AS3677 datasheet(29/68 Pages) AMSCO

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AS3677

Datasheet - D e ta i l e d D e s c r i p t i o n

Figure 21. PWM Control

Automatic Up/Down Dimming

If the register pwm_dim_mode is set to 01 (up dimming) or 10 (down dimming) the value within the register pwm_code

is increased (up dimming) or decreased (down dimming) every time and amount (either 1/4

th or 1/8th) defined by the

exceeded. It is used to smoothly and automatically dim the brightness of the LEDs connected to any of the current

sinks. The PWM code is readable all the time (also during up and down dimming).

The waveform for up dimming looks as follows (cycles omitted for simplicity):

Figure 22. PWM Dimming Waveform for up dimming (pwm_dim_mode = 01); currX_mode = PWM controlled (not

all steps shown)

The internal pwm modulator circuit controls the current sinks as shown in the following figure:

Figure 23. PWM Control Circuit (currX_mode = 10b (PWM controlled)); X = any current sink

The adder logic (available for all current sinks) is intended to allow dimming not only from 0% to 100% (or 100% to 0%)

of currX_current, but also e.g. from 10% to 110% (or 110% to 10%) of currX_current. The starting current for up dim-

ming is defined by 0 + currX_adder and the end current is defined by currX_current + currX_adder.

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AS3677

AS3677 Datasheet(PDF) 29 Page - ams AG