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DS99R105_106 / for USB3.0 cable

Toshiyuki
Mastermind 7075 points
Other Parts Discussed in Thread: DS99R105, DS99R106

 Hi,

Customer is considering DS99R105/106 by using USB3.0 cable.In this case, should the output differential termination resistance(Rt) be changed 90Ω ?

Could they use USB3.0 cable ? Is there sufficient results for that ?

Best Regards,

Kato

  • 0
    TI__Guru* 92040 points
    Greeting Toshiyuki-San,

    1). Please note USB3.0 data rate is specified at up to 5 Gbps. DS99R105 can carry about 960 Mbps or about 1 Gbps of the user payload. DS99R105 additionally sends out control data bits so overall the maximum line rate is 28*40MHz~ 1.12 Gbps.

    2). LVDS Interface expects 100 Ohm termination resistor. Failure to meet this spec, affects return loss and thus signal integrity(ringing on the signal over shoot and undershoot ). Looking on the web, i noticed USB 3.0 termination could be 90 Ohm +/-7 Ohm. Connector should be able to handle 90 +/- 15 Ohm. So during product development this has to be studied carefully to make sure this meets the worst case timing analyses.

    3). DS99R106 minimum input sensitivity is 100mV differential(without pre-emphasis). At the same time, the minimum output differential from DS99CR105 is 250mV(across power voltage and Temperature). This means as long as there is at maximum about 8dB of attenuation at the nyquist frequency then there should not be a problem. After looking at USB 3.0 requirements, it seems at about 1.2Gbps or less there is less than 3.3dB of attenuation. Therefore i don't expect an issue here. This means DS99R105/6 should be able to handle USB 3.0 cable loss characteristics at 1.2Gbps or less data rate.

    Regards,,nasser
  • 0
    TI__Expert 3175 points
    Hi Kato-san
    The DS99R106 has on-chip termination of 100 ohm typ, so changing it to 90 is not an option.
    The DS99R105 has external termination R, so it is possible to change from 100 ohm to 90 ohm if it provides betteer match with the cable.
    I believe USB 2.0 or 3.0 cables are 90-ohm impedance.Regards,TK Chin
  • 0 in reply to T.K. Chin
    Mastermind 7075 points

    Hello Nasser -san, T.K, Chin -san,

    Thank you for the reply.  I understood that it is possible to change the external termination from 100 ohm to 90 ohm. So, do you have the information what the cable and connector impedance are acceptable for signal integrity ? DS99R105 and DS99R106 have the signal integrity margin for USB3.0 cable and connector ?

    In addition, regarding AC coupling connection, 100nF between the serializer and deserializer,  what value is acceptable for production tolerance ?

    Best Regards,

    Kato

     

  • 0 in reply to Toshiyuki
    TI__Guru* 92040 points

    Kato-San,

    DS99R105/6 have been characterized with 100 Ohm impedance in mind. The customer can try 90 ohm termination and check the signal integrity. 

    AC coupling Capacitor value is a function of the data pattern they are planning to use. For 8/10 bit coded data 100nF is fine. On the other hand, if they have data pattern with high low frequency content then at least 4.7uF capacitor is the recommended value.

    Regards,,nasser