DS2756(2006) Просмотр технического описания (PDF) - Maxim Integrated

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DS2756
(Rev.:2006)

High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode

Maxim Integrated 

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

MSb

“S”: sign bit(s)

LSb

MSb

15.625mV/Rsns

Units:20

XX

LSb

=

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

MSb

LSb

“S”: sign bit(s)

27 26 25 24 23 22 21 20

MSb

LSb

Units: 20 = 1.953mV/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 (±7.8125mV). 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 RSNS = 20mW). The ACR value is recovered from EEPROM on power-up or by a Recall Data

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