AS3661 datasheet(20/87 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

8.6.6 Automatic Power Save Mode

Automatic power save mode is enabled when POWERSAVE_EN bit in register address 36H is ‘1’. Almost all analog

blocks are powered down in power save, if an external clock signal is used. Only the charge pump protection circuits

remain active. However, if the internal clock has been selected, only charge pump and LED drivers are disabled during

the power save; the digital part of the LED controller needs stay active. In both cases the charge pump enters to the

weak 1x mode. In this mode the charge pump utilizes a passive current limited keep-alive switch, which keeps the

output voltage at the battery level. During the program execution AS3661 can enter power save if there is no PWM

activity in any of the LED driver outputs. To prevent short power save sequences during program execution, AS3661

has an instruction look-ahead filter. During program execution engine 1, engine 2 and engine 3 instructions are

constantly analyzed, and if there is time intervals of more than 50ms in length with no PWM activity on LED driver

outputs, the device will enter power save. In power save mode program execution continues uninterruptedly. When an

instruction that requires PWM activity is executed, a fast internal startup sequence will be started automatically.

8.6.7 PWM Power Save Mode

PWM cycle power save mode is enabled when register 36 bit [2] PWM_PS_EN is set to '1'. In PWM power save mode

analog blocks are powered down during the "down time" of the PWM cycle. Blocks that are powered down depends

whether external or internal clock is used. While the Automatic Power Save Mode (see above) saves energy when

there is no PWM activity at all, the PWM Power Save mode saves energy during PWM cycles. Like the Automatic

Power Save Mode, PWM Power Save Mode works also during program execution.

Figure 22. PWM Powersave Principle with external clock (VDD =3.6V, 50% PWM, ILED9=5mA)

1ms/Div

INPUT CURRENT ~3.5µA

DURING PWM POWESAVE

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