TIDA-050047: Designing 1S2P /1S3P charger using USB-C PD

Hi Thomas,

I primarily support the USB-C PD controller family of devices, so will help you with those questions. I'm reassigning this thread to colleagues that support the battery charger products to answer questions relating to their part.

Q1. 

The TPS25750 is not recommended for new designs. You need to use the TPS25751 instead. It is a P2P replacement for the TPS25750 and is the direct successor. All of the features are the same, and the TPS25751 has the latest support.

If this is a proof of concept board, I would recommend against tying your ADCIN pins to ground unless you are 100% sure of your ADCIN configuration. Leaving a resistor divider in allows for some flexibility in case it needs to change. If you are confident in the selection, it should be fine.

Drain pins should be attached (see tida schematic)

For the TPS25751, do not tie the IRQ to GND when unused. Tie to LDO3V3 with a pullup resistor to match the other I2C lines.

Q2.

The I2C EEPROM can be programmed using any EEPROM programming tool that supports the EEPROM used. The Aardvark is not required, it is just what we use to program the board.

Q3.

A basic USB-C PD contract starts with the source advertising it's power capabilities. A basic wall adapter may offer these contracts: 5V/3A, 9V/3A, 15V/3A, and 20V/3A. Within the APP Config Tool, you can configure the sink capabilities of the TPS25751. During runtime, the source will advertise it's capabilities, and the sink(TPS25751) will request one of them based off of the sink capabilities you have configured. We will usually attempt to negotiate the highest power contract that both sides support.

One a contract is negotiated, the PD controller will program the BQ25792 input limits to reflect the contract that was negotiated and will limit power based off of that.

To directly answer your questions:

The PD contract is negotiated irrespective of the charge current. I don't know how you are selecting the charge current, but the PD negotiation will depend only on the Source capabilities of the connected adapter and the sink capabilities set in the App Config Tool.

The BQ will then attempt to draw as much power as is available based off of the current contract. See Q4.

I would recommend looking into USB-C PD for more information as well as this user guide for the TPS25751EVM. https://www.ti.com/lit/ug/slvucp9a/slvucp9a.pdf?ts=1732294972660&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS25751

Q4.

The PD controller will automatically set IIN based off of the contract. You should first determine what power levels you want to support in sink capabilities, and that will provide the max current you need to be concerned about for selecting L1.

Q5.

BQ question

Q6.

LDO3V3 was designed to support PD peripheral like the EEPROM, and I2C and GPIO pullups. It will be sufficient for the EEPROM. Do not power any other peripherals off of the LDO3V3 bus though.

Thanks and Regards,

Chris

Hi Thomas,

Regarding Q5, BQ2579x is only a battery charger and is not intended to charge bare cells. The charger inherently regulates only to the VREG register setting and forces only up to the ICHG current level, so it has first level protection for over voltage and over current but no real protection against under voltage or over discharge to a load on SYS.   I recommend adding a battery protector IC to protect against over/under voltage and over discharge current.  1S protectors are at https://www.ti.com/battery-management/protectors/products.html#404=Protection&1152max=1%3B1&.

Regards,

Jeff