AN2168

1 Power supply

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1

Power supply

1.1

Overview

The ST10F27x devices are processed in 0.18 µm technology. ST10F27x core logic and I/O

peripherals need different power supplies. In fact, ST10F27x core logic operates with an 1.8V

power supply while the I/O peripherals operate with a power supply in the 4.5V to 5.5V range.

The ST10F27x devices are single supply. This means that just one external supply of 5V is

necessary to feed both core and peripherals. The power management block includes a

regulator to provide the core logic 1.8V supply from the 5V input supply.

The internally generated 1.8V supply is available on pin V18 (pin 56) of the ST10F27x. No

external supply can be connected to V18. A decoupling ceramic capacitor of a typical value

10nF(max 100nF) has to be connected between the V18 pin and the nearest Vss pin. The main

purposes of this capacitor are to:

●

compensate voltage drops due to pulsive current sinked by the device.

●

close the feedback loop of the internal voltage regulator making the system stable.

A capacitor of a value 100nF has to be connected for each couple VDD and the nearest pin

Vss.

1.2

On the ST10F27x, the pin 99 provides two functionalities:

●

main power is OFF. It must be applied before switching OFF the main power supply.

●

EA functionality which configures the ST10F27x to start from external memory if its level is

low during reset.

Table 1 contains the different configurations and the needed hardware for each case (if stand

by mode is used or not).

Table 1.

EA = 1

EA = 0

Stand by mode used

VSTBY = 5V when VDD is

turned off

Stand by mode not used

VSTBY = 0V

Vstby Ex

Vss

Vss

EA

4 .. 5.5 V

VDD

Vss