DS2764 High-Precision Li+ Battery Monitor With 2-Wire Interface

11 of 20

CURRENT MEASUREMENT

In active mode, the DS2764 continually measures the current flow into and out of the battery by measuring the

voltage drop across a current-sense resistor. The DS2764 is available in two configurations: 1) internal 25m

W

current-sense resistor and 2) external user-selectable sense resistor. In either configuration, the DS2764 considers

indicates current is flowing out of the battery (discharging).

every 88ms with an average of 128 readings. Current measurements outside the register range are reported at the

range limit. Each measurement is internally compensated for offset on a continual basis minimizing error resulting

from variations in device temperature and voltage. Figure 5 shows the format of the current register.

For the internal sense resistor configuration, the DS2764 maintains the current register in units of amps, with a

resolution of 0.625mA and full-scale range of no less than

DS2764 automatically compensates for internal sense resistor process variations and temperature effects when

reporting current.

with a 15.625

mV resolution and a full-scale ±64mV range.

Figure 5. Current Register Format

MSB—Address 0E

LSB—Address 0F

S

2

11

2

10

2

9

2

8

2

7

2

6

2

5

2

4

2

3

2

2

2

1

2

0

X

X

X

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. Figure 6 shows the

format of the current accumulator.

When the internal sense resistor is used, the DS2764 maintains the current accumulator in units of amp-hours, with

a 0.25mAhrs resolution and full-scale

±8.2Ahrs range. When using an external sense resistor, the DS2764

maintains the current accumulator in units of volt-hours, with a 6.25

mVhrs resolution and a full-scale ±205mVhrs

range.

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

Figure 6.

Current Accumulator Format

MSB—Address 10

LSB—Address 11

S

2

14

2

13

2

12

2

11

2

10

2

9

2

8

2

7

2

6

2

5

2

4

2

3

2

2

2

1

2

0

MSb

LSb

MSb

LSb

Units: 0.25mAhrs for Internal Sense Resistor

6.25

mVhrs for External Sense Resistor