AD8237ARMZ-R7 datasheet(25/28 Pages) AD

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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, +VS may require RC decoupling. Use Kelvin sensing methods

to achieve the most accurate results.

AD8237

+IN

–IN

REF

VOUT

VREF

RSHUNT

VBAT

–

VOUT = G(I × RSHUNT) + VREF

+VS

–VS

LOAD

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, RON. RON 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 RON 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

VOUT

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

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