ds2761 Maxim Integrated Products, Inc., ds2761 Datasheet - Page 8

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

Summary. All of the protection conditions described above are OR'ed together to affect the
outputs.
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 25mW current-sense resistor, and 2) external user-selectable sense resistor. In
either configuration, the DS2761 considers the voltage difference between pins IS1 and IS2 (V
V
flowing into the battery (charging), while a negative V
battery (discharging).
V
format every 88ms (128/fsample) with an average of 128 readings. 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 4.
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 I
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 V
register, with a resolution of 15.625mV and a full-scale range of ±64mV.
Figure 4. CURRENT REGISTER FORMAT
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.
IS2
IS
is measured with a signed resolution of 12-bits. The current register is updated in two’s-complement
) to be the filtered voltage drop across the sense resistor. A positive V
bit CE = 0) or (Sleep Mode)
DC
CC
MSb
S
= (Undervoltage) or (Overcurrent, Either Direction) or (Short Circuit) or
= (Overvoltage) or (Undervoltage) or (Overcurrent, Charge Direction) or (Protection Register
2
(Protection Register Bit DE = 0) or (Sleep Mode)
11
MSB—Address 0E
2
10
2
9
2
8
2
7
2
6
LSb
2
5
8 of 24
MSb
IS
2
4
value indicates current is flowing out of the
2
3
Units: 0.625mA for Internal Sense Resistor
LSB—Address 0F
2
2
15.625mV for External Sense Resistor
2
1
IS
2
0
value indicates current is
IS
X
voltage to the current
X
FS
spec for more
LSb
CC
X
IS
and
= V
IS1
DC
-