MAXIM DS2756 Technical data

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 1cell 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-WireÒ interface, the DS2756 gives the host system read/write access to status and control registers, instrumentation registers, and generalpurpose 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

PACK+

INT

DATA

PACK-

150

DS2756

PIO

VIN

VDD

VSS

SNS

IS1

IS2

0.1µF

5.1V5.1V

0.020

150

0.1µF

Protector

5.1V

DS2756

High-Accuracy Battery Fuel Gauge

with Programmable Suspend Mode

FEATURES

§ Programmable Suspend Mode

§ Accurate Current Accumulation

- 2% ±4mV over ±64mV Input Range

- 2% ±200mA over ±3.2A with 20mW 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 0.125°C 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

+ Denotes lead-free package.

PIN CONFIGURATION

1 8

PIO

DS2756E+ on Tape-and-Reel

DQ SNS

IS2

IS1

1-Wire is a registered trademark of Dallas Semiconductor.

DS2756E

TSSOP Packa

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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050806

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 V

-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 £ V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VDD (Note 1) 3.0 5.5 V Data Pin DQ (Note 1) -0.3 +5.5 V

Pin VIN (Note 1) -0.3 +5.5 V

£ 5.5V, TA = -20°C to +70°C.)

DC ELECTRICAL CHARACTERISTICS

(3.0V £ V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

£ 5.5V, TA = -20°C to +70°C.)

DQ = VDD, EEC bit = 0,

Active Mode Supply Current

ACTIVE

3.0V < VDD < 4.2V

DQ = V

Sleep Mode Supply Current

Suspend Mode Supply Current

Current Measurement Input Range

Current Register Offset Error

Current Gain Error I

24 Hour Accumulated Current Error

Current Sampling Frequency IS1-VSS, IS2-SNS Filter Resistors Input Resistance: VIN R

Voltage Offset Error V

Voltage Gain Error V

Temperature Error T

DQ = 0V, PIE = 00b 1 3

SLEEP

SUSPEND

IS1-IS2

OERR

GERR

SAMP

OERR

GERR

ERR

DQ = 0V, PIE ≠ 00b (Note 11)

(Note 2)

(Note 4) ±7.813

(Notes 2, 5)

IS1-IS2

(Notes 2, 3, 6)

1456 Hz

+25°C

VIN = VDD 5 (Note 7)

(Note 8)

EEC bit = 0 120

DD,

= 0, OBEN set,

75 100

1.5 4

±64

mV/R

±1

reading

-200 -100 0 µVhr/R

±5

±2

mV %V

reading

±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 V

DQ Pulldown Current IPD 1

= 4mA (Note 1) 0.4 V

mA DQ Capacitance CDQ 60 pF DQ Low-to-Sleep Time t Suspend Period Accuracy t Minimum Active Mode t

SLEEP

SUS_ERR

ACT_MIN

2.1 s

±30

87 90 93 ms

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DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode

Period Undervoltage Detect VUV Undervoltage Delay t

Internal Timebase Accuracy

UVD

ERR

2.4V < V 79 82 85 ms

(Note 9)

< 5.5V (Note 1)

2.45 2.5 2.55 V

±1 ±2

ELECTRICAL CHARACTERISTICS—1-WIRE INTERFACE

(3.0V £ V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Snapshot Trigger 0 t Snapshot Delay t

STANDARD TIMING

Time Slot t Recovery Time t Write-0 Low Time t Write-1 Low Time t Read Data Valid t Reset Time High t Reset Time Low t Presence-Detect High t Presence-Detect Low t Interrupt Time Low tIL 480 1920

OVERDRIVE TIMING

Time Slot t Recovery Time t Write-0 Low Time t Write-1 Low Time t Read Data Valid t Reset Time High t Reset Time Low t Presence-Detect High t Presence-Detect Low t Interrupt Time Low tIL 48 192

£ 5.5V, TA = -20°C to +70°C.)

1 16

SWL

80 100 120

SDLY

60 120

SLOT

REC

60 119

LOW0

1 15

LOW1

RDV

480

RSTH

480 960

RSTL

15 60

PDH

60 240

PDL

6 16

SLOT

REC

6 16

LOW0

1 2

LOW1

RDV

RSTH

48 80

RSTL

2 6

PDH

8 24

PDL

ms ms

ms ms ms ms ms ms ms ms ms ms

EEPROM RELIABILITY SPECIFICATION

(3.0V £ V

Copy to EEPROM Time t EEPROM Copy Endurance N

Note 1: Note 2: Note 3: Note 4:

Note 5:

Note 6:

Note 7: Note 8:

Note 9:

Note 10: Note 11:

£ 5.5V, TA = -20°C to +70°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

EEC

All voltages are referenced to V Specifications relative to V 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 (±7.8125mV). Individual values reported in the Average Current register have a maximum offset of ±2 LSb’s (±7.8125mV). 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 Interface timings and t Four year data retention at +50°C. Measured during the Suspend Timeout. Does not include active period of suspend cycle.

valid at 3.7V and +25°C. t

ERR

SUS_ERR

- V

IS1

IS2

(Note 10) 50,000 cycles

ERR

2 10 ms

applies to all internal timings (ex. f

SAMP

, t

SLEEP

, t

) except for the 1-Wire

UVD

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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 processmonitoring 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 10mA (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+

DATA

PACK-

DD_MCU

UART

3.3V Reg

VDD

µP

[Data I /O]

[Pul l -up Contr ol ]

VSS

INT\

GPIO

4.7K

PIO

SNS

1 K 150

VIN

DS2756

IS 2 IS 1

0.1 µF 0 .020

VDD

Protector

VSS

0.1 µF

5.1 V

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DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode

Figure 2. Functional Diagram

1-W IRE

THERMAL

SENSE

VIN

INTERFACE

AND

ROM ID

M U

VOLTAGE

REFERENCE

ADC

LOCKABLE EEPROM

BLOCKS

SRAM

TEMPERATURE

VOLTAGE

CURRENT

ACCUM. CURRENT

COMPARATORS

VDD

BIAS

PRECISION

TIMEBASE

Low Power

Oscillator

STATUS / CONTROL

IS2

10KW 10KW

SNS

DETAILED PIN DESCRIPTION

Pin Name Description

1 VIN

2 VSS

3 PIO General-Purpose Programmable I/O Pin or Optional Interrupt Output

4 VDD

Battery Voltage-Sense Input. Voltage measurement performed on V in Voltage Register.

Device Ground and Current-Sense Resistor Connection. V sense resistor.

Input Supply: +3.0V to +5.5V Input Range. Bypass V

to VSS with 0.1mF.

chip ground

input and displayed

attaches to battery end of

PIO

IS1

VSS

5 IS1 Current-Sense Filter Input 1

6 IS2 Current-Sense Filter Input 2

7 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.

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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 t

SLEEP

§ 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 t

§ the UVEN bit in the Status Register is set to 1 AND the voltage on V

for t

(VIN measurement and comparison to VUV, and t

UVD

(minimum 2.1s) AND PIE = 00b

SLEEP

drops below undervoltage threshold

timeout occur in normal Active mode and

UVD

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-tohigh 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, R 687ms (1456

-1

Hz). Multiple samples are averaged to report Current and Average Current values, and accumulated

, connected between SNS and VSS. Individual current samples are taken every

SNS

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 V inputs (IS1 and IS2 pins) from the sense resistor with 10kW 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. Current measurements resume immediately after the snapshot value is obtained, however, the SNAP bit must be cleared to re-enable normal mode current reporting in the Current register. The Average Current register continues to be updated while the SNAP bit is set. Current accumulation also continues while SNAP is set. Although a small

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and IS1, and SNS and IS2. Isolating the ADC

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 (V

> V

values represent discharge currents (V

IS2

). Positive currents above the maximum register value are reported

IS1

> V

) and negative

IS2

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 2

210 29 28 27 26 25 24 23 22 21 20 X X X

MSb LSb MSb LSb

Units:2

“S”: sign bit(s)

15.625mV/Rsns

Figure 4. Average Current Register Format

15-bit + sign resolution (16-bit), 2.8s update interval

MSB-Address 1Ah LSB-Address 1Bh

S 2

MSb LSb MSb LSb

“S”: sign bit(s)

213 212 211 210 29 28 27 26 25 24 23 22 21 20

Units: 2

= 1.953mV/R

SNS

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 (±7.8125mV). Individual values reported in the Average Current register have a maximum offset of ±2 LSb’s (±7.8125mV).

CURRENT ACCUMULATION

The DS2756 measures current for coulomb counting purposes, with an accuracy of ±2% (±3.9mV) over a range of ±64mV. Using a 20mW sense resistor, current accumulation is performed over a range of ±3.2A while measuring standby currents with an accuracy of ±195mA. 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 6.25mVh. 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 loss, the ACR MSB and LSB are automatically backed up to EEPROM after incrementing or decrementing by 100mVh (5.0mAh for R

= 20mW). The ACR value is recovered from EEPROM on power-up or by a Recall Data

SNS

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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 2

MSb LSb MSb LSb

213 212 211 210 29 28 27 26 25 24 23 22 21 20

Units: 6.25mVh/R

SNS

ACR LSB

- V

IS2

20mW 15mW 10mW 5mW

IS1

SNS

6.25mVh 312.5mAh 416.7mAh 625mAh

1.250mAh

ACR RANGE

- V

IS2

20mW 15mW 10mW 5mW

IS1

SNS

±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 15.625mV and 62.5mV are not accumulated in the ACR. Therefore, with R 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 1.95mV increments over a ±250mV range. When using a 20mW sense resistor, the bias control is 100mA 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.

= 0.020W, positive currents between 0.78mA and 3.125mA are blanked from accumulation in

SNS

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