ds2761 Maxim Integrated Products, Inc., ds2761 Datasheet - Page 9

• Manufacturer Part Number: ds2761
• Description: Ds2761 High-precision Li+ Battery Monitor
• Manufacturer: Maxim Integrated Products, Inc.

When the internal sense resistor is used, the DS2761 maintains the current accumulator in units of amp-
hours, with a resolution of 0.25mAhrs and full-scale range of ±8.2Ahrs. When using an external sense
resistor, the DS2761 maintains the current accumulator in units of volt-hours, with a resolution of
6.25mVhrs and a full scale range of ±205mVhrs.
The current accumulator is a read/write register that can be altered by the host system as needed.
Figure 5. CURRENT ACCUMULATOR FORMAT
CURRENT OFFSET COMPENSATION
Current measurement and current accumulation are both internally compensated for offset on a continual
basis minimizing error resulting from variations in device temperature and voltage. Additionally, a
constant bias can be utilized to alter any other sources of offset. This bias resides in EEPROM address
33h in two’s-complement format and is subtracted from each current measurement. The current offset
bias is applied to both the internal and external sense resistor configurations. The factory default for the
current offset bias is a value of 0.
Figure 6. CURRENT OFFSET BIAS
VOLTAGE MEASUREMENT
The DS2761 continually measures the voltage between pins V
voltage register is updated in two’s-complement format every 3.4ms with a resolution of 4.88mV.
Voltages above the maximum register value are reported as the maximum value. The voltage register
format is shown in Figure 7.
MSb
S
2
14
MSB—Address 10
2
13
2
12
2
11
MSb
S
2
10
2
6
2
9
2
Units: 0.625mA for Internal Sense Resistor
5
LSb
2
Address 33
8
15.625mV for External Sense Resistor
2
9 of 24
4
2
MSb
3
2
7
2
2
2
IN
6
Units: 0.25mAhrs for Internal Sense Resistor
2
and V
1
LSB—Address 11
2
6.25mVhrs for External Sense Resistor
LSb
5
2
0
SS
2
over a range of 0 to 4.75V. The
4
2
3
2
2
2
1
LSb
2
0