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PS398CSEE

Precision 8-Ch, Diff. 4-Ch, 17V Analog Multiplexers

Pericom Semiconductor 

PS398/PS399

Precision 8-Ch, Diff. 4-Ch, 17V Analog Multiplexers

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RON

VIN

RS

CCOM(ON)

CL

VS

Figure 10. Equivalent model of one multiplexer channel

The table below shows how many time constants (mτ) are

needed to reach an accuracy of one LSB. τ = RON x CCOM(ON)

Bits Accuracy (%) m

8

0.25

6

12

0.012

9

15

0.0017

11

Now, let’s calculate what the maximum sampling rate for the

PS398. Assume a 12-bit accuracy and room temperature

operation.

In equation (1) above, n = 8, tTRANS = 150ns, tSETTLING = 9τ,

τ = 100ohm x 54pF

fS

=8

__________1_____________

[150ns + 9(100ohm x 54pF)]

,

or fS = 630kHz.

Assuming a x4 oversampling rate, the maximum sampling speed

for the PS398 would be 630÷4 = 157kHz.

10

PS8185F

09/28/04

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