LDO On A-Star 328PB

Support A-Star and Orangutan
1

The A-Star 328PB description only says LDO max current 100mA. I can’t find the part number on the schematic either.

A google search of “328PB LDO site:pololu.com” didn’t produce any results with a part number.

What type of LDO is on the A-Star 328PB boards?
I’m curious to know how much current the LDO will draw when I put the ATmega328PB to sleep.

Thanks.

2

Hi.

We do not want to commit to a specific part for that regulator, but we have been using ST’s LD2981C (and we do not have a reason or expectation to change it sometime soon).

We measured a few here and saw an LDO ground pin current of 100-300uA with the ATmega328PB sleeping, depending on the input voltage and current draw of the board. Also, while sleeping, the current draw of the board is dominated by the power LED which is around 1mA (depending on the version you have), so for very low power applications, you might consider knocking that off.

-Claire

3

Hi @Claire , I have a further question on this.
I’m planning to run my A-Star 328PB micro (3.3V) from a lithium polymer battery. The recommended minimum Vbat is 3.8V… however the datatsheet for the ST LDO you’ve mentioned should put the minimum input voltage around 3.5V with standard condition dropout voltage of about 0.2V (therefore able to use more of the battery’s life)

I’d like to use the board with a LiPo, without adding an extra 3.3 voltage regulator so what are your thoughts on this?
Thanks!

4

Hi, Mica.

I do not know of a better way than a regulator to get the maximum run time out of your battery in your application. However, if you won’t be drawing much power from the A-Star and are able to run the battery down to around 3.5V, that would likely use a good chunk of the capacity of the LiPo without a regulator anyway. This Adafruit guide to LiPo and LiPoly batteries has a typical discharge curve that shows more than half the capacity is used by the time the battery voltage drops to 3.5V.

-Claire

5

Thanks, I will likely end up using a regulator since my project is going to need a bit more power than 100mA after all.

6

On two of my 5V/16MHz A*328PB I’m considering to replace the LD2981C by MCP1755T to give me 300mA instead of 100mA (as 100mA is a bit too tight a budget for some of my use cases). Do you see anything that would speak against that?

Kind regards, Sebastian

7

Hi.

I do not see any obvious issues with swapping the LDO on the A-Star 328PB with a MCP1755.

-Claire

1 Like