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DS90UB954-Q1: PoC filter constant

Tomoaki Yoshida91
Genius 5255 points
Part Number: DS90UB954-Q1

Hi team,

My customer will use 953-954 with PoC.

So, they have a question about Poc filter constant.

They are asuming that the data rate will be switched 3.6Gbps and 4.0Gbps.

The data rate of back channel will be 10Mbps or 50Mbps.

Four patterns are assumed in combination of forward channel and back channel speed.

Should I adjust the optimal PoC network constants respectively?

Since the frequency bands are similar, I think that one setting in the band from 5MHz to 2GHz is good.

Is there a recommended constant for this case?

Best regards,

Tomoaki Yoshida

  • 0
    TI__Expert 8135 points

    Hello-

    The PoC filter provided in Figure 41 of the ds90ub960 datasheet ensure impedance above 1kohm for the frequency range between ~1 MHz and ~1.3 GHz. 

    The PoC filter provided in Figure 40 of the 960 datasheet ensure impedance above 1kohm for the frequency range between ~10 MHz and  more than 3 GHz. 

    To cover the 5 MHz to 2 GHz frequency range, the recommended PoC filter should include 100uH and 10uH inductors plus two ferrite beads.

    Regards,

    Davor

  • 0 in reply to Davor Glisic
    Genius 5255 points

    Hi Davor-san,

    Thank you for your support.

    Because my customer will use 954, we were watching 954's datasheet.

    For the PoC filter, recommended circuits of the same constant are presented in the datasheets 954 and 960.

    In the 954's datasheet, it is described to be isotated with impedance of > 2 kΩ over a specific frequency band.

    It is described 1 kΩ in 960's datasheet and you said that 1 kΩ too.

    I'm confused.

    The 2kΩ in the 954's datasheet is typo and 1kΩ is correct.

    The recommended circuit of 954 also has an impedance of >1 kΩ over a specific frequency band.

    Is this understanding correct?

    Could you illustrate the configuration of the PoC filter to cover 5 MHz to 2 GHz so that we will not make mistake?

    Best regards,

    Tomoaki Yoshida

  • 0 in reply to Tomoaki Yoshida91
    TI__Expert 8135 points

    Hello Yoshida-san,

    The 954 and 960 devices feature equivalent FPD-Link III I/Os, so the 960 PoC examples are applicable to the 954 as well.  

    Our original guidance was to achieve >2kohm impedance over a specified range.  It is a very conservative guidance that has been difficult to achieve, so we had relaxed it to >1kohm.  Apparently,  the 954 datasheet needs to be updated to reflect the latest guidance.

    The below PoC circuit has the impedance >1kohm between ~1MHz and more than 3 GHz.  The FB3 is optional as we only need to cover the range up to 2 GHz.

    Regards,

    Davor