DS2751 Просмотр технического описания (PDF) - Maxim Integrated

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DS2751

Multichemistry Battery Fuel Gauge

Maxim Integrated 

DS2751

CURRENT MEASUREMENT

In the active mode of operation, the DS2751 continually measures the current flow into and out of the

battery by measuring the voltage drop across a current-sense resistor. The DS2751 is available in two

configurations: 1) internal 25mW current-sense resistor, and 2) external user-selectable sense resistor. In

either configuration, the DS2751 considers the voltage difference between pins IS1 and IS2 (VIS = VIS1 -

VIS2) to be the filtered voltage drop across the sense resistor. A positive VIS value indicates current is

flowing into the battery (charging), while a negative VIS value indicates current is flowing out of the

battery (discharging).

VIS is measured with a signed resolution of 12 bits. The Current Register is updated in two’s-complement

format every 88ms with an average of 128 measurements. Currents outside the range of the register are

reported at the limit of the range. The format of the Current Register is shown in Figure 3.

For the internal sense resistor configuration, the DS2751 maintains the Current Register in units of amps,

with a resolution of 0.625mA and full-scale range of no less than ±1.9A (see Note 7 on IFS spec for more

details). The DS2751 automatically compensates for internal sense-resistor process variations and

temperature effects when reporting current.

For the external sense resistor configuration, the DS2751 updates the measured VIS voltage to the Current

Register in units of volts, with a resolution of 15.625mV and a ±64mV full-scale range.

Figure 3. CURRENT REGISTER FORMAT

MSB—Address 0E

S 211 210 29 28 27 26 25

MSb

LSb

LSB—Address 0F

24 23 22 21 20 X X X

MSb

LSb

Units: 0.625mA for internal sense resistor

15.625mV for external sense resistor

CURRENT ACCUMULATOR

The Current Accumulator facilitates remaining capacity estimation by tracking the net current flow into

and out of the battery. Current flow into the battery increments the Current Accumulator, while current

flow out of the battery decrements it. Data is maintained in the Current Accumulator in two’s-

complement format. The format of the Current Accumulator is shown in Figure 4.

When the internal sense resistor is used, the DS2751 maintains the Current Accumulator in units of amp-

hours, with a resolution of 0.25mAhrs and a ±8.2Ahrs full-scale range. When using an external sense

resistor, the DS2751 maintains the Current Accumulator in units of volt-hours, with a resolution of

6.25mVhrs and a ±205mVhrs full-scale range.

The Current Accumulator is a read/write register that can be altered by the host system as needed.

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