AD8236 데이터 시트보기 (PDF) - Analog Devices
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AD8236 Datasheet PDF : 20 Pages
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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:
FilterFreqDIFF
=
1
2πR(2 CD + CC
+ CG )
FilterFreqCM
=
1
2πR(CC
+ CG )
Mismatched CC capacitors result in mismatched low-pass filters.
The imbalance causes the AD8236 to treat what would have been
a common-mode signal as a differential signal. To reduce the
effect of mismatched external CC capacitors, select a value of CD
greater than 10 times CC. This sets the differential filter frequency
lower than the common-mode frequency.
+VS
0.1µF
10µF
CC
R
4.02kΩ
CD
R
4.02kΩ
CC
1nF
10nF
1nF
+IN
AD8236
VOUT
REF
–IN
Figure 40. RFI Suppression
AD8236
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:
A
=
5
4
⎜⎝⎛VCM
−
VDIFF
2
⎟⎠⎞
−
52.5 kΩ
RG VDIFF
−
VREF
4
where:
VDIFF is defined as the difference in input voltages,
VDIFF = VINP − VINM.
VCM is defined as the common mode voltage,
VCM = (VINP + VINM)/2.
If no gain setting resistor, RG, is installed, set RG to infinity.
3. Keep A within 10 mV of either supply rail. This is valid over
the −40°C to +125°C temperature range.
−VS + 10 mV < A < +VS – 10 mV
Rev. 0 | Page 17 of 20
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