SBVS426B December 2022 – October 2024 TPS25772-Q1
PRODUCTION DATA
Refer to the PDF data sheet for device specific package drawings
The TPS25772-Q1 transmits and receives USB-PD data over one of the Px_CCy pins for a given CC pin pair (one pair per USB Type-C port). The Px_CCy pins are also used to determine the cable orientation (see the Cable Plug and Orientation Detection section) and maintain cable/device attach detection. Thus, a DC bias exists on the Px_CCy pins. The transmitter driver overdrives the Px_CCy DC bias while transmitting, but returns to a Hi-Z state allowing the DC voltage to return to the Px_CCy pin when not transmitting. While either Px_CC1 or Px_CC2 may be used for transmitting and receiving, during a given connection only the one that mates with the CC pin of the plug is used; so there is no dynamic switching between Px_CC1 and Px_CC2. Figure 8-22 shows the USB-PD BMC TX and RX driver block diagram.
Figure 8-23 shows the transmission of the BMC data on top of the DC bias. Note, The DC bias can be anywhere between the minimum threshold for detecting a UFP attach and the maximum threshold for detecting a Sink attach to a Source resulting in a DC bias that can be above or below the VOH of the transmitter driver.
The transmitter drives a digital signal onto the Px_CCy lines. The signal peak, VTXHI, is set to meet the TX masks defined in the USB-PD Specifications. Note that the TX mask is measured at the far-end of the cable.
When driving the line, the transmitter driver has an output impedance of ZDRIVER. ZDRIVER is determined by the driver resistance and the shunt capacitance of the source and is frequency dependent. ZDRIVER impacts the noise ingression in the cable.