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DS2756E+-DS2756E+T&R
High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
19-4633; 5/09
DS2756
High-Accuracy Battery Fuel Gauge
with Programmable Suspend Mode
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.
TYPICAL OPERATING CIRCUIT
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
ORDERING INFORMATION
PART TEMP RANGE PIN-PACKAGE DS2756E+ -20°C to +70°C 8 TSSOP
DS2756E+T&R -20°C to +70°C DS2756E+ on
Tape-and-Reel
+ Denotes lead(Pb)-free/RoHS-compliant package.
PIN CONFIGURATION
VINDQ
SNS
IS2 PIO 1 8
7
6
5
VSS 2
3
VDD 4
IS1 DS2756E
TSSOP Package
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
ABSOLUTE MAXIMUM RATINGS Voltage on PIO Pin, Relative to VSS -0.3V to +12V
Voltage on All Other Pins, Relative to VSS -0.3V to +6V
Continuous Sink Current, DQ, PIO 12mA
Operating Temperature Range -40°C to +85°C
Storage Temperature Range -55°C to +125°C
Soldering Temperature 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 VDD 4.5V, TA = -20C to +70C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply Voltage VDD (Note 1) +3.0 +4.5 V
Data Pin DQ (Note 1) -0.3 +5.5 V
VIN Pin VIN (Note 1) -0.3 +4.5 V
DC ELECTRICAL CHARACTERISTICS (3.0V VDD 4.5V, TA = -20C to +70C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DQ = VDD, EEC bit = 0,
3.0V < VDD < 4.2V 75 100 A Active Mode
Supply Current IACTIVE
DQ = VDD, EEC bit = 0 120
Sleep Mode
Supply Current ISLEEP DQ = 0V, PIE = 00b 1 3 A
Suspend Mode
Supply Current ISUSPEND DQ = 0V, PIE ≠ 00b
(Note 11) 1.5 4 A
Current Measurement Input
Range VIS1-IS2 (Note 2) 64 mV
Current Register Offset
Error IOERR (Note 4) ±7.813 V/R
Current Gain Error IGERR (Notes 2, 5) 1 %
reading
24 Hour Accumulated
Current Error qCA VIS1-IS2 = 0, OBEN set,
(Notes 2, 3, 6) -200 -100 0 µVhr/R
Current Sampling
Frequency fSAMP 1456 Hz
IS1-VSS, IS2-SNS Filter
Resistors RKS +25C 10 k
Input Resistance: VIN RIN VIN = VDD 5 M
Voltage Offset Error VOERR (Note 7) 5 mV
Voltage Gain Error VGERR 2 %V
reading
Temperature Error TERR (Note 8) 3 C
Input Logic High: DQ, PIO VIH (Note 1) 1.5 V
Input Logic Low: DQ, PIO VIL (Note 1) 0.4 V
Output Logic Low: DQ, PIO VOL IOL = 4mA (Note 1) 0.4 V
DQ Pulldown Current IPD 1 A
DQ Capacitance CDQ 60 pF
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
Period
Undervoltage Detect VUV 2.4V < VDD < 4.5V (Note 1) 2.45 2.5 2.55 V
Undervoltage Delay tUVD 79 82 85 ms
Internal Timebase
Accuracy tERR (Note 9) 1 2 %
ELECTRICAL CHARACTERISTICS—1-WIRE INTERFACE (3.0V VDD 4.5V, TA = -20C to +70C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Snapshot Trigger 0 tSWL 1 16 s
Snapshot Delay tSDLY 80 100 120 s
STANDARD TIMING Time Slot tSLOT 60 120 s
Recovery Time tREC 1 s
Write-0 Low Time tLOW0 60 119 s
Write-1 Low Time tLOW1 1 15 s
Read Data Valid tRDV 15 s
Reset Time High tRSTH 480 s
Reset Time Low tRSTL 480 960 s
Presence-Detect High tPDH 15 60 s
Presence-Detect Low tPDL 60 240 s
Interrupt Time Low tIL 480 1920 s
OVERDRIVE TIMING Time Slot tSLOT 6 16 s
Recovery Time tREC 1 s
Write-0 Low Time tLOW0 6 16 s
Write-1 Low Time tLOW1 1 2 s
Read Data Valid tRDV 2 s
Reset Time High tRSTH 48 s
Reset Time Low tRSTL 48 80 s
Presence-Detect High tPDH 2 6 s
Presence-Detect Low tPDL 8 24 s
Interrupt Time Low tIL 48 192 s
EEPROM RELIABILITY SPECIFICATION (3.0V VDD 4.5V, TA = -20C to +70C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Copy to EEPROM Time tEEC 2 10 ms
EEPROM Copy Endurance NEEC (Note 10) 50,000 cycles
Note 1: All voltages are referenced to VSS.
Note 2: Specifications relative to VIS1 - VIS2.
Note 3: Summation of worst case time base and current measurement sampling errors.
Note 4: 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).
Note 5: 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.
Note 6: 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.
Note 7: Voltage offset measurement is with respect to 4.2V at +25°C.
Note 8: Self heating due to output pin loading and sense resistor power dissipation can alter the Temperature reading from ambient
conditions.
Note 9: Typical value for tERR valid at 3.7V and +25C. tERR applies to all internal timings (ex. fSAMP, tSLEEP, tUVD) except for the 1-Wire
Interface timings and tSUS_ERR.
Note 10: Four year data retention at +50C.
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 ProtectorDS2756
3.3V
Reg
INT\
PIO
VIN
VDD
SNS
IS2IS1
VSS
PACK+
DATA
PACK-
VDD
GPIO
[Pull-up Control]
UART
VSS
IDD_MCU
GPIO
[Data I/O]
4.7K
4.7K150
0.1µF
0.1µF
5.1V
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
Figure 2. Functional Diagram 1-WIRE
INTERFACE
AND
ROM ID
VOLTAGE
REFERENCETHERMAL
SENSE
ADC
VIN
PRECISION
TIMEBASEM
U -
chip ground
SNS
IS2
VSS
IS1
VDD
PIO
BIAS
Low Power
Oscillator
LOCKABLE EEPROM
BLOCKS
SRAM
TEMPERATURE
VOLTAGE
CURRENT
ACCUM. CURRENT
COMPARATORS
STATUS / CONTROL
10KW10KW
DETAILED PIN DESCRIPTION
Pin Name Description 1 VIN Battery Voltage-Sense Input. Voltage measurement performed on VIN input and displayed
in Voltage Register.
2 VSS Device Ground and Current-Sense Resistor Connection. VSS attaches to battery end of
sense resistor. PIO General-Purpose Programmable I/O Pin or Optional Interrupt Output
4 VDD Input Supply: +3.0V to +4.5V Input Range. Bypass VDD to VSS with 0.1F. IS1 Current-Sense Filter Input 1 IS2 Current-Sense Filter Input 2 SNS Sense Resistor Connection. SNS attaches to pack end of current sense resistor.
8 DQ Serial Interface Data I/O Pin. Bidirection data transmit and receive at 16kbps or 143kbps.
Optional interrupt output.
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
POWER MODES The DS2756 has three power modes: Active, Suspend and Sleep. While in Active mode, the DS2756 continuously
measures voltage, temperature, current, accumulated current, and monitors for an under voltage condition. In
Suspend and Sleep modes, the DS2756 ceases these activities. During Suspend, the DQ input buffer is active and
a low power oscillator runs. In Sleep mode, only the DQ input buffer is active.
The DS2756 enters Suspend mode when PMOD = 1 AND all of the following conditions are true: the DQ line is low for longer than tSLEEP the Programmable Interval Enable (PIE) bits in the Status Register are set to a non-zero value
(PIE =01b, 10b or 11b) Current register value is less than the Charge Suspend Threshold
AND greater than the Discharge Suspend Threshold
Periodically, when a Suspend Period time out occurs, the DS2756 temporarily cycles from Suspend to Active mode
in order to measure current. When the current measurement completes, the result is evaluated against the user
programmed Charge and Discharge Suspend Thresholds. If the Current measurement result does not cross either
threshold, the DS2756 transitions back to Suspend. If the measurement shows that more current is flowing than the
level of either threshold, the DS2756 signals a suspend interrupt by driving the PIO pin low, then remains in Active
mode continuing normal Active mode operation.
The DS2756 enters Sleep mode when PMOD = 1 AND either of the following conditions are true: the DQ line is low for longer than tSLEEP (minimum 2.1s) AND PIE = 00b the UVEN bit in the Status Register is set to 1 AND the voltage on VIN drops below undervoltage threshold
VUV for tUVD (VIN measurement and comparison to VUV, and tUVD timeout occur in normal Active mode and
temporary Active mode cycle from Suspend mode)
The DS2756 returns to Active mode from Suspend or Sleep mode whenever the DQ line is pulled from a low-to-
high state.
The factory default for the DS2756 is UVEN = 0, PMOD = 0 and PIE = 00b. The DS2756 defaults to Active mode
when power is first applied.
CURRENT MEASUREMENT AND ACCUMULATION The DS2756 current measurement system is designed to provide timely data on charge and discharge current at a
moderate resolution level while simultaneously accumulating high resolution average data to support accurate
coulomb counting. Current is measured with an Analog-to-Digital Converter (ADC) by sampling the voltage drop
across a series sense resistor, RSNS, connected between SNS and VSS. Individual current samples are taken every
687s (1456-1 Hz). Multiple samples are averaged to report Current and Average Current values, and accumulated
for coulomb counting.
Current Measurement The voltage signal developed across the sense resistor (between SNS and VSS) is differentially sampled by the
ADC inputs through internal 10kΩ resistors connected between VSSand IS1, and SNS and IS2. Isolating the ADC
inputs (IS1 and IS2 pins) from the sense resistor with 10k facilitates the use of an RC filter by adding a single
external capacitor. The RC filter extends the input range beyond ±64mV in pulse load or pulse charge applications.
The ADC accurately measures large peak signals as long as the differential signal level at IS1 and IS2 does not
exceed ±64mV.
The Current register operates in two modes, normal and snapshot. In normal mode, the Current register reports the
average of 128 individual current samples every 88ms. The reported value represents the average current during
the 88ms measurement period. The Average Current register reports the average of 4096 current samples and is
updated every 2.8s.
In snapshot mode, the Current register holds the current measured immediately following the snapshot trigger.
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
error is introduced into both the Average Current and Accumulated Current values by the current sample timing
discontinuity introduced with each trigger of the Snapshot mode, use of Snapshot once every 5s does not produce
a significant error.
The following register formats specify the update interval and units for the Current and Average Current registers.
Values are posted in two’s complement format. Positive values represent charge currents (VIS1 > VIS2) and negative
values represent discharge currents (VIS2 > VIS1). Positive currents above the maximum register value are reported
at the maximum value, 0x7FFF. Negative currents below the minimum register value are reported at the minimum
value, 0x8000.
Figure 3. Current Register Format 12-bit + sign resolution (13-bit), 88ms update interval MSB-Address 0Eh LSB-Address 0Fh
S 211 210 29 28 27 26 25 24 23 22 21 20 X X X
MSb LSb MSb LSb
“S”: sign bit(s) Units:20=
15.625V/Rsns
Figure 4. Average Current Register Format 15-bit + sign resolution (16-bit), 2.8s update interval MSB-Address 1Ah LSB-Address 1Bh
S 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb
“S”: sign bit(s) Units: 20 = 1.953V/RSNS
CURRENT OFFSET CORRECTION Continuous offset cancellation is performed automatically to correct for offsets 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 ACCUMULATION The DS2756 measures current for coulomb counting purposes, with an accuracy of ±2% (±3.9V) over a range of
±64mV. Using a 20m sense resistor, current accumulation is performed over a range of ±3.2A while measuring
standby currents with an accuracy of ±195A. Current measurements are internally summed, or accumulated, with
the results displayed in the Accumulated Current Register (ACR). The accuracy of the ACR is dependent on both
the current measurement and the accumulation timebase. The 16-bit ACR has a range of ±204.8mVh with an LSb
of 6.25Vh. Accumulation of charge current above the maximum register value is reported at the maximum value;
conversely, accumulation of discharge current below the minimum register value is reported at the minimum value.
Read and write access is allowed to the ACR. The ACR must be written MSB first then LSB. Whenever the ACR is
written, internal fractional accumulation result bits are cleared. In order to preserve the ACR value in case of power
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
command targeting the ACR register address. A write to the ACR results in an automatic copy of the new value to
EEPROM.
Figure 5. Accumulated Current Register Format MSB-Address 10h LSB-Address 11h
S 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb Units: 6.25Vh/RSNS
ACR LSB RSNS VIS1- VIS2 20m 15m 10m 5m
6.25Vh 312.5Ah 416.7Ah 625Ah 1.250mAh
ACR RANGE RSNS VIS1- VIS2 20m 15m 10m 5m
±204.8mVh ±10.24Ah ±13.65Ah ±20.48Ah ±40.96Ah
OFFSET ACCUMULATION BLANKING In order to avoid the accumulation of small positive offset errors over long periods, an offset blanking filter is
provided. The blanking filter is enabled by setting the OBEN bit in the Status Register. When OBEN is set, charge
currents (positive Current register values) between 15.625V and 62.5V are not accumulated in the ACR.
Therefore, with RSNS = 0.020 positive currents between 0.78mA and 3.125mA are blanked from accumulation in
the ACR.
ACCUMULATION BIAS Systematic errors or an application preference can require the application of an arbitrary bias to the current
accumulation process. The Accumulation Bias register is provided to allow a user programmed constant positive or
negative polarity bias to the current accumulation process. The Accumulation Bias value can be used to estimate
battery currents that do not flow through the sense resistor, estimate battery self-discharge, or correct for offset
error in the Current register and ACR register. The user programmed two’s complement value in the Accumulation
Bias register is added to the Current Register once per current sample. The register format supports the
accumulation bias to be applied in 1.95V increments over a ±250V range. When using a 20m sense resistor,
the bias control is 100A over a ±12.5mA range.
The Accumulation Bias register is directly read and write accessible. The user value is made non-volatile with a
Copy Data command targeting EEPROM block 0. The Accumulation Bias register is loaded from EEPROM
memory on power up and a transition from Sleep to Active mode.
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
Figure 6. Accumulation Bias Register Format Address 33h
S 26 25 24 23 22 21 20 MSb LSb“S”: sign bit 1.95V/RSNS
VOLTAGE MEASUREMENT The voltage register operates in two modes, normal and snapshot. In normal mode, the DS2756 continually
measures the voltage between pins VIN and VSS over a 0 to 4.5V range, and the Voltage Register is updated in
two’s-complement format every 3.4ms with a resolution of 4.88mV.
In snapshot mode, the Voltage register holds the voltage measured immediately following the snapshot trigger.
Normal voltage measurements resume after the snapshot value is obtained, however, the SNAP bit must be
cleared to re-enable normal mode reporting of voltage measurement to the Voltage register.
Voltages above the maximum register value are reported as the maximum value.
Figure 7. Voltage Register Format MSB-Address 0Ch LSB-Address 0Dh
S 29 28 27 26 25 24 23 22 21 20 X X X X X
MSb LSb MSb LSb Units: 4.88 mV
TEMPERATURE MEASUREMENT The DS2756 uses an integrated temperature sensor to continually measure battery temperature. Temperature
measurements are updated in the Temperature Register every 220ms in two’s-complement format with a resolution
of 0.125°C over a 127°C range. The Temperature Register format is shown in Figure 8.
Figure 8. Temperature Register Format MSB-Address 18h LSB-Address 19h
S 29 28 27 26 25 24 23 22 21 20 X X X X X
MSb LSb MSb LSb Units: 0.125C
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
PROGRAMMABLE I/O The PIO pin can be configured as a general purpose programmable I/O pin, or as an interrupt output. To use the
PIO pin in the programmable I/O mode described in this section, the PIO interrupt method must not be enabled.
See the Interrupt Signaling section for information on disabling interrupts.
As a programmable I/O pin, PIO provides a digital input or an open drain digital output. Writing a 1 to the PIO bit in
the Special Feature Register disables the output driver. With the PIO pin Hi-Z, it can be used as an input. The logic
level of the PIO pin is reported in the Special Feature Register through the serial interface.
To use the PIO pin as an output, write the desired output value to the PIO bit in the Special Feature Register.
Writing a 0 to the PIO bit enables the PIO output driver, pulling the PIO pin to VSS. As stated above, writing a 1 to
the PIO bit forces the pin to a Hi-Z state. A pullup resistor or current source must be provided to force the pin high.
The PIO pin can be biased several volts above VDD allowing inter-operation with a system voltage which is higher
than the battery voltage. Consult the Absolute Maximum Ratings table when operating the PIO pin significantly
above VDD. The DS2756 turns off the PIO output driver and sets the PIO bit high when in Sleep mode or when DQ
is low for more than tSLEEP, regardless of the state of the PMOD bit.
INTERRUPT SIGNALING The DS2756 interrupt can be configured as the Suspend interrupt that is signaled on the PIO pin, or as an Alarm
Comparator interrupt (based on Current Accumulator and Temperature Alarm Comparator thresholds) that is
signaled on either the PIO pin or DQ pin.
The Suspend interrupt is used to signal that the current level is greater than the user programmable Charge
Suspend Threshold or less than (more negative) than the Discharge Suspend Threshold. The Suspend interrupt is
enabled by setting one or both of the PIE bits in the Status Register. The PIE bits select one of three intervals for
the Suspend Period, tSUS. If either PIE bit is set, the Alarm Comparator interrupt is disabled. The Suspend interrupt
event is signaled by internally clearing the PIO bit in the SFR in order to force the PIO output from high to low. The
PIO output remains low in Active mode until the PIO bit in the SFR is written to a 1 by the host to disable the PIO
output. Note that the PIO output is disabled in Suspend mode, allowing the PIO pin to be pulled high and ensuring
the DS2756 can always signal a Suspend interrupt with a high to low transition.
The Temperature and ACR Alarm Comparator interrupt is enabled by setting the Interrupt Enable (IE) bit in the
Special Feature Register with PIE cleared. When IE is set and both PIE bits are cleared, an interrupt will be
signaled if the Alarm Comparator thresholds are crossed. A 1-Wire RESET always clears the IE bit. The host must
re-enable interrupts by setting IE in the last transaction on the bus. Note that when either PIE bit is set, the state of
IE has no effect.
The interrupt signal pin for the Alarm Comparator interrupt is selected by setting or clearing the Interrupt Output
Select (IOS) bit in the Status Register. When IOS is set, the DQ pin performs Alarm Comparator interrupt signaling,
when IOS is cleared, the PIO pin performs Alarm Comparator interrupt signaling. Note that when either PIE bit is
set, the state of IOS has no effect.
DQ signals an Alarm Comparator interrupt condition by driving the 1-Wire bus low for tIL. The DS2756 and all other
1-Wire devices present on the bus interpret this signal as a 1-Wire RESET. A Presence Pulse should be expected
from all 1-Wire devices, including the DS2756 following the alarm interrupt signal. The host system can sense the
alarm interrupt signal on the falling or rising edge of either the RESET or Presence Pulse.
PIO signals an Alarm Comparator interrupt by driving low. PIO remains low until the host clears the condition by
writing a 1 to the PIO bit (bit 6 in the Special Feature Register). A pullup resistor or current source must be
provided to force the pin high. The host must sense the alarm interrupt on the falling edge of PIO.
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
Table 1. PIO/DQ Pin Function
REGISTER BIT SETTING PIO/DQ PIN FUNCTION PIE IOS IE PIO
xx x x 0 PIO pin: GPIOOutput LOW
00 x 0 1 PIO pin: GPIOOutput High-Z, Input mode
00 0 1 1 PIO pin: Alarm Comparator Interrupt Output
00 1 1 0 DQ pin: Alarm Comparator Interrupt Output (low for tIL)
PIO pin: GPIOOutput LOW
00 1 1 1 DQ pin: Alarm Comparator Interrupt Output (low for tIL)
PIO pin: GPIOOutput High-Z, Input mode
01
10
11 x 1 PIO pin: Suspend Interrupt Output
xDon’t care.
SUSPEND THRESHOLDS The suspend thresholds set the current level to enter and exit Suspend mode. The threshold levels are
programmable with a magnitude range of 0 to 4mV, and are compared against the value in the Current register.
Values are programmed in two’s complement format with an implied sign bit in a virtual 9th bit position. The Charge
Suspend Threshold register is always a positive value. The Discharge Suspend Threshold register is always a
negative value.
The thresholds define an inclusive, continuous range of currents in which the DS2756 enters or re-enters Suspend
mode from Active mode. The Charge Suspend Threshold represents the minimum measured charge current which
will cause the DS2756 to transition modes. The Discharge Suspend Threshold represents the minimum discharge
current which will cause the DS2756 to transition modes.
The user values of the suspend thresholds are programmed into two bytes located within EEPROM block 0. These
memory locations serve as current threshold values only when either PIE bit is set, and can be used as general
purpose EEPROM if PIE = 00b. A copy command is required to save the byte values to EEPROM. See the
Memory section for information on copying shadow RAM to EEPROM.
Figure 9. Charge Suspend Threshold Format Address 35h 7 26 25 24 23 22 21 20 MSb LSb 15.625V/RSNS
Figure 10. Discharge Suspend Threshold Format Address 34h 7 26 25 24 23 22 21 20
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
ALARM COMPARATORS AND INTERRUPT THRESHOLDS Alarm interrupt threshold values can be programmed by the user in the designated SRAM memory registers in the
formats and locations found in Figure 11. Since these thresholds are located in SRAM memory, they must be
reprogrammed if a loss of power to the DS2756 occurs. The DS2756 generates an alarm interrupt to indicate that
one of the following events has occurred: Accumulated Current Current Accumulator Interrupt High Threshold Accumulated Current Current Accumulator Interrupt Low Threshold Temperature Temperature Interrupt High Threshold Temperature Temperature Interrupt Low Threshold
The host may then poll the DS2756 to determine which threshold has been met or exceeded.
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
Figure 11. Alarm Interrupt Threshold Register Formats
Current Accumulator Interrupt High Threshold MSB-Address 80h LSB-Address 81h
S 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb Units: 6.25Vhrs
Current Accumulator Interrupt Low Threshold MSB-Address 82h LSB-Address 83h
S 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb Units: 6.25Vhrs
Temperature Interrupt High Threshold Address 84h
S 26 25 24 23 22 21 20
MSb LSb
Units: 1.0°C
Temperature Interrupt Low Threshold Address 85h
S 26 25 24 23 22 21 20
MSb LSb
Units: 1.0°C
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
Figure 12. Alarm And Suspend Mode Operating Diagram
Interrupt Enable
PIE
Programmable
Interrupt Enable
Charge Suspend
Interrupt Threshold
CURRENT
Discharge Suspend
Interrupt Threshold
High Temperature
Interrupt Threshold
TEMPERATURE
Low Temperature
Interrupt Threshold
High Accumulator
Interrupt Threshold
ACR
Low Accumulator
Interrupt Threshold
DEVICE
STATE
PIO
(IOS = 0)
00b00b
ACTIVEACTIVESUSPENDSUSPEND
Note 2
Note 3
Note 1
Note 5
Note 4
Threshold violations do not generate alarm interrupts until the Interrupt Enable (IE) bit is set.
PIO Interrupts are cleared by resetting the PIO bit in the Special Feature Register.
SUSPEND state shown in this timing diagram refers to the DS2756 cycling between Active
and Suspend mode at a rate determined by the PIE bit settings. Suspend state is entered by
setting PIE bits to a non-zero value, setting PMOD=1, and then driving DQ low for longer
than 2s.
Interrupts on PIO not reset by software are automatically cleared when entering suspend
mode.
Alarm threshold violations do not generate interrupts if Suspend mode is enabled
(PIE ≠00b).
Note 1.
Note 2.
Note 3.
Note 4.
Note 5.
