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Problem with TPS54360

Saqib Bajwa
Prodigy 170 points
Other Parts Discussed in Thread: TPS54360

Hi,

I am designing a power supply for GPRS modem using TPS54360. The circuit I have designed is below;

But I am not getting anything on RT/CLK pin. It should be around 440kHz. And under no load I am getting 3.8V at the output but as soon as I put on some load (100mA) the voltage drops to 0.2V. I have also tried with EN pin floating (without the BC847). Can you please help me out and tell me what I am doing wrong?

Thanks.

Regards

Saqib

  • 0
    TI__Guru**** 191445 points

    You should not see any waveform on the RT/CLK pin.  It should be about 0.5 V dc.  Probing it may cause the circuit to not be stable.

    Do you have any activity on PH?  How did you derive the values for the compensation components?

  • 0 in reply to JohnTucker
    Prodigy 170 points

    Hi,

    Thanks for your quick reply. Sorry the values of the RC components with the compensation are wrong in the above circuit. I have used R=12k and 10nF (in series with this resistor) and then 60pF (parallel to the R and C). I have used the formulas in the datasheet to calculate these values. I have gone through the datasheet a couple of times and reconfirmed all the values and everything seems correct. But I am getting (~0.2V) at the output (instead of 3.8V) when I put some load.

    My Input voltage range is from 8V to 60V and max current is 3A.

    Sorry what do you mean by PH?

    Awaiting for your reply. Thanks.

  • 0 in reply to JohnTucker
    Prodigy 170 points

    Hi John,

    Thanks a lot. I have figured it out :) I was going through the PCB and I have found out that the ground to the catch diode was missing. Our PCB designer missed that track but I think its my mistake because she showed me the final schematic before starting the PCB layout and I missed that :)

    Anyway thanks a lot for your prompt responses. 

  • 0 in reply to Saqib Bajwa
    TI__Guru**** 191445 points

    Good,  I'm glad you could figure it out quickly.

  • 0 in reply to JohnTucker
    Prodigy 170 points

    Hi,

    I am having another problem with TPS54360. Its limiting the current to approx. 900mA. All the values of RC components (mentioned in previous post) have been calculated using the formulas in the datasheet and I have rechecked them and they look fine. But still its limiting the current if it goes above 900mA. 

    The specs. of my design are; Input is 8 to 60V, Output is 3.8V and max. current is 3A. Please see previous post to look at the circuit. 

    Thanks in advance for the help.

    Regards

    Saqib