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TPS543B20: About remote sense (RSP & RSN) connection of TPS543B20

umutk
Prodigy 60 points
Part Number: TPS543B20

Hi,

I'm using TPS543B20 for 1V @10A buck converter. I am taking TPS543B20EVM as a reference. I have the following questions about remote sense:

1)  There are unpopulated components in the EVM schematic that connects RAMP pin to RSP pin. Do I need to add those placeholders for my circuit? I couldn't find anything related to those components in the datasheet.

2) Where do I place filter components (two low value resistors and high freq. capacitor) for sense pins? Near the IC, or near the load? Near the IC makes more sense to me (to filter out the noise coupled on the way) but in Figure-38 in the datasheet filter resistors and capacitor are placed near the output side rather than the IC and it made me confused.

  • 0
    TI__Guru 56795 points

     

    1)  There are unpopulated components in the EVM schematic that connects RAMP pin to RSP pin. Do I need to add those placeholders for my circuit? I couldn't fin anything related to those components in the datasheet.

    [PJM] No, these place holders on the evaluation module were included for comparing the performance of the TPS543B20's advanced current mode control architecture with a similar device that used voltage mode control.  These components are not needed for the TPS543B20's internal compensation loop.

    2) Where do I place filter components (two low value resistors and high freq. capacitor) for sense pins? Near the IC, or near the load? Near the IC makes more sense to me (to filter out the noise coupled on the way) but in Figure-38 in the datasheet filter resistors and capacitor are placed near the output side rather than the IC and it made me confused.

    [PJM] Ideally we would want the high-frequency noise filter close to the IC to minimize noise injection, and when no feedback divider is used to scale the output voltage to the reference voltage, such as for a 1V output, since 1V is an available reference voltage, it is possible to place the differential bypass capacitor from RSP to RSN close to the IC.  However, for node breaking, or when a feedback divider is used, it is generally best to keep the remote sense resistors or feedback divider close to the load in order to prevent accidentally shorting the remote sense net to the output voltage away from the remote sense point.

    In addition, if the remote sense filter resistors are placed after the feedback divider so that they can be located close to the IC pins, the source impedance of the feedback divider (the equivalent impedance of the top and bottom resistors in parallel) drives the capacitor of the filter, so careful attention to the pass-frequency and resulting phase shift must be considered. 

    It is generally advisable for the corner frequency of the RC filter to be at least 2-3x higher than the switching frequency to avoid having this filter negatively affect phase margin at cross-over.