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NRF52840: Using an external DC/DC with fixed 1.8V output OR power directly from battery

Phobios

Hi,

 

I'm developing a new battery powered sensor device with an NRF52840 and have some thoughts about efficient power supply. The main question is: Using an external DC/DC converter to power the NRF52 or power it directly from the battery. If the NRF52 only would have the LDO internally the question would be simple, but with the internal DC/DC and some function which you'll loose if you use an external DC/DC, it's a bit tricky.

 

For the battery I'm using a 3.6 V Lithium-Thionyl Chloride

https://www.dynamis-batterien.de/uploads/tx_userartikelbatteriestockfr/DYNAMIS-LI-LINE-LI-130_ER14505_.pdf

 

 

Scenacio 1: Using an external DC/DC with fixed 1.8V output: Texas Instruments TPS62840

Here I convert the voltage from the battery to 1.8V and power the NRF52 on VDDH and VDD. (I'll still use the internal DC/DC on the second stage).

  • Advantage: Regualted voltage and the power efficiency (according to the power profiler I'll save some µA)
  • Advantage: External sensors are also powered with 1.8V
  • Disadvantage: I cannot use the power fail comparator

Scenacio 2: Powering VDDH and VDD directly from the battery

  • Advantage: I can use the power fail comparator
  • Advantage: Less components and less money in manufactoring
  • Disadvantage: Not so power efficient and no regulated output power
  • Disadvantage: External Sensors are powered by the battery directly and need a little bit more power

 

At both scenarios I'll use several 100µF ceramic capacitors after the battery to prevent voltage drops on high current spikes. I had some problems with voltage drops in the past, so I really want to prevent them this time.

 

So my overall question is:

  • Is it worth using an external DC/DC converter?
  • Are there some disadvantages which I'll not considering at the moment.
  • Does the external DC/DC help me with the voltage drops (or is the solution here just more capacitors)

 

 

Thanks for all your input and Best Regards,

Phobios

Parents
  • +1

    Hi

    To answer your questions:

    1. In my experience, an external DCDC converter hasn't often been necessary with our nRF52 series SoCs, but there are definitely some cases it would do the job, so in the end it comes down to what you need for your application, and what pros/cons in your list weighs the most.
    2. Not that I can think of, I guess cost isn't a big factor here, but it could be relevant if you are planning on having large numbers made.
    3. I'd say capacitors, or a more robust external PMIC like the nPM1300 (sorry to sound like a salesman), but it should definitely be able to help with voltage drops, and current consumption altogether.

    Best regards,

    Simon

Reply
  • +1

    Hi

    To answer your questions:

    1. In my experience, an external DCDC converter hasn't often been necessary with our nRF52 series SoCs, but there are definitely some cases it would do the job, so in the end it comes down to what you need for your application, and what pros/cons in your list weighs the most.
    2. Not that I can think of, I guess cost isn't a big factor here, but it could be relevant if you are planning on having large numbers made.
    3. I'd say capacitors, or a more robust external PMIC like the nPM1300 (sorry to sound like a salesman), but it should definitely be able to help with voltage drops, and current consumption altogether.

    Best regards,

    Simon

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