L99LD21 datasheet(25/73 Pages) STMICROELECTRONICS

25 / 73 page

DS11130 Rev 5

25/73

L99LD21

Functional description

4.2

Programmable functions

4.2.1

Activation of the buck output

In Active mode, the activation of the Buck converters is performed according to the

configuration of control register CR#3<15:14> for Buck1 and CR#3<13:12> for Buck2, as

showed in the following table. See Table 16: CR#3: Control Register 3.

4.2.2

PWM dimming

The device allows modifying the brightness of the LEDs string simply managing the average

current.

Reset mode

– By default, when device leaves Standby mode

– Under following condition, when device is in

Active mode:

VSPI Under voltage

WD failure;

One SPI frame setting (EN,GOSTBY) = (0,0)

Two consecutive SPI frames setting:

UNLOCK = 1

(EN,GOSTBY) = (1,1)

Automatic transition after

400 ns

– All registers reset to

default values

– V3V3>VPOR

– SPI inactive

Limp Home 400 ns after Reset mode

– SPI sequence to enter

Active mode:

UNLOCK = 1

(EN,GOSTBY) = (1,0)

– SPI sequence to enter

Standby mode:

UNLOCK = 1

(EN,GOSTBY) = (0,1)

– Boost controller is

active

– DIN access enabled:

Buck1 is according to

DIN;

Buck2 is OFF

– SPI active

Active

mode

SPI sequence:

– UNLOCK = 1

– EN = 1 and GOSTBY = 0

–VSPI undervoltage

–WD failure

– SPI sequence to enter

Standby mode:

UNLOCK = 1

(EN,GOSTBY) = (0,1)

– Boost controller is

active

– Buck converters are

active

– SPI is active

Table 3. Operating modes (continued)

Operating

mode

Entering conditions

Leaving condition

Characteristics

Table 4. DIN pin Map for Buck1 and Buck2

CR#3<15> or CR#3<13>

CR#3<14> or CR#3<12>

Buck1 and Buck2 status

Buckx always OFF (default for Buck2)

Buckx attached to internal PWM

generator

Buckx always ON

Buckx controlled by DIN Input (default

for Buck1)

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