4-Switch Buck Boost DC-DC Controller Design Advice Needed (USB-C PD)

[chendragon]

Hi all

I'm currently working on a design for a rather powerful power-bank type application. The battery pack will be ~7s 18650 cells and the goal is to support USB Type C/Power Delivery on three ports for both input and output purposes.

For those unfamiliar, USB TypeC/PD runs at 5-20V and outputs up to 4A.

What this means is that I am going to need to build 3 DC-DC converters that support buck-boost for charging the battery and/or outputting the right voltage, and digital control of the voltage and hopefully current is desired for each.

There is something called the OmniCharge out there that does something similar but I can't find out what type of switching controller it is using. I'm considering using the TI LM5175; previously I was going to implement a digital dc-dc converter using a FPGA but ADCs that perform well seem to be very expensive. The FPGA will probably be onboard anyway, due to other requirements.

Any advice on how to go about selecting a controller for this would be appreciated.


Thanks!

[jbb]

This could be fun.

To make your life easier, I suggest an 8S pack so that the pack voltage is > 20 V. That way you can use buck converters, which are cheaper, smaller and more efficienct than buck-boost.

Analogue control might work quite nicely. A decent synchronous buck converter with an output voltage  tracking feature might work for the 5-20V output.

For digital control, I would suggest a microcontroller rather than an FPGA. Writing firmware is still a pain, but much easier than writing VHDL / Verilog. To select a chip, peripherals are everything: you need good PWM (high clock frequency, hot/cold outputs and dead time) and a good ADC (say 12b 1MegSample or higher) and a hardware synchronisation line from the PWM module to the ADC.

The Texas Instruments C2000 piccolo chips are quite good (good PWM, high speed ADC) for power electronics. Alternatively, I think there are some ARM chips which could fit the bill, but haven’t looked into them.

[jbb]

Actually, Blueskull is right.  You're going to be spending some money here, so full digital control is probably better.

Also, you'll need some processing power to run the battery balancing and USB C port negotiations.  The Piccolo chips are quite capable and could do more than just run the power converters.