Other Parts Discussed in Thread: CSD87501L
Tool/software:
I have observed a behavior that I cannot explain yet, and would like someone to point me to the documentation that could explain the behavior. Here is the scenario:
- The TPS25751 chip is not initialized, not connected to EEPROM and not receiving I2C messages from the MCU.
- A battery is connected to the board, supplying 3V3 to VIN_3V3 pin 32.
- Then USB cable is connected to the board, supplying VBUS to pins 26 and 27.
- GATE_VBUS and/or GATE_VSYS (pins 21 and 20) control CSD87501L which connects VBUS from the USB source to VBUS on the MCU. The VBUS connection to MCU measures 0V with this scenario.
The observation is MCU does not see VBUS.
However, if the USB cable is connected first (VBUS on pins 26 and 27), followed by the battery (3V3 on pin 32 VIN_3V3), the MCU continues to see VBUS (VBUS connection to MCU measures 5V). I have not found the reason for this behavior yet. Could you point me to the documentation that explains this behavior please?
Rex