TLC1549C, TLC1549I, TLC1549M

10-BIT ANALOG-TO-DIGITAL CONVERTERS

WITH SERIAL CONTROL

SLAS059C – DECEMBER 1992 – REVISED MARCH 1995

14

POST OFFICE BOX 655303

APPLICATION INFORMATION

simplified analog input analysis

Using the equivalent circuit in Figure 14, the time required to charge the analog input capacitance from 0 V to

The capacitance charging voltage is given by

(1)

where

V

C +

V

S

1–e

–tc RtCi

The final voltage to 1/2 LSB is given by

(2)

(3)

and

(4)

V

S *

V

S

2048

+ V

S

1–e

–tc RtCi

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.

Rs

ri

VS

VC

50 pF MAX

1 k

Ω MAX

Driving Source†

TLC1549

Ci

VI

VI = Input Voltage at ANALOG IN

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.

Figure 14. Equivalent Input Circuit Including the Driving Source