Datasheet

Data Sheet AD8237
Rev. 0 | Page 25 of 28
APPLICATIONS INFORMATION
BATTERY CURRENT MONITOR
The micropower current consumption, unique topology, and rail-to-
rail input of the AD8237 make it ideal for battery-powered current
sensing applications. When configured as shown in Figure 75, the
AD8237 is able to obtain an accurate high-side current measurement
for both charging and discharging. Depending on the nature of the
load, +V
S
may require RC decoupling. Use Kelvin sensing methods
to achieve the most accurate results.
AD8237
+IN
–IN
REF
FB
V
OUT
V
REF
R1 R2
R
SHUNT
V
BAT
+
–
V
OUT
= G(I × R
SHUNT
) + V
REF
+V
S
–V
S
LOAD
10289-077
Figure 75. Battery-Powered Current Sense
PROGRAMMABLE GAIN IN-AMP
Most integrated circuit instrumentation amplifiers use a single
resistor to set the gain, which is in a low impedance path. Any
component placed between the gain setting pins has current flowing
through it, which adds to the gain resistance. Typical CMOS switches
have on resistance, R
ON
. R
ON
is not well controlled, is nonlinear with
input voltage, and has high drift. This creates large gain errors and
distortion at the output of the in-amp. This R
ON
problem has made
it difficult to build a precision programmable gain in-amp in the
past. With the AD8237 topology, the switches can be placed in a high
impedance sense path, eliminating the parasitic resistance effects.
Figure 76 shows one way to accomplish programmable gain. Some
applications may benefit from using a digital potentiometer instead
of a multiplexer.
AD8237
+IN
–IN
470pF
V
OUT
FB
10289-078
20kΩ
ADG604
200Ω
4:1 MUX
2kΩ
200Ω
22.1Ω
G = 10
G = 100
G = 1000
REF
2kΩ
G = 1
Figure 76. Programmable Gain with a Multiplexer