ST72411R datasheet(46/71 Pages) STMICROELECTRONICS

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ST72411R

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5.5 SMARTCARD SUPPLY SUPERVISOR (SSS)

5.5.1 Introduction

The Smartcard Supply Supervisor (SSS) allows

the VSC_PWR Smartcard supply to be switched on

and off by software and protects the smartcard

from overload.

In addition, the SSS supplies power to the I/O lines

used to interface the smartcard. This means that

no external components are needed for adapting

the interface to the levels required for interfacing

the smartcard, except a capacitor on the SC_PWR

output.

5.5.2 Main Features

Software power-on/off control

Hardware cut-off in case of output current

overload

Grounded output level when turned-off

Low consumption mode

5.5.3 General description

The SSS generates the Smartcard SC_PWR sup-

ply from the MCU VDD supply. When disabled, the

regulator ties the output SC_PWR line to ground,

and is placed in low power mode. At the same

time, the interface I/O lines are also tied to ground.

In case of current overload on the output

SC_PWR, the output level drops due to internal

impedance of the regulator. The associated Cur-

rent Overload detector switches-off the SC_PWR

supply and sets a flag into the Status/Control Reg-

ister.

Figure 50 shows the Smartcard Supply Supervisor

(SSS) block diagram.

Figure 36. Smartcard Supply Supervisor (SSS) Block Diagram

Reference voltage

MCU VDD

SC_PWR

SC I/Os

I/O

VDD

SSSCR

VDD

Reference Voltage

CURRENT OVERLOAD

VOLTAGE REGULATOR

OVLD SSSR

OVLD

0 CKOD

CK_AF

SSS

OVLD

OEN

fOSC/2

fOSC/4

SC_CK

OVLD INTERRUP T

Logic

Control

Logic

Control

DETECTOR

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