Datasheet
UART_TX
DM
DP
UART_RX
CK1 CK2
CK3 CK4
037-047
TPS65930/TPS65920
www.ti.com
SWCS037G–MAY 2008–REVISED APRIL 2011
Table 7-4. USB-CEA Carkit UART Timings
Notation Parameter Min Max Unit
CK1 t
d(UART_TXH-DM)
Delay time, UART_TX rising edge to DM transition 4.0 11 ns
CK2 t
d(UART_TXL-DM)
Delay time, UART_TX falling edge to DM transition 4.0 11 ns
At 38.4 MHz 205 234
Delay time, DP rising edge to UART_RX
CK3 t
d(DPH-UART_RX)
ns
transition
At 19.2 MHz 310 364
At 38.4 MHz 205 234
Delay time, DP falling edge to UART_RX
CK4 t
d(DPL-UART_RX)
ns
transition
At 19.2 MHz 310 364
Figure 7-5 shows the USB-CEA carkit UART timings.
Figure 7-5. USB-CEA Carkit UART Timings
7.1.4 PHY Electrical Characteristics
The PHY is the physical signaling layer of the USB 2.0. It contains the drivers and receivers for physical
data and protocol signaling on the DP and DM lines.
The PHY interfaces with the USB controller through the UTMI.
The transmitters and receivers in the PHY are of two main classes:
• FS and LS transceivers (legacy USB1.x transceivers)
• HS transceivers
To bias the transistors and run the logic, the PHY also contains reference generation circuitry which
consists of:
• A DPLL that does a frequency multiplication to achieve the 480-MHz low-jitter lock necessary for USB,
and the clock required for the switched capacitor resistance block
• A switched capacitor resistance block that replicates an external resistor on chip
Built-in pullup and pulldown resistors are used as part of the protocol signaling.
The PHY also contains circuitry that protects it from an accidental 5-V short on the DP and DM lines and
from 8-kV IEC ESD strikes.
7.1.4.1 HS Differential Receiver
The HS receiver consists of the following blocks:
• A differential input comparator to receive the serial data
• A squelch detector to qualify the received data
• An oversampler-based clock data recovery scheme followed by a nonreturn to zero inverted (NRZI)
decoder, bit unstuffing, and serial-to-parallel converter to generate the UTMI DATAOUT
Table 7-5 lists the characteristics of the HS differential receiver.
Copyright © 2008–2011, Texas Instruments Incorporated USB Transceiver 73
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