ST92F120JR9T datasheet(14/320 Pages) STMICROELECTRONICS

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ST92F120 - GENERAL DESCRIPTION

In Figure 6 a true open-drain pin schematic is

shown. In this case all paths to VDD are removed

(P-channel driver, ESD protection diode, internal

weak pull-up) in order to allow the system to turn

off the power supply of the microcontroller and

keep the voltage level at the pin high without in-

jecting current in the device. This is a typical con-

dition which can occur when several devices inter-

face a serial bus: if one device is not involved in

the communication, it can be disabled by turning

off its power supply to reduce the system current

consumption.

When an illegal negative voltage level is applied to

the ST9 I/O pins (both versions, push-pull and true

open-drain output) the clamp diode is always

present and active (see ESD protection circuitry

and N-channel driver).

1.2.4.4 Internal Circuitry: Analog Input pin

Figure 6 shows the internal circuitry used for ana-

log input. It is substantially a digital I/O with an

added analog multiplexer for the A/D Converter in-

put signal selection.

The presence of the multiplexer P-channel and N-

channel can affect the behaviour of the pin when

exposed to illegal voltage conditions. These tran-

sistors are controlled by a low noise logic, biased

through AVDD and AVSS including P-channel N-

well: it is important to always verify the input volt-

age value with respect to both analog power sup-

ply and digital power supply, in order to avoid un-

intended current injections which (if not limited)

could destroy the device.

Figure 6. Digital Input/Output - Push-Pull Output - Analog Multiplexer Input

OUTPUT

BUFFER

INPUT

BUFFER

SDPROTECTION

CIRCUITRY

PORTCIRCUITRY

I/OCIRCUITRY

AVDD

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