ST72361 datasheet(25/224 Pages) STMICROELECTRONICS

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ST72361

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6.4 SYSTEM INTEGRITY MANAGEMENT (SI)

The System Integrity Management block contains

the Low Voltage Detector (LVD) and Auxiliary Volt-

age Detector (AVD) functions. It is managed by

the SICSR register.

6.4.1 Low Voltage Detector (LVD)

The Low Voltage Detector function (LVD) gener-

ates a static reset when the VDD supply voltage is

below a VIT-(LVD) reference value. This means that

it secures the power-up as well as the power-down

keeping the ST7 in reset.

The VIT-(LVD) reference value for a voltage drop is

lower than the VIT+(LVD) reference value for power-

on in order to avoid a parasitic reset when the

MCU starts running and sinks current on the sup-

ply (hysteresis).

The LVD Reset circuitry generates a reset when

VDD is below:

–VIT+(LVD) when VDD is rising

–VIT-(LVD) when VDD is falling

The LVD function is illustrated in Figure 15.

Provided the minimum VDD value (guaranteed for

the oscillator frequency) is above VIT-(LVD), the

MCU can only be in two modes:

– under full software control

– in static safe reset

In these conditions, secure operation is always en-

sured for the application without the need for ex-

ternal reset hardware.

During a Low Voltage Detector Reset, the RESET

pin is held low, thus permitting the MCU to reset

other devices.

Notes:

The LVD allows the device to be used without any

external RESET circuitry.

The LVD is an optional function which can be se-

lected by option byte.

It is recommended to make sure that the VDD sup-

ply voltage rises monotonously when the device is

exiting from Reset, to ensure the application func-

tions properly.

Figure 15. Low Voltage Detector vs Reset

VDD

VIT+(LVD)

RESET

VIT-(LVD)

Vhys

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