RE: Powering the Chengdu Ebyte nRF52840 Dongle (PCA100059-style) without VDDH noted on the board

fe7565 — Tue, 04 May 2021 20:47:05 GMT

Thank you for the recommendation. Will limit one input at a time.

I need a small size board for my project. Since the code is pretty much done I do not need a DK anymore.

By the way, even at 8dB TX it only uses around 2.8mA! connected! Excellent! Also, the Nordic 52840 dongle has a much better range than the third-party modules.

RE: Powering the Chengdu Ebyte nRF52840 Dongle (PCA100059-style) without VDDH noted on the board

Jared — Tue, 04 May 2021 13:44:31 GMT

Connecting the regulated 3V3 and the 5V to the same node can be problematic, most likely the regulator will not like it and will be damaged. I suggest that you only connect on voltage at a time. Is there a specific reason for why you're using the Dongle and not the Devkit? I would think that the latter would be a better fit for you?

regards

Jared

RE: Powering the Chengdu Ebyte nRF52840 Dongle (PCA100059-style) without VDDH noted on the board

fe7565 — Tue, 04 May 2021 00:28:50 GMT

Thank you for the quick reply! I contacted the company but they do not have the schematic or did they misunderstood me.

However, based on your comments where you correctly pointed out what I missed :) in the original Nordic dongle the USB 5V is already connected to VBUS and the VBUS is (internally) shorted to VDDH. And this seems to be the case with this clone dongle as well...even the 4.7Ohm resistor (R7 on the Nordic dongle schematics) registered on my multimeter between VBUS and VDDH.

I agree that without an actual schematics nothing is certain. But let's me assume this dongle is a faithful clone of the actual Nordic dongle. The following should be true (quoted from another thread):

There are two stages of voltage regulators in the nRF52840 (REG0 and REG1). REG0 from VDDH to VDD and REG1 from VDD to internal rails <=1.3V. VUSB powers the USB front-end only. This gives two alternatives:

Apply 2.5-5.5V to VDDH, not shorted with VDD. Uses both regulator stages, and allows you to use the VDD pins to supply external circuitry as long as overall load on the regulator is <50mA (nRF52840 + external)
Apply 1.7-3.6V to VDD, shorted with VDDH. This uses only the REG1 stage and does not allow supplying external circuitry from the nRF52840

On this clone dongle I do not see an SB-2 type solder-bridge between VBUS and VDDH.. Only saw an SB-1 type solder-bridge between VDDH and VDD (open by default). So I cannot separate VBUS from VDDH. That gives Reference circuit #1 as the only option from Table1.of the link below Which is the only one that has VBUS and VDDH shorted.

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fref_circuitry.html

In my application, the dongle will not use a USB for normal operation and will not supply any external circuits. The dongle will be supplied from an external 3.3v regulator. This 3.3V external regulator is supplied from a 2.7-4.2V lipo battery and/or from a lipo charger PMIC. There will be nothing connected to the USB during normal operation. But since the USB/VBUS/VDDH are shorted together with no way to separate VDDH from VBUS I think the best option is to power the dongle via VBUS(VDDH) with the 3.3V external regulator. The only time the USB/VBUS/VDDH will have 5V power is during infrequent firmware updates.

Here comes a concern: I believe that during firmware update when 5V USB is connected and there is 3.3V already going into the VBUS/VDDH from the external 3.3V regulator there will be a voltage conflict . Even if the 5V power source for the USB and the 3.3V external regulator (via the lipo charger) is the same. Do you agree?

Since USB and VBUS and VDDH are shorted together by default, in order to avoid that voltage "conflict" one should disconnect the 3.3V power going into the VBUS/VDDH from the external 3.3V regulator. Could possibly put in a diode in that line that would block voltage going out from the module on VDDH, but that diode could drop my 3.3V by minimum 0.3V which could affect anything connected to the dongle's GPIO pins expecting 3.3V. Or, I could possibly use the 3.3V external regulator's ENABLE line to shut it down when 5V vs 3.3V is connected to the USB/VBUS/VDDH (via a MOSFET). But that complicates things.

Any easier way with a hardware solution? Maybe if I find that 4.7Ohm resistor that is between VBUS and VDDH (R7) and remove it, then I can use the SB1-type solder-bridge and short VDDH and VDD together and still use the 5V USB?

RE: Powering the Chengdu Ebyte nRF52840 Dongle (PCA100059-style) without VDDH noted on the board

Jared — Mon, 03 May 2021 13:13:01 GMT

Hi,

I can't really say anything without at least having seen the schematic. The HW files for our 52 Dongle is available here. The PCB files shows how the VDDH is not routed out to a pin but instead is connected directly to the USB interface. VBUS and the output of the REG0 VDD is routed out.

I suggest that you take contact with the people that have made the dongle.

best regards

Jared