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AS3932

AS3932 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).

One, two, or three LC resonators according to the number of used channels.

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 1and Figure 2

8.2 Operating Modes

8.2.1 Power Down Mode

In Power Down Mode AS3932 is completely switched off. The typical current consumption is 400 nA.

8.2.2 Listening Mode

In listening mode only the active channel amplifiers 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.

If the three dimensional detection is not required it is possible to deactivate one or more channels. In case only two channels are required the

deactivated channel must be the number three, while if only one channel detection is needed the active channel must be the number one.

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

8.2.2.1 Standard Listening mode

All channels are active at the same time

8.2.2.2 Scanning mode (Low Power mode 1)

All used channels are active, but only one per time slot, where the time slot T is defined as 1ms. If, for example all three channels are used in the

first millisecond the only active channel is the number one, after the first millisecond the channel three will be active for the same period of time

and at the end the channel two will be working for one millisecond, handing over to the channel one again. This channel rotation goes on until the

presence of the carrier is detected by any of the channels; then immediately all three channels will become active at the same time. Now AS3932

can perform a simultaneous multidirectional evaluation (on all three channels) of the field and evaluate which channel has the strongest RSSI.

The channel with the highest RSSI will be put through to the demodulator. In this way it is possible to perform multidirectional monitoring of the

field with a current consumption of a single channel, keeping the sensitivity as good as if all channels are active at the same time.

Figure 11. Scanning Mode

tim e

tim e

tim e

C h a nnel1

C h a nnel2

C h a nnel3

tim e

P resenc e

of c a rrier

t0

t0 + T

t0 + 2 T

t 0 + 3 T

t 0 + 4 T

t0 + 5 T

t1