• State Not Answered
  • Replies 12 replies
  • Subscribers 62 subscribers
  • Views 8104 views
  • Users 0 members are here
Attachments (0)
Nordic Case Info
  • Case ID: 121059
Options
This post is older than 2 years and might not be relevant anymore
More Info: Consider searching for newer posts

nRF52832 efficient power management solution

dingari

I'm working on a design that incorporates an nRF52832 along with some sensors and drivers.

Up to this I've been sacrificing power consumption in prototypes by using LDOs since they're cheap, small and easy to work with. But now I'm starting to look into a more efficient power management setup.

The device is small and runs off a single LiPo (3.0 - 4.2V range). Using just the nRF52's internal DCDC converter alone is not sufficient. And since I have to step the supply voltage down for the nRF52 anyway, and the board has sensors and drivers operating on some milliamps, I'm looking for an efficient external buck converter to supply power to all the chips.

I'm thinking of stepping the battery voltage down to 2.5V or 1.8V (depending on chip availability for one of my sensors). The device is never "off" in the sense that the voltage regulator is never shut down. Instead all the chips go into sleep/off mode. The total sleep current (apart from the regulator quiescent current) is about 10uA, so I'll need a pretty efficient regulator.

I'm mainly looking at QFN/DFN/WFN chips that I can easily assemble by hand. Some chips I've been looking at:

The TPS62740 is looking extremely good since it claims to get 90% efficiency at 10uA, while others are typically around 20-30%. However, it is a little bit more pricy, and a little bigger. Are there some chips that are frequently used with nRF52?

Then there is another thing. With a supply voltage of 2.5V (or even 1.8V), how much gain is there by using the nRF52's internal DCDC converter?

Edit: The TPS62740 also offers the benefit of an optional load switch that can be controlled by the nRF52. That way the sleep current would just be 0.3uA (the system OFF current of the nRF52) + regulator quiescent current.

Edit 2: I have white LEDs with a forward voltage of 2.8-3V, and a haptic motor that requires 2.5-3.3V. So if I want to lower the main power rail below 3.0V, I'll run into trouble with the LEDs, and if I go further down, my motor won't work.

What I'm contemplating right now:

  • Use TPS62740 to provide the main voltage rail for the nRF52 (1.8V), and use the LOAD output to power my sensor (this way I'll be able to shut it down completely from the micro).

  • Use another buck converter such as TPS62230 to generate ~3V for the LEDs and the haptic motor.

This way, in "off" mode, only the VOUT of the TPS62740 is active (LOAD disconnected) and the nRF52 is sleeping (total Iq less than 1uA), and the secondary (~3V) regulator can be shut down from the micro.

This is a bit more convoluted and takes up more board space, but I'm looking to maximize the battery life. But the question is, is it worth it?

  • 0

    Hi Dingari,

    as far as I know we do not have any reference designs that incorporate a dedicated power management IC, so we can't really recommend a specific IC based only on the occurrence of it in our customer designs.

    Its primarily the RADIO TX and RX currents that are reduced when the internal DCDC is enabled, please refer this section of the nRF52832 Product Specification. We've only included specifications for 3V with and without the DCDC enabled, for which there is a considerable current consumption reduction with the DCDC enabled.

    Generally, the efficiency of the DCDC will be reduced as you reduce the input voltage, i.e. the difference between the LDO and the DCDC is probably marginal at 1.8V. However, I do not have any specs on this and the actual current consumption is highly application specific, so I advise you to perform some measurements on your own before concluding.

    Best regards

    Bjørn

  • 0 in reply to bjorn-spockeli

    Hi Bjorn, thanks for the reply. I was really just hoping to get the discussion going, since I can't be the only one doing a design like this.

  • 0 in reply to bjorn-spockeli

    No, you're definitely not the only one ;) Hopefully some of the other users will comment if they've used one of the ICs you listed and give you a recommendation.

  • 0 in reply to bjorn-spockeli

    These seem like reasonable choices. They are all synchronous buck in uson or similar packages.

    Though, I would probably choose from a component line that offers several VDD choices with internal feedback. The feedback circuit for an adjustable regulator can take up quite a bit of board space. ST has a large selection of DC/DC you can look at.

    You should be careful if you choose 1.8V for the nRF rail. This forces the GPIO VDD to be 1.8V and you may create problems with off chip communications.

    If I were doing this, I would also look for a converter with a brownout function. LiPo's don't recover from full depletion. Most LiPo's have a built in PMC to protect them from being fully depleted or excess current demands. Your LiPo may/may not have this.

  • 0 in reply to bjorn-spockeli

    This series of parts from TI has a nice small 1x1.5mm uson package, very low quiescent current of 22uA and will operate at 100% duty so you can let it go unregulated if the lipo voltage is below VDD.
    www.ti.com/.../tps62230

    The UVLO (ie, brownout) of 2.05V is a little too low for most lipo's so you will still need to choose a lipo with a built in PMC to protect it. Otherwise the charger side of the system may have a UVLO with load disconnect.

Related