AS3661 datasheet(21/87 Pages) AMSCO

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AS3661

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

8.7 LED Driver Operational Description

AS3661 LED drivers are constant current sources. The output current can be programmed by control registers up to

25.5 mA. The overall maximum current is set by 8-bit output current control registers with 100 µA step size. Each of the

9 LED drivers has a separate output current control register. The LED luminance pattern (dimming) is controlled with

PWM (pulse width modulation) technique, which has internal resolution of 12 bits (8-bit control can be seen by user).

PWM frequency is 312 Hz (see Figure 23 on page 20).

Figure 23. LED Pattern and Current Control Principle

LED dimming is controlled according to a logarithmic or linear scale(see Figure 24). Logarithmic or linear scheme can

be set for both the program execution engine control and direct PWM control.

Figure 24. Logarithmic vs. Linear Dimming

Note: If the temperature compensation is active, the maximum PWM duty cycle is limited to 50% at +25°C. This is

required to allow enough headroom for temperature compensation over the whole temperature range -40 °C to

90°C.

100

128

192

256

Dimming Control [DEC]

linear PWM

logarithmic PWM

AS3661 Datasheet(PDF) 21 Page - ams AG