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DS100BR210: Internal regulator not functioning as expected

Rajil Ramesh
Prodigy 30 points
Part Number: DS100BR210


I'm planning to use DS100BR210 for isolating the network interface of a PC (100 Mbps) upon receiving a digital signal. I tried the basic pin mode control (ENSMB = 1kOhm to GND) with EQ and DEM set to 0 and VOD_SEL set to 1. MODE pin was set to 1 and TX_DIS to 0. VDD_SEL was pulled to 0 for enabling internal regulator. The Tx and Rx lines were given directly without decoupling capacitors. The circuit was NOT working as expected. I tried measuring the Vdd pin which was showing 0.7 V as against expected 2.5 V. I tried removing all connections other than Vin, VDD_SEL and GND but the voltage at Vdd was still 0.7 V. s there anything that I'm doing wrong? Just for the sake of completeness, I did not connect any bypass capacitors across Vdd. But I believe that the regulator output should be available even without it.

  • 0
    TI__Mastermind 39083 points

    Hi,

    Please note that bypass capacitors on an LDO can play an important role in stability and noise.  In your final design, it is important to have bypass capacitors on VDD.  I do not have a way to test if they are critical to establishing 2.5V, but I would recommend adding them in if possible in order to verify that they are not a part of the problem.

    It is also important to have AC coupling capacitors on TX/RX since there is no guarantee that the transmitter and receiver that the redriver is connected to will have the same DC bias as the redriver.

    Just to confirm, is Vin 3.3V?  Also, is it possible to swap your DS100BR210 with another part?  Depending on the DC bias of your transmitter and receiver, it is possible to damage the part by not using AC coupling capacitors.

    Also, I'm not sure what sort of isolation you are looking for in your application, but please note that the DS100BR210 is not designed for galvanic isolation.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Prodigy 30 points

    Thanks Drew. I will be adding the decoupling and AC coupling capacitors in the final design. Vin was indeed 3.3 V. I'll try with another part.

    I'm not using DS100BR210 for galvanic isolation. It is for cutting the ethernet link between PC and network switch upon detecting a failure in the system.

  • +1 in reply to Rajil Ramesh
    TI__Mastermind 39083 points

    Hi,

    When trying with another part, please also try to add AC coupling capacitors in order to ensure that the DC bias on RX/TX is not the issue.  If this is not possible, I would recommend first disconnecting RX/TX from DS100BR210 and see if the 2.5V supply is generated correctly in your system.

    Thanks,

    Drew