AN4092 datasheet(25/38 Pages) STMICROELECTRONICS

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AN4092

ADC

Doc ID 023080 Rev 2

25/38

ADC

The goal of this chapter is to provide hints on how to dimension correctly the external ADC

circuitry in order to reduce errors and, at the same time, to protect the ADC inputs.

Figure 10.

Simplified ADC circuitry

The Figure 10 shows a simplified scheme of the external and internal circuit.

The external analogue source can be represented as a voltage source with its impedance

(Rs). Then it is a common practice to put an RC circuit to filter the analogue source; in

addition Rf can be also useful as current limiter in case of overvoltage.

Table 6.

SPC564Axx / SPC563Mxx ADC parameters

Parameter

Min.

Nominal

Max

12pF

Rsw

-8KOhm

21KOhm

(3 sigma, 150C)

Cs (single ended)

0.8pF

Cs (differential)

1.3pF

ADC clock frequency

16MHz

Sampling time (ADC

clocks)

128

12bit single ended

conversion time (ADC

clocks)

-14

12bit differential

conversion time (ADC

clocks)

-13

Residual voltage on

sample capacitor

1.25V

3.75V

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