AS3977 datasheet(19/47 Pages) AMSCO

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AS3977

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

9 Application Information

Figure 5. Functional Description Diagram of Timers and Data Synchronization

The Prescaler divides the XTAL frequency by fOUT=2

-PSC<2:0>*f

The Compare timer divides by fOUT=fIN/(TCV+1) and the Postscaler divides the input frequency by fOUT=2

-ASC<1:0>*f

which leads into a data

frequency of:

fOUT=2

-(PSC<2:0>+ASC<1:0>+1)* f

/ (TCV+1)

(EQ 2)

9.1 Operation Modes

All modes are controlled by the SDI interface.

Power Down Mode

The AS3977 is connected to the power supply and can be switched to power down mode. The current consumption is limited by the leakage

current.

Clock Enable Mode

In this mode, only the reference frequency generator is switched on and a clock signal is supplied via the clock output.

PLL Enable Mode

The PLL is switched on and locked at the selected output frequency. The power amplifier is in power down mode. This mode enables OOK-

ASK modulation by switching the PA on and off.

Transmit Mode

The PLL is switched on and locked at the selected output frequency. The power amplifier is in power on mode. This is the FSK mode for

transmitting data.

Baudrate

Generator

Data Generator

Data

Synchronization

TXDO

xor

Postscalar

/ 1,2,4,8

ASC

PSC

timer

compare

value

compare

counter

8bit

INV

Powerdown Timer

Powerdown

reset

CLK Source

TXDATA

MCCLK

XTAL

ENABLE

/ 2^16

Set Powerdown

Prescalar

/ 1,2,4,8,…

128

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