Initial surge current nRF52832

RE: Initial surge current nRF52832

Turbo J — Fri, 04 Sep 2020 17:44:36 GMT

Measure Voltage across U8. According to the datasheet, the FET may not be fully "ON" - especially when the battery voltage is "loaded down".

BTW: I would rather just use a reversed diode here as polarity protection - the zinc air cell has not much current output when shorted.

There is no way around the initial 5-7mA during POR.

Consider putting a large capacitor - say 470µF or more - on the primary side in addition to C47. Also use an RC-delay on the EN line of the voltage ragulator in order to allow this capacity to be fully loaded before the regulator turns on. This may buy you just enogh time to go through POR and into the application - only then you are able to go in lower power states.

RE: Initial surge current nRF52832

Lakshmikanth Satyavolu — Fri, 04 Sep 2020 16:11:33 GMT

Hi Ketiljo,

Thanks for exploitation. I'm bit confused about system OFF mode.

How to set system OFF mode even before it starts? I mean is there any way we can program the device before it gets powered up, like by asserting a PIN or something like that?

Best

Lakshmi

RE: Initial surge current nRF52832

ketiljo — Fri, 04 Sep 2020 11:27:11 GMT

The large caps will cause inrush current that can't be avoided. Even if you remove the 22 µF, there are a few large (> 1 µF) caps left that's needed for the regulators to function properly.

The CPU will be on for a few ms after startup. This draws some 3-7 mA at 3 V, so maybe 20 mA at 1.4 V is correct, depends on the boost regulator.

If you set the device into system off mode, you need something external to wake it up again, GPIO, NFC etc. The device will then start from reset.

RE: Initial surge current nRF52832

Lakshmikanth Satyavolu — Tue, 01 Sep 2020 07:38:53 GMT

Hi,

Could someone please look into it?

What exactly is causing initial surge in the current? We removed MOSFET and tested with a load switch in place of it. Also we removed the entire power section in the circuit and powered the circuit directly. Still the inrush current is being observed. it seems this current is from either firmware or any other internal hardware.

How can we confirm where it is coming from? I am using SDK16 BLE HRS example as my reference code.

Any help would be highly appreciated.

Best

Lakshmikanth.

RE: Initial surge current nRF52832

Lakshmikanth Satyavolu — Sun, 30 Aug 2020 07:19:04 GMT

Hi Ketiljo,

We have replaced 100 uF to 22uF. But issue still persists. I came across below post which discusses about SYSTEM_OFF sleep mode control.

https://devzone.nordicsemi.com/f/nordic-q-a/36475/nrf52832-go-system-off-low-power-mode-and-wakeup-by-gpio#:~:text=2%20years%20ago-,In%20order%20to%20put%20nrf52832%20to%20%22system%20OFF%20sleep%20mode,more%20information%20about%20DETECT%20signals

I have few queries regarding SYSTEM OFF sleep mode

1) In order to put system into off mode, is it OK if I call sd_power_system_off(), function in my application main function?

2) Should I use a button in my design to wake the system up using gpio DETECT signal or reset?

3) what if my design doesn't have any reset or application buttons to wake the processor up? How can I wake the processor from sleep?

Best

Lakshmikanth

RE: Initial surge current nRF52832

ketiljo — Tue, 25 Aug 2020 09:16:51 GMT

The inrush current is the large 100 µF cap charging up. But there must be something else that draws a lot of current constantly that leads to the 20 mA draw.