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UCC28C42: Application issues

Reed
Expert 2070 points
Part Number: UCC28C42


Tool/software:

Hi,

PN: UCC28C42DR

UCC28C42DR, The customer received two packages of 2500 pieces each, with two batches and two origins: Malaysia and Mexico.

The UCC28C42DR from Malaysia has 24V overload protection issu es. The performance test of the Mexican origin is OK.

What is the reason for the problem wit h UCC28C42DR produced in Malaysia? How to solv e it?

  • 0
    TI__Genius 15626 points

    Reed,

    Would you be more specific when mentioning "24V overload protection issues". What kind of test was done? What kind of issue is the controller facing? Would you please provide schematic and waveforms of the test that was done?

    Thank you

  • 0 in reply to Manuel Alva Hernandez
    Expert 2070 points

    Hi Manuel ,

    The testing method is that when the 24V output of the switch power supply circuit is short circuited (80-800VDC input, 24V output), there is a significant difference in the COM pin voltage of the 28C42 chip from both sources. The COM pin voltage of the Mexican origin will reach about 5.8V, but the COM pin voltage of the Malaysian origin will only reach about 5V. It is precisely this voltage difference that causes the Malaysian origin cannot reach the voltage value we protect after the backend voltage is divided (compared with the voltage value of the comparator and VREF 5V after resistance division, the comparator output will flip to a low level and pull down the RT/CT protection), so the 28C42 will continue to output and cannot provide protection for short-circuit overload conditions; The specific circuit diagram is still inconvenient to provide. Our product has been shipped steadily for tens of thousands of units, and there must be no problem using the 28C42 chip before the change in this circuit.

  • 0 in reply to Reed
    TI__Genius 15626 points

    Reed,

    I am reaching to a product engineer who can provide a better support for this issue. I will be back to you as soon as I get a response.

    Thank you

  • 0 in reply to Manuel Alva Hernandez
    TI__Genius 15626 points

    Reed,

    I just noticed that there is a Revision History change (see below) from September 2022 to June 2024. Most likely, the Mexican badge has the latest revision and Malaysian has the previous one. You need to adapt the existing design for the new COMP voltage specifications. You can share your schematic and we can help to find the needed changes.

    Thank you

  • 0 in reply to Manuel Alva Hernandez
    Expert 2070 points

    Hi Manuel,

    Do you have the latest version of the PCN document?

    I haven't received the schematic yet.

  • 0 in reply to Reed
    TI__Genius 15626 points

    Hi Reed,

    I am not sure what is PCN? Once you get the schematic, you can share it to provide the help with the needed changes.

    Thank you

  • 0 in reply to Manuel Alva Hernandez
    Expert 2070 points

    Hi Manuel,

    When a normal material experiences a short circuit at the 24V output of the switching power supply, the voltage of the COMP pin is around 5.8V. When an abnormal material experiences a short circuit, the voltage of the COMP pin is around 5V. After voltage division, the voltage value is close to the comparison point of the overload protection we set, resulting in the inability to lower the RTCT and the failure of the overload protection (the previous 5.8V voltage division can trigger the protection). Please provide the relevant design changes and test reports regarding the voltage values of the COMP pins for the materials from these two origins of TI.

    The following is a schematic diagram of UCC28C42.

  • 0 in reply to Reed
    TI__Genius 15626 points

    Reed, thanks for sharing schematic.

    With the "abnormal" material where COMP pin reaches 5V when OUT is shorted, you can set a higher voltage at the positive input of the error amplifier (LP2901DRG4) increasing the 47kohms bottom resistor from the voltage divider. You can increase it to 80kohm so that V(7)=~4V. 4V should be higher than V(6)=~3.4V coming from VREF so that RT/CT is clamped through the diode.

    Thank you

  • 0 in reply to Manuel Alva Hernandez
    Expert 2070 points
    HI Manuel,
    "Can you provide the UCC28C42DR from these two regions with relevant design changes and test reports regarding the COMP pin voltage value?"
    Because changing the protection point will affect the performance of other aspects of the product, the customer wants to know the detailed modifications made to the material itself.
  • 0 in reply to Reed
    TI__Genius 15626 points

    Reed,

    I do not have that information available, and I am not sure if that information is public. Let me reach out to my team and see if is possible to get and share that information with you.

    Thank you