USB-PD DRP from a single LiFePO4 cell - Page 1
Forum section: electronics / projects

author: ewinek
author_rank: Contributor
timestamp: May 18, 2023, 05:12:32 pm
content: I am about starting a project with LiFePO4 pouch cells. The idea is to create a powerbank from a single cell. The powerbank must have an input/output USB C connector with 65W minimum power (100W ideally). The idea is to charge laptops or charge the cell from the same connector.I am searching all around and I don't find what I need to do such configuration. There are manufacturers like TI that have all-in-one solution (DC-DC+PD controller) but that chip works only as source and it is limited to 60W.What I understand so far (maybe I am wrong) is that the PD controller handles the negotiation with the connected device giving a signal to the DC-DC to output the right voltage. However I don't get it yet how this is done, because then the DC-DC must be:Adjustableoutputbuck-boostCompatible with the PD controllerbidirectional (for the application I want)The PD controller must also know which voltage is needed for the powerbank battery cell, if it is configured in a 3S Li-ion then the voltage for the DC-DC given to the cells must be 20V, if it is only one cell then it can be 5V.Any advise?Thank you very much in advance!

author: David Hess
author_rank: Super Contributor
timestamp: May 18, 2023, 06:30:11 pm
content: Some laptops support this with their USB-C PD ports; I know my Thinkbook does. But I think it is more involved than a single chip controller, with an external microcontroller and custom firmware. On mine it also appears to regulate the output current based on how much extra charge current is available.

author: ewinek
author_rank: Contributor
timestamp: May 19, 2023, 06:44:03 am
content: Any guides or ideas how to proceed further on this project? I am a bit lost at the moment.Thanks!

author: inse
author_rank: Super Contributor
timestamp: May 19, 2023, 12:17:44 pm
content: 100W from a single cell is ~27A, are you sure you are able to handle this?That is 0.7W dissipation in every mOhm already.Did you ever design a SMPS?

author: inse
author_rank: Super Contributor
timestamp: May 20, 2023, 06:34:32 am
content: Dead-end topic?

author: ewinek
author_rank: Contributor
timestamp: May 21, 2023, 08:50:38 pm
content: Hi,Actually is around 31A, a LiFePO4 works with 3.2V nominal value. I have cells of 31A with capabilities of 1C discharge, I have cells with 20A/16A with 3C discharge capabilities. The challenge for me is more in the logic of the circuit more than in the power, I can split the current over many MOSFETs and produce a decent DC-DC. I have design few in my life, but not this exact type.The reason to do it with one cell is to avoid the BMS, avoid cell balancing, space/size and connections. Moreover, there are no many available options out there with LiFePO4 technologies in terms of BMS and battery chargers.Some hints? All are welcome

author: brumbarchris
author_rank: Regular Contributor
timestamp: May 23, 2023, 08:37:36 pm
content: Apart from the power circuit, you will also have difficulties with the USB PD implementation and compliance itself. It is obviously not impossible, but only the spec itself is 800+ pages and there is generally quite a lot of firmware involved. I am going through it for a project right now and it is quite daunting!Good luck with you work!Regards,Cristian