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ADVANCED COMMUNICATIONS & SENSING

DATASHEET

SX8124

24 hours timer synchronized on 50/60Hz mains

ACS - Revision 2.4

October 2010

© Semtech Corp.

8

Timer synchronization on a 50Hz or 60Hz external phase

To avoid timing drifts over the time, the SX8124 can be synchronised on a signal from the mains.

The SX8124 permanently checks the duration between two consecutive edges on the PHASE pin.

8.1

External phase available for synchronization

Please note that for correct phase detection the edges on the PHASE pin must be sharp . A sinus or triangular

wave is not recommended.

8.2

No phase available for synchronization

If there is no clean 50Hz or 60Hz signal on PHASE pin, the system timing switch on the internal RC oscillator. In

this case the timer will be 10% precise. The LED output is sending 2Hz burst to indicate that the timer is not

synchronized and counting based on the internal base time.

The maximum frequency on PHASE pin should not exceed 20kHz. If the signal on this pin has a frequency

potentially higher than 20kHz it must be low pass filtered with a capacitor.

Figure 9. Example: timer synchronized on a 50Hz phase

Figure 10. Timer not synchronized on an external phase

LED

60 Hz

detect

Burst gen

PHASE

50 Hz

detect

RC

Oscillator

24H

TIMER

Output

control

If OUT and NOUT are on :

If OUT and NOUT are off :

50 Hz

signal

LED

60 Hz

detect

Burst gen

PHASE

50 Hz

detect

RC

Oscillator

24H

TIMER

Output

control

No signal

or noise