LTC2931 Configurable Six Supply Monitor with Adjustable Reset and Watchdog Timers DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Simultaneously Monitors Six Supplies 16 User Selectable Combinations of 5V, 3.3V, 3V, 2.5V, 1.8V, 1.5V and ± Adjustable Voltage Thresholds Guaranteed Threshold Accuracy: ±1.5% Adjustable Reset and Watchdog Timeout Low Supply Current: 52μA Comparator/Monitor Output for Each Supply Power Supply Glitch Immunity Guaranteed RST for VCC ≥ 1V High Temperature Operation to 125°C 20-Lead TSSOP Package The LTC®2931 is a configurable supply monitor for systems with up to six supply voltages. One of 16 preset or adjustable voltage monitor combinations can be selected using an external resistive divider connected to the mode select pin. The preset voltage thresholds are accurate to ±1.5% over temperature. The LTC2931 also features adjustable inputs with a 0.5V nominal threshold. All six open-drain voltage comparator outputs are connected to separate pins for individual supply monitoring. The reset and watchdog timeout periods are adjustable using external capacitors. Tight voltage threshold accuracy and glitch immunity ensure reliable reset operation without false triggering. The RST output is guaranteed to be in the correct state for VCC down to 1V. Each status output has a weak internal pull-up and may be externally pulled up to a user defined voltage. APPLICATIONS ■ ■ ■ ■ ■ ■ Desktop and Notebook Computers Multivoltage Systems Telecom Equipment Portable Battery-Powered Equipment Network Servers Automotive The 52μA supply current makes the LTC2931 ideal for power conscious systems and it may be configured to monitor fewer than six inputs. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6967591, 7239251, 7119714. TYPICAL APPLICATION Six Supply Monitor 12V (ADJ), 5V, 3.3V, 2.5V, 1.8V, 1.2V (ADJ) 12V 5V 3.3V 2.5V SYSTEM LOGIC 1.8V 1.2V 10k POWER GOOD V3 0.1μF WDI V4 0.1μF LTC2931 V5 100k 1% 100k 1% R1 59k 1% WDO V6 VREF RST 2931 TA01 VPG GND R2 40.2k 1% COMP6 COMP5 COMP4 V2 COMP3 V1 COMP2 124k 1% COMP1 2150k 1% CWT CRT CWT 47nF tRST = 94ms tWD = 940ms CRT 47nF Voltage Threshold Configuration Table V1 (V) V2 (V) V3 (V) V4 (V) V5 (V) V6 (V) 5.0 3.3 2.5 1.8 ADJ ADJ 5.0 3.3 2.5 1.5 ADJ ADJ 5.0 3.3 2.5 ADJ ADJ ADJ 5.0 3.3 1.8 ADJ ADJ ADJ 5.0 3.3 1.8 –ADJ ADJ ADJ 5.0 3.3 ADJ ADJ ADJ ADJ 5.0 3.3 ADJ –ADJ ADJ ADJ 5.0 3.0 2.5 ADJ ADJ ADJ 5.0 3.0 1.8 ADJ ADJ ADJ 5.0 3.0 ADJ ADJ ADJ ADJ 3.3 2.5 1.8 1.5 ADJ ADJ 3.3 2.5 1.8 ADJ ADJ ADJ 3.3 2.5 1.8 –ADJ ADJ ADJ 3.3 2.5 1.5 ADJ ADJ ADJ 3.3 2.5 ADJ ADJ ADJ ADJ 3.3 2.5 ADJ –ADJ ADJ ADJ 2931fb 1 LTC2931 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2, 3) TOP VIEW V1, V2, V3, V4, V5, V6, VPG ........................ –0.3V to 7V RST , COMP1-6............................................ –0.3V to 7V CWT, WDO .................................................... –0.3V to 7V CRT, VREF, WDI .............................–0.3V to (VCC + 0.3V) Reference Load Current (IVREF) ..............................±1mA V4 Input Current (–ADJ Mode) ..............................–1mA RST , WDO, COMP1-6 Currents ...........................±10mA Operating Temperature Range LTC2931C ................................................ 0°C to 70°C LTC2931I.............................................. –40°C to 85°C LTC2931H .......................................... –40°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C COMP5 1 20 COMP6 V5 2 19 V6 COMP3 3 18 COMP2 COMP1 4 17 COMP4 V3 5 16 V2 V1 6 15 V4 CRT 7 14 VREF RST 8 13 VPG WDO 9 12 GND WDI 10 11 CWT F PACKAGE 20-LEAD PLASTIC TSSOP TJMAX = 130°C, θJA = 90°C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2931CF#PBF LTC2931CF#TRPBF LTC2931F 20-Lead Plastic TSSOP 0°C to 70°C LTC2931IF#PBF LTC2931IF#TRPBF LTC2931F 20-Lead Plastic TSSOP –40°C to 85°C LTC2931HF#PBF LTC2931HF#TRPBF LTC2931F 20-Lead Plastic TSSOP –40°C to 125°C Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ This product is only offered in trays. For more information go to: http://www.linear.com/packaging/ ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise specified. (Note 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VCC Minimum Internal Operating Voltage RST, COMPn in Correct Logic State ● 1 V VCCMINP Minimum Required for Mode Selection VCC Rising ● 2.4 V VCCMINC Minimum Required for Comparators VCC Falling ● 2.3 V VRT50 5V, 5% Reset Threshold V1 Input Threshold ● 4.600 4.675 4.750 V VRT33 3.3V, 5% Reset Threshold V1, V2 Input Threshold ● 3.036 3.086 3.135 V VRT30 3V, 5% Reset Threshold V2 Input Threshold ● 2.760 2.805 2.850 V VRT25 2.5V, 5% Reset Threshold V2, V3 Input Threshold ● 2.300 2.338 2.375 V VRT18 1.8V, 5% Reset Threshold V3, V4 Input Threshold ● 1.656 1.683 1.710 V VRT15 1.5V, 5% Reset Threshold V3, V4 Input Threshold ● 1.380 1.403 1.425 V VRTA ADJ Reset Threshold V3, V4, V5, V6 Input Threshold ● 492.5 500 507.5 mV VRTAN –ADJ Reset Threshold V4 Input Threshold ● –18 0 18 mV 2931fb 2 LTC2931 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 specified. (Note 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VREF Reference Voltage VCC ≥ 2.3V, IVREF = ±1mA, CREF ≤ 1000pF ● 1.192 1.210 1.228 V VPG Mode Selection Voltage Range VCC ≥ VCCMINP ● 0 VREF V IVPG VPG Input Current VPG = VREF ● ±20 nA 52 75 μA 0.8 2 μA 0.52 1.2 15 μA nA 0.34 IV1 V1 Input Current V1 = 5V, IVREF = 12μA (Note 4) ● IV2 V2 Input Current V2 = 3.3V ● IV3 V3 Input Current V3 = 2.5V V3 = 0.55V (ADJ Mode) ● ● –15 V4 = 1.8V V4 = 0.55V (ADJ Mode) V4 = –0.02V (–ADJ Mode) ● ● ● –15 –15 0.8 15 15 μA nA nA 15 nA IV4 V4 Input Current IV5, IV6 V5, V6 Input Current V5, V6 = 0.55V ● –15 ICRT(UP) CRT Pull-Up Current VCRT = GND ● –1.4 –2 –2.6 μA ICRT(DN) CRT Pull-Down Current VCRT = 1.3V ● 10 20 30 μA tRST Reset Timeout Period CRT = 1500pF ● 2 3 4 ms tUV Vn Undervoltage Detect to RST or COMPn Vn Less Than Reset Threshold by More than 1% VOL Voltage Output Low RST, COMPn ISINK = 3mA, VCC = 3V ISINK = 100μA, VCC = 1V ● ● ICOMPn COMPn Pull-Up Current VCOMPn = GND ● VOL Voltage Output Low WDO ISINK = 3mA ● VOH Voltage Output High RST, WDO, COMPn ISOURCE = –1μA (Note 5) ● V2-1 ICWT(UP) CWT Pull-Up Current VCWT = GND ● –1.4 –2 –2.6 μA ICWT(DN) CWT Pull-Down Current VCWT = 1.3V ● 10 20 30 μA 20 30 40 ms 1.6 150 –2 tWD Watchdog Timeout Period CWT = 1500pF ● VIH WDI Input Threshold High VCC = 3.3V to 5.5V ● VIL WDI Input Threshold Low VCC = 3.3V to 5.5V ● tWP WDI Input Pulse Width VCC = 3.3V ● 150 IWDI WDI Pull-Up Current VWDI = 1V ● –4 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). μs 0.15 0.05 0.4 0.3 V V –6 –12 μA 0.15 0.4 V V V 0.4 V ns –10 –16 μA Note 4: Under static no-fault conditions, V1 will necessarily supply quiescent current. If at any time V2 is larger than V1, V2 must be capable of supplying the quiescent current, programming (transient) current and reference load current. Note 5: The output pins RST, WDO, and COMPn have diode protected internal pull-ups to V2 of typically 6μA. However, external pull-up resistors may be used when faster rise times are required or for VOH voltages greater than V2. 2931fb 3 LTC2931 TIMING DIAGRAMS Vn Monitor Timing Vn VRT tRST tUV RST 2931 TD COMPn Watchdog Timing tRST RST WDI tWP t < tRST tRST tRST WDO tWD tWD tWD 2931 TD2 2931fb 4 LTC2931 TYPICAL PERFORMANCE CHARACTERISTICS –ADJ Threshold Voltage vs Temperature 1.010 1.005 1.000 0.995 0.990 0.985 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 18 1.228 12 1.222 6 1.216 VREF (V) 1.015 THRESHOLD VOLTAGE, VRTAN (mV) NORMALIZED THRESHOLD VOLTAGES (V/V) Normalized Threshold Voltages vs Temperature 0 1.204 –12 1.198 50 25 75 0 TEMPERATURE (oC) 100 300 –10μ 125°C IV4 (A) –1μ –100n 50 –10n 45 –1n 90°C 25°C 100 125 –100p –300 –250 –200 –150 –100 V4 (mV) –50 250 200 RESET OCCURS ABOVE CURVE 150 100 50 0 0 2931 G05 0.1 1 10 100 RESET COMPARATOR OVERDRIVE (% OF VRTX) 2931 G06 RST Output Voltage vs V1, VPG = GND RESET OCCURS ABOVE CURVE 225 150 75 0 36 TA = 25oC 10k PULL-UP FROM RST TO V1 5 375 RST OUTPUT VOLTAGE (V) TYPICAL TRANSIENT DURATION (Ms) 6 TA = 25oC Watchdog Timeout Period vs Temperature WATCHDOG TIMEOUT PERIOD, tWD (ms) Transient Duration vs Comparator Overdrive (V3, V4, V5, V6) 300 4 3 2 1 0.1 1 10 100 RESET COMPARATOR OVERDRIVE (% OF VRTX) 2931 G07 125 TA = 25oC 2931 G04 450 100 Transient Duration vs Comparator Overdrive (V1,V2) TYPICAL TRANSIENT DURATION (Ms) V1 = 5V V2 = 3.3V 65 V3 = 2.5V V4 = 1.8V V5 = V6 = 1V 60 55 50 25 75 0 TEMPERATURE (°C) 2931 G03 –100μ 70 50 25 75 0 TEMPERATURE (oC) 1.192 –50 –25 I(V4) vs V4 in Negative Adjust Mode Supply Current vs Temperature SUPPLY CURRENT, IV1 (MA) 125 2931 G02 2931 G01 40 –50 –25 1.210 –6 –18 –50 –25 125 VREF vs Temperature 0 0 1 2 3 4 5 V1 (V) 2931 G08 CWT = 1500pF (SILVER MICA) 34 32 30 28 26 24 –50 –25 50 25 75 0 TEMPERATURE (oC) 100 125 2931 G09 2931fb 5 LTC2931 TYPICAL PERFORMANCE CHARACTERISTICS Reset Timeout Period vs Temperature Watchdog Timeout Period vs CWT 100 4 3 TA = 25oC 10 1 100m 2 1 –50 75 0 25 50 TEMPERATURE (oC) –25 100 125 10m 1m 100μ 10p 100p 1n 10n CWT (F) 100n 10m 1m 100M 10M 10p 500 TA = 25oC 125oC PULL-UP CURRENT (MA) 85oC VOL (mV) 6 300 25oC 200 –40oC 100 3 0 1 3 2 V1 OR V2 (V) 4 5 0 0 2 6 4 ISINK (mA) 8 TA = 25oC 9 6 0 10 1 2 3 V2 (V) 4 5 2931 G15 TA = 25oC 15 PULL-UP CURRENT (MA) COMPn PROPAGATION DELAY (Ms) 12 RST Pull-Up Current vs V2 18 200 150 V1, V2 100 0 TA = 25oC COMPn = WDO = GND 2931 G14 COMPn Propagation Delay vs Input Overdrive Above Threshold 50 1M 3 2931 G13 250 100n 15 400 VOL = 0.2V 1n 10n CRT (F) COMPn and WDO Pull-Up Current vs V2 18 V1 = 5V V2 = 3V VOL = 0.4V 9 100p 2931 G12 Voltage Output Low vs Output Sink Current (RST, WDO, COMPn) 12 0 100m 2931 G11 ISINK vs Supply Voltage (RST, WDO, COMPn) 15 TA = 25oC 1 1M 2931 G10 ISINK (mA) Reset Timeout Period vs CRT 10 RESET TIMEOUT PERIOD tRST (s) CRT = 1500pF (SILVER MICA) WATCHDOG TIMEOUT PERIOD tWD (s) RESET TIMEOUT PERIOD, tRST (ms) 5 V3, V4, V5, V6 12 9 VRT33 VRT30 6 3 VRT25 1000 10 100 INPUT OVERDRIVE ABOVE THRESHOLD (mV) 2931 G16 0 2.0 2.5 3.0 3.5 V2 (V) 4.0 4.5 5.0 2931 G17 2931fb 6 LTC2931 PIN FUNCTIONS COMP5 (Pin 1): Comparator Output 5. Real-time logic output with weak 6μA pull-up to V2. Pulls high when V5 is above reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. V5 (Pin 2): Adjustable Voltage Input 5. High impedance comparator input with 0.5V typical threshold. See Applications Information for details. Tie to V1 if unused. COMP3 (Pin 3): Comparator Output 3. Real-time logic output with weak 6μA pull-up to V2. Pulls high when V3 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. COMP1 (Pin 4): Comparator Output 1. Real-time logic output with weak 6μA pull-up to V2. Pulls high when V1 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. V3 (Pin 5): Voltage Input 3. Select from 2.5V, 1.8V, 1.5V, or ADJ. See Applications Information for details. Tie to V1 if unused. V1 (Pin 6): Voltage Input 1. Select from 5V or 3.3V. See Applications Information for details. The greater of V1 or V2 is also VCC for the device. Bypass this pin to ground with a 0.1μF (or greater) capacitor. CRT (Pin 7): Reset Timeout Capacitor. Attach an external capacitor (CRT) to GND to set a reset timeout of 2ms/nF. Leaving the pin open generates a minimum delay of approximately 25μs. A 47nF capacitor generates a 94ms reset delay time. RST (Pin 8): Reset Output. Logic output with weak 6μA pull-up to V2. Pulls low when any voltage input is below the reset threshold and held low for the configured delay time after all voltage inputs are above threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. WDO (Pin 9): Watchdog Output. Logic output with weak 6μA pull-up to V2. May be pulled greater than V2 using external pull-up. The watchdog timer is enabled when RST is high. The watchdog output pulls low if the watchdog timer times out and remains low for one reset timeout period. The watchdog output is cleared with a WDI transition or anytime RST is low.The output will toggle between high and low as long as the watchdog and reset timers are allowed to time out. Leave open if unused. WDI (Pin 10): Watchdog Input. A logic input whose rising or falling edge must occur on this pin (while RST is high) within the selected watchdog time-out period, prohibiting a high-to-low transition on the WDO pin. The capacitor attached to the CWT pin sets the watchdog time-out period. A rising or falling edge on the WDI pin clears the voltage on the CWT capacitor, preventing WDO from going low. Tie WDI to V1 or GND if unused. Tie CWT to GND to disable the watchdog function. CWT (Pin 11): Watchdog Timeout Capacitor. Attach a capacitor (CWT) between CWT and GND to set a watchdog time-out period of 20ms/nF. Leaving the pin open generates a minimum timeout of approximately 200μs. A 47nF capacitor generates a 940ms watchdog time-out period. Tie CWT to GND to disable the watchdog function. GND (Pin 12): Ground. VPG (Pin 13): Threshold Select Input. Connect to an external 1% resistive divider between VREF and GND to select 1 of 16 combinations and/or ±adjustable voltage thresholds (See Table 1). Do not add capacitance on the VPG pin. VREF (Pin 14): Buffered Reference Voltage Output. A 1.210V nominal reference used for the mode selection voltage (VPG) and for the offset of negative adjustable applications. The buffered reference can source and sink up to 1mA. The reference can drive a bypass capacitor of up to 1000pF without oscillation. V4 (Pin 15): Voltage Input 4. Select from 1.8V, 1.5V, ADJ or –ADJ. See Applications Information for details. Tie to V1 if unused and configured for positive voltage. V2 (Pin 16): Voltage Input 2. Select from 3.3V, 3V or 2.5V. See Applications Information for details. The greater of V1, V2 is also VCC for the device. Bypass this pin to ground with a 0.1μF (or greater) capacitor. All status outputs are weakly pulled up to V2. COMP4 (Pin 17): Comparator Output 4. Real-time logic output with weak 6μA pull-up to V2. Pulls high when V4 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. 2931fb 7 LTC2931 PIN FUNCTIONS COMP2 (Pin 18): Comparator Output 2. Real-time logic output with weak 6μA pull-up to V2. Pulls high when V2 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. COMP6 (Pin 20): Comparator Output 6. Real-time logic output with weak 6μA pull-up to V2. Pulls high when V6 is above its reset threshold. May be pulled greater than V2 using external pull-up. Leave open if unused. V6 (Pin 19): Adjustable Voltage Input 6. High impedance comparator input with 0.5V typical threshold. See Applications Information for details. Tie to V1 if unused. BLOCK DIAGRAM BUFFER VREF 14 V2 V2 1.210V BANDGAP REFERENCE 6μA V2 6μA VPG 13 A/D COMP1 4 V2 6μA 4 COMP2 18 COMP3 3 6μA V1 6 V2 16 V3 5 RESISTIVE DIVIDER MATRIX 4 – 4 + COMP4 17 V2 CMP1-4 4 6μA V2 COMP5 1 V4 15 6μA V5 – 2 COMP6 20 + V2 CMP5 6μA 0.5V RST 4 + CMP6 V6 19 – 8 ADJUSTABLE RESET PULSE GENERATOR V2 2μA VCC CRT 6μA 22μA 7 WDO 9 10μA CRT VCC V1 TRANSITION DETECT VCC GND 12 WATCHDOG TIMER POWER DETECT VCC 2μA 22μA V2 10 WDI 11 CWT CWT 2931 BD 2931fb 8 LTC2931 APPLICATIONS INFORMATION 5V Supply Monitoring The LTC2931 is a low power, high accuracy configurable six supply monitoring circuit with six real-time monitor outputs, a common reset output and a watchdog timer. External capacitors set the reset and watchdog timeout periods. An external resistive divider between VREF, VPG and GND selects 1 of 16 possible input voltage monitor combinations. All six voltage inputs must be above their predetermined thresholds for the reset not to be activated. The LTC2931 asserts the reset and comparator outputs during power-up, power-down and brownout conditions on any one of the voltage inputs. SUPPLY TOLERANCE MINIMUM RELIABLE SYSTEM VOLTAGE IDEAL SUPERVISOR THRESHOLD 4.75V ±1.5% THRESHOLD BAND NOMINAL SUPPLY VOLTAGE –5% 4.675V –6.5% 4.6V –8% REGION OF POTENTIAL MALFUNCTION Power-Up Figure 1. 1.5% Threshold Accuracy Improves System Reliability The greater of V1 and V2 serves as the internal supply voltage (VCC). On power-up, VCC powers the drive circuits for the RST pin. This ensures that the RST output will be low as soon as either V1 or V2 reaches 1V. The RST output remains low until the part is configured. Once voltage thresholds are set, if any of the supply monitor inputs is below its configured threshold, RST will be a logic low. Once all the monitor inputs rise above their thresholds, an internal timer is started and RST is released after the delay time. If VCC < (V3 – 1.0V) and VCC < 2.4V, the V3 input impedance will be low (10kΩ typical). 4.675V. The threshold is guaranteed to lie in the band between 4.750V and 4.600V over temperature. The powered system must work reliably down to the low end of the threshold band, or risk malfunction before a reset signal is properly issued. Threshold Accuracy Consider a 5V system with ±5% tolerance. The 5V supply may vary between 4.75V to 5.25V. System ICs powered by this supply must operate reliably within this band (and a little more as explained below). A perfectly accurate supervisor for this supply generates a reset at exactly 4.75V, however no supervisor is this perfect. The actual reset threshold of a supervisor varies over a specified band; the LTC2931 varies ±1.5% around its nominal threshold voltage (see Figure 1) over temperature. The reset threshold band and the power supply tolerance bands should not overlap. This prevents false or nuisance resets when the power supply is actually within its specified tolerance band. The LTC2931 has a ±1.5% reset threshold accuracy, so a “5%” threshold is typically set to 6.5% below the nominal input voltage. Therefore, a typical 5V, “5%” threshold is A less accurate supervisor increases the required system voltage margin and increases the probability of system malfunction. The LTC2931 ±1.5% specification improves the reliability of the system over supervisors with wider threshold tolerances. Monitor Configuration Select the LTC2931 input voltage combination by placing the recommended resistive divider from VREF to GND and connecting the tap point to VPG, as shown in Figure 2. Table 1 offers recommended 1% resistor values for each of the 16 modes. The last column in Table 1 specifies optimum VPG/VREF ratios (± 0.01), when configuring with a ratiometric DAC. At power-up, once V1 or V2 reaches 2.4V, the monitor enters a setup period of approximately 150μs. During the setup time, the voltage on the VPG pin is sampled and the monitor is configured to the desired input combinaLTC2931 VREF VPG GND R1 1% R2 1% 2931 F02 Figure 2. Mode Selection 2931fb 9 LTC2931 APPLICATIONS INFORMATION Table 2. Suggested 1% Resistor Values for the ADJ Inputs Table 1. Voltage Threshold Modes* MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ) VPG VREF VSUPPLY (V) VTRIP (V) R3 (kΩ) R4 (kΩ) 12 11.25 2150 100 1780 100 0 5.0 3.3 ADJ ADJ Open Short 0.000 10 9.4 1 5.0 3.3 ADJ –ADJ 93.1 9.53 0.094 8 7.5 1400 100 2 3.3 2.5 ADJ ADJ 86.6 16.2 0.156 7.5 7 1300 100 3 3.3 2.5 ADJ –ADJ 78.7 22.1 0.219 6 5.6 1020 100 4 3.3 2.5 1.5 ADJ 71.5 28.0 0.281 5 4.725 845 100 5 5.0 3.3 2.5 ADJ 66.5 34.8 0.344 3.3 3.055 511 100 6 5.0 3.3 2.5 1.8 59.0 40.2 0.406 3 2.82 464 100 2.325 365 100 7 5.0 3.3 2.5 1.5 53.6 47.5 0.469 2.5 8 5.0 3.0 2.5 ADJ 47.5 53.6 0.531 1.8 1.685 237 100 9 5.0 3.0 ADJ ADJ 40.2 59.0 0.594 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 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 *V5 and V6 are always adjustable (ADJ). tion. The comparators are enabled and supply monitoring begins. Do not add capacitance to the VPG pin. Using The Adjustable Thresholds The reference inputs on the V3 and/or V4 comparators are set to 0.5V when the positive adjustable modes are selected (Figure 3). The reference inputs on the V5 and V6 comparators are always set to 0.5V. The tap point on an external resistive divider, connected between the positive voltage being sensed and ground, is connected to the high VTRIP Table 3. Suggested 1% Resistor Values for the –ADJ Inputs 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 impedance, adjustable inputs (V3, V4, V5, V6). Calculate the trip voltage from: R3 VTRIP = 0.5V • 1+ R4 In the negative adjustable mode, the reference level on the V4 comparator is connected to ground (Figure 4). The tap point on an external resistive divider, connected between LTC2931 R3 1% VREF V3, V4, V5 OR V6 R4 1% R4 1% LTC2931 V4 R3 1% + – 0.5V VTRIP 2931 F03 Figure 3. Setting the Positive Adjustable Trip Point 2931 F04 Figure 4. Setting the Negative Adjustable Trip Point 2931fb 10 LTC2931 APPLICATIONS INFORMATION the negative voltage being sensed and the VREF pin, is connected to the high impedance adjustable input (V4). VREF provides the necessary level shift required to operate at ground. The negative trip voltage is calculated from: VTRIP = –VREF • R3 ; V = 1.210V Nominal R4 REF In a negative adjustable application, the minimum value for R4 is limited by the sourcing capability of VREF (±1mA). With no other load on VREF, R4 (minimum) is: 1.210V =1.210kΩ 1mA Tables 2 and 3 offer suggested 1% resistor values for various positive and negative supply adjustable applications assuming 5% monitor thresholds. Although all six supply monitor comparators have builtin glitch immunity, bypass capacitors on V1 and V2 are recommended because the greater of V1 or V2 is also the VCC for the device. Filter capacitors on the V3, V4, V5 and V6 inputs are allowed. Power-Down On power-down, once any of the monitor inputs drops below its threshold, RST is held at a logic low. A logic low of 0.4V is guaranteed until both V1 and V2 drop below 1V. If the bandgap reference becomes invalid (VCC < 2V typical), the LTC2931 will enter the 150μs setup period when VCC rises above 2.4V max. Watchdog Timer The watchdog circuit monitors a microprocessor’s (μP) 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. Whenever RST is low, the watchdog timer is cleared and WDO is set high. The watchdog timer starts when RST goes high. Subsequent edges received on the WDI pin clear the watchdog timer. The watchdog timer continues to run until it times out. Once it times out, internal circuitry brings the WDO pin low. WDO remains low for one reset timeout period unless it is cleared by another edge on the WDI pin or RST goes low. WDO toggles between high and low as long as the watchdog and reset timers are allowed to time out repeatedly. To disable the watchdog timer, simply ground the CWT pin (Pin 11). With CWT held at ground, any reset event forces WDO high indefinitely. It is safe to leave the WDI pin unconnected because the weak internal pull-up (10μA typical) pulls WDI high. Tying WDI to V1 or ground is also allowed, but grounding the WDI pin forces the pull-up current to be drawn continuously. Selecting the Reset Timing Capacitor The reset timeout period is adjustable in order to accommodate a variety of microprocessor applications. The reset timeout period, tRST, is adjusted by connecting a capacitor, CRT, between the CRT pin and ground. The value of this capacitor is determined by: CRT = tRST = 500 ⎡⎣pF / ms⎤⎦ • tRST 2MΩ Leaving the CRT pin unconnected generates a minimum reset timeout of approximately 25μs. Maximum reset timeout is limited by the largest available low leakage capacitor. The accuracy of the timeout period is affected by capacitor leakage (the nominal charging current is 2μA) and capacitor tolerance. A low leakage ceramic capacitor is recommended. Selecting The Watchdog Timing Capacitor The watchdog timeout period is adjustable and can be optimized for software execution. The watchdog timeout period, tWD, is adjusted by connecting a capacitor, CWT, between the CWT pin and ground. The value of this capacitor is determined by: CWT = tWD = 50 ⎡⎣pF / ms⎤⎦ • tWD 20MΩ Leaving the CWT pin unconnected generates a minimum watchdog timeout of approximately 200μs. Maximum watchdog timeout is limited by the largest available low leakage capacitor. The accuracy of the timeout period is affected by capacitor leakage (the nominal charging current is 2μA) and capacitor tolerance. A low leakage ceramic capacitor is recommended. 2931fb 11 LTC2931 APPLICATIONS INFORMATION Supply and Temperature Monitor Five Supply Power-up Sequencer Figure 5 illustrates how to configure the LTC2931 to monitor temperature. Temperature is sensed by a thermistor, RNTC, as part of a voltage divider driving adjustable input V6. Output COMP6 goes low when the temperature is higher than the trip point, and is fed back through RHYST to provide hysteresis. In Figure 6, the LTC2931’s real-time COMP outputs are used to enable DC/DC converters sequentially. The system is powered by a 12V source. The system is started when the push-button is pressed and the LTC2950-1 brings the RUN pin of the LTM4600 high. Subsequently, the LTM4600 generates a 5V output which applies power to each of the 4 DC/DC converters. Assume a thermistor (RNTC) with values RHOT at the upper threshold and RCOLD at the lower threshold. Minimize errors arising from V6 input current (15nA maximum) by choosing RCOLD ≤ 100kΩ, and to limit the loading on VREF, choose RHOT ≥ 1kΩ. RBIAS and RHYST are calculated from: The LTC2931 is configured to mode 13 (see Table 1). When the threshold is reached on V1, COMP1 pulls high. COMP1 then enables the 3.3V converter first. When the threshold is reached on V2, COMP2 pulls high and enables the 1.8V converter next. When all the converters have been enabled and are good, COMP5 pulls high. RST pulls high 9.4ms after COMP5. Figure 7 shows the power-up sequence of the five supplies and the DONE and RST outputs. RBIAS = (RHOT/VRTA) • (VREF – VRTA) = 1.42 • RHOT RHYST = V1 (RCOLD • RHOT ) • VRTA (RCOLD−RHOT ) If the KILL input on the LTC2950-1 does not receive a logic high within 512ms of initial power-up, EN pulls low and the LTM4600 is powered down. V1 is the nominal operating voltage at input V1, VREF = 1.210V, VRTA = 0.5V, and RPU < RHYST. The closest 1% value was chosen for RHYST. In the event that the external 12V supply drops below 9.6V, COMP6 and RST will pull low. The LTC2950-1 then receives a logic low on the KILL input, which powers down the LTM4600 and the sequencing circuit. In Figure 5, the trip points are 115°C with RHOT = 11.1kΩ (COMP6 goes low) and 100°C with RCOLD = 18.5kΩ (COMP6 goes high). A reset is generated in the event of an over-temperature condition. COMP6 (Temp Good) and COMP5 (Power Good) distinguish over-temperature and undervoltage faults. 5V 10k 0.1μF LTC2931 3.3V 2150k 1% 12V 28V 5110k 1% –5.2V 467k 1% RHYST 280k 1% V1 COMP1 V2 COMP2 V3 COMP3 V5 COMP4 V4 COMP5 121k 1% COMP6 R1 93.1k 1% MANUAL RESET PUSH BUTTON 100k 1% 100k 1% RNTC* 470k R2 9.53k 1% POWER GOOD TEMP GOOD SYSTEM LOGIC WDO WDI V6 VPG GND CRT 10k** 10k RST VREF RBIAS 15.8k 1% RPU 10k *PANASONIC ERTJOEV474J **OPTIONAL FOR ESD PROTECTION CWT CRT 47nF 2931 F05 CWT 47nF tRST = 94ms tWD = 940ms Figure 5. Supply and Temperature Monitor (5V, 3.3V, 28V, -5.2V, 12V, 115°C) 2931fb 12 LTC2931 APPLICATIONS INFORMATION 12V (9.6V THRESHOLD) LTM4600 VIN VOUT 5V 5V RUN VIN VIN LTC2950-1 VIN INT PB LT3028 VOUT 1.8V 1.8V SYSTEM LOGIC LTC3704 VOUT –5.2V VIN 10k –5.2V RUN/UVLO VIN 10k 3.3V SHDN 10k KILL 10k SHDN 10k EN 10k LT3028 VOUT 3.3V LT3028 VOUT 2.5V 2.5V SHDN DONE 12V SUPPLY STATUS COMP1 COMP2 COMP3 COMP4 COMP5 COMP6 2931 F06 V1 10k 0.1μF 365k 1% V2 487k 1% V3 1820k 1% V4 LTC2931 V5 WDO V6 RST 100k 1% 100k 1% 121k 1% VREF R1 16.2k 1% R2 86.6k 1% VPG CRT WDI GND CWT 4.7nF tRST = 9.4ms Figure 6. Five Supply Power-Up Sequencer with Push Button (Watchdog Functions Disabled) 2931fb 13 LTC2931 APPLICATIONS INFORMATION PB 5V 3.3V 2.5V 1.8V 2V/DIV –5.2V DONE RST 10ms/DIV 2931 FO7 Figure 7. Five Supply Power-Up Sequencing (Based on Circuit in Figure 6) 2931fb 14 LTC2931 PACKAGE DESCRIPTION F Package 20-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1650) 6.40 – 6.60* (.252 – .260) 1.05 ±0.10 6.60 ±0.10 20 19 18 17 16 15 14 13 12 11 4.50 ±0.10 0.45 ±0.05 6.40 (.252) BSC 0.65 BSC 1 2 3 4 5 6 7 8 9 10 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50** (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.25 REF 1.10 (.0433) MAX 0° – 8° 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 0.65 (.0256) BSC 0.19 – 0.30 (.0075 – .0118) TYP 0.05 – 0.15 (.002 – .006) F20 TSSOP 0204 3. DRAWING NOT TO SCALE *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE **DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE 2931fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LTC2931 TYPICAL APPLICATION System Reset Generated by Watchdog Timing or Supply Voltage Failure 5V 10k 0.1μF LTC2931 V1 COMP1 3.3V V2 COMP2 2.5V V3 COMP3 1.8V V4 COMP4 V5 COMP5 V6 COMP6 182k 1% 1.5V RESET RST VREF R1 59k 1% 100k 1% POWER GOOD SYSTEM LOGIC WDO VPG CRT 4.7nF R2 40.2k 1% CWT WDI 10 4.7nF tWD = 94ms tRST = 9.4ms GND 2931 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC690 5V Supply Monitor, Watchdog Timer and Battery Backup 4.65 Threshold LTC694-3.3 3.3V Supply Monitor, Watchdog Timer and Battery Backup 2.9V Threshold LTC1232 5V Supply Monitor, Watchdog Timer and Pushbutton Reset 4.37V/4.62V Threshold LTC1326 Micropower Triple Supply Monitor for 5V/2.5V, 3.3V and ADJ 4.725V, 3.118V, 1V Threshold (±0.75%) and ADJ LTC1726 Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Adjustable Reset and Watchdog Timeouts LTC1727 Micropower Triple Supply Monitor with Open-Drain Reset Individual Monitor Outputs in MSOP LTC1728 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package LTC1985 Micropower Triple Supply Monitor with Push-Pull Reset Output 5-Lead SOT-23 Package LTC2900 Programmable Quad Supply Monitor Adjustable Reset, 10-Lead MSOP and DFN Packages LTC2901 Programmable Quad Supply Monitor Adjustable Reset and Watchdog Timer LTC2902 Programmable Quad Supply Monitor Adjustable Reset and Tolerance LTC2903 Precision Quad Supply Monitor 6-Lead SOT-23 Package LTC2904-LTC2907 Three-State Programmable Precision Dual Supply Monitor 8-Lead SOT-23 and DFN Packages LTC2908 Precision Six Supply Monitor (Four Fixed & Two Adjustable) 8-Lead TSOT-23 and DFN Packages LTC2909 Precision Triple/Dual Input UV, OV and Negative Voltage Monitor Shunt Regulated VCC Pin, Adjustable Threshold and Reset, 8-Lead SOT-23 and DFN Packages LTC2910 Precision Octal Positive/Negative Voltage Supply Monitor 16-Lead SSOP and 5mm × 3mm DFN Packages, H-Grade Temperature Range LTC2912-LTC2914 Single/Dual/Quad UV and OV Voltage Monitors Separate VCC Pin, Adjustable Reset Timer, H-Grade Temperature Range LTC2915-LTC2918 Single Supply Monitor with 27 Pin-Selectable Thresholds Manual Reset, Watchdog, TSOT-8/MSOP-10 and 3mm × 2mm DFN Packages, H-Grade Temperature Range LTC2928 Quad Power Supply Sequencer and Supervisor Easily Configure Power Management without Software, 36-Lead 5mm × 7mm QFN and SSOP Packages 2931fb 16 Linear Technology Corporation LT 0508 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 2008