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TPS92692-Q1: Schematic is wrong????

Ta Quoc Hung
Prodigy 20 points
Part Number: TPS92692-Q1

Hello!

I have issue with TPS92692-Q1

Load is Nichia LED: 6 led parallel 

+ Vf: 34.9V

+ Iout: 0.81A

I designed schematic but It isn't work. When I use power supply 6V - 3A, this schematic is exhaust the current (Load isn't change). I don't know why it this situation. 

I can't find the cause, anyone help me? 

Thanks ! 

  • 0
    TI__Mastermind 28655 points
    Hello,

    Iadj is set to 2.24V, 2.24V/14 = 0.160V, 0.160V/0.160 ohm = 1A.

    Also, 34.9V * 0.81A = 28.3 watts, you supply is only 18 watts (6V * 3A), it needs to be higher current. You also may run into hitting the peak current limit protection from Ris at 36 mohm, this you can find out after providing a larger power source. Without ripple or efficiency factored in the input current will be 28.3W/5.5V = 5.15A average. With the above set-up it will be 37A/5.5V = 6.7A. RADJ1 needs to go from 41.2K to 28.7K ohm to set current to 0.81A with Rcs = 0.160 ohm

    Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 20 points
    Thanks for your support.
    First, can you tell me is this schematic I am designing right, please?
    I tried 6V - 6A but it isn't change, it just take 6A but voltage down still about 0.8 or 0.9V.
    I don't know if the IC is working or not?
  • 0 in reply to Ta Quoc Hung
    TI__Mastermind 28655 points
    Hello,

    Is D1 SS12P2? That is a 20V diode and needs to be at least 60V.

    Did you change the RADJ1 to a lower value? You can try this. Change RADJ1 to 4.99K and see if it powers up, or change Rcs to 1 ohm.

    The circuit will draw more current if the input voltage is low so it might be better to set the output current much lower to see if it powers up and start increasing when it starts working. If it doesn't at much lower power something else is wrong.

    6V at 6A is still not enough when powering up. Also you have to make sure there is little drop on the wires going to your board.

    Regards,