RTC chip recomendation for WP76xx

IoT Modules WP Series
1

Dear all,

We are about to add a RTC support for our WP76xx based design. From WP76xx specification I understand that there is no RTC integrated within a module (like it is done at WP8548). Can you recommend me a RTC chip that already has support in latest WP76xx Linux kernel (https://source.sierrawireless.com/resources/airprime/software/wp76xx/wp76xx-firmware-release-10,-d-,1-components/) ?

Thank you in advance,
Aleksandar

2

Hi @aleksandarzivkovic
114_RX8010SJ_E141.pdf (270.5 KB)

Did you fix your problem?

WP76xx module is able output 32kHz(clock) signal, but it is a bit different(offset -103ppm) with general RTC clock(32k768Hz).

You still possible to have RTC, if your system accept this frequency.

On another hand, you could consider ESPON RX8010SJ.
It can operate below 1V6(still keep counter content in 1V0) and has build crystal(no matching issue).

3

Hi,

Thanks for reply. We have decided to go with external I2C RTC with super capacitor backup but we are still in schematic drawing (perhaps we can change decision based on your further details). Can you give more details about WP76xx 32kHz output:

  • Which pin is used for that?
  • This signal is generated when WP76xx is powered off? Which pin is used for battery backup?
  • Are you saying that accuracy is ±100ppm or only offset? If you are talking about offset what is accuracy?
  • What is power consumption of such an integrated RTC (so we can calculate battery backup capacity)?

Regards,

4

Hi, @aleksandarzivkovic

  • Which pin is used for that?
    [LChing] The 32k signal output pin is LGA #23.

  • This signal is generated when WP76xx is powered off? Which pin is used for battery backup?
    [LChing] This signal is divided from system clock and WP76xx haven’t battery backup function. So clock signal will be stopped when module power off.

  • Are you saying that accuracy is ±100ppm or only offset? If you are talking about offset what is accuracy?
    [LChing] Sorry for my wrong presentation in before. The 32k signal has a offset(~-103ppm) to general RTC signal(32k768Hz). It is frequency offset issue and not accuracy(stability) issue.

  • What is power consumption of such an integrated RTC (so we can calculate battery backup capacity)?
    [LChing] 1) 320nA(3V, no I2C clock=0Hz, nIRQ1,2=off), 2) 900nA(3V, no I2C clock=0Hz, nIRQ2=1024Hz ON)

NOTE, the current leakage & function of I2C bus when module power off.

To compare another RTC chip, the consumption is higher than it and need to buy & SMT processing for a crystal. Also the manufacturer take the responsibility of accuracy issue(to reduce risk of SMT or components) .

BRS35390A_E.pdf (709.2 KB)

5

Hi,

thanks for quick reply. For our usecase RTC should not lose time between power downs so we cannot use WP76xx generated clock.

Regards,
Aleksandar

6

Hi! @aleksandarzivkovic

Now a day, you could get a RTC information such from GPS or internet.
Mean you can have real time information when connected world like your smart phone.

BR

7

Thanks for the information.