Powering NRF52

[yulya]

Hi During schematic design, i read regarding proper powering of NRF52 (the product is battery powered 2xAAA). somehow i can't find this info now and i would like to verify that i am not wrong: "It is not recommended to connect the SOC to Booster output for example " - am i right? i am connecting it directly to the battery cell, but i do have booster with bypass in the system in order to supply correct voltage to the Motor driver and Buzzer, when battery voltage goes low (for example up to 2v). Can anyone point me to relevant document? thank you Yulya

[Roger Clark]

Check the operating voltage range in the spec.

Its something like 3.3V to 1.8V

A normal AAA will give you 1.5V, so 2 x AAA = 3V which should run the nRF52

I don't know why you want to run via a booster, I presume you mean buck-converter? Those devices normally take power all the time and will flatten your battery quite quickly

If you need to supply more voltage to the motor, you could consider having a multi cell battery pack and tap off after 3 V to feed the nRF52

[yulya]

I know the operating voltage, that is why i connected the SOC directly to the battery pack. I need the Booster (not buck-converter, i mean what i wrote), for the buzzer and motor driver as their Vmin =2.5vv and the battery pack can reach even 1.8v when it is almost empty. This booster is with bypass operation, so as long as battery is ok, everything is connected directly and it doesn't drain the battery as you wrote. My question was regarding the SOC input. Am i right that it is not recommended to connect it to the Booster output as it needs low noise input power? i read it somewhere and i can't find it again.

[ovrebekk]

Hi

It is a bit hard to define exactly how much noise you can accept on the supply lines, but a rule of thumb is that the noise should be less than 100mV peak-to-peak.

The frequency of the noise is also a factor, and some frequencies will inherently be more problematic than others.

I would try to measure the noise on a scope, and see how large it is. If it is close to 100mV p-2-p then you could try adding more decoupling capacitors, or change the routing of the supply signals, to reduce it.

Best regards
Torbjørn

[yulya]

thank you for your help. When you do the measurement - what is your power source? and what do you think is better option:

1. connect SOC to the battery pack directly as i did and noisy sources through dedicated booster or
2. connect the whole circuit to the booster output and keep in this way the input power voltage always higher than 2.5v?

thank you Yulya

[ovrebekk]

Option 1 sounds like the best one by far. Then you get more isolation between the noisy sources and the Nordic device, and any power loss in the booster won't affect the nRF52 current draw.

The only thing you have to consider is if you need a buffer between the control signals going from the nRF52 to the motor driver, since they could be running at different supply voltages.

Best regards