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Revision 1.7

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AS3932

Datasheet - Detailed Descr i p ti on

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 1 and Figure 2

8.1 Operating Modes

8.1.1 Power Down Mode

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

8.1.2 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 two, 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:

Thus, if all three channels are active the procedure is as follows (see Figure 11): for the first millisecond only channel one is active while channel

two and three are powered down; for the next millisecond only channel three is active while channel one and two are powered down; finally,

channel two is active while the other two are deactivated. 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

time

time

time

Channel 1

Channel 3

Channel 2

time

Presence

of carrier

t0

t0 + T

t 0 + 2 T

t 0 + 3 T

t 0 + 4 T

t0 +5 T

t1