PM6641 datasheet(33/47 Pages) STMICROELECTRONICS

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PM6641

Device description

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7.11

Fault management

PM6641 has been conceived to constantly monitor the rails output voltage. In order to

protect itself from failure and the load from damage, the device is able to:

●

Limit the power MOSFETs current

●

Detect output over voltage

●

Detect output under voltage

●

Monitor the device temperature

●

Detect input power supply under voltage

The current limit is an auto-recovery protection, monitoring cycle by cycle the regulators

high side MOSFET current (see Chapter 7.10: Peak current limit on page 31 section for

details).

The output Over Voltage and Under Voltage and the input Under Voltage are latched

protections, whereas the thermal shutdown is auto-recovery; all these features are

described in the following sections.

7.11.1

Output over voltage

If the output voltage of a switching regulator (memory supply rail VDDQ (1.8 V), chipset

supply rails 1.5 V or 1.05 V) becomes greater than 120 % of its nominal value, an over

voltage (OV) protection for that rail is triggered. As a consequence the regulator stops

switching, the internal low-side power MOSFET of that rail is turned on and the high-side

MOSFET is turned off. The OV protection effect is the very quick discharge of the rail output

capacitor.

The OV condition is latched, and it can be reset only by toggling the enable pin of that rail or

by turning off and on the IC power supply (AVCC pin).

An OV condition for one of the outputs of the PM6641 has no effect on the operation of the

other outputs (e.g., if the OV protection is triggered for the VDDQ regulator, the 1.5 V and

1.05 V regulators continue to work normally).

7.11.2

Output under voltage

If the output voltage of a switching regulator (memory supply rail VDDQ (1.8 V), chipset

supply rails 1.5 V or 1.05 V) becomes lower than 60 % of its nominal value (e.g. because the

rail was shorted to ground or the output load is increased dramatically), an under voltage

(UV) protection for that rail is triggered.

An UV condition causes the soft-end of the rail, which implies the regulator turn off and the

rail discharge MOSFET turn on (see Chapter 7.7: Outputs Soft-End on page 29 section for

details); the UV condition is latched, and it can be reset only by toggling the enable pin of

that rail or by turning off and on the PM6641 power supply (AVCC pin).

As for OV protection, each switching regulator can perform under voltage protection without

affecting other regulators.

The over-current feature is implemented in the PM6641 by limiting the output current of

each rail (see Chapter 7.10: Peak current limit on page 31 section for details) and triggering

a latched UV protection if the output voltage falls because of a load requesting more current

than the limit.

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