Other Parts Discussed in Thread: TPD6S300, TPS65987, TPS65987D
Hi,
We're using the TPS65987DDK in a design and have noticed a "reverse charging" behavior when the system is unpowered and a USB device capable of sourcing VBUS is plugged in. When in this state, we see PP_HV1 = 5V, which indicates the PP_HV1 switch is closed. In the scope capture below, you can see the PP_HV1 switch close about 50ms after VBUS is powered.
We have SPI_POCI = 0 and DIV = .14 (R1=100k, R2=16.2k), which should give set the Dead Battery Mode to BP_NoResponse and the Device Configuration to Infinite Wait, according to Table 8-5. Table 8-6 states that BP_NoResponse means "No power switch is enabled and the device does not start-p until VIN_3V3 is present". This can't be true given that we're seeing the PP_HV1 switch is closed while VIN_3V3 = 0V, as shown above. I have also probed ADC1IN and the voltage = .464V, which corresponds to a DIV value of .14.
Am I correct that the Table 8-6 statement about BP_NoResponse is false? If it is indeed false, then that's very disappointing because closing that switch by default could inject 5V into a system that is otherwise unprepared for it.
We have another device (TPD6S300) which is providing transient protection on the CC pins. The RPD_G1/2 pins of the TPD6S300 are tied to ground, so in a dead battery situation, it is off. This prevents external USB C devices from sourcing VBUS by default (because they don't see Rd on the CC lines), but other situations (such as a USB-C to A cable) will source VBUS because a USB A endpoint has no knowledge of the CC lines.
Thanks,
Cletus
