Internal DCDC vs LDO for nRF52 series

[Lakerno]

I will be using a 3.7V LiPo to power my NRF52 system. As far I understand, using the internal DCDC regulator is a better choice as it can save power compared to internal LDO. I assume this the case for most applications.

Can anyone enlighten me what is the use case for internal LDO when you have a internal DCDC already?

[Nenik]

Well, you can't really go directly with 3.7V LiPo, as it is more like 4.2V when charged and that's waaay out of spec. So you'd need some external power management solution anyway to get into acceptable Vdd range, thus likely end up using the LDO as the last step anyway. For nRF51, DCDC was also reducing radio performance (to the point that it was specifically discouraged for older silicon revisions).

[Øyvind Karlsen]

Hi,

Using the internal DCDC is better when you have high current draws, such as the radio TX current spikes.

The LDO is more efficient at low current draws. When DCDC is enabled, our system will automatically switch between these two modes (LDO and DCDC) to ensure maximum power efficiency.

For more information about this see the infocenter section on power management.

As discussed in this post, you need to somehow reduce your 3.7V to somewhere between 1.8 and 3.6V.

Best regards,

Øyvind

[Lakerno]

Hi Øyvind, I am using an external DCDC converter to reduce my Vdd from 3.7-4.2(LiPo) to 1.8V before supplying to NRF52. I am still not clear whether to go with internal DCDC or Internal LDO after this. I can save 2 passives if I go with internal LDO. Since the supply to NRF52 is @1.8V from an external DCDC, I feel using internal LDO may help me reduce supply noise in addition to saving passives. Also no loss in power, since external DCDC already reduces the voltage to 1.8V.

Now my system is intended for realtime data streaming. Or sometimes occasional data streaming with some data processing done on the CortexM4F. I am not sure if this is considered "low current draw" or "high current draw". Can you clarify this?

Also in your reply you suggest , with refresh mode enabled, NRF52 can automatically switch between internal DCDC and LDO. So for refresh mode, which schematic should I follow? The one with internal DCDC or the one with internal LDO.?

Thank you in advance :)

[Øyvind Karlsen]

If you use the radio you will have high current draws, using the LDO you would consume roughly 6mA when transmitting 0dBm. If you use the internal DCDC you would use about 4mA.

If you want to use refresh mode you need the schematic for DCDC. If you do not care about energy efficiency as much and want a cheaper/smaller board, go for the LDO, as it saves you two components.

[puz_md]

Hi Øyvind,

your link to infocenter doesn't work anymore. What is "refresh mode" and how is it enabled/disabled? And does the SoftDevice (currently using s132_nrf52_2.0.0-4.alpha) automatically configure the system for use with DCDC?

Is it possible that we will get radio problems if we don't place the coils between DCC and DEC4 on the PCB?