SABRE-LL-I datasheet(19/141 Pages) STMICROELECTRONICS

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SABRE-LL-I

Supervisory system

19/141

Supervisory system

5.1

Overview

The supervisory circuitry monitors the state of several functions inside S.A.B.Re and resets

the device (and other ICs if connected to nRESET pin) when the monitored functions are

outside their normal range. Supervisory circuitry can be divided into three main blocks:

–

Power on reset (POR) generation circuitry.

–

nRESET (nRST_int) generation circuitry.

–

Thermal shut down (TSD) generation circuitry.

POR circuitry monitors the voltages that S.A.B.Re needs to guarantee its own functionality;

nRESET circuitry controls if S.A.B.Re’s main voltages are inside their normal range; TSD is

the thermal shut down of the chip in case of overheating.

5.2

Power on reset (POR) circuit

Power on reset circuit monitors VSupply, and V3v3 voltages. The purpose of this circuit is to

set the device is in a stable and controlled status until the minimum supply voltages that

guarantee the device functionality are reached. The output signal of this circuit (in the

following indicated as “POR”) becomes active when VSupply or V3v3 go under their falling

threshold.

When POR output signal is active, all functions and all flags inside S.A.B.Re are set in their

reset state; once POR signal comes back from off state (meaning monitored voltages are

above their rising threshold), the power up sequence is re-initialized

5.3

nRESET generation circuit

The nRESET circuit monitors VSupply, VSupply_int, VPump, VGPIO_SPI and all system

regulators (VSystem) voltages. The purpose of this circuit is to prevent the device

functionality until the monitored voltages reach their operative value (please note that V3v3

Table 7.

Power on reset specifications

Parameter

Description

Test condition

Min

Typ

Max

Unit

VSupply_POR_valid VSupply voltage for POR valid

InRESET = 1mA

VSupply_POR_fall

VSupply POR

falling threshold

VSupply falling

tSupply_POR_filt

VSupply POR

filter Time

3µs

V3V3_POR_fall

V3v3 POR falling threshold

V3V3 falling

1.9

2.2

V3V3_POR_rise

V3v3 POR

rising threshold

V3V3 rising

2.7

V3V3_POR_hys

V3v3 POR hysteresis

0.5

t3V3_POR_filt

V3v3 PORfilter time

1.5

µs

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