L99LD21 datasheet(24/73 Pages) STMICROELECTRONICS

24 / 73 page

Functional description

L99LD21

24/73

DS11130 Rev 5

Limp home characteristics are:

•

Direct Input access enabled

•

Boost active

•

Buck1 according DIN

•

Buck2 OFF

•

SPI active:

–

All SPI write operations must be allowed without any effects on the device

behavior.

When the device leaves this mode, it can enter Standby or Active mode.

If the microcontroller sends to the device the following SPI frames sequence:

•

The first SPI frame sets UNLOCK bit = 1

(see bit <1> on Table 14: CR#1: Control Register 1)

•

The second consecutive SPI frame sets GOSTBY bit = 1 and EN bit = 0

(see bit <3> and bit <2> on Table 15: CR#2: Control Register 2)

The device enters Standby mode.

If the microcontroller sends to the device the sequence of the following SPI frames:

•

The first SPI frame sets UNLOCK bit = 1;

(see bit <1> on Table 14: CR#1: Control Register 1)

•

The second consecutive SPI frame sets GOSTBY bit = 0 and EN bit = 1.

(see bit <3> and bit <2> on Table 15: CR#2: Control Register 2)

The device enters Active mode.

In Limp Home, after setting bit 27 on GSB (FE1, functional error bit), an auto restart procedure

is implemented: every tAUTORESTART, functional error bit eventually set is automatically cleared.

4.1.5

Active mode

The device enters the Active mode if the microcontroller sends the following SPI frames

sequence:

•

In a first SPI frame set the UNLOCK bit to 1

(see bit <1> on Table 14: CR#1: Control Register 1)

•

In a second frame, set EN bit to 1 and GOSTBY bit to “0”

(see bit <2> and bit <3> on Table 15: CR#2: Control Register 2)

Table 3. Operating modes

Operating

mode

Entering conditions

Leaving condition

Characteristics

Standby

mode

– By default, once powered on (VS present);

– SPI active and micro sending following

consecutive frames:

UNLOCK = 1

(EN,GOSTBY) = (0,1)

DIN = High for tWAKEUP

and/or

CSN = Low for tWAKEUP

– V3V3 < VPOR;

–VS and VSPI low

consumption;

– SPI inactive

Pre-standby

mode

– Under the following conditions:

Two following consecutive SPI frames setting:

UNLOCK = 1

(EN,GOSTBY) = (0,1)

CSN High and DIN Low

for a time t > tSTDBY

– V3V3 > VPOR

– Boost disabled

– Bucks disabled

– SPI active

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