19-4633; 5/09
DS2756
High-Accuracy Battery Fuel Gauge
with Programmable Suspend Mode
www.maxim-ic.com
GENERAL DESCRIPTION
The DS2756 high-precision battery fuel gauge is a
data-acquisition and information-storage device
tailored for cost-sensitive and space-constrained 1-
cell Li+/polymer battery-pack applications. The
DS2756 provides the key hardware components
required to accurately estimate remaining capacity by
integrating low-power, precision measurements of
temperature,
voltage,
current,
and
current
accumulation, as well as nonvolatile (NV) data
storage, into the small footprint of a 3.0mm x 4.4mm
8-pin TSSOP package.
Through its 1-Wire interface, the DS2756 gives the
host system read/write access to status and control
registers, instrumentation registers, and general-
purpose data storage. Each device has a unique
factory-programmed 64-bit net address that allows it
to be individually addressed by the host system,
supporting multibattery operation.
FEATURES
Programmable Suspend Mode
Accurate Current Accumulation
-
2% ±4V over ±64mV Input Range
-
2% ±200A over ±3.2A with 20m Sense
Current Measurement
-
9-Bit Snapshot Measurement
-
12-Bit Average Updated Every 88ms
-
15-Bit Average Updated Every 2.8s
Voltage Measurement
-
9-Bit Snapshot Measurement
-
10-Bit Average Updated Every 4ms
Temperature Measurement
-
10-Bit with 0.125C Resolution
Snapshot Mode Allows Instantaneous Power
Measurement
Host Alerted When Accumulated Current or
Temperature Exceeds Programmable Limits
96 Bytes of Lockable EEPROM
8 Bytes of General-Purpose SRAM
Dallas 1-Wire Interface with Unique 64-Bit
Address and Standard or Overdrive Timing
3mm Dimension of 8-Pin TSSOP Package
Allows Mounting on Side of Thin Prismatic
Li+ and Li+/Polymer Cells
TYPICAL OPERATING CIRCUIT
ORDERING INFORMATION
PART
DS2756E+
DS2756E+T&R
TEMP RANGE
-20°C to +70°C
-20°C to +70°C
PIN-PACKAGE
8 TSSOP
DS2756E+ on
Tape-and-Reel
+ Denotes lead(Pb)-free/RoHS-compliant package.
PIN CONFIGURATION
V
IN
V
SS
PIO
V
DD
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
1
1
2
2
3
2
4
8
7
6
5
DQ
SNS
IS2
IS1
DS2756E
TSSOP Package
Note:
Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here:
www.maxim-ic.com/errata.
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DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
ABSOLUTE MAXIMUM RATINGS
Voltage on PIO Pin, Relative to V
SS
Voltage on All Other Pins, Relative to V
SS
Continuous Sink Current, DQ, PIO
Operating Temperature Range
Storage Temperature Range
Soldering Temperature
-0.3V to +12V
-0.3V to +6V
12mA
-40°C to +85°C
-55°C to +125°C
See J-STD-020A Specification
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
(3.0V
V
DD
4.5V, T
A
= -20C to +70C.)
PARAMETER
Supply Voltage
Data Pin
V
IN
Pin
SYMBOL
V
DD
DQ
V
IN
CONDITIONS
(Note 1)
(Note 1)
(Note 1)
MIN
+3.0
-0.3
-0.3
TYP
MAX
+4.5
+5.5
+4.5
UNITS
V
V
V
DC ELECTRICAL CHARACTERISTICS
(3.0V
V
DD
4.5V, T
A
= -20C to +70C.)
PARAMETER
SYMBOL
CONDITIONS
DQ = V
DD
, EEC bit = 0,
3.0V < V
DD
<
4.2V
DQ = V
DD,
EEC bit = 0
Sleep Mode
Supply Current
Suspend Mode
Supply Current
Current Measurement Input
Range
Current Register Offset
Error
Current Gain Error
24 Hour Accumulated
Current Error
Current Sampling
Frequency
IS1-VSS, IS2-SNS Filter
Resistors
Input Resistance: V
IN
Voltage Offset Error
Voltage Gain Error
Temperature Error
Input Logic High: DQ, PIO
Input Logic Low: DQ, PIO
Output Logic Low: DQ, PIO
DQ Pulldown Current
DQ Capacitance
DQ Low-to-Sleep Time
Suspend Period Accuracy
Minimum Active Mode
I
SLEEP
I
SUSPEND
DQ = 0V, PIE = 00b
DQ = 0V, PIE
≠
00b
(Note 11)
(Note 2)
(Note 4)
(Notes 2, 5)
V
IS1-IS2
= 0, OBEN set,
(Notes 2, 3, 6)
-200
-100
1456
+25C
V
IN
= V
DD
(Note 7)
5
5
2
(Note 8)
(Note 1)
(Note 1)
I
OL
= 4mA (Note 1)
3
1.5
0.4
0.4
1
60
2.1
87
0
90
30
93
10
64
±7.813
1
0
1
1.5
MIN
TYP
75
MAX
100
UNITS
A
Active Mode
Supply Current
I
ACTIVE
120
3
4
A
A
V
IS1-IS2
I
OERR
I
GERR
q
CA
f
SAMP
R
KS
R
IN
V
OERR
V
GERR
T
ERR
V
IH
V
IL
V
OL
I
PD
C
DQ
t
SLEEP
t
SUS_ERR
t
ACT_MIN
mV
V/R
%
reading
µVhr/R
Hz
k
M
mV
%V
reading
C
V
V
V
A
pF
s
%
ms
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DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
Period
Undervoltage Detect
Undervoltage Delay
Internal Timebase
Accuracy
V
UV
t
UVD
t
ERR
2.4V < V
DD
<
4.5V (Note 1)
(Note 9)
2.45
79
2.5
82
1
2.55
85
2
V
ms
%
ELECTRICAL CHARACTERISTICS—1-WIRE INTERFACE
(3.0V
V
DD
4.5V, T
A
= -20C to +70C.)
PARAMETER
Snapshot Trigger 0
Snapshot Delay
STANDARD TIMING
Time Slot
Recovery Time
Write-0 Low Time
Write-1 Low Time
Read Data Valid
Reset Time High
Reset Time Low
Presence-Detect High
Presence-Detect Low
Interrupt Time Low
OVERDRIVE TIMING
Time Slot
Recovery Time
Write-0 Low Time
Write-1 Low Time
Read Data Valid
Reset Time High
Reset Time Low
Presence-Detect High
Presence-Detect Low
Interrupt Time Low
SYMBOL
t
SWL
t
SDLY
t
SLOT
t
REC
t
LOW0
t
LOW1
t
RDV
t
RSTH
t
RSTL
t
PDH
t
PDL
t
IL
t
SLOT
t
REC
t
LOW0
t
LOW1
t
RDV
t
RSTH
t
RSTL
t
PDH
t
PDL
t
IL
CONDITIONS
MIN
1
80
60
1
60
1
480
480
15
60
480
6
1
6
1
48
48
2
8
48
TYP
100
MAX
16
120
120
119
15
15
960
60
240
1920
16
16
2
2
80
6
24
192
UNITS
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
EEPROM RELIABILITY SPECIFICATION
(3.0V
V
DD
4.5V, T
A
= -20C to +70C.)
PARAMETER
Copy to EEPROM Time
EEPROM Copy Endurance
Note 1:
Note 2:
Note 3:
Note 4:
SYMBOL
t
EEC
N
EEC
CONDITIONS
(Note 10)
MIN
50,000
TYP
2
MAX
10
UNITS
ms
cycles
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
All voltages are referenced to V
SS
.
Specifications relative to V
IS1
- V
IS2
.
Summation of worst case time base and current measurement sampling errors.
Continuous offset cancellation corrects offset errors in the current measurement system. Individual values reported by the
Current register have a maximum offset of ±0.5 LSb’s (±7.8125V). Individual values reported in the Average Current register
have a maximum offset of ±2 LSb’s (±7.8125V).
Current Gain Error specifies the gain error in the Current register value compared to a reference voltage between IS1 and IS2.
The DS2756 does not compensate for sense resistor characteristics, and any error terms arising from the sense resistor should
be taken into account when calculating total current measurement error.
Achieving the 24 Hour Accumulated Current Error assumes positive offset accumulation blanking is enabled (OBEN bit set) and
can require a one time 3.5s in-system calibration after mounting to the printed circuit board. Variations in temperature and supply
voltage are compensated for by periodic offset corrections performed automatically during
Active
mode operation.
Voltage offset measurement is with respect to 4.2V at +25°C.
Self heating due to output pin loading and sense resistor power dissipation can alter the Temperature reading from ambient
conditions.
Typical value for t
ERR
valid at 3.7V and +25C. t
ERR
applies to all internal timings (ex. f
SAMP
, t
SLEEP
, t
UVD
) except for the 1-Wire
Interface timings and t
SUS_ERR
.
Four year data retention at +50C.
Measured during the Suspend Timeout. Does not include active period of suspend cycle.
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DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
DETAILED DESCRIPTION
The DS2756 performs temperature, voltage, and current measurement to a resolution sufficient to support process-
monitoring applications such as battery charge control and remaining capacity estimation. Temperature is
measured using an on-chip sensor, eliminating the need for a separate thermistor. Bidirectional current
measurement supporting current accumulation (coulomb counting) is accomplished using an external current
sense resistor.
The host system can configure the DS2756 to signal critical conditions to reduce polling overhead. The alarm
interrupt fires when programmable upper and lower thresholds of temperature or coulomb count are crossed. The
user can select either the DQ pin or PIO pin as the alarm interrupt signal.
PIO can also function as a
Suspend
mode interrupt output to reduce idle current drain within a battery pack. In
Suspend
mode, the DS2756 cycles between
Active
and
Suspend
power modes to reduce DS2756 supply current
and the PIO pin can be used to wake up a microcontroller or other pack circuitry if current flowing through the pack
exceeds programmable charge and discharge thresholds (See Figure 12). The interval between current
measurements can be programmed to achieve an average current as low as 10A (See Table 3).
As a general purpose I/O pin, PIO allows the host system to sense and control other electronics in the pack,
including switches, vibration motors, speakers, and LEDs.
Three types of memory are provided on the DS2756 for battery information storage: EEPROM, lockable EEPROM,
and SRAM. EEPROM memory saves important battery data in true NV memory that is unaffected by severe battery
depletion, accidental shorts, or ESD events. Lockable EEPROM becomes ROM when locked to provide additional
security for unchanging battery data. SRAM provides inexpensive storage for temporary data.
Figure 1. Application Example with Microcontroller in Pack
PACK+
I
DD_MCU
VDD
INT\
4.7K
PIO
VIN
3.3V
Reg
1K
150
µP
DATA
DS2756
GPIO
[Data I/O]
DQ
4.7K
VDD
Protector
UART
GPIO
[Pull-up Control]
VSS
SNS
IS2
IS1
VSS
0.1µF
PACK-
0.1µF
0.020
5.1V
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DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
Figure 2. Functional Diagram
1-WIRE
INTERFACE
AND
ROM ID
THERMAL
SENSE
VOLTAGE
REFERENCE
VDD
LOCKABLE EEPROM
BLOCKS
SRAM
TEMPERATURE
VOLTAGE
PRECISION
TIMEBASE
BIAS
DQ
VIN
M
U
X
ADC
CURRENT
ACCUM. CURRENT
COMPARATORS
STATUS / CONTROL
Low Power
Oscillator
PIO
IS1
10KW
IS2
10KW
-
+
SNS
chip ground
VSS
DETAILED PIN DESCRIPTION
Pin
1
2
3
4
5
6
7
8
Name
V
IN
V
SS
PIO
V
DD
IS1
IS2
SNS
DQ
Description
Battery Voltage-Sense Input. Voltage measurement performed on V
IN
input and displayed
in Voltage Register.
Device Ground and Current-Sense Resistor Connection. V
SS
attaches to battery end of
sense resistor.
General-Purpose Programmable I/O Pin or Optional Interrupt Output
Input Supply: +3.0V to +4.5V Input Range. Bypass V
DD
to V
SS
with 0.1F.
Current-Sense Filter Input 1
Current-Sense Filter Input 2
Sense Resistor Connection. SNS attaches to pack end of current sense resistor.
Serial Interface Data I/O Pin. Bidirection data transmit and receive at 16kbps or 143kbps.
Optional interrupt output.
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