3PI power

I’d like to redo the battery arrangement on my 3PI bot using Lithium Ion cells. Currently the maximum voltage the voltage converter input will see from the current battery arrangement is about 6 volts. I’d like to replace the current batteries with series 2 lithium ion cells at 4.2 volts each. That’s about 8.4 volts max at the input to the converter.

My question is: Is 8.4 volts too much or does it fall within the spec. range of the converter.


The problem is not just with the converter, but also all of the circuitry before that. Depending on which revision of the 3pi you have, you should be able to use the 8.4V. If you have an SOT-223 5V regulator on yours, you should be okay. (It’s a pretty distinctive part, with three leads on one side and a bigger tab on the other; if you don’t have it, there would be a 6-pin part, with 3-pins on each side, instead.)

- Jan

Hmm… I’m a little perplexed by your answer. It is my understanding that the 3PI power management section consists of a switching regulator that boosts the varying battery voltage up to a constant 9 volts, followed by a linear regulator that regulates down to 5V to power for the digital stuff. If my understanding is correct the 5VDC regulator should be unaffected by the VBAT since it should always be presented with VBoost (9V). It is the switching regulator section that would be exposed to the higher voltage provided by the 2 lithium ion cells (8.4V as opposed to the max 6V of your regular 4 battery source).

My other concern is that the voltage divider used to drop VBAT to less that the maximum 5V input to the battery level sensing ADC input might exceed 5V if provided with an 8.4V input.

I would also like to add that the lack of a detailed schematic makes it difficult for me to ascertain the answers to these questions! Why don’t you provide one?

I was mentioning the 5V regulator only as a means of determining what revision of the design you have.

The schematic is fairly detailed for the parts we expect to be relevant to our customers. For example, the reverse protection MOSFET is specifically called out, and that is one of the parts that could have a limit below 8.4V. The only way we could give you enough detail to know that is to give you specific part numbers, and we don’t want to commit to those particular parts. In the case of the 5V regulator, which is shown as a block, we had to change it because the original one went out of production. Since that detail does not matter to 99% of our customers, we prefer having a single, simpler schematic.

- Jan

Ah, I understand. My 3PI is a recent one (got it 3 weeks ago) and the 5V regulator is the SOT-223 part. Thanx