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TPS7H4001-SP: RT Resistance for Fsw=500kHz

John Lally
Intellectual 505 points
Part Number: TPS7H4001-SP

Hello E2E,

  Using equation (4) on pg 27 of the datasheet, to achieve Fsw=500kHz, RT=166.2k.  This is also reported by the TPS7H4001-SP Buck Converter Calculator spread-sheet.

However, the TPS7H4001-SP evaluation boards (multi & single channels) have RT=174K which equates to Fsw=480kHz, which is unexpected because per the datasheet multi-channel operation uses Fsw=500kHz.

Why does TI use RT=174k instead of something closer to 166k?  There appear to be standard resistor values available close to 166k.

Our system will have both single channel and 2 channel (one master & one slave) instances of the TPSH4001-SP down-converting 5V to 0.95V (with very low ripple, noise & transient voltage targets), what RT resistance(s) do you recommend for these instances: single and 2 channel?

Thank you,

-John

  • 0
    TI__Genius 14540 points

    Hi John,

    Thanks for highlighting this discrepancy.  The 174kohm value for the RT resistor is an artifact of an older equation that was updated after characterization of the device to the present equation shown in the datasheet.  The original EVM used 174kohm RT since the hardware predated the release of the device.  However, all EVM inventory in the TI store was recently reworked to use 165kohms for the RT resistor (closest value I could procure to target of 166kohms).  Unfortunately, the documentation was not updated to reflect this rework.  So you are correct, 166kohms is the correct RT value to use for a switching frequency of 500kHz.  I have made a note to update all documentation upon the next revision release.  Thanks for the feedback.

    Regards

    Christian