nRF52840 VBUS state when on battery power

RE: nRF52840 VBUS state when on battery power

Stian Røed Hafskjold — Tue, 09 Apr 2019 15:50:34 GMT

Ok, then I don't know what the problem is. But in general if you remove the power to an external device, you must also disconnect the data lines between the nRF52 chip and the external device, otherwise you might power the external peripheral through the data lines.

What you can do is to set all GPIOs on the nRF52 to inputs, then they will all be disconnected, and you can be sure that no leakage current is going out from the GPIOs. If you still see 2.5V on the 5V line there must be something external to the nRF52 that is leaking.

RE: nRF52840 VBUS state when on battery power

ilia — Tue, 09 Apr 2019 13:22:14 GMT

I use an array of w2812b RGB LEDs. They are controlled via commands. I use SPIM to deliver commands. LED changes its color after receiving a command, and stays in this state until it receives command with new color. Particular command is basically a sequence of bits representing RGB color bytes.

I don't think that leakage occurs in the LEDs, because even if all LEDs are physically disconnected, I have current around 2.5V on the power pin for those LEDs.

RE: nRF52840 VBUS state when on battery power

Stian Røed Hafskjold — Tue, 09 Apr 2019 13:07:36 GMT

Can you describe the LEDs you are using? Is it just normal LEDs you control by pulling the GPIOs high or low, or is it a more fancy RGB LED you control with commands? Like your "black color" command..? If the data bus between the nRF chip and the LEDs are still active there's a good chance that these are pulling up the 5V power line to the LEDs.

RE: nRF52840 VBUS state when on battery power

Stian Røed Hafskjold — Tue, 09 Apr 2019 12:54:40 GMT

I think you should try to remove one component after another to see where the leakage current goes.

RE: nRF52840 VBUS state when on battery power

ilia — Wed, 03 Apr 2019 08:10:38 GMT

I have control over the LEDs signal input pin, and not over the power pin. To turn off the LEDs I just send "black color" signal. But it should not be necessary if there is no power on the LEDs power pin.

RE: nRF52840 VBUS state when on battery power

ilia — Wed, 03 Apr 2019 07:57:33 GMT

Here it is. It uses Fanstel BT840F module.

RE: nRF52840 VBUS state when on battery power

Stian Røed Hafskjold — Tue, 02 Apr 2019 12:14:36 GMT

I can't see anything obviously wrong with the regulator design. The diode D1 should prevent any leakage back from 3.3V to 5V.

How do you turn off the LEDs? Are you pulling the GPIOs high?

Can you post the rest of the schematics, including the nRF52 and the GPIOs. Thanks

RE: nRF52840 VBUS state when on battery power

ilia — Mon, 01 Apr 2019 15:18:40 GMT

That is good.

I am wondering where is the mistake. Maybe I missed something in the power schematic? Is schematic from my previous reply looks good for you?

RE: nRF52840 VBUS state when on battery power

Stian Røed Hafskjold — Mon, 01 Apr 2019 13:25:05 GMT

There's no internal leakage from the VDD domain back to the VBUS pin in the nRF52840 chip.

RE: nRF52840 VBUS state when on battery power

ilia — Wed, 27 Mar 2019 17:00:47 GMT

Here is the power supply part. LEDs are connected to the 5v line

RE: nRF52840 VBUS state when on battery power

Stian Røed Hafskjold — Wed, 27 Mar 2019 11:12:25 GMT

Can you please post the schematics? To which pins have you connected the battery and the USB power? Thanks

RE: nRF52840 VBUS state when on battery power

ilia — Mon, 25 Mar 2019 08:48:51 GMT

Hello,

I found this schematic of VBUS

What is the internal structure of LDO here?

If I have connected battery (and disconnected USB cable), then I have power on 3.3v line. Does that mean that I will have power on 5v line too?