ST52T400 datasheet(50/94 Pages) STMICROELECTRONICS

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ST52T400/T440/E440/T441

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7 ANALOG COMPARATOR (ST52X440/441)

7.1 Analog Module Overview

The ST52x440/441 includes an Analog Compara-

tor (AC) among its peripherals.

The Analog Comparator is endowed with analog

and digital elements in order to also allow the user

to make use of it as a single slope Analog to Digi-

tal converter. In particular, ST52x440/441 is

endowed with:

Analog Comparator;

7 channels analog mux (6 external lines, 1

internal voltage reference);

a current source providing 7 programmable

values;

16 bit Timer with a Capture Register and 12 bit

Prescaler;

The Analog Comparator peripheral can also be

used as a single slope A/D, supplying a ramp sig-

nal to the pin CS. The selection of the working

mode, as either Analog Comparator or single

slope

A/D

can

performed

via

the

REG_CONF3[(0)] bit.

7.2 Comparator Mode

In Analog Comparator mode, REG_CONF3[(0)] is

set to “0”. The AC inputs are available on the

external pins. The reference signal must be con-

nected to the CS pin, the signal to be compared

goes to the analog input AC0.

When the input becomes lower than the refer-

ence, the Analog Comparator output changes to

value “1”. The output can be read on the less sig-

nificative bit of Input Register 1 AC_CHAN0H

(Table 2.1).

7.3 A/D Converter Mode

To use the Analog Comparator for A/D Conver-

sion, REG_CONF3[(0)] bit must be set to “1”.

In A/D Mode either the insertion of an external

capacitor to pin CS or the connection to an exter-

nal signal to generate the reference ramp may be

chosen.

In the first case REG_CONF16[(1)] bit must be set

to “0”. The internal current generator, utilized to

charge the capacitor, provides 7 possible current

values,

which

can

selected

via

REG_CONF3[(7:5)]. The current values are in the

range between 0 to 70

µA withstepof 10µA.

The capacitor should have a low voltage coeffi-

Figure 7.1 Analog Peripheral Block Diagram

AC0

AC1

Bandgape Ref.=2.5V

Vcc

16 bit Timer

Stop Count

12 bit Presc.

CLK

Timer CLK

A/D Configuration Registers

43210

A/D Configuration Registers

Start

Current Sel.

Converted

Value

AC2

AC3

AC4

AC5

GNDA

43210

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