Long story short: I’m trying to power an Arduino Nano33 IoT from a 19V supply, but its 3V3 regulator gets so noisy at voltages over approx. 8V that the setup becomes extremely unstable.
The only other thing apart from the Nano itself that’s powered by the onboard regulator is a LumenRadio TimoTwo radio transceiver. Its current draw is specified to 150mA typ., 250mA max. I’m only using it as a receiver, so I wouldn’t expect it to be near the max spec, and in any case, according to the datasheet for the Nano’s regulator, this shouldn’t be a problematic load. I’m currently not using the Nano’s WiFi, BLE or IMU sensor.
There’s a SEPIC DC-DC converter on the same PCB that the Nano is attached to, and I was worried that it might be causing some kind of noise on the supply lines that could disturb the Nano, but I’ve checked the 19V supply with a scope and I can’t see any extra noise at all when the DC-DC converter is connected. I believe it’s well filtered too – I used TI WEBENCH Power Designer to verify the design, so it’s all within mfgr specs. I don’t think it’s a problem with RF noise from the SEPIC converter either, in that case it shouldn’t have worked when even when the Arduino was USB powered instead, right?
I’ve tried throwing in some extra caps between 3V3 and GND, but the difference I’m seeing is absolutely minimal, not enough to make any practical difference at all. I only have 100nF and 330nF on hand to test though.
The Nano’s regulator does not get warm at all – I checked with a thermal imager, it’s barely above room temperature.
I’ve attached a couple of scope shots of the 3V3 line with 5V and 19V as supply voltages. You can probably see which is which …
Are there any ways to solve this, apart from just cobbling in a better 3V3 regulator? I’d prefer not to do that, as this is a very space constrained application, and the PCBs are already made. They’re a tight squeeze as is.