BQ25798: USB PD and Solar Charge Schematic Recommendations and Validation

Egemen Aksoy

Part Number: BQ25798
Other Parts Discussed in Thread: TPS25730,

Tool/software:

Hello,

For our Sensor node project, we shall use a single-cell 3.6V Li-Ion Battery pack that can reach up to 17500mAh capacity.

The Sensor node shall be charged with USB (USB TypeC PD, we are using TPS25730 USB PD Controller) and, a 12V Solar panel or from 5V out SMPS. (VCC pin is for solar panel, 5V stands for SMPS out)

The schematic is attached,

What topology should I use for that application at BQ25798's VBUS side (VBUS VAC and ACDRV connections?) for our application?

Should I use Back-to-Back FETs?

What shall be the SYS output (Voltage) when the Prog pin is tied to GND with a 3K resistor?

Could you validate the schematic?

Best regards,

Egemen Aksoy

26 days ago

+1 Jeff F 26 days ago

TI__Guru*** 148315 points

Hi Egemen,

For the BQ25798 VAC and ACDRV connections, if there is no physical way for the solar panel and USB-C inputs to be attached at the same time, then you don't need the MUX ACFETs. In this case, ACDRVx = GND and VACx = VBUS. Otherwise, I recommend ACFETs to MUX between the input sources. The SYS voltage follows the BAT pin up to VREG (i.e.4.2V). The SYSMIN voltage must be set lower than VREG to provide a minimum system voltage when the battery is discharged. The default MINSYS voltage with PROG = 3k is 3.5V per the table below. The host can send I2C command to change that value: