Hi all,
I'm using BQ25750 to design a MPPT Charger for Li-Battery. My verification board testing environment is as follows:
- The VAC interface is powered by an adjustable switch power supply, with a voltage range within the VAC window range.
- ICHG & ILIM_HIZ use resistors with the corresponding resistance value to pull down the pin to ground to set the current limit
- The Battery interface and SYS interface are not connected to any devices.
- CE pin has been pulled to PCB GND.
I assume that the above Pin configuration causes BQ25750 to operate in independent mode, and the VAC is in the operable window at this time. The relevant measurement phenomena are as follows:
- The drain voltage of two common source MOSFETs and found that there was no VAC voltage at the drain of the MOS connected to the Buck-Boost circuit side, which means that the MOS is not conducting properly,
- The voltage of ACDRV was only one 10V ramp signal relative to GND on this pin, while it was a negative signal relative to VAC.
- At the same time, there is no 5V output on the output pin REGN of the internal LDO.
I have checked the switch parameters of the MOS transistor I am using and compared it with the MOS transistor used in TI's reference design. The MOS transistor I am using is easier to conduct compared to the MOS transistor recommended by TI, so there should be no problem with the driving capability. At the same time, I have replaced the IC to confirm if the chip is damaged, but this is not very useful.
Please give me some suggestions to solve this problem. I would greatly appreciate it. Thank you.
