TPS65983B datasheet(32/117 Pages) TI1

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Data in

BMC

Decoder

SOP

Detect

4b5b

Decoder

CRC

from PD_RX

Data

TPS65983B

SLVSDM6A – OCTOBER 2016 – REVISED OCTOBER 2016

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Feature Description (continued)

Figure 13. 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 TPS65983B 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, a transition occurs at the start of every bit time and a second transition occurs 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 14 shows the Biphase Mark Coding.

Figure 14. 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. Because a BMC coded as 1 contains a signal

edge at the beginning and middle of the UI, and the BMC coded as 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 TPS65983B 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 15 shows the USB-PD BMC TX/Rx driver block diagram.

TPS65983B Datasheet(PDF) 32 Page - Texas Instruments

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