TUSB542: USB eye-pattern tests using a cable tester platform.

Luis

I am not familiar with this Total Phase cable tester platform, do you have a block diagram showing your test setup?

If you probe the SEL pin, does the SEL pin toggle appropriately depending on your CC1/2 connection?

Thanks
David

Hi David,

Please find attached a couple of block diagrams showing the setup.

CC1/2 toggle appropriately to set the correct side of the SS lines.

The Total Phase Cable Tester platform is designed to test USB cables, they confirmed this should work with their platform provided RxDetect can be forced.

Thanks,

Luis.

Block diagrams for TI support.pdf

Luis

How do you place the AC coupling caps on SSTX and SSRX on both side of the TUSB542? Does Total Phase platform have AC coupling caps on the TX and no caps on the RX?

Thanks
David

Hi David,

Yes, AC coupling caps were placed on both sides of TUSB542 on all SS lines. I'll have to ask Total Phase for that information. What AC coupling setup would make the Total Phase platform work with the TUSB542?

Thanks,
Luis.

Luis

AC coupling caps must be needed for the RX detection. The recommended value is 0.22uF on the TX and 0.33uF on the RX.

Per USB spec,

The Receiver Detection circuit is implemented as part of a Transmitter and shall correctly detect whether a load impedance equivalent to a DC impedance RRX-DC (Table 6-21) is present. The Rx detection operates on the principle of the RC time constant of the circuit. This time constant changes based on the presence of the receiver termination. This is conceptually illustrated in Figure 6-39. In this figure, R_Detect is the implementation specific charging resistor. C_AC is the AC capacitor that is in the circuit only if R_Term is also present, otherwise, only C_Parasitic is present.

From TUSB542 perspective, it periodically checks for far-end receiver termination on both TX. Upon detection of the far-end receiver’s termination on both ports, the TUSB542 will transition to U0 mode. When does Total Phase tester enables its RX termination on the U and D port?

Thanks
David

Hi David,

Thanks for the detailed information. I passed your queries to the Total Phase team.

Would there be a way to force the RX-Detect mode to set the chip in U0 mode manually?

Thanks,

Luis.

Luis

No, TUSB542 TX would check for far-end termination to be enabled, but there is no way to force it from disconnect mode to U0 mode.

Thanks
David

Hi David,

This is the information I received from Total Phase:

1. Does the Total Phase platform have AC coupling caps on the TX line and no caps on the RX?
The SS TX lines are DC coupled and the SS RX, HS TX, and HS RX lines are AC coupled for Advanced Cable Tester.

2.Does the Total Phase platform have RX termination on the U and D ports?
There is termination in our receiver of 100 ohms differential and 50 ohms single ended. It is DC or AC coupled as described in the previous answer.

Please let me know what you think of this.

Thanks,
Luis.