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TPS7A78: as 15 and 5V dual output

Mat1980
Intellectual 1210 points
Part Number: TPS7A78

Hello Team, 

can I set the LDO_in voltage to 15V and use as intermediate supply and the 5V as a low voltage output?
My goal is to use the device as a supply for gate drivers. So I need 15V for the FETs and 5V logic level voltage.

Thanks,

  • 0
    TI__Mastermind 29150 points

    Hello,

    The datasheet states that you cannot use the LDO_IN voltage.  See the note is section 7.3.4.  If you need to use this pin as a voltage rail, I may have a workaround after consulting with the IC designer but I need to test it on an EVM.  Regardless of whether you can use LDO_IN or not, it will be set at 5.6V typical if LDO_OUT is set to 5V (see the datasheet snapshot below).

    The preferred option would be to add another regulator off of SCIN, and down convert SCIN to 15V.  See figures 19 and 20 for SCIN waveforms to get a sense of the voltage, especially during turn on.  You may want to gate the regulator off of SCIN based on the PG feature of LDO_OUT so that SCIN is a clean rail.  You will need to size the CS capacitor and RS resistor accordingly for the additional current.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Intellectual 1210 points

    Helllo Stephen, 

    thanks for the quick feedback. How much current can I pull from this pin? If the 16V works for me, can I also directly drain current from the SCIN? 

    Thanks!

    Mat

  • 0 in reply to Mat1980
    TI__Mastermind 29150 points

    Hi Mat,

    You can directly pull current from SCIN.  You have to take the current from SCIN into consideration when designing the CS and RS components.  The switching stage of this device divides the current from LDO_OUT by 4x going back to the input of the TPS7A78.  The current taken from SCIN is not divided down. 

    Thanks,

    - Stephen