10

®

IVC102

The input resistance seen at pin 2 includes an additional

1.5k

Ω, the on-resistance of S

1. The total input resistance is

the sum of the switch resistance and R

IN, or 2.5kΩ in this

example.

Slew rate limit of the internal op amp is approximately

3V/

µs. For most applications, the slew rate of V

OUT should

be limited to 1V/

µs or less. The rate of change is propor-

tional to IIN and inversely proportional to CINT:

This can be important in some applications since the slew-

induced input voltage is applied to the sensor or signal

source. The slew-induced input voltage can be reduced by

increasing CINT, which reduces the output slew rate.

NONLINEARITY

Careful nonlinearity measurements of the IVC102 yield

typical results of approximately

±0.005% using the internal

input capacitors (C

INT = 100pF). Nonlinearity will be de-

graded by using an external integrator capacitor with poor

voltage coefficient. Performance with the internal capacitors

is typically equal or better than the sensors it is used to

measure. Actual application circuits with sensors such as a

photodiode may have other sources of nonlinearity.

1/10T

INT

1/T

INT

10/T

INT

qq

q

–20dB/decade

slope

Frequency

0

–10

–20

–30

–40

–50

Corner at

f = 0.32/T

INT

–3dB at

f = 0.44/T

INT

FIGURE 5. Frequency Response of Integrating Converter.

Slew Rate

=

I

IN

C

INT