L99LD20 datasheet(18/61 Pages) STMICROELECTRONICS

18 / 61 page

Functional description

L99LD20

18/61

DS11366 Rev 3

3.2

Programmable functions

3.2.1

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 15: CR#3: Control Register 3.

3.2.2

PWM dimming

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

current.

The PWM dimming could be achieved in two different ways:

•

Through direct input, DIN

•

With integrated PWM generator

Dimming with direct input

The signal applies to buck1, buck2 or both, depending on DIN mapping bit configuration

(see bits <15:14> and bits <13:12> on Table 15: CR#3: Control Register 3). If the control

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)

– 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)

– Buck converters are

active

– SPI is active

Table 2. Operating modes (continued)

Operating

mode

Entering conditions

Leaving condition

Characteristics

Table 3. 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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