LTC2901 Programmable Quad Supply Monitor with Adjustable Reset and Watchdog Timers U FEATURES DESCRIPTIO ■ The LTC®2901 is a programmable supply monitor for systems with up to four supply voltages. One of 16 preset or adjustable voltage monitor combinations can be selected using an external resistor divider connected to the program pin. The preset voltage thresholds are accurate to ±1.5% over temperature. All four voltage comparator outputs are connected to separate pins for individual supply monitoring. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Simultaneously Monitors Four Supplies 16 User Selectable Combinations of 5V, 3.3V, 3V, 2.5V, 1.8V, 1.5V and/or ±Adj Voltage Thresholds Guaranteed Threshold Accuracy: ±1.5% of Monitored Voltage Over Temperature Selectable Supply Tolerance: 5% and 10% Below Monitored Voltage (LTC2901-3/LTC2901-4) Low Supply Current: 43μA Typ Adjustable Reset Time Adjustable Watchdog Time Open-Drain RST Output (LTC2901-1/LTC2901-3) Push-Pull RST Output (LTC2901-2/LTC2901-4) Individual Nondelayed Monitor Output for Each Supply Power Supply Glitch Immunity Guaranteed RST for VCC ≥ 1V 16-Lead Narrow SSOP Package U APPLICATIO S ■ ■ ■ ■ The 43μA supply current makes the LTC2901 ideal for power conscious systems and it may be configured to monitor less than four inputs. The parts are available in the 16-lead narrow SSOP package. Desktop and Notebook Computers Multivoltage Systems Telecom Equipment Portable Battery-Powered Equipment Network Servers , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Patent Pending. U ■ The reset and watchdog delay times are adjustable using external capacitors. Tight voltage threshold accuracy and glitch immunity ensure reliable reset operation without false triggering. The RST output is guaranteed to be in the correct state for VCC down to 1V. The LTC2901-1/ LTC2901-3 features an open-drain RST output, while the LTC2901-2/LTC2901-4 has a push-pull RST output. TYPICAL APPLICATIO Quadruple Supply Monitor (5V, 3.3V, 2.5V, 1.8V) 10% Undervoltage Monitoring, Watchdog Asserts RST Quadruple Supply Monitor (5V, 3.3V, 2.5V, 1.8V) 5V 5V 3.3V DC/DC CONVERTER 3.3V SYSTEM LOGIC 2.5V 1.8V SYSTEM LOGIC 2.5V 1.8V V3 C1 0.1μF DC/DC CONVERTER V1 COMP1 V2 COMP2 LTC2901-2 COMP3 C2 0.1μF R2 40.2k 1% V3 COMP4 VREF R1 59k 1% R3 10k POWER GOOD V4 C1 0.1μF WDI WDO VPG RST GND CRT 2901 TA01 CWT CRT 47nF CWT 47nF tRST = 216ms tWD = 940ms V1 COMP1 V2 COMP2 LTC2901-4 COMP3 C2 0.1μF R1 59k 1% R2 40.2k 1% R3 10k POWER GOOD V4 COMP4 VREF WDI VPG RST TOL GND CRT 5V 2901 TA01b CWT CRT 47nF CWT 47nF tRST = 216ms tWD = 940ms 2901fb 1 LTC2901 W W W AXI U U ABSOLUTE RATI GS (Notes 1, 2, 3) V1, V2, V3, V4, VPG ..................................... – 0.3V to 7V RST (LTC2901-1/LTC2901-3) ..................... – 0.3V to 7V RST (LTC2901-2/LTC2901-4) ....... – 0.3V to (V2 + 0.3V) COMPX ....................................................... – 0.3V to 7V CWT, WDI, WDO ......................................... – 0.3V to 7V VREF, CRT, TOL ............................ – 0.3V to (VCC + 0.3V) Reference Load Current (IVREF) ............................ ±1mA V4 Input Current (–ADJ Mode) ............................. –1mA Operating Temperature Range LTC2901-1C/LTC2901-2C/ LTC2901-3C/LTC2901-4C ....................... 0°C to 70°C LTC2901-1I/LTC2901-2I/ LTC2901-3I/LTC2901-4I .................... –40°C to 85°C Storage Temperature Range .................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................... 300°C U U W PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW COMP3 1 16 COMP2 COMP1 2 15 COMP4 V3 3 14 V2 V1 4 13 V4 CRT 5 12 VREF RST 6 11 VPG WDO 7 10 GND WDI 8 9 LTC2901-1CGN LTC2901-2CGN LTC2901-1IGN LTC2901-2IGN COMP3 1 16 COMP2 COMP1 2 15 COMP4 V3 3 14 V2 V1 4 13 V4 CRT 5 12 VREF RST 6 11 VPG TOL 7 10 GND WDI 8 9 GN16 PART MARKING CWT GN PACKAGE 16-LEAD PLASTIC SSOP TJMAX = 125°C, θJA = 110°C/W ORDER PART NUMBER TOP VIEW 29011 29012 29011I 29012I LTC2901-3CGN LTC2901-4CGN LTC2901-3IGN LTC2901-4IGN GN16 PART MARKING 29013 29014 29013I 29014I CWT GN PACKAGE 16-LEAD PLASTIC SSOP TJMAX = 125°C, θJA = 110°C/W Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Consult LTC Marketing for parts specified with wider operating temperature ranges. Lead Free Part Marking: http://www.linear.com/leadfree/ ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. (Notes 3, 4) SYMBOL VRT50 VRT33 VRT30 VRT25 VRT18 VRT15 VRTA VRTAN VCC PARAMETER 5V, 5% Reset Threshold 5V, 10% Reset Threshold 3.3V, 5% Reset Threshold 3.3V, 10% Reset Threshold 3V, 5% Reset Threshold 3V, 10% Reset Threshold 2.5V, 5% Reset Threshold 2.5V, 10% Reset Threshold 1.8V, 5% Reset Threshold 1.8V, 10% Reset Threshold 1.5V, 5% Reset Threshold 1.5V, 10% Reset Threshold ADJ, 5% Reset Threshold ADJ, 10% Reset Threshold – ADJ Reset Threshold Minimum Internal Operating Voltage CONDITIONS V1 Input Threshold ● ● V1, V2 Input Threshold ● ● V2 Input Threshold ● ● V2, V3 Input Threshold ● ● V3, V4 Input Threshold ● ● V3, V4 Input Threshold ● ● V3, V4 Input Threshold ● ● V4 Input Threshold RST, COMPX in Correct Logic State; VCC Rising Prior to Program ● ● MIN 4.600 4.350 3.036 2.871 2.760 2.610 2.300 2.175 1.656 1.566 1.380 1.305 0.492 0.466 – 18 TYP 4.675 4.425 3.086 2.921 2.805 2.655 2.338 2.213 1.683 1.593 1.403 1.328 0.500 0.473 0 MAX 4.750 4.500 3.135 2.970 2.850 2.700 2.375 2.250 1.710 1.620 1.425 1.350 0.508 0.481 18 1 UNITS V V V V V V V V V V V V V V mV V 2901fb 2 LTC2901 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. (Notes 3, 4) SYMBOL VCCMINP VCCMINC VREF PARAMETER Minimum Required for Programming Minimum Required for Comparators Reference Voltage VPG IVPG IV1 IV2 IV3 Programming Voltage Range VPG Input Current V1 Input Current V2 Input Current V3 Input Current IV4 V4 Input Current ICRT(UP) ICRT(DN) tRST tUV CRT Pull-Up Current CRT Pull-Down Current Reset Time-Out Period VX Undervoltage Detect to RST or COMPX VOL Output Voltage Low RST, COMPX VOH VOL VOH Output Voltage High RST, WDO, COMPX (Note 6) Output Voltage Low WDO Output Voltage High RST (LTC2901-2/LTC2901-4) (Note 7) ICWT(UP) CWT Pull-Up Current ICWT(DN) CWT Pull-Down Current tWD Watchdog Time-Out Period VIH WDI Input Threshold High VIL WDI Input Threshold Low tWP WDI Input Pulse Width IWDI WDI Pull-Up Current Digital Input T0L VIL T0L Low Level Input Voltage VIH T0L High Level Input Voltage IINTOL T0L Input Current CONDITIONS VCC Rising VCC Falling VCC ≥ 2.3V, IVREF = ±1mA, CREF ≤ 1000pF T0L Low T0L High VCC ≥ VCCMINP VPG = VREF V1 = 5V, IVREF = 12μA, (Note 5) V2 = 3.3V V3 = 2.5V V3 = 0.55V (ADJ Mode) V4 = 1.8V V4 = 0.55V (ADJ Mode) V4 = –0.05V (–ADJ Mode) VCRT = 0V VCRT = 1.3V CRT = 1500pF VX Less Than Reset Threshold VRTX by More Than 1% ISINK = 2.5mA; V1 = 3V, V2 = 3V; V3, V4 = 0V; VPG = 0V ISINK = 100μA; V2 = 1V; V1, V3, V4 = 0V ISINK = 100μA; V1 = 1V; V2, V3, V4 = 0V ISOURCE = 1μA MIN TYP MAX 2.42 2.32 UNITS V V 1.192 1.128 0 1.210 1.146 1.228 1.163 VREF ±20 75 2 1.2 15 0.8 15 15 –2.6 30 9 V V V nA μA μA μA nA μA nA nA μA μA ms μs ● ● ● ● ● ● ● 43 0.8 0.52 ● ● ● ● ● ● ● ● ● –15 0.34 –15 –15 –1.4 10 5 ● 0.15 0.4 V ● ● 0.05 0.05 0.3 0.3 V V V 0.15 0.4 V ● V2 – 1 ISINK = 2.5mA; V1 = 5V, V2 = 3.3V; V3, V4 = 1V; VPG = 0V ISOURCE = 200μA ● ● 0.8 • V2 VCWT = 0V VCWT = 1.3V CWT = 1500pF VCC = 3.3V to 5.5V VCC = 3.3V to 5.5V VCC = 3.3V VWDI = 0V ● –1.4 10 20 VCC = 3.3V to 5.5V VCC = 3.3V to 5.5V TOL = VCC ● 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: 10% thresholds apply to the LTC2901-3/LTC2901-4 only when the TOL pin is set to a logic high. –2 20 7 150 ● ● V –2 20 30 ● ● ● –2.6 30 40 1.6 μA μA ms V V ns μA 0.3VCC V V μA 0.4 150 –10 ● ● 0.7VCC ±0.1 ±1 Note 5: 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 6: The output pins RST, WDO and COMPX have internal pull-ups to V2 of typically 6μA. However, external pull-up resistors may be used when faster rise times are required or for VOH voltages greater than V2. Note 7: The push-pull RST output pin on the LTC2901-2/LTC2901-4 is actively pulled up to V2. 2901fb 3 LTC2901 TEST CIRCUITS V1 V2 V3 V4 RST, WDO LTC2901-1 OR COMPX LTC2901-3 V1 V2 V3 V4 ISOURCE 1μA LTC2901-1 LTC2901-3 RST, WDO OR COMPX 2901 F01 V1 V2 V3 V4 ISINK 2.5mA, 100μA LTC2901-2 RST LTC2901-4 ISOURCE 200μA 2901 F02 Figure 1. RST, WDO, COMPX VOH Test 2901 F03 Figure 2. RST, WDO, COMPX VOL Test Figure 3. Active Pull-Up RST VOH Test W UW TI I G DIAGRA S VX Monitor Timing VX VRTX tRST tUV 1.5V RST 2901 TD COMPX Watchdog Timing (LTC2901-1/LTC2901-2) tRST RST WDI tWP WDO tWD tWD 2901 TD2 Watchdog Timing (LTC2901-3/LTC2901-4) tRST tRST RST tWP tWD WDI 2901 TD3 2901fb 4 LTC2901 U W TYPICAL PERFOR A CE CHARACTERISTICS 5V Threshold Voltage vs Temperature 3.3V Threshold Voltage vs Temperature THESHOLD VOLTAGE, VRT50 (V) 4.725 4.700 4.675 4.650 4.625 3.135 2.850 3.125 2.840 THRESHOLD VOLTAGE, VRT30 (V) THRESHOLD VOLTAGE, VRT33 (V) 4.750 3V Threshold Voltage vs Temperature 3.115 3.105 3.095 3.085 3.075 3.065 3.055 3.035 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 80 100 2901 G01 2.810 2.800 2.790 2.780 80 2.760 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 100 2901 G02 2.5V Threshold Voltage vs Temperature 1.425 1.705 1.420 2.3450 2.3375 2.3300 2.3225 2.3150 2.3075 THRESHOLD VOLTAGE, VRT15 (V) 1.710 2.3675 2.3525 1.700 1.695 1.690 1.685 1.680 1.675 1.670 1.665 80 1.655 –60 –40 –20 0 20 40 60 TEMPERATURE (°C) 100 ADJ Threshold Voltage vs Temperature 1.405 1.400 1.395 1.390 80 1.380 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 100 0.504 0.502 0.500 0.498 0.496 0.494 80 100 2901 G07 1.228 0.012 1.222 0.006 1.216 0 1.210 –0.006 1.204 –0.012 1.198 –0.018 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 100 VREF vs Temperature 0.018 VREF (V) THRESHOLD VOLTAGE, VRTAN (V) 0.506 80 2901 G06 – ADJ Threshold Voltage vs Temperature 0.508 THRESHOLD VOLTAGE, VRTA (V) 1.410 2901 G05 2901 G04 0.492 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 1.415 1.385 1.660 2.3000 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 100 1.5V Threshold Voltage vs Temperature 2.3750 2.3600 80 2901 G03 1.8V Threshold Voltage vs Temperature THRESHOLD VOLTAGE, VRT18 (V) THRESHOLD VOLTAGE, VRT25 (V) 2.820 2.770 3.045 4.600 20 40 60 –60 –40 –20 0 TEMPERATURE (°C) 2.830 80 100 2901 G08 1.192 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 80 100 2901 G23 2901fb 5 LTC2901 U W TYPICAL PERFOR A CE CHARACTERISTICS IV1 vs Temperature IV2 vs Temperature IV3 vs Temperature 1.5 1.1 V1 = 5V 1.4 V2 = 3.3V V3 = 2.5V 1.3 V4 = 1.8V 1.2 V1 = 5V 1.0 V2 = 3.3V V3 = 2.5V 0.9 V4 = 1.8V 0.8 60 1.1 0.7 50 40 IV3 (μA) V1 = 5V 90 V2 = 3.3V V3 = 2.5V 80 V4 = 1.8V 70 IV2 (μA) 1.0 0.9 0.4 20 0.7 0.3 10 0.6 0.2 0.5 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 100 IV4 vs Temperature 0.5 0.4 0.3 0.2 0.1 0 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 80 100 Typical Transient Duration vs Comparator Overdrive (V3, V4) 220 TA = 25°C RESET OCCURS ABOVE CURVE 300 250 200 150 100 50 WATCHDOG TIME-OUT PERIOD, tWD (ms) 2 1 0 0 140 120 100 80 60 40 20 Reset Time-Out Period vs Temperature Watchdog Time-Out Period vs Temperature 3 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 V1 (V) 2901 G14 RESET OCCURS ABOVE CURVE 160 2901 G22 8.9 38 4 180 2901 G13 2901 G12 V1 = V2 = V3 = V4 10k PULL-UP FROM RST TO V1 TA = 25°C TA = 25°C 200 0 1 10 100 0.1 RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX) 0 1 10 100 0.1 RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX) 5 100 Typical Transient Duration vs Comparator Overdrive (V1, V2) 350 RST Output Voltage vs V1, VPG = 0V 80 2901 G11 400 TYPICAL TRANSIENT DURATION (μs) 0.6 0.1 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) 100 2901 G10 450 1.0 V1 = 5V 0.9 V2 = 3.3V V3 = 2.5V 0.8 V4 = 1.8V 0.7 80 TYPICAL TRANSIENT DURATION (μs) 80 2901 G09 IV4 (μA) 0.5 0.8 0 – 60 –40 – 20 0 20 40 60 TEMPERATURE (°C) RST OUTPUT VOLTAGE (V) 0.6 30 CWT = 1500pF 36 (SILVER MICA) RESET TIME-OUT PERIOD, tRST (ms) IV1 (μA) 100 34 32 30 28 26 24 22 20 40 60 –60 –40 –20 0 TEMPERATURE (°C) 80 100 2901 G15 CRT = 1500pF 8.4 (SILVER MICA) 7.9 7.4 6.9 6.4 5.9 5.4 4.9 –60 –40 –20 0 20 40 60 TEMPERATURE (°C) 80 100 2901 G16 2901fb 6 LTC2901 U W TYPICAL PERFOR A CE CHARACTERISTICS Reset Time-Out Period vs Capacitance Watchdog Time-Out Period vs Capacitance 10 TA = 25°C 10 1 10m 1m 10p 100p 10n 1n CWT (FARAD) 100n 1μ ISINK (mA) 10m 1m 100p 100n 10n 1n CRT (FARAD) 3.0 – 40°C VOH (V) VOL (V) V1 = 5V V2 = 3V V3 = 2.5V V4 = 1V 0.5 2.0 – 40°C 1.5 25°C 70 80 90 20 0.5 2 1 1.5 ISOURCE (mA) 1.5 2 2.5 3 3.5 V2 (V) 4 4.5 5 2901 G24 RST Pull-Up Current vs V2 (LTC2901-2/LTC2901-4) 6 TA = 25°C TA = 25°C 5 PULL-UP CURRENT (mA) PULL-UP CURRENT (μA) 16 14 12 10 8 VRT33 6 VRT30 VRT25 4 50 1 2.5 18 200 V1, V2 6 RST Pull-Up Current vs V2 (LTC2901-1/LTC2901-3) TA = 25°C 100 8 2901 G21 COMPX Propagation Delay vs Input Overdrive Above Threshold 150 10 0 0 2901 G20 250 14 12 2 0 50 60 ISINK (mA) 40 6 4 0.5 30 5 16 85°C 20 3 4 V1 OR V2 (V) TA = 25°C 18 1.0 10 2 COMPX and WDO Pull-Up Current vs V2 (COMPX and WDO Held at 0V) 2.5 0 1 2901 G19 20 3.5 25°C 1.0 COMPX PROPAGATION DELAY (μs) 0 RST High Level Output Voltage vs Output Source Current (LTC2901-2/LTC2901-4) 2.0 4 3 VRT33 VRT30 2 VRT25 1 2 V3, V4 0 0 1μ 2901 G18 2.5 0 VOL = 0.2V 2 100μ 10p 3.0 1.5 4 1 RST, WDO, COMPX Voltage Output Low vs Output Sink Current 85°C 6 5 3 2901 G17 V2 = 3V V1 = 5V VOL = 0.4V 7 100m 100m TA = 25°C 8 PULL-UP CURRENT (μA) 1 10 TA = 25°C 9 RESET TIME-OUT PERIOD, tRST (sec) WATCHDOG TIME-OUT PERIOD, tWD (sec) 100 RST, WDO, COMPX ISINK vs Supply Voltage 0 1000 10 100 INPUT OVERDRIVE ABOVE THRESHOLD (mV) 2901 G25 0 2 2.5 3 3.5 V2 (V) 4 4.5 5 2901 G26 2 2.5 3 3.5 V2 (V) 4 4.5 5 2901 G27 2901fb 7 LTC2901 U U U PI FU CTIO S COMP3 (Pin 1): Comparator Output 3. Nondelayed, active high logic output with weak pull-up to V2. Pulls high when V3 is above reset threshold. May be pulled greater than V2 using external pull-up. COMP1 (Pin 2): Comparator Output 1. Nondelayed, active high logic output with weak pull-up to V2. Pulls high when V1 is above reset threshold. May be pulled greater than V2 using external pull-up. V3 (Pin 3): Voltage Input 3. Select from 2.5V, 1.8V, 1.5V or ADJ. See Table 1 for details. V1 (Pin 4): Voltage Input 1. Select from 5V or 3.3V. See Table 1 for details. The greater of (V1, V2) is also VCC for the device. Bypass this pin to ground with a 0.1μF (or greater) capacitor. CRT (Pin 5): Reset Delay Time Programming Pin. Attach an external capacitor (CRT) to GND to set a reset delay time of 4.6ms/nF. Leaving the pin open generates a minimum delay of approximately 50μs. A 47nF capacitor will generate a 216ms reset delay time. RST (Pin 6): Reset Logic Output. Active low with weak pull-up to V2 (LTC2901-1/LTC2901-3) or active pull-up to V2 (LTC2901-2/LTC2901-4). Pulls low when any voltage input is below the reset threshold and held low for the programmed delay time after all voltage inputs are above threshold. May be pulled above V2 using an external pullup (LTC2901-1/LTC2901-3 only). A rising or falling edge on the WDI pin clears the voltage on the CWT capacitor, preventing WDO from going low. When disabling the watchdog function, tie CWT to GND. For the LTC2901-3/LTC2901-4, a watchdog time-out due to a missed WDI edge issues an RST pulse on the RST pin (the WDO function is merged into the RST function). CWT (Pin 9): Watchdog Time-Out Programming Pin. Attach a capacitor (CWT) between CWT and GND to set a watchdog time-out period of 20ms/nF. Leaving the pin open generates a minimum time-out of approximately 200μs. A 47nF capacitor will generate a 940ms watchdog time-out period. GND (Pin 10): Ground. VPG (Pin 11): Voltage Threshold Combination Select Input. Connect to an external 1% resistive divider between VREF and GND to select 1 of 16 combinations of preset and/ or ±adjustable voltage thresholds (see Table 1). Do not add capacitance on the VPG pin. VREF (Pin 12): Buffered Reference Voltage. A 1.210V nominal reference used for programming voltage (VPG) and for the offset of negative adjustable applications. The buffered reference can source and sink up to 1mA. The reference can drive a bypass capacitor of up to 1000pF without oscillation. V4 (Pin 13): Voltage Input 4. Select from 1.8V, 1.5V, ADJ or – ADJ. See Table 1 for details. WDO (Pin 7): LTC2901-1/LTC2901-2 Watchdog Output. Active low logic output with weak pull-up to V2. May be pulled greater than V2 using external pull-up. The watchdog output pulls low if the watchdog timer is allowed to time out and remains low until set high by the next WDI transistion or anytime RST is low. The watchdog timer is enabled when RST is high. V2 (Pin 14): Voltage Input 2. Select from 3.3V, 3V or 2.5V. See Table 1 for details. The greater of (V1, V2) is also VCC for device. Bypass this pin to ground with a 0.1μF (or greater) capacitor. All logic outputs (COMP1, COMP2, COMP3, COMP4, RST, WDO) are weakly pulled up to V2 (LTC2901-1/LTC2901-3). RST is actively pulled up to V2 in the LTC2901-2/LTC2901-4. T0L (Pin 7): LTC2901-3/LTC2901-4 Digital Input for Supply Tolerance Selection (5% or 10%). A logic low selects 5% thresholds; a logic high selects 10% thresholds. COMP4 (Pin 15): Comparator Output 4. Nondelayed, active high logic output with weak pull-up to V2. Pulls high when V4 is above reset threshold. May be pulled greater than V2 using external pull-up. WDI (Pin 8): Watchdog Input. A logic input whose rising or falling edge must occur on this pin (while RST is high) within the selected watchdog time-out period, prohibiting a high-to-low transition on the WDO pin (LTC2901-1/ LTC2901-2). The watchdog time-out period is set by the value of the capacitor that is attached to the CWT pin. COMP2 (Pin 16): Comparator Output 2. Nondelayed, active high logic output with weak pull-up to V2. Pulls high when V2 is above reset threshold. May be pulled greater than V2 using external pull-up. 2901fb 8 LTC2901 W BLOCK DIAGRA LTC2901-1/LTC2901-2 V1 V2 POWER DETECT VCC 6μA COMP1 – V2 2 + V2 – V1 4 V2 14 V3 6μA + COMP2 16 RESISTIVE DIVIDER MATRIX 3 – V4 13 + V2 6μA GND 10 COMP3 – + VPG 11 1 A/D V2 BUFFER 6μA VREF 12 BANDGAP REFERENCE COMP4 15 ADJUSTABLE RESET PULSE GENERATOR VCC V2 LTC2901-1 2μA 6μA 22μA RST 6 LTC2901-2 V2 10μA TRANSITION DETECT VCC WATCHDOG TIMER RST 6 VCC 2μA 6μA 22μA 5 CRT CRT 8 V2 WDO WDI 7 9 CWT CWT 2901 DB-1 2901fb 9 LTC2901 W BLOCK DIAGRA LTC2901-3/LTC2901-4 V1 V2 POWER DETECT VCC 6μA COMP1 – V2 2 + V2 – V1 4 V2 14 V3 6μA + COMP2 16 RESISTIVE DIVIDER MATRIX 3 – V4 13 + V2 6μA GND 10 COMP3 – + VPG 11 1 A/D V2 BUFFER 6μA VREF BANDGAP REFERENCE 12 COMP4 15 ADJUSTABLE RESET PULSE GENERATOR BUFFER GAIN ADJUST TOL VCC V2 LTC2901-3 2μA 7 6μA 22μA RST 6 LTC2901-4 V2 10μA TRANSITION DETECT VCC WATCHDOG TIMER RST 6 VCC 2μA 22μA 5 CRT CRT 8 WDI 9 CWT CWT 2901 DB-1 2901fb 10 LTC2901 U W U U APPLICATIO S I FOR ATIO Power-Up The greater of V1, V2 is the internal supply voltage (VCC). On power-up, VCC will power the drive circuits for the RST and the COMPX pins. This ensures that the RST and COMPX outputs will be low as soon as V1 or V2 reaches 1V. The RST and COMPX outputs will remain low until the part is programmed. After programming, if any one of the VX inputs is below its programmed threshold, RST will be a logic low. Once all the VX inputs rise above their thresholds, an internal timer is started and RST is released after the programmed delay time. If VCC < (V3 – 1) and VCC < 2.4V, the V3 input impedance will be low (1kΩ typ). Monitor Programming The LTC2901 input voltage combination is selected by placing the recommended resistive divider from VREF to GND and connecting the tap point to VPG, as shown in Figure 4. Table 1 offers recommended 1% resistor values for the various modes. The last column in Table 1 specifies optimum VPG/VREF ratios (±0.01) to be used when programming with a ratiometric DAC. During power-up, once V1 or V2 reaches 2.4V max, the monitor enters a programming period of approximately Table 1. Voltage Threshold Programming MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ) VPG VREF 0 5.0 3.3 ADJ ADJ Open Short 0.000 1 5.0 3.3 ADJ –ADJ 93.1 9.53 0.094 2 3.3 2.5 ADJ ADJ 86.6 16.2 0.156 3 3.3 2.5 ADJ –ADJ 78.7 22.1 0.219 4 3.3 2.5 1.5 ADJ 71.5 28.0 0.281 5 5.0 3.3 2.5 ADJ 66.5 34.8 0.344 6 5.0 3.3 2.5 1.8 59.0 40.2 0.406 7 5.0 3.3 2.5 1.5 53.6 47.5 0.469 8 5.0 3.0 2.5 ADJ 47.5 53.6 0.531 9 5.0 3.0 ADJ ADJ 40.2 59.0 0.594 10 3.3 2.5 1.8 1.5 34.8 66.5 0.656 11 3.3 2.5 1.8 ADJ 28.0 71.5 0.719 12 3.3 2.5 1.8 –ADJ 22.1 78.7 0.781 13 5.0 3.3 1.8 –ADJ 16.2 86.6 0.844 14 5.0 3.3 1.8 ADJ 9.53 93.1 0.906 15 5.0 3.0 1.8 ADJ Short Open 1.000 LTC2901 12 VREF 11 VPG 10 GND R1 1% R2 1% 2901 F04 Figure 4. Monitor Programming 150μs during which the voltage on the VPG pin is sampled and the monitor is configured to the desired input combination. Do not add capacitance to the VPG pin. Immediately after programming, the comparators are enabled and supply monitoring will begin. Supply Monitoring The LTC2901 is a low power, high accuracy programmable quad supply monitoring circuit with four nondelayed monitor outputs, a common reset output and a watchdog timer. Watchdog and reset timing are both adjustable using external capacitors. Single pin programming selects 1 of 16 input voltage monitor combinations. All four voltage inputs must be above predetermined thresholds for the reset not to be invoked. The LTC2901 will assert the reset and comparator outputs during power-up, powerdown and brownout conditions on any one of the voltage inputs. The inverting inputs on the V3 and/or V4 comparators are set to 0.5V when the positive adjustable modes are selected (Figure 5). The tap point on an external resistive divider, connected between the positive voltage being sensed and ground, is connected to the high impedance noninverting inputs (V3, V4). The trip voltage is calculated from: ⎛ R3 ⎞ VTRIP = 0.5V⎜ 1 + ⎟ ⎝ R4 ⎠ In the negative adjustable mode, the noninverting input on the V4 comparator is connected to ground (Figure 6). The tap point on an external resistive divider, connected between the negative voltage being sensed and the VREF pin, is connected to the high impedance inverting input (V4). VREF provides the necessary level shift required to operate at ground. The trip voltage is calculated from: ⎛ R3 ⎞ VTRIP = – VREF ⎜ ⎟ ; VREF = 1.210 V No min al ⎝ R4 ⎠ 2901fb 11 LTC2901 U W U U APPLICATIO S I FOR ATIO VTRIP Table 2. Suggested 1% Resistor Values for the ADJ Inputs LTC2901 R3 1% + V3 OR V4 R4 1% – + – 0.5V 2901 F05 Figure 5. Setting the Positive Adjustable Trip Point 12 R4 1% VREF 13 V4 R3 1% LTC2901 – + VTRIP VSUPPLY (V) VTRIP (V) R3 (kΩ) R4 (kΩ) 12 11.25 2150 100 10 9.4 1780 100 8 7.5 1400 100 7.5 7 1300 100 6 5.6 1020 100 5 4.725 845 100 3.3 3.055 511 100 3 2.82 464 100 2.5 2.325 365 100 1.8 1.685 237 100 1.5 1.410 182 100 1.2 1.120 124 100 1 0.933 86.6 100 0.9 0.840 68.1 100 Table 3. Suggested 1% Resistor Values for the –ADJ Input 2901 F06 Figure 6. Setting the Negative Adjustable Trip Point In a negative adjustable application, the minimum value for R4 is limited by the sourcing capability of VREF (±1mA). With no other load on VREF, R4 (minimum) is: 1.21V ÷ 1mA = 1.21kΩ. Tables 2 and 3 offer suggested 1% resistor values for various adjustable applications. Once the resistor divider is set in the 5% tolerance mode (LTC2901-3/LTC2901-4), there is no need to change the divider for the 10% mode because the internal and external reference is scaled accordingly, moving the trip point by –5%. Although all four supply monitor comparators have builtin glitch immunity, bypass capacitors on V1 and V2 are recommended because the greater of V1 or V2 is also the VCC for the device. Filter capacitors on the V3 and V4 inputs are allowed. Power-Down On power-down, once any of the VX inputs drop below their threshold, RST and COMPX are held at a logic low. A logic low of 0.4V is guaranteed until both V1 and V2 drop below 1V. If the bandgap reference becomes invalid VSUPPLY (V) VTRIP (V) R3 (kΩ) R4 (kΩ) –2 –1.87 187 121 –5 –4.64 464 121 –5.2 –4.87 487 121 –10 –9.31 931 121 –12 –11.30 1130 121 (VCC < 2V typ), the part will reprogram once VCC rises above 2.4V max. Monitor Output Rise and Fall Time Estimation All of the outputs (RST, COMPX, WDO) have strong pulldown capability. If the external load capacitance (CLOAD) for a particular output is known, output fall time (10% to 90%) is estimated using: tFALL ≈ 2.2 • RPD • CLOAD where RPD is the on-resistance of the internal pull-down transistor. The typical performance curve (VOL vs ISINK) demonstrates that the pull-down current is somewhat linear versus output voltage. Using the 25°C curve, RPD is estimated to be approximately 40Ω. Assuming a 150pF load capacitance, the fall time is about 13.2ns. Although the outputs are considered to be “open-drain,” they do have a weak pull-up capability (see COMPX or RST 2901fb 12 LTC2901 U W U U APPLICATIO S I FOR ATIO Pull-Up Current vs V2 curve). Output rise time (10% to 90%) is estimated using: tRISE ≈ 2.2 • RPU • CLOAD where RPU is the on-resistance of the pull-up transistor. The on-resistance as a function of the V2 voltage at room temperature is estimated using: RPU = 6 • 105 Ω V2 – 1 with V2 = 3.3V, RPU is about 260k. Using 150pF for load capacitance, the rise time is 86μs. If the output needs to pull up faster and/or to a higher voltage, a smaller external pull-up resistor may be used. Using a 10k pullup resistor, the rise time is reduced to 3.3μs for a 150pF load capacitance. The LTC2901-2 has an active pull-up to V2 on the RST output. The typical performance curve (RST Pull-Up Current vs V2 curve) demonstrates that the pull-up current is somewhat linear versus the V2 voltage and RPU is estimated to be approximately 625Ω. A 150pF load capacitance makes the rise time about 206ns. Watchdog Timer The watchdog circuit typically monitors a μP’s activity. The μP is required to change the logic state of the WDI pin on a periodic basis in order to clear the watchdog timer and prevent the WDO pin (LTC2901-1/LTC2901-2) from going low. Whenever RST is low, the watchdog timer is cleared and WDO is set high. The watchdog timer is started when RST pulls high. Subsequent edges received on the WDI pin will clear the watchdog timer. The timer will continue to run until the watchdog timer times out. Once the watchdog timer times out, internal circuitry will bring the WDO pin low. WDO will remain low and the watchdog timer will remain cleared until the next edge is received on the WDI pin or until RST goes low. In the LTC2901-3/LTC2901-4, there is no WDO pin. Instead, the RST pin is pulled low for the programmed reset timeout period whenever a WDI edge is missed. In this manner, a full system reset can be issued after a watchdog failure. To disable the watchdog timer, simply ground the CWT pin (Pin 9). With CWT held at ground, any reset event will force WDO high indefinitely. It is safe to leave the WDI pin (Pin 8) unconnected because the weak internal pull-up (10μA typ) will pull WDI high. Tying WDI to V1 or ground is also allowed, but grounding the WDI pin will force the pull-up current to be drawn continuously. Selecting the Reset Timing Capacitor The reset time-out period is adjustable in order to accommodate a variety of microprocessor applications. The reset time-out period, tRST, is adjusted by connecting a capacitor, CRT, between the CRT pin and ground. The value of this capacitor is determined by: CRT = tRST • 217 • 10 –9 with CRT in Farads and tRST in seconds. The CRT value per millisecond of delay can also be expressed as CRT/ms = 217 (pF/ms). Leaving the CRT pin unconnected will generate a minimum reset time-out of approximately 50μs. Maximum reset time-out is limited by the largest available low leakage capacitor. The accuracy of the time-out period will be affected by capacitor leakage (the nominal charging current is 2μA) and capacitor tolerance. A low leakage ceramic capacitor is recommended. Selecting the Watchdog Timing Capacitor The watchdog time-out period is adjustable and can be optimized for software execution. The watchdog time-out period, tWD, is adjusted by connecting a capacitor, CWT, between the CWT pin and ground. Given a specified watchdog time-out period, the capacitor is determined by: CWT = tWD • 50 • 10–9 with CWT in Farads and tWD in seconds. The CWT value per millisecond of delay can also be expressed as CWT/ms = 50 (pF/ms). Leaving the CWT pin unconnected will generate a minimum watchdog time-out of approximately 200μs. Maximum time-out is limited by the largest available low leakage capacitor. The accuracy of the time-out period will be affected by capacitor leakage (the nominal charging current is 2μA) and capacitor tolerance. A low leakage ceramic capacitor is recommended. 2901fb 13 LTC2901 U W U U APPLICATIO S I FOR ATIO Monitoring Power Supply Controller Activity Figure 7 demonstrates how the LTC2901 can be used to monitor switcher activity. The monitor is configured to supervise 3.3V, 2.5V, 1.8V and one adjustable input. Because 2.5V does not exist in this application, the V2 input is tied to the V1 (3.3V) input. The feedback voltage on the LTC1772 (0.8V typ) is monitored with the adjustable input (V4). The RST pin will go high 216ms (CRT = 47nF) after the 3.3V and 1.8V supplies and the feedback voltage are above threshold. Individual input status is available at the COMPX pins. While the voltage monitors can detect low voltage or shorted inputs, the watchdog circuit can be used to detect an open circuit to the primary load. With the CWT pin unconnected, the watchdog time-out is approximately 200μs. At low load currents on the 1.8V supply, the LTC1772 will go into Burst Mode® operation. With an open-ciruit load, the duty cycle at the gate of M1 will drop, and the pulse spacing will exceed the watchdog time-out LTC1772 6 ITH PGATE 2 5 VIN GND 3 4 VFB SENSE – R6 10k C3 220pF C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T C2: SANYO POSCAP 6TPA47M D1: MOTOROLA MBRM120T3 L1: COILTRONICS UP1B-100 M1: Si3443DV R5: DALE 0.25W M1 Ensuring Reset Valid for VCC Down to 0V (LTC2901-2/LTC2901-4) Some applications require the reset output (RST) to be valid with VCC down to 0V. The LTC2901-2 is designed to handle this requirement with the addition of an external resistor from RST to ground. The resistor will provide a path for stray charge and/or leakage currents, preventing the RST output from floating to undetermined voltages when connected to high impedance (such as CMOS logic inputs). The resistor value should be small enough to provide effective pull-down without excessively loading the active pull-up circuitry. Too large a value may not pull down well enough. A 100k resistor from RST to ground is satisfactory for most applications. Burst Mode is a registered trademark of Linear Technology Corporation. VIN 3.3V C1 10μF 10V R5 0.15Ω 1 period. The WDO pin will go low indicating the low load condition. The WDO pin will return high on the next pulse to the gate of M1. The WDO pin will remain high if the load is restored. 14 3 L1 10μH D1 4 + C2 47μF 6V R3 100k R4 80.6k 13 VOUT 1.8V 0.5A 8 12 R1 28k 1% R2 71.5k 1% 11 10 LTC2901-2 2 V1 COMP1 16 V2 COMP2 1 V3 COMP3 15 V4 COMP4 6 WDI RST 7 VREF WDO 5 CRT VPG 9 CWT GND 3.3V MONITOR 1.8V MONITOR FEEDBACK MONITOR COMMON RESET OUT LOW LOAD INDICATOR CRT 47nF 2901 F07 Figure 7. Monitor Input, Output, Feedback Voltage and Low Load Conditions on DC/DC Controller 2901fb 14 LTC2901 U TYPICAL APPLICATIO S Quad Supply Monitor with Watchdog Timer Disabled 5V, 3V, 1.8V, 12V (ADJ) 1 2 1.8V 5V 3 4 5 SYSTEM RESET 6 7 8 CRT COMP3 COMP2 COMP1 COMP4 V3 V2 V1 LTC2901 V4 CRT VREF RST VPG WDO GND WDI CWT 5V, –5V Monitor with Watchdog Timer Disabled and Unused V2, V3 Inputs Pulled Above Trip Thresholds 16 1 15 14 2 R3 2.15M 1% 3V 13 3 12V VTRIP = 11.25V 12 11 R4 100k 1% 10 4 5V 5 6 SYSTEM RESET 9 7 CRT 8 COMP3 COMP2 COMP1 COMP4 V3 V2 V1 LTC2901 V4 CRT VREF RST VPG WDO GND WDI CWT 16 15 R3 464k 1% 14 13 –5V 12 VTRIP = –4.64V R1 R4 16.2k 121k 1% 1% 11 10 9 R2 86.6k 1% 2901 TA02 2901 TA03 Quad Supply Monitor with LED Undervoltage Indicators 5V, 3.3V, 2.5V, 1.5V RL1 1k LED RL3 1k LED 1 2 2.5V 3 4 5V 5 SYSTEM RESET WATCHDOG STATUS WDI RL2 1k 6 7 8 LED COMP3 COMP2 COMP1 COMP4 V3 V2 V1 LTC2901 V4 CRT VREF RST VPG WDO GND WDI CWT CRT RL4 1k LED 16 15 14 3.3V 13 1.5V 12 R1 53.6k 1% 11 10 9 R2 47.5k 1% CWT 2901 TA04 Generate RESET Pulse Through Watchdog Timeout (LTC2901-1/LTC2901-2) 1 2 ADJ 3 4 5V 10k 5 6 RST 7 8 WDI CRT COMP3 COMP2 COMP1 COMP4 V3 V2 V1 LTC2901 V4 CRT VREF RST VPG WDO GND WDI CWT 16 tRST 15 14 3.3V RST 13 12 11 WDO 10 ~20μs 9 CWT WDI tWD 2901 TA06 2901fb 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 LTC2901 U TYPICAL APPLICATIO Monitor Seven Supplies (12V, 5V, 3.3V, 2.5V, 1.8V, –2V, –5.2V) with Sequenced Reset and AC Present Indication 5V 12V 5V 3.3V 2.5V 1.8V –2V –5.2V AC/DC DC/DC CONVERTERS 10k 0.1μF 4 14 3.3V 3 1.8V 13 8 120V AC 12 LOW VOLTAGE SECONDARY 11 121k 16.2k 1% 1% 10 LTC2901-1 2 V1 COMP1 16 V2 COMP2 1 V3 COMP3 15 V4 COMP4 6 WDI RST 7 VREF WDO 5 CRT VPG 9 CWT GND 10k 4 5V MONITOR 0.1μF 3.3V MONITOR 2.5V 14 3 1.8V MONITOR 13 –5.2V MONITOR 8 12 12V 487k 86.6k 1% 1% CRT1 47nF 100k 2.15M 1% 121k 78.7k 1% 1% 100k 1% 187k 22.1k 1% 1% 11 10 LTC2901-1 2 V1 COMP1 16 V2 COMP2 1 V3 COMP3 15 V4 COMP4 6 WDI RST 7 VREF WDO 5 CRT VPG 9 CWT GND 2.5V MONITOR 12V MONITOR –2V MONITOR COMMON RESET OUT AC PRESENT CWT 680pF –2V –5.2V 100k 1N4148 CRT2 47nF 2901 TA05 1N4148 tRST1 + tRST2 = 432ms tWD = 13.6ms Q1 2N3904 U PACKAGE DESCRIPTIO GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) .015 ± .004 × 45° (0.38 ± 0.10) .0532 – .0688 (1.35 – 1.75) .007 – .0098 (0.178 – 0.249) .004 – .0098 (0.102 – 0.249) 16 15 14 13 12 11 10 9 .009 (0.229) REF .045 ±.005 0° – 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE .229 – .244 .0250 .008 – .012 (5.817 – 6.198) (0.635) (0.203 – 0.305) BSC TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE .150 – .157** (3.810 – 3.988) .254 MIN .150 – .165 GN16 (SSOP) 0204 1 2 3 4 5 6 7 8 .0165 ± .0015 .0250 BSC RECOMMENDED SOLDER PAD LAYOUT RELATED PARTS PART NUMBER LTC694-3.3 LTC1326 LTC1726-2.5 LTC1727-2.5/LTC1727-5 LTC1728-1.8/LTC1728-3.3 LTC2900 DESCRIPTION 3.3V Supply Monitor, Watchdog Timer and Battery Backup Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ Micropower Triple Supply Monitors with Open-Drain Reset Micropower Triple Supply Monitor with Open-Drain Reset Programmable Quad Supply Monitor LTC2902 Programmable Quad Supply Monitor LTC2903 LTC2904/LTC2905 LTC2906/LTC2907 LTC2908 Precision Quad Supply Monitor in 6-Lead SOT-23 Precision Dual Supply Monitors COMMENTS 2.9V Threshold 4.725V, 3.118V, 1V Thresholds (±0.75%) Adjustable RESET and Watchdog Time-Outs Individual Monitor Outputs in MSOP 5-Lead SOT-23 Package Adjustable Reset Timer, 10-Lead MSOP and 3mm × 3mm 10-Lead DFN Adjustable Reset Timer, Supply Tolerance and Margining Functions, 16-Lead Narrow SSOP A Variety of Factory Trimmed Voltage Combinations Pin Selectable Thresholds Precision Six Supply Monitor 8-Lead SOT-23 and DFN Packages 2901fb 16 Linear Technology Corporation LT 0807 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2002