AD8236

Rev. 0 | Page 17 of 20

To eliminate high frequency common-mode signals while using

smaller source resistors, a low-pass RC network can be placed

at the input of the instrumentation amplifier (see Figure 40).

The filter limits the input signal bandwidth according to the

following relationship:

)

2

(

π

2

1

G

C

D

DIFF

C

C

C

R

FilterFreq

+

+

=

)

(

π

2

1

G

C

CM

C

C

R

FilterFreq

+

=

The imbalance causes the AD8236 to treat what would have been

a common-mode signal as a differential signal. To reduce the

lower than the common-mode frequency.

R

R

AD8236

–IN

+IN

10µF

0.1µF

REF

1nF

1nF

10nF

4.02kΩ

4.02kΩ

Figure 40. RFI Suppression

COMMON-MODE INPUT VOLTAGE RANGE

The common-mode input voltage range is a function of the

input voltages, reference voltage, supplies, and the output of

Internal Op Amp A. Figure 34 shows the internal nodes of the

AD8236. Figure 20 to Figure 23 show the common-mode

voltage ranges for typical supply voltages and gains.

If the supply voltages and reference voltage is not represented in

Figure 20 to Figure 23, the following methodology can be used

to calculate the acceptable common-mode voltage range:

1.

Adhere to the input, output, and reference voltage ranges

shown in Table 2 and Table 3.

2.

Calculate the output of the internal op amp, A. The following

equation calculates this output:

4

R

kΩ

52.5

2

4

5

G

REF

DIFF

DIFF

CM

V

V

V

V

A

−

−

⎟

⎠

⎞

⎜

⎝

⎛

−

=

where:

3.

Keep A within 10 mV of either supply rail. This is valid over

the −40°C to +125°C temperature range.