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Original question:

DS15BR400: Unused Pins

DS15BR400: DS15BR400

bahram afghani
Prodigy 170 points
Part Number: DS15BR400

Dear TI associate, back in January of 2020 Lee replied back to Lindsey as:

Hi Lindsey,

The unused inputs should be tied off as listed below to ensure the outputs remain in a stable state.

IN+ = 3.3K to VDD

IN- = 3.3K to GND

This will ensure 50mV of offset at the input which is enough to keep the output from switching.

Regards,

Lee

We have the same issue, with no cable attached while providing 68mV of DC bias delta between the plus and minus inputs of the part, we are still observing 100mV of oscillation at the out plus pin. Is there a way to get rid of this oscillation? The output is not switching between high and low level which is a good thing, however the plus side oscilating is not of favor.

The part's case temperature is around 70C, when idle, is this normal? We followed the layout guidelines by providing 5 x 0.2mm size vias to GND plane on middle thermal pad. I look forward to your response.

Thanks,

Bahram

  • 0
    TI__Mastermind 35130 points

    Hi Bahram,

    Have you checked if there are any oscillations on the plus input?

    Also, you can try decreasing the termination resistors to increase the DC bias on the input (e.g. use 2k resistors instead of 3.3k).

    Regards,

    I.K.

  • 0 in reply to Ikechukwu Anyiam
    Prodigy 170 points

    Hi I.K.,

    Thank you for your reply.

    I am getting output oscillation in the magnitude of 250 mV when there is no ac applied (no signal) to the inputs.

    Increasing the bias delta on the inputs did not do any changes. I am thinking maybe the parasitic capacitors at input pins could be the cause. The resonance frequency is around 4MHz, with amplitude as high as 250mV on output plus line.

    Thanks,

    We ordered the eval kit from digikey, but I have not yet received it and it has been over 3 weeks!

    Bahram

  • 0
    Prodigy 170 points

    I.K., btw, the initial 100mV output swing as the part heats up increase to 250mV.

    The other question is the high power consumption . I think if we somehow manage to diminish output oscillation at idle the part should could down. We are using 20 of these parts and average case temperature is over 60 degrees at idle.

    Bahram

  • 0 in reply to bahram afghani
    TI__Mastermind 35130 points

    Hi Bahram,

    Are you still having issues here? I agree the high power consumption may be caused by the oscillating output, and 60 degree case temperature at idle does not sound normal. Since increasing the bias did not do anything then there may already be some oscillation on the input that is getting passed to the output. 

    If the EVMs you ordered have arrived yet, have you been able to test them and see if you get the same result?

    Regards,

    I.K.