RE: DC-DC SUPPLY

zcmm — Thu, 28 Sep 2017 10:48:09 GMT

thank you.

RE: DC-DC SUPPLY

John — Wed, 27 Sep 2017 12:00:13 GMT

Exactly what was happening

RE: DC-DC SUPPLY

Bjørn Kvaale — Wed, 27 Sep 2017 05:30:47 GMT

Most likely, you were using the LDO all the time until you switched to DC-DC mode in the FW. Assuming the radio was on quite frequently, this explains why you had higher power consumption (DC-DC is more efficient at higher current consumption than LDO, see my answer below and the devzone post I mention).

RE: DC-DC SUPPLY

Bjørn Kvaale — Wed, 27 Sep 2017 05:27:39 GMT

If I were you, I would definitely take a look at this great devzone post. As it says in the first paragraph, make sure to check whether you have the third revision nrf51 HW or not. As Stefan says: "For the second revision of the nRF51 hardware, we do not recommend customers to use the DC/DC together with the BLE softdevices, see “limitations” section in the S110 softdevice release notes." If you are using the third revision, it isn't an issue to use the DC-DC converter.

To paraphrase from the post, if you are using the DC-DC schematic, you can switch between LDO and DC-DC in the SW. In the LDO mode (i.e. LDO schematic), it is not possible to switch to DC-DC mode in the software. I would definitely use the DC-DC schematic, as you can decide whether to use the LDO or DC-DC in SW.

If you are using the second revision nrf51822 HW, it is advantageous (i.e. more efficient) to use the DC-DC when you have a current consumption of about 5 mA or greater. If the supply voltage is 3.6 V (e.g. Li-Ion battery), it is more efficient to use the DC-DC vs LDO at >= 3 mA current consumption. A good example is during radio activity: when the radio is on turn the DC-DC on, but once radio activity is turned off you should use the built in LDO instead of DC-DC regulator (because radio activity can lead to current consumption >= 3 mA). The DC-DC consumes 300 uA for operation. Also remember that the DC-DC must be manually disabled if supply voltage < 2.1 V. The LDO can remain operational until about 1.8 V.

As for distance, I don't think distance is affected if you use an LDO or DC-DC. For any given range, assuming the supply voltage is 3.6 V and radio activity is on, then it will be more efficient to use a DC-DC during radio activity and use the LDO when the radio is off.

I would highly suggest you to take a closer look at the blog post I refer to at the beginning. Stefan explains this much better than I could.

RE: DC-DC SUPPLY

John — Tue, 26 Sep 2017 14:12:10 GMT

I can't speak for distance, but on the nRF52 our HW guys set it up for DC-DC mode without telling me and the device drew a significant amount of additional power until I enabled DC-DC mode in the FW.