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MIC2755
Micrel
MIC2755
Battery System Supervisor Preliminary Information
General Description
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 2A. 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.
Features
* 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 2A 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 MIC2755BMM Junction Temp. Range -40C to +85C Package 8-pin MSOP
Typical Application
VBAT VBAT(OK) = 3.6V VBAT(low) = 3.1V VBAT(dead) = 2.9V 656k 344k 100k 576k MIC2755 26.7k VDD PTH /POF /NMI /NMI /RST Boost or Buck Converter IN EN OUT 100k 100k Controller or Processor SUPPLY
SW
RESET
NTH /RST RTH(/MR) GND 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
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MIC2755
MIC2755
Micrel
Pin Configuration
RTH(/MR) 1 NTH 2 PTH 3 GND 4
8 VDD 7 /RST 6 /NMI 5 /POF
8-Lead MSOP (MM)
Pin Description
Pin Number 1 Pin Name RTH(/MR) Pin Function 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. 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. 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). Ground: Power and signal return for all IC functions. 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. 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. 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). (Analog Input): Power supply input.
2
NTH
3
PTH
4 5
GND /POF
6
/NMI
7
/RST
8
VDD
MIC2755
2
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MIC2755
Micrel
Absolute Maximum Ratings (Note 1)
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) ....................... -65C to +150C ESD Rating, Note 3 ...................................................... 2kV
Operating Ratings (Note 2)
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) ............. -40C to +85C Package Thermal Resistance 1-layer PCB (JA) .............................................. 206C/W 4-layer PCB (JA) .............................................. 113C/W
Electrical Characteristics
Symbol IDD IRTH(/MR), INTH, IPTH, I/RST, I/NMI, I/POF VREF1 VREF2 VHYST Parameter Operating Supply Current Condition
VDD = 3.3V; TA = 25C, bold values indicate -40C TA +85C; unless noted Min Typ 2.0 1.7 5 10 Max 4.0 Units A A pA nA outputs open, VRTH, VNTH, VPTH > 1.24V outputs open, VRTH, VNTH, VPTH < 1.24V Leakage Current
Threshold Voltage Threshold Voltage Hysteresis Voltage on NTH Comparator
for RTH(/MR) and PTH inputs for NTH inputs
1.215 1.215
1.240 1.240 20
1.265 1.265
V V mV
Reset Output (/RST) t/RST t/MR V/RST Reset Pulse Width Manual Reset Pulse Width /RST Output Voltage Low, Note 4 /RST asserted, ISINK = 1.6mA, VDD 1.6V /RST asserted, ISINK = 100A, VDD 1.2V Reset Input [RTH(/MR)] V/MRTV tDBNC tPROP Manual Reset Trip Voltage Debounce Time Propogation Delay V/MRTV(min) < VRTH < V/MRTV(max), Note 5 from (V/MR < VRTH(/MR)(min) - 100mV) to RST Asserted 275 22 9 310 345 38 mV ms s 700 175 1200 300 0.3 0.4 ms ms V V
Nonmaskable Interrupt Output (/NMI) tPROP V/NMI Propagation Delay /NMI Output Voltage Low (VREF(max) + 100mV) < VNTH < (VREF(min) - 100mV) /NMI asserted, ISINK = 1.6mA, VDD 1.6V /NMI asserted, ISINK = 100A, VDD 1.2V Power-Off Output (/POF) tPROP V/POF Propagation Delay /POF Output Voltage Low (VREF(max) + 100mV) < VPTH < (VREF(min) - 100mV) /POF asserted, ISINK = 1.6mA, VDD 1.6V /POF asserted, ISINK = 100A, VDD 1.2V
Note 1. Note 2. Note 3. Note 4. Note 5. Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model, 100pF in series with 1.5k . VDD operating range is 1.5V to 5.5V. Output is guaranteed to be held low down to VDD = 1.2V.
9 0.3 0.4
s V V s 0.3 0.4 V V
9
tDBNC =
t /RST 32
=
t /MR . These relationships are guaranteed by design. 8
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MIC2755
MIC2755
Micrel
Timing Diagram
VRTH VNTH VBAT V PTH
NOT TO SCALE.
20mV
0V V/MR V/RST V/NMI V/POF V/MRH V/MRL V/RSTH V/RSTL V/NMIH V/NMIL V/POFH V/POFL
Propagation delays not shown for clarity.
VBAT EXPANDED VERTICALLY TO SHOW DETAIL.
>tDBNC t/MR
tRST
tRST
The MIC2755 ignores very brief transients. See "Application Information" for details.
Block Diagram
VDD
NTH 20mV Hysteresis 1.24V Ref2
/NMI
/RST
PTH Logic-State Machine
RTH(/MR)
/POF
310mV
GND
MIC2755
4
Oscillator
1.24V Ref1
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 C or P, 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").
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MIC2755
MIC2755
Micrel
To determine the resistor values for VBAT(low) threshold, set R4 = 344k 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 R1 + R2 + R3 + R4 R4
1M 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.
1M VBAT(dead) = 2.9V = 1.24V R2 + 55.6k + 344k
R2 = 27.4k R1 = 1M - 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.
VBAT R6 656k R7 344k SW R10 400k R8 573k R9 26.7k 100k 100k 100k MIC2755 VDD PTH NTH RTH(/MR) /POF /NMI /RST GND POF NMI RST VBAT
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 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 1M 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 3M.
VBAT R1 572k R2 28k R3 55.6k R4 344k MIC2755 VDD /POF POF NMI RST PTH /NMI NTH /RST RTH(/MR) GND 100k 100k 100k VBAT
Figure 2. Example Circuit with Manual Reset R6 + R7 VBAT(OK) = VREF R7 R8 + R9 + R10 VBAT(low) = VREF R10 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 = 1M and solve for R7.
Figure 1. Example Circuit without Manual Reset 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:
1M VBAT(fresh) = 3.6V = 1.24V R7
R7 = 344k R6 = 1M - 344k = 656k The remaining resistor values are solved in a similar manner as the above. 1M = R8 + R9 + R10
1M VBAT(OK) = 3.6V = 1.24V R4
R4 = 344k MIC2755 6
February 2000
MIC2755
1M VBAT(low) = 3.1V = 1.24V R10
R10 = 400k 1M = R10+R11
Input Transient Response (VPOF)
Micrel
MAX. TRANSIENT DURATION (s)
200 180 160 140 120 100 80 60 40 20 0
1M VBAT(dead) = 2.9V = 1.24V R9 + 400k
R9 = 27k R8 = 1M - 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
0
5
10
15
20
25
30
RESET COMP. OVERDRIVE, VREF-VPTH (mV)
Figure 3. Input Transient Response
Input Transient Response (VNMI)
MAX. TRANSIENT DURATION (s)
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.
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MIC2755
MIC2755
Backup Power VMAIN R1 1.77M R4 436k R5 564k R2 13.2k RPULLUP MIC2755 VDD PTH NTH RTH(/MR) /POF /NMI /RST GND EN GND RPULLUP RPULLUP Power Fail Warning Flag System Reset MIC5205-3.3 IN OUT 3.3V Power Rail Lithium Coin Cell R3 1.21M
MIC2755
Figure 5. Voltage Supervisor and Backup Battery Monitor
8
VBAT R4 651k R5 349k R1 1.77M R2 13.2k RPULLUP MIC2755 VDD PTH NTH RTH(/MR) /POF /NMI /RST GND EN GND RPULLUP RPULLUP Power Fail Warning Flag System Reset MIC5245-3.3 IN OUT 3.3V Power Rail R3 1.21M
Figure 6. Voltage Supervisor With Power Fail Warning
February 2000
Micrel
February 2000 9
SW
MIC2755
VBAT(OK) = 3.6V VBAT(low) = 3.1V VBAT(dead) = 2.9V R1 569k Li-Ion Cell R2 28k R3 55.6k R4 344k
8 3 2 1
L1a 33H C1 10F 16V MIC3172 IN EN COMP SW FB
C7 10F 16V
3.3V @ 200mA
Controller or Processor SUPPLY C4 0.1F R10 3.01k R11 1.82k
MIC2755 VDD /POF PTH /NMI NTH /RST RTH(/MR) GND
R6 100k
5 6 7 4
L1b 33H
C2 220F 10V
C3 220F 10V
R9 R8 100k 100k NMI RST
R7 4.75k C5 0.01F
SGND PGND1 PGND2 C6 3300pF
GND
Figure 7. Typical Application Without Manual Reset
VBAT(OK) = 3.6V VBAT(low) = 3.1V VBAT(dead) = 2.9V C1 10F 16V
L1a 33H R7 100k
5 6 7 4
C2 10F 16V
3.3V @ 200mA
Controller or Processor SUPPLY C5 0.1F R11 3.01k R12 1.82k
R4 656k Li-Ion Cell R5 344k
R1 576k R2 26.7k
8 3 2 1
MIC3172 IN EN COMP SW FB
MIC2755 VDD /POF PTH /NMI NTH /RST RTH(/MR) GND
L1b 33H
C3 220F 10V
C4 220F 10V
R9 R10 100k 100k NMI RST
R3 400k
R8 4.75k C5 0.01F
SGND PGND1 PGND2 C6 3300pF
GND
Figure 8. Typical Application With Manual Reset
MIC2755
Micrel
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
0.007 (0.18) 0.005 (0.13)
0.012 (0.03) 0.0256 (0.65) TYP
0.008 (0.20) 0.004 (0.10)
5 MAX 0 MIN
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
Micrel
February 2000
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MIC2755
MIC2755
Micrel
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
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. (c) 2000 Micrel Incorporated
MIC2755
12
February 2000

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