TUSB1004 datasheet(22/53 Pages) TI

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7.3.2.2 Full Adaptive Equalization

The Full AEQ mode attempts to find what it believes is the best equalization value for CRX1 and CRX2 receivers

by starting at the lowest EQ value and sweeping through all EQ combinations up to the value programmed

into FULLAEQ_UPPER_EQ field. The default is to sweep through nine EQ values (zero to eight). The number

of EQ combinations can be adjusted by programming FULLAEQ_UPPER_EQ register. The TUSB1004 also

provides the ability to add or subtract some over/under equalization to compensate for channel in front of

TUSB1004 by programming OVER_EQ_CTRL field to a non-zero value. If OVER_EQ_SIGN = 0, the TUSB1004

will add the value programmed into OVER_EQ_CTRL to the EQ value determined by the full adaptation. If

OVER_EQ_SIGN = 1, the TUSB1004 will subtract the value programmed into OVER_EQ_CTRL from the EQ

value determined by the full adaptation. For example, if full adaptation determines the best equalization value to

be 4 and OVER_EQ_CTRL is 2 and OVER_EQ_SIGN = 0, the EQ setting used by TUSB1004 will be 6. The

TUSB1004 hardware will always limit the sum of OVER_EQ_CTRL and the determined optimal EQ from full

adaptation to be less than or equal to 15.

Note

Full AEQ is supported in both pin-strap and I2C mode. In pin-strap mode, enable or disable of Full

AEQ is determined by the state of AEQENZ pin.

7.3.2.3 Fast Adaptive Equalization

The Fast AEQ mode is used to distinguish two channels (short channel and a long channel) and choose the

appropriate receiver equalization setting for that channel. Because Fast AEQ only distinguishes between two

choices, the AEQ time is a lot shorter than Full AEQ mode which minimizes impact to USB link training.

When Fast AEQ is enabled and channel is determined to be short, the TUSB1004 will use the value

programmed into the CEQx_SEL, where x = 1 or 2. If the TUSB1004 determines channel is not short, the

TUSB1004 will switch to EQ value programmed into LONG_EQx register, where x = 1 or 2. During initial

system evaluation, it is recommended to perform both short and long channel USB 3.1 RX JTOL Gen2 testing

and program CEQx_SEL and LONG_EQx to the value which produced the best results for each channel

configuration.

The TUSB1004 will determine short and long based on the estimate eye height. The value programmed into

FASTAEQ_LIMITS register will determine the eye height limits. Software can change the defaults of this register

to lower or raise the limits.

Note

Fast AEQ is only supported in I2C mode.

EQ_OVERRIDE field must be set for values programmed into CEQx_SEL and LONG_EQx to be

used.

7.3.3 USB Transmitter

7.3.3.1 Linearity VOD

Linearity VOD defines the linearity range of the TUSB1004. When TUSB1004 is in linear VOD mode, the output

VOD is a linear function of the input VID. For example, if the signal at TUSB1004's input (VID) is at 600 mVpp

then the TUSB1004's output VOD will be around 600 mVpp. Linearity VOD mode is the default operation of the

TUSB1004. Linear VOD mode is supported on SSRX1/2 and CTX1/2 transmitters.

The TUSB1004 provides four different linearity VOD settings. All four settings are available in I2C mode through

TUSB1004

SLLSFL3 – APRIL 2022

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