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TPS543C20: TPS543C20RVFT - Remote Sense Pins

Ajmal Rashid
Prodigy 60 points
Part Number: TPS543C20

We are using the TI part TPS543C20RVFT in our design for generating 0.72V with 40A ( two stacked), since the output voltage is very low and there is an high current requirement, i worried about the power path loss. Below are my concern,

1- Since this part will support RSP and RSN, if we route the remote sense till the destination, will help to compensate the path drop?
2- What are the things we have to taken care if we are routing the RSP and RSN pins till destination? Is there any application note for routing the Remote Sense Pins for this part?

  • 0
    TI__Guru 52115 points
    Ajmal Rashid said:
    1- Since this part will support RSP and RSN, if we route the remote sense till the destination, will help to compensate the path drop?

    Yes, that is the purpose of the remote sense pins

    Ajmal Rashid said:
    2- What are the things we have to taken care if we are routing the RSP and RSN pins till destination? Is there any application note for routing the Remote Sense Pins for this part?

    There is not an applications note covering remote sense, but I will offer some guidance

    1) Route the output voltage sense and the ground sense back to the TPS543C20 as a differential part to minimize noise injection

    2) Place a 10-50 ohm resistor in series with each sense line to ensure node separation as well as provide a small resistance for a differential filter to react with.

    3) Include a place for a capacitor from the local VOUT at the TPS543C20's SW to VOUT inductor to feed local sense back into the feedback in case the added delay of the inductance in the power path is too high for the control loop to handle.

    4) Add a small differential capacitor to sense VOUT and sense ground just before the feedback divider to remove any noise that might be picked up by the remote sense lines.  The bandwdith of this low-pass filter with the sum of the series VOUT and Ground sense resistors should be 8-10x the cross-over frequency to avoid adding phase delay.

    5) Avoid routing the remote sense line near high- frequency switching edges, like the SW or digital communications.

  • 0 in reply to Peter James Miller
    Prodigy 60 points

    Thanks for the update.

    I need some clarification on the guidance that you provided

    2) Place a 10-50 ohm resistor in series with each sense line to ensure node separation as well as provide a small resistance for a differential filter to react with.

    Question: This 10-50 ohm should be placed in source side or load side?

    3) Include a place for a capacitor from the local VOUT at the TPS543C20's SW to VOUT inductor to feed local sense back into the feedback in case the added delay of the inductance in the power path is too high for the control loop to handle.

    Question: what you mean by local VOUT and what is the value and package of the capacitor? Could please share some reference circuit for the same?

    4) Add a small differential capacitor to sense VOUT and sense ground just before the feedback divider to remove any noise that might be picked up by the remote sense lines.  The bandwdith of this low-pass filter with the sum of the series VOUT and Ground sense resistors should be 8-10x the cross-over frequency to avoid adding phase delay.

    Question: what do you mean by sense VOUT and sense ground? what is the value and package of the capacitor? Could please share some reference circuit for the same?

  • 0 in reply to Ajmal Rashid
    TI__Expert 5345 points

    Hello,

    Peter will respond by tomorrow.

    Thank you,

    Calan

  • 0 in reply to Ajmal Rashid
    TI__Guru 52115 points
    Ajmal Rashid said:
    Question: This 10-50 ohm should be placed in source side or load side?

    10Ω-50Ω resistor should be placed between the VOUT/GND and the traces returning to the IC for the RSP/RSN divider.

    The resistor can be placed at the load, provide net separation and prevent accidentally shorting to VOUT or GND and creating a regulation point other than intended, or they can be placed close to the IC.  Either is fine.

    If Net Separation is not required to ensure proper routing, there is a small advantage to placing the resistors close to the IC.

    Ajmal Rashid said:
    Question: what you mean by local VOUT and what is the value and package of the capacitor? Could please share some reference circuit for the same?

    The package can generally be small, 0402 or 0603.  With 10Ω resistors, the capacitor value could be in the μF range.

    The value depends on the parasitic inductance and remote capacitance, and the LC filter they create, along with the resistance value used in series with the feedback.  The high-pass crossover the of this capacitor with the remote sense resistor should be well below the LC double pole of the parasitic double-pole added to the power path.

    Below you can see the circuit drawn out with the parasitic L as Lroute, and an additional 100Ω resistor from the local output to the remote sense.  This isn't necessary but can be helpful, especially if the remote sense is made through a connector or socket and could become disconnected.

    Also, this shows VOUT Sense (VOSNS) and Ground Out Sense (GOSNS)  the VOUT to RSP/RSN divider would be after that point.