[WP8548] [MangOH] RTC start sequence (file attached)

Test environnement :

  • Mangoh board + WP8548 module with latest firmware release 11 (legato 16.04)
  • And Prototype board including WP8548 module with latest firmware release 11 (legato 16.04)

We need some explanations on the start sequence for the RTC backup.
Indeed we use a battery and the mangOH kit which uses a 1.5mF capacitor but in any case we’re missing some information to use it correctly.
You’ll find enclosed a screenshot detailing start sequence and voltage level at RTC input(/output), and here’s my description :
Channel3 = Voltage accross a 10k resistor between 3V batterie and RTC input :
Phase 1 : At power on, during init, for 10 seconds : null consumption
Phase 2 : Then consumption of 2,4uA (24mV voltage shoot).
Phase 3 : When power is off, 5,5uA (55mV voltage shoot) consumption during a few seconds
Phase 4 : Then 150uA (1,5V)…
Why ?
Could you provide information on the software code managing this sequence ? And by which mean could we stop the « charge » function as we only want to use RTC as an input to our backup battery ?

The 150 uA is due to the RTC being calibrated, but It should only last in the 10s of ms. At extreme temperatures the RTC may drift more and would need to be calibrated more often, which might explain why it is on so long. What temperature is your circuit operating at? How long does it draw 150 uA?