MIC2755 - Micrel

MIC2755
Battery Operated Supervisor
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 can detect 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 non-maskable 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-pin microsmall-outline package.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
• Optimized for PDAs, pagers, and other handheld
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-pin MSOP
Typical Application
Supervised Boost Converter and Microcontroller or Microprocessor
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
May 21, 2015
Revision 2.0
Micrel, Inc.
MIC2755
Ordering Information
Part Number
Junction Temperature Range
Lead Finish
Package
MIC2755YMM
–40°C to +85°C
Pb-Free
8-Pin MSOP
Pin Configuration
8-Pin MSOP (MM)
(Top View)
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 de-asserted.
2
NTH
Non-maskable 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.
6
/NMI
Non-maskable Interrupt (Output). Active-low, open-drain output. Asserted when VPTH < VREF,
which is a “low battery” condition. This indicates high-power 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.
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MIC2755
Absolute Maximum Ratings(1)
Operating Ratings(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(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 (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(4)
VIN = 3.3; TA = 25°C, bold values indicate –40°C≤ TA ≤ +85°C, unless noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
IDD
Operating Supply Current
outputs open, VRTH, VNTH, VPTH > 1.24V
2.0
4.0
µA
outputs open, VRTH, VNTH, VPTH < 1.24V
1.7
µA
IRTH(/MR), INTH,
IPTH, I/RST, I/NMI,
I/POF
Leakage Current
5
pA
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
10
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 5
/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)]
275
V/MRTV
Manual Reset Trip Voltage
310
tDBNC
Debounce Time
V/MRT(min) < VRTH < V/MRTV(max), Note 6
tPROP
Propagation Delay
from (V/MR < VRTH(/MR)(min)–100mV) to RST
Asserted
9
µs
(VREF(max) +100mV) < VNTH < (VREF(min) – 100mV)
9
µs
22
Non–maskable Interrupt Output (/NMI)
tPROP
Propagation Delay
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)
tPROP
Propagation Delay
V/POF
/POF Output Voltage Low
(VREF(max) +100mV) < VPTH < (VREF(min) – 100mV)
9
µs
/POF asserted, ISINK = 1.6mA, VDD ≥ 1.6V
0.3
V
/POF asserted, ISINK = 100µA, VDD ≥ 1.2V
0.4
V
Notes:
1. Exceeding the absolute maximum ratings may damage the device.
2. The device is not guaranteed to function outside its operating ratings.
3. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 100pF in series with 1.5kΩ.
4. Specification for packaged product only.
5. VDD operating range is 1.5V to 5.5V. Output is guaranteed to be held low down to VDD = 1.2V.
6.  =
/
32
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=
/
8
. These relationships are guaranteed by design.
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MIC2755
Timing Diagram
Propagation delays not shown for clarity.
The MIC2755 ignores very brief transients. See “Application Information” for details.
Block Diagram
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MIC2755
Power-Off Output
The /POF 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.
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 lowbattery 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.”
The /POF pin 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. The /POF pin may be pulled up to any voltage not
exceeding V/POF(max) even if this voltage is higher than VDD
(see “Electrical Characteristics”).
Reset Output
The /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. The /RST pin 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. The /RST pin may be pulled up to any voltage not
exceeding V/RST(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.
Non-maskable Interrupt Output
The /NMI pin 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 non-inverting input connected to NTH, and its
output on /NMI. This comparator does not affect any other
MIC2755 functions and may be used independently.
Manual Reset
An internal circuit monitors RTH(/MR), the comparing pin 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.
The /NMI pin 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.
The /NMI pin 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
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:
Applications Information
Output
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.
VBAT(OK) = 3.6V = 1.24V �
R4 = 344KΩ
VBAT(LOW) = 3.1V = 1.24V �
R4 = 56KΩ
Configuration Without Manual Reset
See Figure 1. The battery-OK threshold is calculated
using:
1 + 2 + 3 + 4
�
4
where, for all equations:
1Ω
3+ 4
VBAT(DEAD) = 2.9V = 1.24V �
1 + 2 + 3 + 4
�
3 + 4
R2 = 27.4k
The dead-battery threshold is calculated using:
() = 
�
�
Once R3 and R4 are determined, the equation for
VBAT(DEAD) can be used to determine R2. A single lithiumion 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.
The low-battery threshold is calculated using:
() =  �
4
To determine the resistor values for VBAT(low) threshold, set
R4 = 344kΩ and solve for R3.
Programming Thresholds
There are separate resistive-divider configurations for
circuits that require or do not require manual reset
capability.
() =  �
1Ω
1Ω
�
2+55.6Ω+ 344Ω
R1 = 1MΩ – R2 – R3 – R4 = 572k
1 + 2 + 3 + 4
�
�
3 + 4
Configuration with Manual Reset
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 three-resistor
ladder. See Figure 2.
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.
Figure 2. Example Circuits with Manual Reset
6 + 7
�
7
8 + 9 + 10
() =  �
�
10
8 + 9 + 10
() =  �
�
9 + 10
() =  �
where, for all equations:
VREF = 1.24V
Figure 1. Example Circuit without Manual Reset
Once the desired trip points are determined, set the
VBAT(OK) threshold first.
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MIC2755
Once the desired trip points are determined, set R6 + R7
=1MΩ and solve for R7.
capability can be added as discussed in the Manual Reset
and Configuration with Manual Reset sections.
1Ω
�
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.
The remaining resistor values are solved in a similar
manner as the above.
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 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.
VBAT(fresh) = 3.6V = 1.24V�
R7 = 344kΩ
R7
R6 = 1MΩ – 344k = 656kΩ
1MΩ = R8 + R9 + R10
VBAT(low) =3.1V = 1.24V �
R10 = 400kΩ
1Ω
10
�
1MΩ = R10 + R11
VBAT(dead) =2.9V = 1.24V �
R9 = 27kΩ
1Ω
�
9+400Ω
R8 = 1MΩ – R9 – R10 – = 573kΩ
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 negative
going “glitches.” Very brief transients may cross the
VBAT(LOW) or VBAT(dead) thresholds without tripping the
output(s).
As shown in Figure 3 and Figure 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
configurations beside 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.
Figure 3. Input Transient Response
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
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Figure 4. Input Transient Response
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MIC2755
Supervised Boost Converter and Microcontroller or
Microprocessor
In Figure 7 and Figure 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 Liion 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
Figure 5. Voltage Supervisor and Backup Battery Monitor
Figure 6. Voltage Supervisor with Power Fail Warning
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MIC2755
Typical Application Schematic
Typical Application without Manual Reset
Typical Application with Manual Reset
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MIC2755
Package Information and Recommended Landing Pattern(7)
8-Pin MSOP (MM)
Note:
7. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com.
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MIC2755
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel, Inc. is a leading global manufacturer of IC solutions for the worldwide high performance linear and power, LAN, and timing & communications
markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock
management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company customers
include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products.
Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and
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of distributors and reps worldwide.
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability
whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical
implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
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© 2000 Micrel, Incorporated.
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