset Threshold 5V, 15% Reset Threshold ● ● ● 4.600 4.350 4.100 4.675 4.425 4.175 4.750 4.500 4.250 V V V VMT33 3.3V, 5% Reset Threshold 3.3V, 10% Reset Threshold 3.3V, 15% Reset Threshold ● ● ● 3.036 2.871 2.706 3.086 2.921 2.756 3.135 2.970 2.805 V V V VMT25 2.5V, 5% Reset Threshold 2.5V, 10% Reset Threshold 2.5V, 15% Reset Threshold ● ● ● 2.300 2.175 2.050 2.338 2.213 2.088 2.375 2.250 2.125 V V V VMT18 1.8V, 5% Reset Threshold 1.8V, 10% Reset Threshold 1.8V, 15% Reset Threshold ● ● ● 1.656 1.566 1.476 1.683 1.593 1.503 1.710 1.620 1.530 V V V VMT15 1.5V, 5% Reset Threshold 1.5V, 10% Reset Threshold 1.5V, 15% Reset Threshold ● ● ● 1.380 1.305 1.230 1.403 1.328 1.253 1.425 1.350 1.275 V V V VMT12 1.2V, 5% Reset Threshold 1.2V, 10% Reset Threshold 1.2V, 15% Reset Threshold ● ● ● 1.104 1.044 0.984 1.122 1.062 1.002 1.140 1.080 1.020 V V V VMT10 1V, 5% Reset Threshold 1V, 10% Reset Threshold 1V, 15% Reset Threshold ● ● ● 0.920 0.870 0.820 0.935 0.885 0.835 0.950 0.900 0.850 V V V VMTADJ ADJ (0.5V), 5% Reset Threshold ADJ (0.5V), 10% Reset Threshold ADJ (0.5V), 15% Reset Threshold ● ● ● 460.0 435.0 410.0 467.5 442.5 417.5 475.0 450.0 425.0 mV mV mV RVM VM Input Impedance (Note 4) Fixed Threshold Modes ● 0.5 8 MΩ IVM(ADJ) ADJ Input Current VM = 0.5V ● ±15 nA 0.5 V Three-State Inputs (SEL1, SEL2), (TOL, LTC2917) VTPIN, LOW Low Level Input Voltage ● VTPIN, HIGH High Level Input Voltage ● VTPIN, Z Pin Voltage when Open ITPIN, Z Allowable Leakage in Open State ITPIN, H/L Pin Input Current 1.4 I = 0μA V 0.9 V ● ±5 μA VTPIN = 0V, VCC ● ±20 μA Reset Timer Control (RT) IRT(UP) RT Pull Up Current VRT = 0.25V ● –2 –3 –4 μA IRT(DOWN) RT Pull Down Current VRT = 1.1V ● 2 3 4 μA IRT(INT) Internal RT VCC Detect Current VRT = VCC ● 1 8 μA VRT(INT, LH) RT Internal Timer Threshold VRT Rising, Referenced to VCC ● –100 –160 –300 mV 29178f 4 LTC2917/LTC2918 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 2.5V, unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS tRST(INT) Internal Reset Timeout Period VRT = VCC ● 150 200 260 ms tRST(EXT) Adjustable Reset Timeout Period CRT = 2.2nF ● 16 20 25 ms tUV VOL VM Undervoltage Detect to ⎯R⎯S⎯T Asserted ⎯ S ⎯ T⎯ Output Voltage Low R VM Less Than Reset Threshold VMTX by More Than 5% ● 10 80 150 μs VCC = 3.3V, IRST = 2.5mA VCC = 1V, IRST = 100μA VCC = 0.8V, IRST = 15μA ⎯R⎯S⎯T = VCC ● ● ● 0.15 0.15 0.05 0.4 0.3 0.2 V V V IOH(RST) ⎯R⎯S⎯T Output Voltage High Leakage ±1 μA Reset Output (⎯R⎯S⎯T) ● Watchdog Timer Control (WT) IWT(UP) WT Pull Up Current VWT = 0.25V ● –2 –3 –4 μA IWT(DOWN) WT Pull Down Current VWT = 1.1V ● 2 3 4 μA VWT(INT, LH) WT Internal Timer Threshold VWT Rising, Referenced to VCC ● –100 –160 –300 mV ● 1 8 μA IWT(INT) Internal WT VCC Detect Current VWT = VCC IWT(DIS) Watchdog Disable Hold Current VWT = 0V –3.5 μA Watchdog Input (WDI) tWDU(INT) Internal Watchdog Upper Boundary VWT = VCC ● 1.3 1.6 2 tWDL(INT) Internal Watchdog Lower Boundary (Note 5) B Versions, VWT = VCC ● 37.5 50 62.5 ms tWDU(EXT) External Watchdog Upper Boundary CWT = 2.2nF ● 130 160 200 ms tWDL(EXT) External Watchdog Lower Boundary (Note 5) B Versions, CWT = 2.2nF ● VIL(WDI) Input Low Voltage ● VIH(WDI) Input High Voltage ● 1.1 V tPW(WDI) Input Pulsewidth ● 400 ns WDI Leakage Current ● ±1 μA 0.2 • VCC V tWDU(EXT)/32 s ms 0.4 V Manual Reset Input (LTC2918) VIL(MR) Input Low Voltage ● VIH(MR) Input High Voltage ● 0.8 • VCC RPU Pull Up Resistance ● 50 tPW(MR) Pulsewidth ● 250 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 V 100 150 kΩ ns 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 ⎯R⎯S⎯T is invoked. For the LTC2917-A/LTC2918-A, the edges must simply occur before the upper boundary. See Applications Information. 29178f 5 LTC2917/LTC2918 TYPICAL PERFORMANCE CHARACTERISTICS Quiescent Supply Current vs Temperature 40 QUIESCENT SUPPLY CURRENT, ICC (μA) 1.5 0.5 VMTADJ 0 –0.5 VMT25 VMT120 –1.0 –1.5 –50 –25 50 25 75 0 TEMPERATURE (˚C) 100 SEL1 = 0V SEL2 = 2.5V TOL = OPEN 35 VCC = 5.5V VCC = 2.5V 30 VCC = 1.5V 25 20 –50 125 –25 75 0 25 50 TEMPERATURE (°C) 100 250 RESET TIMEOUT PERIOD, tRST(INT) (ms) RESET TIMEOUT PERIOD, tRST(EXT) (ms) 1000 100 10 1 0.01 0.1 1 10 100 RT PIN CAPACITANCE, CRT (nF) 1000 230 210 190 170 150 –50 –25 150 100 50 0 29178 G03 50 25 0 75 TEMPERATURE (°C) 100 125 2.0 1.8 1.6 1.4 1.2 1.0 –50 –25 SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V) 100 10 100 29178 G07 50 25 0 75 TEMPERATURE (°C) 100 Shunt Regulation Voltage vs Supply Current 6.4 ICC = 5mA 6.3 ICC = 1mA ICC = 100μA 6.2 6.1 –50 –25 75 0 25 50 TEMPERATURE (°C) 125 29178 G06 Shunt Regulation Voltage vs Temperature 1000 WT = VCC 29178 G05 Watchdog Timeout Period vs Capacitance 10000 RESET OCCURS ABOVE CURVE Internal Watchdog Timeout Period vs Temperature RT = VCC 29178 G04 WATCHDOG TIMEOUT PERIOD, tWDU(EXT) (ms) 200 Internal Reset Timeout Period vs Temperature 10000 0.01 0.1 1 10 WT PIN CAPACITANCE, CWT (nF) 250 1 10 100 0.1 GLITCH PERCENTAGE PAST THRESHOLD (%) WATCHDOG TIMEOUT PERIOD, tWDU(INT) (ms) Reset Timeout Period vs RT Capacitance 1 0.001 300 29178 G02 29178 G01 0.1 0.001 125 SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V) NORMALIZED VMTnn (%) 1.0 Allowable Glitch Duration vs Magnitude MAXIMUM ALLOWABLE GLITCH DURATION (μs) Threshold Voltage vs Temperature 100 125 29178 G08 7.0 6.8 6.6 6.4 6.2 6.0 0.01 1 0.1 10 SUPPLY CURRENT, ICC (mA) 100 29178 G09 29178f 6 LTC2917/LTC2918 TYPICAL PERFORMANCE CHARACTERISTICS ⎯R⎯S⎯T Output Voltage vs VCC ⎯R⎯S⎯T Pull-Down Current vs VCC 6 4 3 2 1 0 1 2 3 4 SUPPLY VOLTAGE, VCC (V) 5 5 NO PULL-UP R VCC = 2.5V 0.8 RST VOLTAGE (V) PULL-DOWN CURRENT, IRST (mA) RST VOLTAGE (V) 10k PULL-UP R TO VCC SEL1 = SEL2 = TOL = 0V 5 VM = 0.5V 0 ⎯R⎯S⎯T VOL vs IRST 1.0 6 4 RST AT 150mV 3 2 1 TA = 125°C 0.6 TA = 25°C 0.4 0.2 RST AT 50mV 0 0 0 1 2 3 4 SUPPLY VOLTAGE, VCC (V) 29178 G10 5 29178 G11 TA = –40°C 0 2 6 4 IRST (mA) 8 10 29178 G12 PIN FUNCTIONS GND: Device Ground. ⎯ ⎯R (LTC2918 only): Manual Reset Input (Active Low). A M low level on the ⎯M⎯R 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. ⎯R⎯S⎯T: Open Drain ⎯R⎯S⎯T 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 400μs. 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 0.1μF 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. ⎯ S ⎯ T⎯ comparator. SEL1, SEL2 VM: Voltage Monitor Input to R and TOL inputs select the exact threshold that asserts the ⎯R⎯S⎯T output. WDI: Watchdog Input. This pin must be driven to change state within a time less than the watchdog upper boundary time, or ⎯R⎯S⎯T 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. 29178f 7 LTC2917/LTC2918 BLOCK DIAGRAM LTC2917 SEL1 SEL2 LTC2918 TOL MR RT VCC 3 STATE DECODE MONITOR DIVIDER MATRIX 0.5V VCC 6.2V 100k VM + – VCC VCC DETECT INTERNAL 200ms TIMER RST – + RESET DRIVER LOGIC REFERENCE DIVIDER MATRIX GND ADJUSTABLE RESET TIMER INTERNAL 1.6 SECOND TIMER WATCHDOG LOGIC ADJUSTABLE WATCHDOG TIMER VCC DETECT WT WDI 29178 BD TIMING DIAGRAM VMTx VM tUV RST tRST 1V 29178 TD01 Monitor Input Timing WDI RST tWDU 29178 TD01 tRST Watchdog Timing (LTC2917-A, LTC2918-A) WDI RST t > tWDL t < tWDL tWDU tRST 29178 TD03 tRST Watchdog Timing (LTC2917-B, LTC2918-B) 29178f 8 LTC2917/LTC2918 APPLICATIONS INFORMATION Supply Monitoring Monitor Threshold Control 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 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 LTC2917/LTC2918 asserts the ⎯R⎯S⎯T 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 ⎯R⎯S⎯T pin. Therefore, as soon as VCC reaches 0.8V during power up, the ⎯R⎯S⎯T output asserts low. Until VCC reaches the undervoltage lockout threshold (guaranteed less than 1.5V), ⎯R⎯S⎯T 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 ⎯R⎯S⎯T 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, ⎯R⎯S⎯T asserts logic low. 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 ±5μA. 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 5μA of leakage in the open state. Table 1. Voltage Threshold Settings NOMINAL VOLTAGE SEL1 SEL2 12V VCC VCC 5V VCC Open 3.3V VCC GND 2.5V Open VCC 1.8V Open Open *1.5V Open GND *1.2V GND VCC *1V GND Open *ADJ (0.5V) GND GND *Require a separate supply for VCC Table 2. System Voltage Tolerance Settings TOLERANCE TOL –5% VCC –10% Open –15% GND 29178f 9 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. 5V±10%). 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 4.425V±75mV 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 ⎯R⎯S⎯T, 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 ⎯R⎯S⎯T output. When the voltage at VM goes below the threshold, the ⎯R⎯S⎯T pin asserts low. When the supply recovers past the threshold, the reset timer starts (assuming it is not disabled), and ⎯R⎯S⎯T 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 – VM + R1 + – 0.5V 29178 F01 Figure 1. Setting the Trip Point Using the Adjustable Threshold. 29178f 10 LTC2917/LTC2918 APPLICATIONS INFORMATION Typically, the user will pick a value of R1 based on acceptable current draw. Current used by the resistor divider will be approximately: 10000 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. 1000 100 10 1 0.1 0.001 0.01 0.1 1 10 100 RT PIN CAPACITANCE, CRT (nF) 1000 29178 F02 ⎛ 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) Figure 2. Reset Timeout Period vs RT Capacitance ⎯R⎯S⎯T Output Characteristics The DC characteristics of the ⎯R⎯S⎯T pull-down strength are shown in the Typical Performance Characteristics section. ⎯R⎯S⎯T is an open-drain pin and thus requires an external pull-up resistor to the logic supply. ⎯R⎯S⎯T may be pulled above VCC, providing the voltage limits of the pin are observed. Resistor tolerances must be taken into account when determining the overall accuracy. The open-drain of the ⎯R⎯S⎯T pin allows for wired-OR connection of several LTC2917/LTC2918’s. Selecting the Reset Timing Capacitor Watchdog 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: LTC2917-A/LTC2918-A 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 400μs. Shorting RT to VCC generates a reset timeout of approximately 200ms. 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 ⎯R⎯S⎯T low for the reset timeout period, issuing a system reset. Once the reset timeout completes, ⎯R⎯S⎯T is released to go high and the watchdog timer starts again. During power-up, the watchdog timer remains cleared while ⎯R⎯S⎯T is asserted low. As soon as the reset timer times out, ⎯R⎯S⎯T goes high and the watchdog timer is started. 29178f 11 LTC2917/LTC2918 APPLICATIONS INFORMATION LTC2917-B/LTC2918-B Manual Reset (LTC2918 Only) 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 ⎯R⎯S⎯T low (releasing again after the reset timeout period as described above). The LTC2917-B/LTC2918-B WDI input only responds to falling edges. The LTC2918 includes the ⎯M⎯R pin for applications where a manual reset is desired. ⎯M⎯R is internally pulled up, making it ready to interface with a push button with no external components required. Asserting ⎯M⎯R low when ⎯R⎯S⎯T is high initiates a reset, resulting in ⎯R⎯S⎯T 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 250μA 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] where VS(MIN) and VS(MAX) are the operating minimum and maximum of the supply. For example, using a standard capacitor value of 0.047μF would give a 3.4s watchdog timeout period. 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. 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 3.3V R2 1.15M RCC 11k RPU 10k CBYPASS 0.1μF VCC VCC μP LTC2917 R1 49.9k VM RST RST SEL1 WDI I/O GND SEL2 TOL GND 29178 F03 RT WT CWT CRT Figure 3. 12V Supply Monitor Powered From 12V, Utilizing the Internal Shunt Regulator with 3.3V Logic Out 29178f 12 LTC2917/LTC2918 TYPICAL APPLICATIONS 1V Supply Monitor with Windowed Watchdog Timeout and Internal Timers Selected 12V Supply Monitor with 20ms Reset Timeout and 3.4s Watchdog Timeout, with 3.3V Logic Out 3.3V 3.3V CBYPASS 0.1μF CBYPASS 0.1μF RPU 10k VCC μP VM RST RST SEL1 WDI I/O SEL2 TOL GND WT VCC VCC LTC2917-B 1V VCC μP LTC2917-A 12V GND VM RST RST SEL1 WDI I/O SEL2 29178 TA02 TOL GND RT 3.3V RPU 10k 29178 TA03 WT RT CWT 0.047μF tWDU = 1.6s tWDL = 50ms tRST = 200ms GND CRT 0.0022μF 9V, –15% Tolerance Supply Monitor with 1.8V Logic Out 1.8V CBYPASS 0.1μF 9V R2 866k RPU 10k VCC VCC μP LTC2917-A R1 51.1k VM RST RST SEL1 WDI I/O SEL2 TOL GND GND 29178 TA04 WT RT CWT CRT 29178f 13 LTC2917/LTC2918 TYPICAL APPLICATIONS 3.3V, –10% Tolerance Supply Monitor with Disabled Watchdog 1.8V, –5% Supply Monitor with Manual Reset 3.3V 1.8V CBYPASS 0.1μF CBYPASS 0.1μF RPU 10k VCC μP LTC2917 RST SEL1 WDI VCC μP LTC2918 RST GND SEL2 TOL GND VCC VCC VM RPU 10k VM RST RST SEL1 WDI I/O SEL2 29178 TA06 GND 29178 TA07 MR WT 10k* RT GND MANUAL RESET PUSH BUTTON CRT RT WT 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 0.1μF RPU 10k VCC VCC μP LTC2917 1.5V VM RST RST SEL1 WDI I/O SEL2 TOL I/O –15% –5% GND GND 29178 TA08 RT WT CWT CRT 29178f 14 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 0.254 (.010) 0.889 ± 0.127 (.035 ± .005) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0.497 ± 0.076 (.0196 ± .003) REF 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 5.23 (.206) MIN 0.53 ± 0.152 (.021 ± .006) 3.20 – 3.45 (.126 – .136) 0.86 (.034) REF 1.10 (.043) MAX DETAIL “A” 0.18 (.007) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP 0.1016 ± 0.0508 (.004 ± .002) 0.50 (.0197) BSC MSOP (MS) 0307 REV E 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 DDB Package 10-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1722 Rev Ø) 0.64 ±0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) R = 0.05 TYP R = 0.115 TYP 6 0.40 ± 0.10 10 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) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 2.00 ±0.10 (2 SIDES) 0.75 ±0.05 0.64 ± 0.05 (2 SIDES) 5 0.25 ± 0.05 0 – 0.05 PIN 1 R = 0.20 OR 0.25 × 45° CHAMFER 1 (DDB10) DFN 0905 REV Ø 0.50 BSC 2.39 ±0.05 (2 SIDES) BOTTOM VIEW—EXPOSED PAD 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 29178f 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 0.1μF C1 0.1μF VCC VCC LTC2916 VM MANUAL RESET PUSH BUTTON RPU 10k RST VCC μP LTC2917-B 12V VM RST RST SEL1 SEL1 WDI I/O SEL2 SEL2 MR TOL GND WT GND RT GND 29178 TA10 RT 1.8V 1.8V RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC690 5V Supply Monitor, Watchdog Timer and Battery Backup 4.65V Threshold LTC694-3.3 3.3V Supply Monitor, Watchdog Timer and Battery Backup 2.9V Threshold LTC1232 5V Supply Monitor, Watchdog Timer and Push-Button Reset 4.37V/4.62V Threshold LTC1326 Micro Power Precision Triple Supply Monitor 4.725V, 3.118V, 1V Threshold (±0.75%) LTC1536 Precision Triple Supply Monitor for PCI Applications Meets PCI tFALL Timing Specifications LTC1726 Micro Power Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Adjustable ⎯R⎯E⎯S⎯E⎯T and Watchdog Time-Outs LTC1727 Micro Power Triple Supply Monitor with Open-Drain Reset Individual Monitor Outputs in MSOP LTC1728 Micro Power Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package LTC2900 Programmable Quad Supply Monitor Adjustable ⎯R⎯E⎯S⎯E⎯T, 10-Lead MSOP and 3mm × 3mm 10-Lead DFN LTC2901 Programmable Quad Supply Monitor Adjustable ⎯R⎯E⎯S⎯E⎯T and Watchdog Timer, 16-Lead SSOP Package LTC2902 Programmable Quad Supply Monitor Adjustable ⎯R⎯E⎯S⎯E⎯T and Tolerance, 16-Lead SSOP Package, Margining LTC2903 Precision Quad Supply Monitor 6-Lead SOT-23 Package, Ultra Low Voltage Reset LTC2904 3-State Programmable Precision Dual Supply Monitor Adjustable Tolerance, 8-Lead SOT-23 Package LTC2905 3-State Programmable Precision Dual Supply Monitor Adjustable ⎯R⎯E⎯S⎯E⎯T and Tolerance, 8-Lead SOT-23 Package LTC2906 Precision Dual Supply Monitor 1 Selectable and 1 Adjustable Separate VCC Pin, RST/⎯R⎯S⎯T Outputs LTC2907 Precision Dual Supply Monitor 1 Selectable and 1 Adjustable Separate VCC Pin, Adjustable Reset Timer LTC2908 Precision Six Supply Monitor (Four Fixed and 2 Adjustable) 8-Lead SOT-23 and DDB Packages LTC2909 Precision Triple/Dual Input UV, OV 2 ADJ Inputs LTC2910 Octal Positive/Negative Voltage Monitor 16-Lead SSOP and 5mm × 3mm DFN Packages LTC2912 Single UV/OV Voltage Monitor, Adjustable UV and OV 8-Lead TSOT and 3mm × 2mm DFN Packages LTC2913 Dual UV/OV Voltage Monitor 10-Lead MSOP and 3mm × 3mm DFN Packages LTC2914 Qual UV/OV Positive/Negative Voltage Monitor 16-Lead SSOP and 5mm × 3mm DFN Packages LTC2915 Single Supervisor with 27 Selectable Thresholds 10-Lead MSOP and 3mm × 2mm DFN-10 Packages LTC2916 Single Supervisor with 9 Selectable Thresholds Manual Reset, 10-Lead MSOP and 3mm × 2mm DFN-10 Packages 29178f 16 Linear Technology Corporation LT 0907 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007