AD7705/AD7706
Battery Monitoring
can be kept low reducing undesired power dissipation. Operat-
ing 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. In order to obtain specified
performance in unbuffered mode, the common mode range of
the input is from GND to VDD provided that the absolute value
of the analog input voltage lies between GND – 30 mV and
VDD + 30 mV. Absolute voltages of GND – 200 mV can be
accommodated on the AD7705 at 25°C without any degrada-
tion in performance, but leakage current increases significantly
at elevated temperatures.
Another area where the low power, single supply operation is a
requirement is battery monitoring in portable equipment appli-
cations. Figure 26 shows a block diagram of a battery monitor
that includes the AD7705 and an external multiplexer used to
differentially measure the voltage across a single cell. The sec-
ond channel on the AD7705 is used to monitor current drain
from the battery. The AD7705 with its dual input channel is
ideally suited to measurement systems requiring two input chan-
nels, as in this case, to monitor voltage and current. Since the
AD7705 can accommodate very low input signals the RSENSE
ON/OFF SWITCH
4-TO-1
DIFFERENTIAL
MULTIPLEXER
VCELL 1
+3V
+5V
VOLTAGE
REGULATORS
VDIFF1
VDIFF2
VDIFF3
VDIFF4
VCELL 2
VCELL 3
VCELL 4
V
DD
DC BATTERY
CHARGING
SOURCE
AD7705
REF IN(+)
AIN1(+)
1.225V
REF
LOAD
AIN1(–)
AIN2(+)
AIN2(–)
R
SENSE
REF IN(–)
GND
Figure 26. Battery Monitoring Using the AD7705
REV. A
–31–
ADI [ ADI ]
