ALED1262ZT datasheet(21/69 Pages) STMICROELECTRONICS

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Device local dimming function

The brightness of each channel can be adjusted through a 7-bit PWM grayscale brightness control according to

local dimming register PWM_gain_x.

Figure 9. Device local dimming function logic

Brightness data are loaded through I²C bus, PWM signal for each channel is generated by comparing the content

of the brightness register to a 7-bit counter. The counter’s clock source is provided by 3.3 MHz internal oscillator.

Brightness register default configuration is all “0” (0x00) this means minimum LED brightness.

Note:

PWM_gain_x registers are made visible internally to the PWM generator, after an I²C transaction, when the

internal 7-bit counter reaches the value 7Fh. Internal 7-bit counter stops when exiting PWM local dimming

configuration (PWM_En and/or BDM_Flag set to '0'). When re-entering in PWM local dimming configuration 7-bit

counter restarts from previous stopped value (unless HW reset), so first period of PWM waveform could be

shorter.

The schematic below summarizes this functionality.

Figure 10. Channel dimming feature

…….

inte rnal

c o unte r

Inte rnal o s c illato r fe eds the

c ounte r

Brig htne s s re g is te r

Counts from 0 to 127 (7bit)

Compares the value

generated by the

counter and the value

s tored in the brightnes s

regis ter

200Hz PWM

s ignal that

drives the

current

generator

VLED

inte rnal

o s c illator

Channel x

AMG090320171210MT

ALED1262ZT

Device local dimming function

DS12631 - Rev 4

page 21/69

ALED1262ZT Datasheet(PDF) 21 Page - STMicroelectronics