L99LD01 datasheet(10/69 Pages) STMICROELECTRONICS

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Functional description

L99LD01

10/69

DocID025319 Rev 3

2.1.4

Normal mode

•

Normal mode with microcontroller: the device enters this mode after a successful start

up (VCC1 > VCC1_TH) and a microcontroller is detected. The device keeps this mode as

long as the watchdog is retriggered before a timeout event.

•

Normal mode in standalone configuration: the device enters this mode if a standalone

configuration is detected, independently from VCC1 errors. The L99LD01 keeps this

mode even in case of watchdog timeouts.

In both cases, the converter behaves according to the PWM_L pin.

2.1.5

Software limp home

This device enters software limp home mode in case the Lh_Sw bit is set (see Section :

Control registers 3).

The control registers are set to their default values, with the exception of the Lh_Sw bit,

which remains unchanged.

The converter behaves according to the signal on the LHM pin:

–

Turned on if a high signal is detected at the LHM pin

–

Turned off if a low signal is detected at the LHM pin

2.1.6

Limp home mode

The device enters limp home mode, if a microcontroller is detected, in the following cases:

–

Watchdog timeout in normal mode

–VCC1 under voltage (VCC1 < VCC1_TH) for more than 2 ms in normal mode

–VCC1 is below the VCC1_FAIL threshold for more than 4 ms during start-up

–VCC1 is below Vcc1uv for more than 100 ms during start-up and VS is above

VSMIN threshold

–

Thermal shutdown of VCC1

–

SDI stuck at 0 or 1

In Limp Home mode, all the control registers are set to their default values, except Lh_Sw

(see Section : Control registers 3), which remains unchanged.

The converter behaves according to the voltage level on the LHM pin:

•

Turned on if a High signal is detected at the LHM pin

•

Turned off if a Low signal is detected at the LHM pin

Depending on the root cause, the action taken to quit the limp home mode (provided that the

limp home condition has disappeared) is different. Some of the recovery paths require the

microcontroller to be supplied by external supply.

A power on reset is always possible.

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