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Original question:

[FAQ] How to design the UVP resistor divider for TPS922055 / TPS922054 / TPS922053 / TPS922052?

TPS922055: Question about UVP terminal function.

Kazuya Nakai59
Guru 20700 points
Part Number: TPS922055

Hello guys,

One of my customers is considering using TPS922055 for their new products.

At this moment, they have the following question.
Could you please give me your reply?

Q.
The following FAQ says that TPS922055 operates with CC (Constant Current) mode when UVP voltage is more than 1.4V.

 https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1288219/faq-how-to-design-the-uvp-resistor-divider-for-tps922055-tps922054-tps922053-tps922052?tisearch=e2e-sitesearch&keymatch=faq%3Atrue

Also the device datasheet says that the device stops switching when UVP is less than 1.0V.
The customer wants to know what TPS922055 operation is when UVP is between 1.0V and 1.4V.

Is it hysteresis for LED open detection? So TPS922055 stops switching when the OVP terminal voltage goes less than 1.0V and goes back CC mode operation when the OVP terminal voltage goes higher than 1.4V?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Mastermind 18140 points

    Hi Kazuya,

    • When the UVP pin is above the 1.4V, the device will work in CC mode. The output current won't be affected by the CV mode.
    • When the UVP pin falls below 1.4V (above 1.0V), the CV mode will gradually step in to interfere until the device is fully controlled by CV mode. The output current will be affected during this stage.
    • When the UVP pin falls one step further below 1.0V, the "LED open load" protection will be triggered.

    Please be noticed that the 1.4V is the maximum value of the threshold where CV mode will step in. Please also be noticed that the 1.0V is the minimum value of the threshold where "LED open load" protection will be triggered.

    Therefore, if you do not want you output current to be affected during normal constant-current operation, you should keep UVP pin voltage above 1.4V.

    Hope this helps.

    Best Regards,
    Steven

  • 0 in reply to Steven Li
    Guru 20700 points

    Hi Steven,

    Thank you very much for your reply.

    Could I ask you two additional questions as the follows?

    Q1. I can't find any detail description about CV (Constant Voltage) mode function in TPS92055 datasheet.
          So please give me your reply.
          What is the behavior of the SW pin when UVP drops below 1.4V?
    　  Is SW on duty decreased to avoid UVP voltage dropping below 1.4V?

     Q2. Is there any spec of UVP pin voltage accuracy or Min/Max values?

    Thank you again and best regards,
    Kazuya.

    　

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 18140 points

    Hi Kazuya,

    Kazuya Nakai59 said:
    Q1. I can't find any detail description about CV (Constant Voltage) mode function in TPS92055 datasheet.
          So please give me your reply.
          What is the behavior of the SW pin when UVP drops below 1.4V?
    　  Is SW on duty decreased to avoid UVP voltage dropping below 1.4V?

    When UVP pin drops below 1.4V, the CV mode will gradually step in to interfere the error amplifier output, which will make the V_COMP drop. (Please refer to Section 8.3.1 Adaptive Off-Time Current Mode Control from the datasheet) This will lead to the switching-on duty decrease.

    Kazuya Nakai59 said:
     Q2. Is there any spec of UVP pin voltage accuracy or Min/Max values?

    Sorry but there is no such spec.

    Best Regards,

    Steven