DS2761AX datasheet(8/24 Pages) DALLAS

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DS2761

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Summary. All of the protection conditions described above are OR'ed together to affect the CC and DC

outputs.

DC = (Undervoltage) or (Overcurrent, Either Direction) or (Short Circuit) or

(Protection Register Bit DE = 0) or (Sleep Mode)

CC = (Overvoltage) or (Undervoltage) or (Overcurrent, Charge Direction) or (Protection Register

bit CE = 0) or (Sleep Mode)

CURRENT MEASUREMENT

In the active mode of operation, the DS2761 continually measures the current flow into and out of the

battery by measuring the voltage drop across a current-sense resistor. The DS2761 is available in two

configurations: 1) internal 25m

W current-sense resistor, and 2) external user-selectable sense resistor. In

either configuration, the DS2761 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 (128/fsample) with an average of 128 readings. Currents outside the range of the

For the internal sense resistor configuration, the DS2761 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 DS2761 automatically compensates for internal sense resistor process variations and

temperature effects when reporting current.

For the external sense resistor configuration, the DS2761 writes the measured VIS voltage to the current

mV and a full-scale range of ±64mV.

Figure 4. CURRENT REGISTER FORMAT

MSB—Address 0E

LSB—Address 0F

S211 210 29

MSb

LSb

MSb

LSb

Units: 0.625mA for Internal Sense Resistor

15.625

mV 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 5.

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