AS3661 datasheet(22/87 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

8.7.1 Powering LEDs

Although the AS3661 is very suitable for white LED and general purpose applications, it is particularly well suited to

use with RGB LEDs. The AS3661 architecture is optimized for use with three RGB LEDs. Typically, the red LEDs have

forward voltages below 2V and thus red LEDs can be powered directly from VBAT. In AS3661 the LED7, LED8 and

LED9 drivers are directly powered from the battery voltage (VBAT), not from the charge pump output. The LED1 to

LED6 drivers are internally connected to the charge pump output and these outputs can be used for driving green and

blue (VF = 2.7V to 3.7V) or white LEDs. Of course, LED7, LED8 and LED9 outputs can be used for green, blue or white

LEDs if the VBAT voltage is high enough. An RGB LED configuration example is given in the Typical Applications

section.

8.7.2 Controlling the High-side LED Drivers

Direct PWM Control

All AS3661 LED drivers, LED1 to LED9, can be controlled independently through the two-wire serial I²C compati-

ble interface. For each high-side driver there is a PWM control register. Direct PWM control is active by default.

Controlling by Program Execution Engines

Engine control is used when the user wants to create programmed sequences. The program execution engine has

higher priority than direct control registers. Therefore if the user has set to PWM register a certain value it will be

automatically overridden when the program execution engine controls the driver. LED control and program execu-

tion engine operation is described in the chapter Control Register Details.

Master Fader Control

In addition to LED-by-LED PWM register control, the AS3661 is equipped with so called master fader control,

which allows the user to fade in or fade out multiple LEDs by writing to only one register. This is an useful function

to minimize serial bus traffic between the MCU and the AS3661. The AS3661 has three master fader registers, so

it is possible to form three master fader groups. Master fader control can be used with the engines as well.

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