VDD drops.

[Shimon_nohayo]

Hi,

I'm using nRF52832-CIAA.

VDD,Pin A7,  tide with Cap 4.7uF 0603

VDD Pin H7 tide with Cap 100nF 0201 

DEC3 100pF 0201

DEC2 100pF 0201

DEC4 1uF 0402

Using LDO 

VDD = 3V

When the device start advertising the VDD drops to 2.6 V  for the advertising duration and then returns to 3V.

Please advise if this is normal?

Shimon

[awneil]

Show the full schematic - where is VDD_nRF coming from?

Shimon_nohayo said:

When the device start advertising the VDD drops to 2.6 V

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

Shimon_nohayo said:

Please advise if this is normal

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.

[Shimon_nohayo]

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.

[awneil]

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.

[Shimon_nohayo]

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

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

[RK]

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.