The VBUS pin of the TPS65950 on our board is at 3.1V and I can't figure out why.
There's nothing besides the TPS65950 attached to the VBUS line that would drive a voltage, so it must be coming from the VBUS pin on the TPS65950, but I can't see why that voltage is present. The TPS65950 TRM indicates that it can be driven with the charge pump up to 5V (4.8V), and when I flip the DRVVBUS bit in OTG_CTRL[5] to turn on the charge pump the VBUS line does go to 5V. It might make sense that VBUS was at 3.1V, if it is driven through RB_SRP_UP from VUSB3V1 as shown in figure 15-31 on page 834 of the TRM (rev. G) when CHRGVBUS is set to a 1. However, inspecting OTG_CTRL[4].CHRGVGUS finds that the bit is zero. In addition, when I disable VUSB3V1 the voltage on VBUS isn't affected.
A register dump of the USB area is attached:
0x00: 0x51 0x01: 0x04 0x02: 0x02 0x03: 0xc0 0x04: 0x45 0x05: 0x45 0x06: 0x45 0x07: 0x18 0x08: 0x18 0x09: 0x18 0x0a: 0x04 0x0b: 0x04 0x0c: 0x04 0x0d: 0x1f 0x0e: 0x1f 0x0f: 0x1f 0x10: 0x1f 0x11: 0x1f 0x12: 0x1f 0x13: 0x14 0x14: 0x00 0x15: 0x01 0x16: 0x00 0x17: 0x00 0x18: 0x00 0x19: 0x00 0x1a: 0x00 0x1b: 0x00 0x1c: 0x52 0x1d: 0x00 0x1e: 0x00 0x1f: 0x00 0x20: 0x01 0x21: 0x00 0x22: 0x00 0x23: 0x00 0x24: 0x00 0x25: 0x1b 0x26: 0x0c 0x27: 0xa0 0x28: 0x00 0x29: 0x00 0x2a: 0x00 0x2b: 0x00 0x2c: 0x00 0x2d: 0x00 0x2e: 0x00 0x2f: 0x00 0x30: 0x00 0x31: 0x00 0x32: 0x00 0x33: 0x04 0x34: 0x04 0x35: 0x04 0x36: 0x00 0x37: 0x00 0x38: 0x00 0x39: 0x00 0x3a: 0x00 0x3b: 0x00 0x3c: 0x00 0x3d: 0x00 0x3e: 0x00 0x3f: 0x00 0x40: 0x00 0x41: 0x00 0x42: 0x00 0x43: 0x00 0x44: 0x00 0x45: 0x00 0x46: 0x00 0x47: 0x00 0x48: 0x00 0x49: 0x00 0x4a: 0x00 0x4b: 0x00 0x4c: 0x00 0x4d: 0x00 0x4e: 0x00 0x4f: 0x00 0x50: 0x00 0x51: 0x00 0x52: 0x00 0x53: 0x00 0x54: 0x00 0x55: 0x00 0x56: 0x00 0x57: 0x00 0x58: 0x00 0x59: 0x00 0x5a: 0x00 0x5b: 0x00 0x5c: 0x00 0x5d: 0x00 0x5e: 0x00 0x5f: 0x00 0x60: 0x00 0x61: 0x00 0x62: 0x00 0x63: 0x00 0x64: 0x00 0x65: 0x00 0x66: 0x00 0x67: 0x00 0x68: 0x00 0x69: 0x00 0x6a: 0x00 0x6b: 0x00 0x6c: 0x00 0x6d: 0x00 0x6e: 0x00 0x6f: 0x00 0x70: 0x00 0x71: 0x00 0x72: 0x00 0x73: 0x00 0x74: 0x00 0x75: 0x00 0x76: 0x00 0x77: 0x00 0x78: 0x00 0x79: 0x00 0x7a: 0x00 0x7b: 0x00 0x7c: 0x00 0x7d: 0x00 0x7e: 0x00 0x7f: 0x00 0x80: 0x00 0x81: 0x00 0x82: 0x00 0x83: 0x80 0x84: 0x80 0x85: 0x80 0x86: 0x00 0x87: 0x00 0x88: 0x00 0x89: 0x00 0x8a: 0x00 0x8b: 0x00 0x8c: 0xa2 0x8d: 0x00 0x8e: 0x00 0x8f: 0x00 0x90: 0x00 0x91: 0x00 0x92: 0x00 0x93: 0x00 0x94: 0x08 0x95: 0x00 0x96: 0x10 0x97: 0x00 0x98: 0x00 0x99: 0x00 0x9a: 0x00 0x9b: 0x00 0x9c: 0x00 0x9d: 0x00 0x9e: 0x00 0x9f: 0x00 0xa0: 0x00 0xa1: 0x10 0xa2: 0x10 0xa3: 0x10 0xa4: 0x00 0xa5: 0x00 0xa6: 0x00 0xa7: 0x00 0xa8: 0x00 0xa9: 0x01 0xaa: 0x00 0xab: 0x00 0xac: 0x20 0xad: 0x20 0xae: 0x20 0xaf: 0x00 0xb0: 0x00 0xb1: 0x00 0xb2: 0x00 0xb3: 0x00 0xb4: 0x00 0xb5: 0x00 0xb6: 0x00 0xb7: 0x00 0xb8: 0x00 0xb9: 0x00 0xba: 0x00 0xbb: 0x08 0xbc: 0x08 0xbd: 0x08 0xbe: 0x00 0xbf: 0x00 0xc0: 0x1f 0xc1: 0x34 0xc2: 0x64 0xc3: 0x7f 0xc4: 0x6c 0xc5: 0x75 0xc6: 0x64 0xc7: 0x20 0xc8: 0x01 0xc9: 0x17 0xca: 0x01 0xcb: 0x02 0xcc: 0x00 0xcd: 0x36 0xce: 0x44 0xcf: 0x07 0xd0: 0x3b 0xd1: 0x17 0xd2: 0x6b 0xd3: 0x06 0xd4: 0x00 0xd5: 0x00 0xd6: 0x00 0xd7: 0x00 0xd8: 0x00 0xd9: 0x00 0xda: 0x00 0xdb: 0x00 0xdc: 0x00 0xdd: 0x00 0xde: 0x00 0xdf: 0x00 0xe0: 0x00 0xe1: 0x00 0xe2: 0x00 0xe3: 0x00 0xe4: 0x00 0xe5: 0x00 0xe6: 0x00 0xe7: 0x00 0xe8: 0x00 0xe9: 0x00 0xea: 0x10 0xeb: 0x10 0xec: 0x00 0xed: 0x00 0xee: 0x00 0xef: 0x00 0xf0: 0x00 0xf1: 0x00 0xf2: 0x00 0xf3: 0x00 0xf4: 0x04 0xf5: 0x08 0xf6: 0x00 0xf7: 0x00 0xf8: 0x00 0xf9: 0x00 0xfa: 0x00 0xfb: 0x00 0xfc: 0x29 0xfd: 0x00 0xfe: 0x06 0xff: 0x01
Any suggestions as to why VBUS is at 3.1V would be greatly appreciated.
