• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 16 subscribers
  • Views 745 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TS3A44159: Questions

Allan Fan
Expert 7190 points
Part Number: TS3A44159
Other Parts Discussed in Thread: TMUX1574, SN74CB3Q3257

Hi expert,

Customer's system failed communication through TS3A44159. They have tried to bypass it using reserved 0ohm (R1053/R1051/R1039/R1030) and it's ok. 

Could you please advise what might goes wrong and also help clarify below questions? 

Schematic:

Bypass MUX

Bypass MUX(zoom in)

With MUX

We are wondering maybe we violate dynamic timing spec.

Q1: tBBM is measured from COM 90% falling to 90% rising? They measured 562ns > DS spec 35ns

IN=high, NO1 to COM1

Additional information, with MUX, the output COM signal seems meet one of transceiver spec Tw minimum 25ns(measured 31ns). but we still don't know why communication failed. 

Transceiver spec: 


Regards,

Allan

  • 0
    TI__Genius 10974 points

    Hi Allan,

    Thanks for providing all of these details!

    I do not believe the break before make timing is being violated in this case as there seems to be plenty of time between signal switching as annotated in your scope shots (have almost 500ns between switching).

    What looks to be happening is that the multiplexer is introducing enough capacitance to the line (typical ON-capacitance is around 164pF) that it is causing the signals to charge/discharge at a slower rate. This needs to be evaluated by the customer to figure out if this extra capacitance is acceptable or not. If not, a lower on-capacitance may need to be used (such as TMUX1574 or SN74CB3Q3257).

    Lastly, this multiplexer only has a bandwidth of 35MHz, so if you are approaching this frequency, there is a chance the multiplexer may not be able to pass signal entirely.

    Let me know if you have any other questions.

    Thanks!

    Bryan

  • 0 in reply to Bryan Marshall
    TI__Expert 7190 points

    Hi Bryan,

    From the bypass waveform, we can see the signalis just 8.006KHz. Even TS3A44159 has 164pf Ccom(on), as you mentioned it supports 35Mhz, why it would still cause charger/discharge at a slower rate? Also, we found out once the signal pass through the mux, the frequency become 1.728Mhz, do you have any idea?

    Bypass mux time interval=100ns

    Bypass mux, freq. = 8.006Khz

    With MUX, freq. = 1.728Mhz

    Regards,

    Allan

  • 0 in reply to Allan Fan
    TI__Genius 10974 points

    Hi Allan,

    1) The multiplexer will certainly not be able to upscale the frequency as you are describing. So this needs to be further investigated by the customer as it is not expected behavior of the overall system.

    2) While the input capacitance is 164pF typical, the bandwidth also depends on the loading conditions of your circuit. From the datasheet, we specify our bandwidth to be 35MHz with a load of 50 ohms only. So anything different that this will alter the overall bandwidth of the multiplexer (so any extra capacitance or resistance on the line will most likely reduce the bandwidth performance).

    Thanks,

    Bryan