AD8202YCSURF datasheet(13/20 Pages) AD

13 / 20 page

AD8202

Rev. D | Page 13 of 20

–140

2.5

DIFFERENTIAL-MODE VOLTAGE (V)

–120

–100

–80

–60

–40

–20

0.5

1.0

1.5

2.0

VSUPPLY = 5V

TEMPERATURE RANGE =

+125

°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.

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