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TPS65279: Operation at low Vin - Vout differential

Ryan.Bishop
Expert 3900 points
Part Number: TPS65279

Hello,

I am considering this part for a 6V to 5V conversion at 1.6MHz. This results in an ON time of 521ns, and an OFF time of 104ns.

  1. How can I verify the voltage droop of the bootstrap capacitor during this ON time?
  2. Will it get fully charged in that OFF time?

It seem like the datasheet would need to spec the gate charge of the internal FETs for me to answer #1.

For #2, since the LDO is limited to 200mA, over the course of 100ns it can only charge a .1uF cap up by 200mV.

Is it possible for me to figure this out with the datasheet alone?

Thank you,
Ryan B.

  • 0
    TI__Genius 15135 points

    Hi, Ryan 

    I check the Qg data, this is not included in DS. 

    high side=4.3nC

    low side=5.5nC. 

    In normal operation, the BST cap is charged to ~6V, assume the Cbst=47nF

    The total Q is 282nC, when high side is on, it will consume 4.3nC, so the BST cap droop voltage is about 92mV. 

    When low side is on, the BST cap is charged by 200mA, the BST cap will rise about 442mV. 

    So during normal operation, after several cycles, BST cap will be fully charged.