Clamping circuit update

[erikwelsh]

The clamping circuit is intended to solve a reliability issue that is caused when the voltage difference between the VDDS and VDDSHVx pins exceeds 2V which can occur during power down. See https://octavosystems.com/clamping-circuit/ for more information about the clamping circuit. Inside the SiP, the VDDS pin of the AM335x is connected to the SYS_RTC_1P8V (VDD_RTC in the BeagleBone Black Wireless design) power rail and the VDDSHVx pins are connected to the VDDSHV_3P3V (VDD_3V3A in the BealgeBone Black Wireless design).

Therefore, the clamping circuit between VDD_3V3B and VDD_1V8 (T2, IC6, R48, R49, R50, and R51) should be removed. Also, the clamping circuit between VDD_3V3A and VDD_1V8 (T1, IC5, R44, R45, R46, and R47) should be modified to be between VDD_3V3A and VDD_RTC.