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TPS40210: Adjust Vout into 22V hardware modification

Oliver Lin
Expert 4475 points
Part Number: TPS40210

Hi expert,

Our customer has couple questions as below

(1)Does TPS40210 has the minimum Voltage between Vout and Vin ? If does, what the voltage would be?

(2)Now we have Vin 19.5V and try to make Vout into 22V, do we have any components needed to be modified for compensation adjustment except the divider resistor at FB pin ?

Thank you for your help

Best regards,

Oliver Lin

  • 0
    TI__Guru* 78400 points
    (1) The minimum voltage from Vout to Vin is determined by the minimum ON time, or min duty cycle, because the boost Vout = Vin / (1-D). To regulate Vout, the max Vin is limited by Vin_max = Vout * (1 -Dmin). So the min voltage difference is Vout * Dmin.

    According to the TPS40210 datasheet, the min ON time can be 400ns. Assume switching at 250kHz, this min ON time means a min duty cycle of 10%. Then your max Vin to regulate Vout at 22V is 2.2V below the Vout.

    (2) Reducing the switching frequency will allow higher Vin to stay in Vout regulation. In the above mentioned example, if you switch at 100kHz, the equivalent min duty cycle is 4%, and your Vout can stay in regulation for Vin up to about 21V.

    Hope this clarifies.
  • 0 in reply to Youhao Xi
    TI__Intellectual 2295 points

    Hi Youhao,

    Thanks for your answer. Customer connected the VDD to 19.5V. Can you please clarify if the min ON time 200nS or 400nS should be followed? Now customer sets the switching frequency to 600KHz(R=261K ohm, C=100pF). If the min ON time 200nS is the case, I would suggest customer to change the switching frequency to 500KHz to get the cycle time 2uS and meet the min ON time 200nS(max) spec.

    Best regards,

    Randy Chen

  • 0 in reply to Randy Chen
    TI__Guru* 78400 points

    The datasheet does not give the min ON time for 20Vin. It seems the min ON time should be between 200ns and 400ns.  However, to be safe, I would use 400ns as the worst case to avoid any surprise later.