AX5243 datasheet(22/42 Pages) ONSEMI

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AX5243

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Table 22. 4−FSK MODULATION

Modulation

DiBit = 00

DiBit = 01

DiBit = 11

DiBit = 10

Main Lobe Bandwidth

Max. Bitrate

4−FSK

Df = −3fdeviation

Df = −fdeviation

Df = +fdeviation

Df = +3fdeviation

BW = (1 + 3 h) ⋅BITRATE

115.2 kBit/s

4−FSK Frequency shaping is always hard.

Automatic Frequency Control (AFC)

The AX5243 features an automatic frequency tracking

loop which is capable of tracking the transmitter frequency

within the RX filter band width. On top of that the AX5243

has a frequency tracking register TRKRFFREQ to

synchronize the receiver frequency to a carrier signal. For

AFC adjustment, the frequency offset can be computed with

the following formula:

Df + TRKRFFREQ

224

fXTAL

The pull−in range of the AFC can be programmed with the

MAXRFOFFSET Registers.

PWRMODE Register

The PWRMODE register controls, which parts of the chip

are operating.

Table 23. PWRMODE REGISTER

PWRMODE Register

Name

Description

0000

POWERDOWN

All digital and analog functions, except the register file, are disabled. The core supply

voltages are switched off to conserve leakage power. Register contents are preserved and

accessible registers via SPI, but at a slower speed.

Access to the FIFO is not possible and the contents are not preserved. POWERDOWN

mode is only entered once the FIFO is empty.

0001

DEEPSLEEP

AX5243 is fully turned off. All digital and analog functions are disabled. All register

contents are lost.

To leave DEEPSLEEP mode the pin SEL has to be pulled low. This will initiate startup and

reset of the AX5243. Then the MISO line should be polled, as it will be held low during

initialization and will rise to high at the end of the initialization, when the chip becomes

ready for operation.

0101

STANDBY

The crystal oscillator and the reference are powered on; receiver and transmitter are off.

Access to the FIFO is not possible and the contents are not preserved. STANDBY is only

entered once the FIFO is empty.

0110

FIFO

The reference is powered on. Register contents are preserved and accessible registers via

SPI.

Access to the FIFO is possible and the contents are preserved.

1000

SYNTHRX

The synthesizer is running on the receive frequency. Transmitter and receiver are still off.

This mode is used to let the synthesizer settle on the correct frequency for receive.

1001

FULLRX

Synthesizer and receiver are running.

1011

WOR

Receiver wakeup−on−radio mode.

The mode the same as POWERDOWN, but the 640 Hz internal low power oscillator is

running.

1100

SYNTHTX

The synthesizer is running on the transmit frequency. Transmitter and receiver are still off.

This mode is used to let the synthesizer settle on the correct frequency for transmit.

1101

FULLTX

Synthesizer and transmitter are running. Do not switch into this mode before the

synthesizer has completely settled on the transmit frequency (in SYNTHTX mode),

otherwise spurious spectral transmissions will occur.

NOTE: For the corresponding currents see table in section DC Characteristics.

Table 24. A TYPICAL PWRMODE SEQUENCE FOR A TRANSMIT SESSION

Step

PWRMODE

Remarks

POWERDOWN

STANDBY

The settling time is dominated by the crystal used, typical value 3ms.

FULLTX

Data transmission

POWERDOWN

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