AS3932 데이터 시트보기 (PDF) - austriamicrosystems AG

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AS3932

3D Low Frequency Wakeup Receiver

austriamicrosystems AG 

AS3932

Data Sheet - Detailed Description

8.9.1 Crystal Oscillator

Table 22. Characteristics of XTAL

Symbol

Parameter

Crystal accuracy

(initial)

Crystal motional resistance

Frequency

Contribution of the oscillator to the

frequency error

Start-up Time

Duty cycle

Current consumption

Conditions

Overall accuracy

Crystal dependent

Min Typ Max Units

±120 p.p.m.

60

KΩ

32.768

kHz

±5

p.p.m

1

s

45

50

55

%

1

µA

8.9.2 RC-Oscillator

Table 23. Characteristics of RCO

Symbol

Parameter

Frequency

Calibration time

Current consumption

Conditions

If no calibration is performed

If calibration is performed

Periods of reference clock

Min Typ Max Units

27 32.768 42

kHz

31 32.768 34.5 kHz

65 cycles

200

nA

To trim the RC-Oscillator, set the chip select (CS) to high before sending the direct command trim_osc over SDI. Then 65 digital clock cycles of

the reference clock (e.g. 32.768 kHz) have to be sent on the clock bus (SCL), as shown in Figure 22. After that the signal on the chip select (CS)

has to be pulled down.

The calibration is effective after the 65th reference clock edge and it will be stored in a volatile memory. In case the RC-oscillator is switched off

or a power-on-reset happens (e.g. battery change) the calibration has to be repeated.

Figure 22. RC-Oscillator Calibration via SDI

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Revision 1.2

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