MIC2755 Micrel MIC2755 Battery System Supervisor Preliminary Information General Description Features The MIC2755 is composed of multiple comparators, a reset pulse generator, and logic. It is designed for monitoring the battery supply of portable digital systems, including PDAs and pagers. The MIC2755 detects three different battery states: battery OK, low battery, and dead battery. The reset (/RST) output is asserted for at least 700ms when a fresh battery is inserted. The nonmaskable interrupt output (/NMI) is asserted when the battery voltage is below the NTH threshold, indicating that high-power system operations should not occur. If and when battery voltage falls below the power-off threshold (PTH), the reset output is asserted and latched, inhibiting system operation until the battery is replaced or recharged. All three voltage thresholds are set using external resistors. A manual reset function can be implemented by connecting a switch directly to the power on reset/manual reset [RTH(/MR)] input. Internal circuitry detects switch activation and generates a minimum 175ms debounced reset signal. The MIC2755’s power supply input is separate from the detector inputs to allow it to be powered from a down-stream voltage, such as the output of a boost converter. Inputs and outputs can be pulled above VDD (up to 7V absolute maximum) without adverse effects or excessive current draw. Supply current is typically a low 2µA. Hysteresis is included on all voltage detectors to prevent chattering due to noise. The MIC2755 is available in the tiny 8-lead micro-smalloutline package. • Optimized for PDAs, pagers and other hand-held devices. • Detects multiple battery states: - battery OK - low battery - dead battery • Adjustable voltage thresholds • High accuracy ±2% voltage thresholds • Reset generation at power-on (700ms min.) • Debounced manual reset function • Internal logic prevents chatter if battery voltage fluctuates • Extremely low 2µA typical supply current • I/Os can be pulled above VDD (7V absolute maximum) • Immune to brief power supply transients • Low cost • 8-lead MSOP Applications • • • • • • PDAs Pagers Consumer electronics Embedded controllers Portable instruments Data loggers Ordering Information Part Number Junction Temp. Range Package MIC2755BMM –40°C to +85°C 8-pin MSOP Typical Application Boost or Buck Converter VBAT VBAT(OK) = 3.6V VBAT(low) = 3.1V VBAT(dead) = 2.9V 656k 344k IN 100k OUT SUPPLY 100k 100k 576k MIC2755 26.7k VDD PTH /POF /NMI NTH /RST RTH(/MR) GND SW RESET EN µController or µProcessor /NMI /RST 400k GND Supervised Boost Converter and Microcontroller or Microprocessor Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com February 2000 1 MIC2755 MIC2755 Micrel Pin Configuration RTH(/MR) 1 8 VDD NTH 2 7 /RST PTH 3 6 /NMI GND 4 5 /POF 8-Lead MSOP (MM) Pin Description Pin Number Pin Name Pin Function 1 RTH(/MR) Power-On Reset Threshold (Analog Input): Comparator input assigned to battery-OK condition detection. When the level on this pin first exceeds VREF, the reset generator cycles. The /RST output is held low for a minimum of 700ms and the /POF threshold output is deasserted. 2 NTH Nonmaskable Interrupt Threshold (Analog Input): Voltage monitor input assigned to “low battery” condition detection. When the level on this pin falls below VREF, the /NMI output is asserted. 3 PTH Power-Off Threshold (Analog Input): Voltage monitor input assigned to “dead battery” condition detection. When the level on this pin falls below VREF, the /RST and /POF outputs are asserted. The condition is latched until a reset cycle occurs (VRTH > VREF). 4 GND Ground: Power and signal return for all IC functions. 5 /POF Power-off (Output): Active-low, open-drain output. Asserted and latched when VPTH < VREF, which is a “dead battery” condition. The system is held in reset until the battery is replaced and a power-on reset cycle occurs. 6 /NMI Nonmaskable Interrupt (Output): Active-low, open-drain output. Asserted when VNTH < VREF, which is a “low battery” condition. This indicates highpower system operation should not be allowed. 7 /RST Reset (Output): Active-low, open-drain output. Asserted for a minimum of 700ms at power-on or anytime VPTH drops below VREF. Also asserted for 175ms minimum when RTH (/MR) is externally pulled low (manual reset). 8 VDD (Analog Input): Power supply input. MIC2755 2 February 2000 MIC2755 Micrel Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) Supply Voltage (VDD) ..................................... –0.3V to +7V Input Voltage (VRTH), (VNTH), (VPTH) ............. –0.3V to +7V Output Voltage (V/RST), (V/NMI), (V/POF) ........ –0.3V to +7V /RST Output Current (I/RST) ....................................... 20mA Storage Temperature (TS) ....................... –65°C to +150°C ESD Rating, Note 3 ...................................................... 2kV Supply Voltage (VDD) .................................. +1.5V to +5.5V Input Voltage (VRTH), (VNTH), (VPTH) ............. –0.3V to +6V Output Voltage (V/RST), (V/NMI), (V/POF) ........ –0.3V to +6V Ambient Temperature Range (TA) ............. –40°C to +85°C Package Thermal Resistance 1-layer PCB (θJA) .............................................. 206°C/W 4-layer PCB (θJA) .............................................. 113°C/W Electrical Characteristics VDD = 3.3V; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted Symbol Parameter Condition IDD Operating Supply Current Min Typ Max Units outputs open, VRTH, VNTH, VPTH > 1.24V 2.0 4.0 µA outputs open, VRTH, VNTH, VPTH < 1.24V 1.7 IRTH(/MR), INTH, IPTH, I/RST, I/NMI, I/POF Leakage Current VREF1 Threshold Voltage for RTH(/MR) and PTH inputs 1.215 VREF2 Threshold Voltage for NTH inputs 1.215 VHYST Hysteresis Voltage on NTH Comparator µA 5 10 pA nA 1.240 1.265 V 1.240 1.265 V 20 mV Reset Output (/RST) t/RST Reset Pulse Width 700 1200 ms t/MR Manual Reset Pulse Width 175 300 ms V/RST /RST Output Voltage Low, Note 4 /RST asserted, ISINK = 1.6mA, VDD ≥ 1.6V 0.3 V /RST asserted, ISINK = 100µA, VDD ≥ 1.2V 0.4 V 345 mV 38 ms Reset Input [RTH(/MR)] V/MRTV Manual Reset Trip Voltage 275 310 tDBNC Debounce Time V/MRTV(min) < VRTH < V/MRTV(max), Note 5 tPROP Propogation Delay from (V/MR < VRTH(/MR)(min) – 100mV) to RST Asserted 9 µs 9 µs 22 Nonmaskable Interrupt Output (/NMI) tPROP Propagation Delay (VREF(max) + 100mV) < VNTH < (VREF(min) – 100mV) V/NMI /NMI Output Voltage Low /NMI asserted, ISINK = 1.6mA, VDD ≥ 1.6V 0.3 V /NMI asserted, ISINK = 100µA, VDD ≥ 1.2V 0.4 V Power-Off Output (/POF) µs tPROP Propagation Delay (VREF(max) + 100mV) < VPTH < (VREF(min) – 100mV) V/POF /POF Output Voltage Low /POF asserted, ISINK = 1.6mA, VDD ≥ 1.6V 0.3 V /POF asserted, ISINK = 100µA, VDD ≥ 1.2V 0.4 V Note 1. Exceeding the absolute maximum rating may damage the device. Note 2. The device is not guaranteed to function outside its operating rating. Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 100pF in series with 1.5k . Note 4. VDD operating range is 1.5V to 5.5V. Output is guaranteed to be held low down to VDD = 1.2V. Note 5. tDBNC = February 2000 t /RST 32 = 9 t /MR . These relationships are guaranteed by design. 8 3 MIC2755 MIC2755 Micrel Timing Diagram NOT TO SCALE. VRTH VNTH VBAT V PTH 20mV VBAT EXPANDED VERTICALLY TO SHOW DETAIL. 0V V/MR V/MRH V/MRL V/RST V/RSTH V/RSTL V/NMI V/POF <tDBNC tRST tRST >tDBNC t/MR V/NMIH V/NMIL V/POFH V/POFL Propagation delays not shown for clarity. The MIC2755 ignores very brief transients. See “Application Information” for details. Block Diagram VDD NTH /NMI 20mV Hysteresis 1.24V Ref2 /RST Logic-State Machine PTH RTH(/MR) /POF 310mV Oscillator 1.24V Ref1 GND MIC2755 4 February 2000 MIC2755 Micrel Power-Off Output This output and the /RST output are asserted and latched when VPTH < VREF, indicating a “dead battery.” The system is held in reset until the battery is replaced or recharged and a power-on reset cycle occurs; that is, VRTH > VREF1. The /POF output may be used to control a linear or switching regulator, shutting down the regulator when the battery reaches it end-of-life voltage. /POF is an active-low, open-drain digital output and may be wire-ORed with other open-drain logic signals. Most applications will require a pull-up resistor on this output. /POF may be pulled up to any voltage not exceeding V/POF(max) even if this voltage is higher than VDD (see “Electrical Characteristics”). Power-On Reset The RTH(/MR) and PTH inputs work together to provide predictable battery monitoring with user-programmable hysteresis and without chatter. The /RST output is asserted for a minimum of 700ms at power-on. Power-on is determined by RTH(/MR) exceeding VREF1. Once this event has occurred, the internal logic ignores further transitions on the RTH(/MR) input, instead monitoring for a low voltage on PTH or the manual reset condition. If VPTH drops below VREF1, the /POF and /RST outputs are asserted and latched, holding the system in its reset state. Manual Reset An internal circuit monitors RTH(/MR), comparing it to an internal 310mV reference, V/MRTV. When RTH(/MR) is pulled below V/MRTV, and VPTH is still above VREF1, the internal circuitry initiates a manual reset cycle and asserts /RST for at least 175ms. A momentary push-button switch is typically connected such that RTH(/MR) is forced to ground when the switch contacts close. This switch is internally debounced. Each closure of the switch longer than tDBNC results in a single output pulse of no less than 175ms and no more than 300ms being generated. (The manual reset pulse is derived from the same oscillator and counter as t/RST. The length of t/MR is always equal to one fourth of t/RST.) This prevents a user who may hold the switch closed from keeping the system in reset for an extended period of time. Functional Description Typically the MIC2755 is used to monitor the battery supply of intelligent circuits such as microcontrollers and microprocessors. By connecting the reset output of a MIC2755 to the reset input of a µC or µP, the processor will be properly reset at power-on and during power-down and low battery conditions. The /NMI output provides low-battery warnings to the system. In addition, a system whose battery voltage declines below the PTH threshold is held in reset to prevent spurious operation. Thus the MIC2755 effectively detects three battery states: “battery OK,” “low battery,” and “dead battery.” Reset Output /RST is an active-low, open-drain digital output. This output is asserted for a minimum of 700ms at power-on and for a minimum of 175ms when RTH(/MR) is externally pulled low, indicating that a manual reset should be initiated. /RST is an active-low, open-drain digital output and may be wire-ORed with other open-drain logic signals. Most applications will require a pull-up resistor on this pin. /RST may be pulled up to any voltage not exceeding V/RST(max) even if this voltage is higher than VDD (see “Electrical Characteristics”). Nonmaskable Interrupt Output /NMI is the output of a comparator that constantly compares the level on the NTH pin with the internal voltage reference, VREF2. This output is asserted when VNTH < VREF2, indicating high-power system operation should not occur; that is, the battery is low but not dead. Effectively, this function is an uncommitted comparator with its inverting input connected to the internal reference, VREF2, its noninverting input connected to NTH, and its output on /NMI. This comparator does not affect any other MIC2755 functions and may be used independently. /NMI is an active-low, open-drain digital output and may be wire-ORed with other open-drain logic signals. Most applications will require a pull-up resistor on this pin. /NMI may be pulled up to any voltage not exceeding V/NMI(max) even if this voltage is higher than VDD (see “Electrical Characteristics”). February 2000 5 MIC2755 MIC2755 Micrel To determine the resistor values for VBAT(low) threshold, set R4 = 344kΩ and solve for R3. Applications Information Outputs Since the MIC2755 outputs are open-drain MOSFETs, most applications will require pull-up resistors. The value of the resistors should not be too large or leakage effects may dominate. Programming Thresholds There are separate resistive-divider configurations for circuits that require or do not require manual reset capability. Configuration Without Manual Reset See Figure 1. The battery-OK threshold is calculated using: VBAT(OK) = VREF 1MΩ VBAT(low) = 3.1V = 1.24V R3 + R4 R3 = 56k Once R3 and R4 are determined, the equation for VBAT(dead) can be used to determine R2. A single lithium-ion cell should not be discharged below 2.5V. Many applications limit the drain to 2.9V. Using 2.9V for the VBAT(dead) threshold allows calculating the following resistor values. 1MΩ VBAT(dead) = 2.9V = 1.24V R2 + 55.6k + 344k R1 + R2 + R3 + R4 R4 R2 = 27.4k R1 = 1MΩ – R2 – R3 – R4 = 572k Configuration With Manual Reset See Figure 2. To use manual reset, the MIC2755 requires a separate resistor ladder for the switch and fresh-battery threshold. The remaining two thresholds are set by the threeresistor ladder. The low-battery threshold is calculated using: R1 + R2 + R3 + R4 VBAT(low) = VREF R3 + R4 The dead-battery threshold is calculated using: R1 + R2 + R3 + R4 VBAT(dead) = VREF R2 + R3 + R4 VBAT where, for all equations: VREF = 1.24V In order to provide the additional criteria needed to solve for the resistor values, the resistors can be selected such that they have a given total value, that is, R1 + R2 + R3 + R4 = Rtotal. A value such as 1MΩ for Rtotal is a reasonable value because it draws minimum battery current per resistor ladder but has no significant effect on system accuracy. When working with large resistors, a small amount of leakage current can cause voltage offsets that degrade system accuracy. The maximum recommended total resistance from VBAT to ground is 3MΩ. VBAT R2 28k R3 55.6k R6 656k R8 573k R7 344k R9 26.7k SW 100k 100k 100k MIC2755 VDD PTH NTH RTH(/MR) /POF /NMI /RST GND POF NMI RST R10 400k Figure 2. Example Circuit with Manual Reset R6 + R7 VBAT(OK) = VREF R7 VBAT R1 572k VBAT R8 + R9 + R10 VBAT(low) = VREF R10 100k 100k 100k MIC2755 VDD /POF POF PTH /NMI NTH /RST RTH(/MR) GND NMI RST R8 + R9 + R10 VBAT(dead) = VREF R9 + R10 where, for all equations: VREF = 1.24V Once the desired trip points are determined, set R6 + R7 = 1MΩ and solve for R7. R4 344k Figure 1. Example Circuit without Manual Reset 1MΩ VBAT(fresh) = 3.6V = 1.24V R7 Once the desired trip points are determined, set the VBAT(OK) threshold first. For a typical single-cell lithium ion battery, 3.6V is a reasonable “OK threshold” because at 3.6V the battery is moderately charged. Solving for R4: R7 = 344k R6 = 1MΩ – 344k = 656k The remaining resistor values are solved in a similar manner as the above. 1MΩ = R8 + R9 + R10 1MΩ VBAT(OK) = 3.6V = 1.24V R4 R4 = 344kΩ MIC2755 6 February 2000 MIC2755 Micrel MAX. TRANSIENT DURATION (µs) 1MΩ VBAT(low) = 3.1V = 1.24V R10 R10 = 400k 1MΩ = R10+R11 1MΩ VBAT(dead) = 2.9V = 1.24V R9 + 400k R9 = 27k R8 = 1MΩ – R9 – R10 = 573k The accuracy of the resistors can be chosen based upon the accuracy required by the system. Input Transients The MIC2755 is inherently immune to very short negativegoing “glitches.” Very brief transients may cross the VBAT(lo) or VBAT(dead) thresholds without tripping the output(s). As shown in Figures 3 and 4, the narrower the transient, the deeper the threshold overdrive that will be ignored by the MIC2755. The graph represents the typical allowable transient duration for a given amount of threshold overdrive that will not cause the corresponding output to change state. Alternate Configurations The MIC2755 can be used in a variety of ways. It is especially flexible due to the fact that the NMI comparator is completely independent. There are other useful configuration besides a three-state battery monitor. The NMI comparator can be used to provide power-fail indication (PFI/PFI), monitor an auxiliary battery (LBI/LBO), or detect the presence of an ac adapter. Voltage Supervisor and Backup Battery Monitor Figure 5 illustrates the MIC2755 being used as a voltage supervisor and a battery monitor in a 3.3V system with a Lithium coin-cell backup. The primary voltage monitor is configured as a voltage supervisor with a nominal trip point of 3.034V and 33mV of hysteresis as set by R1, R2, and R3. The NMI comparator is used to detect a low-battery condition so the system is aware that the backup battery is discharged. In this example, the /NMI output will be asserted if battery voltage falls below 2.2V. Manual reset capability can be added as discussed in the Manual Reset and Configuration With Manual Reset sections. This same configuration can be used to detect the presence of an auxiliary power source such as an ac adapter instead of monitoring a battery. R4 and R5 would be selected such that the /NMI output is deasserted when the proper input voltage is applied. Voltage Supervisor with Power Fail Warning Figure 6 illustrates the MIC2755 being used as a voltage supervisor and a power-fail detector in a 3.3V system. The primary voltage monitor is configured as a voltage supervisor February 2000 Input Transient Response (VPOF) 200 180 160 140 120 100 80 60 40 20 0 0 5 10 15 20 25 30 RESET COMP. OVERDRIVE, VREF–VPTH (mV) MAX. TRANSIENT DURATION (µs) Figure 3. Input Transient Response Input Transient Response (VNMI) 120 100 80 60 40 20 0 0 5 10 15 20 25 30 35 40 45 RESET COMP. OVERDRIVE, VREF–VNTH (mV) Figure 4. Input Transient Response with a nominal trip point of 3.034V and 33mV of hysteresis as set by R1, R2, and R3. The NMI comparator is used to detect an impending power failure such as a low-battery condition or ac power outage. The /NMI output will be asserted if the input voltage to the LDO regulator falls below 3.55V. (The MIC5245 has a specified maximum dropout of 250mV at 150mA output current. If the input voltage falls below 3.55V, the output may droop.) By monitoring the input of the LDO regulator, the system receives the earliest warning of an impending power loss. Manual reset capability can be added as discussed in the Manual Reset and Configuration With Manual Reset sections. Supervised Boost Converter and Microcontroller or Microprocessor In Figures 7 and 8, the MIC2755 is used to monitor the battery and the MIC3172 is used to maintain the output voltage at 3.3V by boosting the input voltage. When the Li-ion battery voltage drops to 3.1V, the MIC2755 alerts the microcontroller or the microprocessor. When the battery voltage drops to 2.9V, the MIC2755 turns off the MIC3172. 7 MIC2755 MIC2755 MIC2755 Backup Power R1 1.77M R4 436k Lithium Coin Cell 3.3V Power Rail MIC5205-3.3 VMAIN R5 564k R2 13.2k IN OUT EN GND RPULLUP MIC2755 VDD PTH NTH RTH(/MR) RPULLUP RPULLUP Power Fail Warning Flag /POF /NMI /RST System Reset GND R3 1.21M Figure 5. Voltage Supervisor and Backup Battery Monitor 8 3.3V Power Rail MIC5245-3.3 VBAT R4 651k R1 1.77M R5 349k R2 13.2k R3 1.21M IN OUT EN GND RPULLUP MIC2755 VDD PTH NTH RTH(/MR) /POF /NMI /RST GND RPULLUP RPULLUP Power Fail Warning Flag System Reset Micrel February 2000 Figure 6. Voltage Supervisor With Power Fail Warning MIC2755 February 2000 VBAT(OK) = 3.6V VBAT(low) = 3.1V VBAT(dead) = 2.9V L1a 33µH R1 569k Li-Ion Cell R2 28k 8 3 R3 55.6k 2 1 MIC2755 VDD /POF PTH /NMI NTH /RST RTH(/MR) GND C1 10µF 16V R6 100k 5 6 7 R7 4.75k C5 0.01µF 4 R4 344k 3.3V @ 200mA MIC3172 IN EN COMP µController or µProcessor C7 10µF 16V L1b 33µH SW C2 220µF 10V C3 220µF 10V SUPPLY C4 0.1µF R10 3.01k R9 R8 100k 100k NMI RST FB R11 1.82k SGND PGND1 PGND2 C6 3300pF GND Figure 7. Typical Application Without Manual Reset 9 VBAT(OK) = 3.6V VBAT(low) = 3.1V VBAT(dead) = 2.9V Li-Ion Cell R4 656k R1 576k R5 344k R2 26.7k L1a 33µH 8 3 2 1 SW R3 400k MIC2755 VDD /POF PTH /NMI NTH /RST RTH(/MR) GND R7 100k C1 10µF 16V 5 6 7 4 R8 4.75k C5 0.01µF 3.3V @ 200mA MIC3172 IN EN COMP µController or µProcessor C2 10µF 16V SW L1b 33µH C3 220µF 10V C4 220µF 10V SUPPLY C5 0.1µF R11 3.01k FB SGND PGND1 PGND2 R9 R10 100k 100k NMI RST R12 1.82k C6 3300pF GND Figure 8. Typical Application With Manual Reset Micrel MIC2755 MIC2755 Micrel Package Information 0.122 (3.10) 0.112 (2.84) 0.199 (5.05) 0.187 (4.74) DIMENSIONS: INCH (MM) 0.120 (3.05) 0.116 (2.95) 0.036 (0.90) 0.032 (0.81) 0.043 (1.09) 0.038 (0.97) 0.012 (0.30) R 0.012 (0.03) 0.0256 (0.65) TYP 0.008 (0.20) 0.004 (0.10) 5° MAX 0° MIN 0.007 (0.18) 0.005 (0.13) 0.012 (0.03) R 0.039 (0.99) 0.035 (0.89) 0.021 (0.53) 8-Lead MSOP (MM) MIC2755 10 February 2000 MIC2755 February 2000 Micrel 11 MIC2755 MIC2755 Micrel MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB USA http://www.micrel.com This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. © 2000 Micrel Incorporated MIC2755 12 February 2000