L6460 datasheet(32/139 Pages) STMICROELECTRONICS

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Supervisory system

L6460

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Doc ID 17713 Rev 1

Supervisory system

The supervisory circuitry monitors the state of several functions inside L6460 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 L6460 needs to guarantee its own functionality;

nRESET circuitry controls if L6460’s main voltages are inside the normal range; TSD is the

thermal shut down of the chip in case of overheating.

5.1

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 L6460 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.

5.2

nRESET generation circuit

The nRESET circuit monitors VSupply, VSupplyInt, 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 is monitored by POR,

so it must be above its minimum value, otherwise nRESET circuit is not active).

This circuit generates an internal reset signal (in the following indicated as “nRST_int”) that

will also be signaled to external circuits by pulling low the nRESET pin.

The signal nRST_int becomes active in the following cases:

When one of the following voltages is lower than its own under voltage threshold:

–VSupply and VSupplyInt.

–VPump.

–VSystem (all switching or linear system regulators voltages).

–VGPIO_SPI.

When watchdog timer counter (see Chapter 6) elapse the watchdog timeout time (only

if watchdog function is enabled).

When L6460 is in “Low Power mode”.

When EnExtSoftRst bit in SoftResReg register is at logic level = “1” and a “SoftRes”

command is applied (see SoftResReg register description in Chapter 25).

When an nRST_int event is caused by above cases, the nRESET pin will stay low for a

“stretch” time that starts from the moment that nRST_int signal returns in the operative

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