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PTN78000W - low output current

Caroline Paulin
Prodigy 80 points
Other Parts Discussed in Thread: PTN78000W, LMZ35003

Hi

We would like to use the PTN78000W to step down the 24V to 5V.  The max output current will be around 15mA.  In the data sheet, I cannot find what is the minimum Output current is for 24V to 5V but for 24V to 12V or for 20V to 5V.

I out min for 20V to 5V is 0A

I out min for 24V to 12V is 0.1A 

For our application, what will be the minimum output current?

Thank you

Caroline

  • 0
    TI__Mastermind 38230 points

    PTN78000W will function with no load. However, he light load of <75mA can decrease the  ripple frequency  to  asynchronous operation and < 100kHz.

    I recommend  the 5V is pre-loaded to 50mA.

    tom

  • 0 in reply to Tom Guerin
    Prodigy 60 points
    This may be a bit late to get some help on this topic seeing as how old it is, but it is close to the problem I'm having.

    I'm trying to run a 5V 400mA transmitter with a 36v driver using the TI PTN78000WAH as a step down, and I'm not getting adequate current. I have followed the data sheet in choosing the right Rset (13Kohms and getting 4.99V) and capacitors ( 2.2UF 50V Ceramic and 100UF 6.3V Electrolytic). I need to know if it is possible to get the current at that voltage, and what I can do to fix the issue I am having.

    Thank you

    Mark
  • 0 in reply to Mark Lozano
    TI__Mastermind 38230 points

     

    Mark;

    The thermal derating data indicates at 36Vin and 5Vout at 400mA load, the maximum ambient operating  temperature is85°C .

    Note: The maximum input voltage rating is 36V on this power module. Do no t operate above 36V vin.

    I recommend the LMZ35003 for this  application when the input voltage is 36Vor higher.

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 60 points

    Tom,

    Thank you for the reply.

    I'm testing the PTN78000WAH on a DC power supply at exactly 36V. At no point between 12V and 36V am I seeing 1.5A.

    According to the test data at 32Vi, 5Vo I should see around 400mA. What was the external component (Rset and Capacitor) configuration at time of testing?

    Can the LMZ35003 be integrated into a Step Down Buck with the same dimensions as the PTN78000WAH; If so can I obtain that Buck from TI.

    The size of the PTN78000WAH is just as crucial as the input/output Voltage and current.

    Thank you for your help and the suggestion on a replacement.

    Mark Lozano

  • 0 in reply to Mark Lozano
    TI__Mastermind 38230 points

    Mark;

    PTN78000W  output current cannot be controlled. It is a buck regulator which sources  current required  by the  load.

    PTN78000w product t schematic and specification has Rset at 21kΩ with 100uf polarized output capacitor and 2.2uf input ceramic capacitor. Its dimensions are 0.745" x0.495"

     LMZ35003 is smaller, 0.482" x 0384" and requires  ceramic capacitor only on the input and output buses.

    Tom  .