AD7705_06 datasheet(41/44 Pages) AD

41 / 44 page

AD7705/AD7706

Rev. C | Page 41 of 44

BATTERY MONITORING

An application where the low power, single-supply operation is

required is battery monitoring in portable equipment applications.

Figure 29 shows a block diagram of a battery monitor using the

AD7705 and an external multiplexer to measure differentially

the voltage across a single cell.

The second channel on the AD7705 is used to monitor current

drain from the battery. The AD7705, with its dual-input

channel, is ideally suited for measurement systems requiring

two input channels, as in this case, to monitor voltage and

current.

Because the AD7705 can accommodate very low input signals,

RSENSE can be kept low, reducing undesired power dissipation.

Operating with a gain of 128, a ±9.57 mV full-scale signal can

be measured with a resolution of 2 μV, giving 13.5 bits of flicker-

free performance in such a system.

To obtain specified performance in unbuffered mode, the

common-mode range of the input is GND to VDD, provided that

the absolute value of the analog input voltage lies between

GND − 100 mV and VDD + 30 mV. Absolute voltages of

GND − 200 mV can be accommodated on the AD7705 at 25°C

without any degradation in performance, but with significantly

increased leakage at elevated temperatures.

VCELL 1

RSENSE

AIN1(+)

AIN1(–)

AIN2(+)

AIN2(–)

REF IN(–)

AD7705

VDD

REF IN(+)

1.225V

REF

VOLTAGE

REGULATORS

VCELL 2

VCELL 3

VCELL 4

VDIFF1

VDIFF2

VDIFF3

VDIFF4

DC BATTERY

CHARGING

SOURCE

LOAD

ON/OFF SWITCH

GND

4-TO-1

DIFFERENTIAL

MULTIPLEXER

Figure 29. Battery Monitoring Using the AD7705

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