Current peak in system off mode

RE: Current peak in system off mode

PATA — Mon, 10 May 2021 19:01:41 GMT

Thank you!

RE: Current peak in system off mode

hmolesworth — Mon, 10 May 2021 03:39:50 GMT

Yes; in general more capacitance is better though if using ceramic capacitors keep in mind derating issues where rated voltage should be double actual working voltage to avoid reduction in capacitance. Also although Tantalum performs better in that respect, leakage in tantalum capacitors (typ 3uA) usually rules them out. In a target design typically 2 x 47uF rated at 6.3 volts or 10 volts works well; more is better but then of course more board space and cost.

RE: Current peak in system off mode

PATA — Sun, 09 May 2021 22:15:48 GMT

Just in case, I'd like to ask if that reservoir cap means the decoupling capacitors connected to VDD. Thanks

RE: Current peak in system off mode

PATA — Sun, 09 May 2021 22:07:33 GMT

Thank you for clarification!

RE: Current peak in system off mode

hmolesworth — Sun, 09 May 2021 22:03:23 GMT

Quite so though keep in mind you can modify the frequency and hence magnitude of the current spikes by increasing or decreasing the reservoir capacitance; that does not affect average power consumption however, which is effectively fixed.

RE: Current peak in system off mode

PATA — Sun, 09 May 2021 21:45:06 GMT

I read the article (periodic-current-spikes-on-sleep) and found this peak current results from LDO refresh operation for better energy efficiency at low-power mode.

Also, I found it is regardless of the power mode (LDO mode or DC/DC mode) and we cannot not remove it.

Please correct me if I misunderstood. Thank you.

RE: Current peak in system off mode

hmolesworth — Sun, 09 May 2021 20:43:09 GMT

You may be viewing the LDO (linear Low Dropout Regulator) "skipping", over which there is no control other than to increase the reservoir capacitance; have a look at periodic-current-spikes-on-sleep for a similar discussion

RE: Current peak in system off mode

PATA — Sun, 09 May 2021 19:55:43 GMT

I set PPK switches as follow.
- SW2 (DK)
- SW4 (Reg.)
- SW3 (DK)

For SW4, I tried both Reg. and DK, but Reg. showed lower current.