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AS3930

Data Sheet - D e t a i l e d D e s c r i p t i o n

AS3930 needs the following external components:

Power supply capacitor - CBAT – 100 nF

32.768 kHz crystal with its two pulling capacitors – XTAL and CL (it is possible to omit these components if the internal RC oscillator is used

instead of the crystal oscillator).

Input LC resonator.

In case the internal RC-oscillator is used (no crystal oscillator is mounted), the pin XIN has to be connected to the supply, while pin XOUT should

stay floating. Application diagrams with and without crystal are shown in Figure 1 and Figure 2

8.2 Operating modes

8.2.1 Power Down Mode

In Power Down Mode AS3930 is completely switched off. The typical current consumption is 400 nA.

8.2.2 Listening Mode

In listening mode only the channel amplifier and the RTC are running. In this mode the system detects the presence of a carrier. In case the

carrier is detected the RSSI can be displayed.

Inside this mode it is possible to distinguish the following three sub modes:

8.2.2.1 Standard Listening mode

The channel amplifier, capable to detect the presence of the carrier frequency, is active all the time.

8.2.2.2 ON/OFF mode (Low Power mode)

The channel amplifier is active for one millisecond to be than switched-off for a certain time. The OFF-time is programmable see R4<7:6>.

Figure 11. ON/OFF Mode

For both sub modes it is possible to enable a further feature called Artificial Wake-up. If the Artificial Wakeup is enabled the AS3930 produces an

interrupt after a certain time regardless whether any activity is detected on the input. The period of the Artificial Wake-up is defined in the register

R8<2:0>. The user can distinguish between Artificial Wake-up and Wake-up based on the field detection (frequency or pattern detection) since

the Artificial Wake-up interrupt lasts only 128 μs. With this interrupt the microcontroller (μC) can get feedback on the surrounding environment

(e.g. read the false wakeup register, see relator register R13<7:0>) and/or take actions in order to change the setup.

8.2.3 Preamble Detection / Pattern Correlation

The chip can go in to this mode after detecting a LF carrier only if the data correlator function is enabled see R1<1>. The correlator searches

first for preamble frequency (constant frequency of Manchester clock defined according to bit-rate transmission) and then for data pattern.

If the pattern is matched the wake-up interrupt is displayed on the WAKE output and the chip goes in data receiving mode. If the pattern fails the

internal wake-up is terminated and no IRQ is produced.

Channel

Presence of

Carrier

t0

t0 + 1ms

t0 + T

t0 + T + 1ms

t0 + 2T

Time

Time