ST7LITE3XF2 datasheet(30/173 Pages) STMICROELECTRONICS

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ST7LITE3xF2

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7.6 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.

Note: A reset can also be triggered following the

detection of an illegal opcode or prebyte code. Re-

fer to section 12.2.1 on page 128 for further de-

tails.

7.6.1 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 17.

The voltage threshold can be configured by option

byte to be low, medium or high.

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.

Use of LVD with capacitive power supply: with this

type of power supply, if power cuts occur in the ap-

plication, it is recommended to pull VDD down to

0V to ensure optimum restart conditions. Refer to

circuit example in Figure 99 on page 154 and note

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 17. Low Voltage Detector vs Reset

VDD

VIT+(LVD)

RESET

VIT-(LVD)

Vhys

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