ST7MC1 datasheet(232/308 Pages) STMICROELECTRONICS

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10.7 OPERATIONAL AMPLIFIER (OA)

10.7.1 Introduction

The ST7 Op-Amp module is designed to cover

various

types

microcontroller

applications

where analog signals amplifiers are used.

It may be used to perform a variety of functions

such as: differential voltage amplifier, comparator/

threshold detector, ADC zooming, impedance

adaptor, general purpose operational amplifier.

10.7.2 Main Features

This module includes:

■ 1 stand alone Op-Amp that may be externally

connected using I/O pins

■ Op-Amp output can be internally connected to

the ADC inputs as well as to the motor control

current feedback comparator input

■ Input offset compensation with optional average

■ On/Off bit to reduce power consumption and to

enable

the

input/output

connections

with

external pins

10.7.3 General Description

This Op-Amp can be used with 3 external pins

(see device pinout description) and can be inter-

nally connected to the ADC and the Motor Control

cells. The gain must be fixed with external compo-

nents.

The input/output pins are connected to the Op-

Amp as soon as it is switched ON (through the

OACSR register).

The analog input ports must be configured as in-

put, no pull-up, no interrupt. Refer to the “I/O ports”

chapter. Using these pins as analog inputs does

not affect the ability of the port to be read as a logic

input.

The output is not connected (HiZ) when the Op-

Amp is OFF. However the pin can still be used as

an ADC or MTC input in this case.

When the Op-Amp is ON the output is connected

to a dedicated pin which is not a standard I/O port.

The output can be also be connected to the ADC

or the MTC. The switches are controlled software

(refer to the MTC and ADC chapters).

10.7.4 Input Offset Compensation

The Op-Amp incorporates a method to minimize

the input offset which is dependant on process lot.

It is useable by setting the OFFCMP bit of the con-

trol register, which launch the compensation cycle.

The CMPVR bit is set by hardware as soon as this

cycle is completed. The compensation is valid as

long as the OFFCMP bit is high. It can be re-per-

formed by cycling OFFCMP ‘0’ then ‘1’.

The compensation can be improved by averaging

the calculation (over 16 times) setting the AVGC-

MP bit.

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