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

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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 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:





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

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for coulomb counting.

Current Measurement

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.

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