Datasheet

Data Sheet AD8202
Rev. H | Page 13 of 20
–140
0
0
2.5
04981-053
DIFFERENTIAL-MODE VOLTAGE (V)
A2 INPUT BIAS CURRENT (nA)
–120
–100
–80
–60
–40
–20
0.5
1.0 1.5
2.0
V
SUPPLY
= 5V
TEMPERATURE RANGE =
+1
25°C TO –40°C
Figure 41. A2 Input Bias Current vs. Input Voltage and Temperature. The
Shaded Area is the Bias Current from +125°C to −40°C.
An increase in the A2 bias current, in addition to the output
saturation voltage of A1, directly affects the output voltage of
the AD8202 system (Pin 3 and Pin 4 shorted). An example of
how to calculate the correct output voltage swing of the
AD8202, by taking all variables into account, follows:
• Amplifier A1 output saturation potential can drop as low
as 20 mV at its output.
• A2 typical input bias current of 40 nA multiplied by the
100 kΩ preamplifier output resistor produces
40 nA × 100 kΩ = 4 mV at the A2 input
• Total voltage at the A2 input equals the output saturation
voltage of A1 combined with the voltage error generated
by the input bias current
20 mV + 4 mV = 24 mV
• The total error at the input of A2, 24 mV, multiplied by the
buffer gain generates a resulting error of 48 mV at the
output of the buffer. This is AD8202 system output low
saturation potential.
• The high output voltage range of the AD8202 is specified
as 4.8 V. Therefore, assuming a typical A2 input bias
current, the output voltage range for the AD8202 is 48 mV
to 4.8 V.
For an example of the effect of changes in A2 input bias current
vs. applied input potentials, see Figure 41. The change in bias
current causes a change in error voltage at the input of the
buffer amplifier. This results in a change in overall error
potential at the output of the buffer amplifier.