VDD drops.

RE: VDD drops.

Shimon_nohayo — Mon, 01 Jul 2019 19:17:35 GMT

Thanks I will try it and check it

RE: VDD drops.

hmolesworth — Mon, 01 Jul 2019 15:33:41 GMT

I recommend 150uF on VDD, typically by using 3 x 0603 connected in parallel. Less may work, it depends on your application and how close you want to operate the coin cell to it's end-of-life where the coin cell impedance is significantly higher (several k Ohm). This app note from TI might help: swra349.pdf

RE: VDD drops.

RK — Sun, 30 Jun 2019 23:47:16 GMT

you have 4.7uF already, that ought to be enough. I seem to recalls abystomalabs talking about this a few times and perhaps he recommended 10uF but 4.7uF isn't unreasonable. So as awneil suggests, test with bench power to see if it's just the coin cell and also measure the resistance as well as you can between the coin cell holder and the power pin and the coin cell holder and ground; if you have a truly dreadful solder joint that would make your power issues worse. There's always going to be some drop with a coin cell, but 0.3v seems quite a lot.

RE: VDD drops.

Shimon_nohayo — Sun, 30 Jun 2019 19:49:12 GMT

Do you think that adding a capacitor in parallel can improve?

If yes, can you recommend on a range of values?

RE: VDD drops.

awneil — Thu, 20 Jun 2019 09:59:39 GMT

Coin batteries are quite poor at supplying large current pulses.

Poor battery contacts, and poor PCB layout (long, thin tracks) will make it worse.

You didn't say where, exactly, you are measuring.

Try measuring again when powered from a good, solid lab PSU.

Post a screenshot (not a photo!) of your scope trace.

RE: VDD drops.

Shimon_nohayo — Thu, 20 Jun 2019 09:48:00 GMT

VDD is taken directly from a Coin battery CR2032

I measure with an oscilloscope the voltage, between advertising the voltage is flat 3V and then a drop. The duration and reputation of the Drop meet the advertised duration and period definitions.

I fully understand that RF radio consumes more energy, but a coin battery should hold that.

RE: VDD drops.

awneil — Thu, 20 Jun 2019 09:22:40 GMT

Show the full schematic - where is VDD_nRF coming from?

[quote userid="52874" url="~/f/nordic-q-a/48808/vdd-drops"]When the device start advertising the VDD drops to 2.6 V[/quote]

How & where, exactly, are you measuring this? Mark it up on the schematic.

[quote userid="52874" url="~/f/nordic-q-a/48808/vdd-drops"]Please advise if this is normal[/quote]

Advertising means that the transmitter is transmitting - which takes a far higher current than when idle.

See: https://devzone.nordicsemi.com/f/nordic-q-a/48644/pca10040---any-pins-to-measure-current-consumption-of-the-soc/193098#193098

This is in the nature of radio devices.

If VDD drops, it indicates that the supply impedance is high.