MIC2755
Battery Operated Supervisor
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 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 micro-
small-outline package.
Datasheets and support documentation are available on
Micrel’s web site at:
www.micrel.com.
Features
•
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
MIC2755YMM
Junction Temperature Range
–40°C to +85°C
Lead Finish
Pb-Free
Package
8-Pin MSOP
Pin Configuration
8-Pin MSOP (MM)
(Top View)
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 V
REF
, the reset generator cycles. The /RST
output is held low for a minimum of 700ms and the /POF threshold output is de-asserted.
Non-maskable Interrupt Threshold (Analog Input). Voltage monitor input assigned to “low battery”
condition detection. When the level on this pin falls below V
REF
, 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 (V
RTH
> V
REF
).
Ground. Power and signal return for all IC functions.
Power-Off (Output). Active-low, open-drain output. Asserted and latched when V
PTH
< V
REF
, which
is a “dead battery” condition.
Non-maskable Interrupt (Output). Active-low, open-drain output. Asserted when V
PTH
< V
REF
,
which is a “low battery” condition. This indicates high-power system operation should not be
allowed.
Reset (Output). Active-low, open-drain output. Asserted for a minimum of 700ms at power-on or
anytime V
PTH
drops below V
REF
. Also asserted for 175ms minimum when RTH (/MR) is externally
pulled low (manual reset).
Analog Input. Power supply input.
2
NTH
3
4
5
PTH
GND
/POF
6
/NMI
7
8
/RST
VDD
May 21, 2015
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Revision 2.0
Micrel, Inc.
MIC2755
Absolute Maximum Ratings
(1)
Supply Voltage (V
DD
) ....................................... –0.3V to +7V
Input Voltage (V
RTH
, V
NTH,
V
PTH
) ....................... –0.3V to +7V
Output Voltage (V
/RST
, V
/NMI,
V
/POF
) .................. –0.3V to +7V
/RST Output Current (I
/RST
) ......................................... 20mA
Storage Temperature (T
S
) ........................... –65°C to 150°C
ESD Rating
(3)
.................................................................. 2kV
Operating Ratings
(2)
Supply Voltage (V
DD
) .................................... +1.5V to +5.5V
Input Voltage (V
RTH
, V
NTH,
V
PTH
) ....................... –0.3V to +6V
Output Voltage (V
/RST
, V
/NMI,
V
/POF
) .................. –0.3V to +6V
Ambient Temperature (T
A
) .......................... –40°C to +85°C
Package Thermal Resistance
1-layer PCB (θ
JA
) ............................................. 206°C/W
4-layer PCB (θ
JA
) ............................................. 113°C/W
Electrical Characteristics
(4)
V
IN
= 3.3; T
A
= 25°C,
bold
values indicate –40°C≤ T
A
≤ +85°C, unless noted.
Symbol
I
DD
I
RTH(/MR)
, I
NTH
,
I
PTH
, I
/RST
, I
/NMI
,
I
/POF
V
REF1
V
REF2
V
HYST
Parameter
Operating Supply Current
Condition
outputs open, V
RTH
, V
NTH
, V
PTH
> 1.24V
outputs open, V
RTH
, V
NTH
, V
PTH
< 1.24V
Min.
Typ.
2.0
1.7
5
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
10
1.265
1.265
Max.
4.0
Units
µA
µA
pA
nA
V
V
mV
Reset Output (/RST)
t
/RST
t
/MR
V
/RST
Reset Pulse Width
Manual Reset Pulse Width
/RST Output Voltage Low,
Note 5
/RST asserted, I
SINK
= 1.6mA, V
DD
≥ 1.6V
/RST asserted, I
SINK
= 100µA, V
DD
≥ 1.2V
275
V
/MRT(min)
< V
RTH
< V
/MRTV(max)
,
Note 6
from (V
/MR
< V
RTH(/MR)(min)–
100mV) to RST
Asserted
22
9
310
700
175
1200
300
0.3
0.4
ms
ms
V
V
Reset Input [RTH(/MR)]
V
/MRTV
t
DBNC
t
PROP
Manual Reset Trip Voltage
Debounce Time
Propagation Delay
345
38
mV
ms
µs
Non–maskable Interrupt Output (/NMI)
t
PROP
V
/NMI
Propagation Delay
/NMI Output Voltage Low
(V
REF(max)
+100mV) < V
NTH
< (V
REF(min)
– 100mV)
/NMI asserted, I
SINK
= 1.6mA, V
DD
≥ 1.6V
/NMI asserted, I
SINK
= 100µA, V
DD
≥ 1.2V
(V
REF(max)
+100mV) < V
PTH
< (V
REF(min)
– 100mV)
/POF asserted, I
SINK
= 1.6mA, V
DD
≥ 1.6V
/POF asserted, I
SINK
= 100µA, V
DD
≥ 1.2V
9
0.3
0.4
9
0.3
0.4
µs
V
V
Power–Off Output (/POF)
t
PROP
V
/POF
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.
6.
=
5. V
DD
operating range is 1.5V to 5.5V. Output is guaranteed to be held low down to V
DD
= 1.2V.
32
8
/
Propagation Delay
/POF Output Voltage Low
µs
V
V
=
/
. These relationships are guaranteed by design.
May 21, 2015
3
Revision 2.0
Micrel, Inc.
MIC2755
Timing Diagram
Propagation delays not shown for clarity.
The MIC2755 ignores very brief transients. See “Application Information” for details.
Block Diagram
May 21, 2015
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Revision 2.0
Micrel, Inc.
MIC2755
Power-Off Output
The /POF output and the /RST output are asserted and
latched when V
PTH
< V
REF
, 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, V
RTH
> V
REF1
. 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.
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”).
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 V
REF1
. 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 V
PTH
drops below V
REF1
, the /POF and /RST outputs are
asserted and latched, holding the system in its reset state.
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 V
PTH
is still above V
REF1
, 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 t
DBNC
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
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”).
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, V
REF2
. This output is asserted when
V
NTH
< V
REF2
, 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,
V
REF2
, 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.
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”).
May 21, 2015
5
Revision 2.0
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