TLC545C, TLC545I, TLC546C, TLC546I

8-BIT ANALOG-TO-DIGITAL CONVERTERS

WITH SERIAL CONTROL AND 19 INPUTS

SLAS066B – DECEMBER 1985 – REVISED OCTOBER 1996

9

POST OFFICE BOX 655303

PARAMETER MEASUREMENT INFORMATION

simplified analog input analysis

within 1/2 LSB can be derived as follows:

The capacitance charging voltage is given by

(

)

(1)

where

The final voltage to 1/2 LSB is given by

(2)

(

)

(3)

and

(4)

Therefore, with the values given the time for the analog input signal to settle is

(5)

This time must be less than the converter sample time shown in the timing diagrams.

VI = Input Voltage at INPUT A0 – A18

VS = External Driving Source Voltage

Rs = Source Resistance

ri = Input Resistance

Ci = Input Capacitance

† Driving source requirements:

• Noise and distortion for the source must be equivalent to the

resolution of the converter.

• Rs must be real at the input frequency.

Rs

ri

VS

VC

50 pF MAX

1 k

Ω MAX

Driving Source†

TLC545 / 6

Ci

VI

Figure 1. Equivalent Input Circuit Including the Driving Source