Data Sheet

© 2009 Microchip Technology Inc. DS22088C-page 33
MCP3422/3/4
6.2 Application Examples
The MCP3422/3/4 devices can be used for broad
ranges of sensor and data acquisition applications.
Figure 6-5 shows a circuit example measuring both the
battery voltage and current using the MCP3422 device.
Channels 1 and 2 are measuring the voltage and the
current, respectively.
When the input voltage is greater than the internal ref-
erence voltage (V
REF
= 2.048V), it needs a voltage
divider circuit to prevent the output code from being
saturated. In the example, R
1
and R
2
form a voltage
divider. The R
1
and R
2
are set to yield V
IN
to be less
than the internal reference voltage (V
REF
= 2.048V).
For the current measurement, the device measure the
voltage across the current sensor, and converts it by
dividing the measured voltage by a known resistance
value. The voltage drops across the sensor is waste.
Therefore, the current measurement often prefers to
use a current sensor with smaller resistance value,
which, in turn, requires high resolution ADC device.
The device can measure the input voltage as low as
2 µV range (or current in ~ µA range) with 18 bit
resolution and PGA = 8 settings.
The MSB (= sign bit) of the output code determines the
direction of the current, which identifies the charging or
the discharging current.
FIGURE 6-5: Battery Voltage and Charging/Discharging Current Measurement.
5kΩ
V
DD
V
SS
0.1 µF
10 µF
To MCU
(MASTER)
SCL
SDA
5kΩ
CH2+
SCL
CH2-
R
1
R
2
Battery
(Rechargeable)
2
3
4
5
6
7
CH1-
SDA
1
8
CH1+
V
DD
Current Sensor
To Load
To Battery
Discharging Current
Charging
Current
R
1
and R
2
= Voltage Divider
V
IN
R
2
R
1
R
2
+
------------------
V
BAT
×=
V
IN
V
BAT
MCP3422