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UCD9240: UCD9240 3 rails cannot work together

Part Number: UCD9240


My customer has some queries need help.

They use UCD9240 to control the following modules, which are:
Rail 1: PTD08A020WAD, designed to output 1V0;
Rail 2: PTD08A010WAD, designed to output 2V5;
Rail 3: NA;
Rail 4: PTD08A020WAD, designed to output 1V5;

Within the debuging with Fusion Digital Power Designer, they can set the Rail 1 to Rail 4 to turn on/off according to Control Pin and Operation.

During the debug, they found:
Rail 1: turn on/off normal, output voltage is 1V0, multiple test passed;
Rail 2: turn on/off abnormal, output voltage is 2V5, sometimes turn on normal, sometimes not, no output, it seems 1st, 3rd, 5th, turning on are good, while 2nd, 4th, 6th turning on are bad;
Rail 4: turn on/off normal, output voltage is 1V5, multiple test passed.
3 rails cannot work together.

please help to solve this query.



  • Hi Star,

    Please connect the device to Fusion GUI. In the Status and the Monitor section, the GUI will report the fault detected by the device which caused shut down. Based on the fault, we can debug further.



  • Hi Star and Zhiyuan:

         Really thanks for your help.

        With the Fusion digital power designer,  I captured several pictures, which are listed below:

    Step 1: start Rail1, 1V0, OK:

    Step 2: Rail2, 2V5, OK

    Step 3: Rail4, 1V5, abnormal, cannot reach 1V5

    Step 4: After step 3, i did a review on Rail 2, found 2V5 was still ok

    Step 5: then reviewed Rail 1, 1V0 disappeared, complains about FLT and Mfr falut.

  • FLT is power stage over current fault. OVF is Vout OV.

    Check if loop is stable, and try increase soft start ramp time.

  • Hi, Zhiyuan:

         My current soft startup sequence for Rail 1-4 is listed below:

    The result is still not ok, while the soft ramp time is indeed affects the Rail performance.

    Could you kindly tell me how to check the stablity of the loop? If there are some guidelines,

    that's even better. Are there some key points to improve the stablity of the loop?

    Best Regards,



  • Eric,

    I think the debug should start with observing waveforms on scope. From the waveforms we can analyze the root cause. For example, check current sense signal, SW node, Vout, FLT, and so on. Do you have local FAE to support you?

  • Hi, Zhiyuan,

    OK. Later i will check the above waveforms according your hints, and then update the results here.
    If possible, i really want some TI expert to give me some instructions in my office. Could you kindly recommend
    someone for me? My office is in Haidian District, Beijing City.

    Really thanks for you and Star!

    Best Regards,

  • Hi, Zhiyuan and Star:

    The above problem has been solved, and the AGND and GND of the power modules PTD08A010WAD and PTD08A020WAD are not properly connected. After i connected them directly, then with proper configurations, all the 3 power rails start to function well.
    Really thanks for your insightful advice, Zhiyuan.
    Really thanks for your instant response and help, Star.

    Best Regards,
  • Final Solution: connect the AGND and GND of the power modules PTD08A010WAD and PTD08A020WAD directly.