TPS65982ABZBHR datasheet(34/121 Pages) TI1

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Data in

BMC

Decoder

SOP

Detect

4b5b

Decoder

CRC

from PD_RX

Data

TPS65982

SLVSD02D – MARCH 2015 – REVISED JUNE 2019

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Feature Description (continued)

Figure 12. USB-PD Baseband Receiver Block Diagram

The USB-PD baseband signal is driven on the C_CCn pins with a tri-state driver. The tri-state driver is slew rate

limited to reduce the high frequency components imparted on the cable and to avoid interference with

frequencies used for communication.

9.3.1.2 USB-PD Bi-Phase Marked Coding

The USBP-PD physical layer implemented in the TPS65982 is compliant to the USB-PD Specifications. The

encoding scheme used for the baseband PD signal is a version of Manchester coding called Biphase Mark

Coding (BMC). In this code, there is a transition at the start of every bit time and there is a second transition in

the middle of the bit cell when a 1 is transmitted. This coding scheme is nearly DC balanced with limited disparity

(limited to 1/2 bit over an arbitrary packet, so a very low DC level). Figure 13 shows Biphase Mark Coding.

Figure 13. Biphase Mark Coding Example

The USB PD baseband signal is driven onto the C_CC1 or C_CC2 pins with a tri-state driver. The tri-state driver

is slew rate to limit coupling to D+/D– and to other signal lines in the Type-C fully featured cables. When sending

the USB-PD preamble, the transmitter will start by transmitting a low level. The receiver at the other end will

tolerate the loss of the first edge. The transmitter will terminate the final bit by an edge to ensure the receiver

clocks the final bit of EOP.

9.3.1.3 USB-PD Transmit (TX) and Receive (Rx) Masks

The USB-PD driver meets the defined USB-PD BMC TX masks. Since a BMC coded 1 contains a signal edge at

the beginning and middle of the UI, and the BMC coded 0 contains only an edge at the beginning, the masks are

different for each. The USB-PD receiver meets the defined USB-PD BMC Rx masks. The boundaries of the Rx

outer mask are specified to accommodate a change in signal amplitude because of the ground offset through the

cable. The Rx masks are therefore larger than the boundaries of the TX outer mask. Similarly, the boundaries of

the Rx inner mask are smaller than the boundaries of the TX inner mask. Triangular time masks are

superimposed on the TX outer masks and defined at the signal transitions to require a minimum edge rate that

will have minimal impact on adjacent higher speed lanes. The TX inner mask enforces the maximum limits on the

rise and fall times. Refer to the USB-PD Specifications for more details.

9.3.1.4 USB-PD BMC Transmitter

The TPS65982 transmits and receives USB-PD data over one of the C_CCn pins. The C_CCn pin is 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 will exist on the C_CCn. The transmitter driver will overdrive the

C_CCn DC bias while transmitting, but will return to a Hi-Z state allowing the DC voltage to return to the C_CCn

pin when not transmitting. Figure 14 shows the USB-PD BMC TX/Rx driver block diagram.

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