nRF9160 capacitors for VDD pins

[bojan]

Hello, guys!

We are desiging our custom board based on nRF9160 SiP. The board will be battery powered. Li-Ion rechargeable batteries will be used to supply the device.

I noticed you did not put any capacitor in parallel with the battery in your Thingy:91 design.

- Is it recommended to have some capacitor in parallel with Li-Ion battery that will help during short moments in time when nRF9160 requires high amount of current?

Also, 4.7uF capacitors are placed close to nRF9160 VDD pins (VDD1, VDD2, VDD_GPIO). nRF9160-DK contains ZRB15XR61A475KE01D but they are out of stock.

Can you help me to find appropriate replacement? Is 4.7uF enough capacity? I am aware capacitor should have low ESR. Is there any other parameter of the capacitor we need to pay attenttion to?

Thanks in advance for your time and efforts!

Sincerely,

Bojan.

[Andreas]

Hi,

 

See the nRF9160 Hardware Design Guidelines whitepaper: https://infocenter.nordicsemi.com/topic/nwp_037/WP/nwp_037/nwp_037_intro.html?cp=16_1

If your supply can provide >500mA for sufficient amount of time with a stable supply, then additional capacitors are not needed. You should make sure to add the described caps close to the pins though. Note that the current specification indicates 47µF, not 4.7µF, on VDD. As for VDD_GPIO and DEC0, any 4.7µF with similar specs can be used.

 

Best regards,
Andreas

[bojan]

Hello, @Andreas

Thanks for  your feedback.

The official versions of Thingy:91 and nRF9160-DK schematics have 4.7uF on VDD pins and 47uF on DEC0 pin as you can see here:

Hardware Design guidelines contain the opposite info. Anyway, it makes more sense to me to design by respecting Hardware Design guidelines document. Thanks for pointing it out.

All those capacitors connected VDD pins should be low leakage from the battery point of view. It can happen very easily that more current leaks through those capacitors than through the nRF9160 and the rest of the chips in sleep mode! This will obviously have a negative impact on battery life.

In that sense, can you recommend me some low leakage capacitors that we can use? Is it generally better to use tantalum instead of ceramic?

Thanks in advance.

Sincerely,

Bojan.

[Andreas]

Hi Bojan,

 

Thingy91 and nRF9160-DK(pre v0.15) follow the reference circuit for Rev1 of nRF9160. nRF9160-DK v0.15 (and later), and the Hardware Design Guidelines follow the reference circuit for Rev2 of nRF9160. Rev2 will take over eventually, and Rev1 works better in Rev2 circuits than the other way around, therefore this recommendation.

We do not specify specific part numbers for our boards or designs, but from experience I know Murata GRM is used quite a bit. Also note that the specified current consumption is measured with these capacitors in place, you will not get worse current consumption by populating these and I doubt there is significant difference at least between parts from recognized vendors.

 

Best regards,
Andreas

[bojan]

Andreas said:

Also note that the specified current consumption is measured with these capacitors in place

This is great to read! :-)

I see you mention Rev1 and Rev2 of nRF9160. When speaking about versions, I can see many different flavors of nRF9160 on DigiKey, for example - link (NRF9160-SICA-R, NRF9160-SICA-R7, NRF9160-SIBA-R7, NRF9160-SICA-B1A-R7, NRF9160-SIAA-B1A-R7...). Which one is the latest or the most suitable to use?

Regards,

Bojan.

[Andreas]

Hi,

 
See the compatibility matrix: https://infocenter.nordicsemi.com/topic/comp_matrix_nrf9160/COMP/nrf9160/nrf9160_ic_revision_overview.html?cp=2_0_3_0

Rev2 is indicated by 'B1' in the build code, rev1 is 'B0'. For new designs I recommend you use Rev2.

 

Best regards,
Andreas