AS3665 datasheet(15/78 Pages) AMSCO

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AS3665

Datasheet, Confidential - D e ta i l e d D e s c r i p t i o n C l o c k G e n e r a t i o n

Clock Generation

The AS3665 has an internal oscillator running at fCLK and an external clock input CLK32K:

Figure 17. Clock Generation

The charge pump and the PWM generator use the fCLK clock signal from the internal oscillator. Depending on the sig-

nal sel_ext_clock, the internal timers and ramp generators use either the pin CLK32K as input or fCLK divided by 2 and

31:

The external clock on CLK32K is monitored and if the internal clock is enabled and no valid clock are detected the reg-

ister bit no_extclock_detected (see page 37) is set and an interrupt can be triggered.

The internal oscillator is enabled and disabled automatically if register bit osc_always_on is reset:

Table 7. GPO_Control Register

Addr: 04h

GPO_Control Register

Bit

Bit Name

Default Access

Description

sel_ext_clock

R/W

Enables the external clock on CLK32K (see Figure 17)

Use internal fCLK clock divided by 31*2

Use external clock on CLK32K (also

osc_always_on=0)

1. Using an external clock has two advantages:

a) Reduced quiescent current: the internal clock is switched off whenever possible and the timers run from

CLK32K.

b) All timings (e.g. ramp-up, wait) are as accurate as the external clock (usually derived from a crystal).

Table 8. Supervision Register

Addr: 08h

Supervision Register

Bit

Bit Name

Default Access

Description

osc_always_on

R/W

Enables the internal oscillator (see Figure 17)

Enable internal oscillator only if required

The internal oscillator is always running (except in

shutdown mode)

&'()

- #$

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AS3665

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