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Original question:

[FAQ] List of FAQs for TPS922055 / TPS922054 / TPS922053 / TPS922052 LED driver

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

Steven Li
Mastermind 20110 points
Other Parts Discussed in Thread: TPS922052, TPS922055, TPS922054, TPS922053

How to choose the value for the UVP resistor divider for TPS922055 / TPS922054 / TPS922053 / TPS922052?

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    TI__Mastermind 20110 points

    Below are some guidelines on how to design the UVP resistor divider.

    1. The UVP pin of TPS922055 / TPS922054 / TPS922053 / TPS922052 has two thresholds,
      1. The first one is 1.4V. (Please refer to Section 8.3.6 and Figure 8-5 from the datasheet.) When the voltage of the UVP pin is above 1.4V, the output current won't be affected by the CV mode.
      2. The second one is 1V. (Please refer to Section 8.3.7 and Table 8-3 from the datasheet.) When the voltage of the UVP pin is below 1V, "LED open load" protection will be triggered.
    2. To make sure your output current won't be affected in all working condition, you should make sure (Vin_min - Vout_max) * R_UVP2 / (R_UVP1 + R_UVP2) > 1.4V. 
      1. Vin_min: minimum input voltage
      2. Vout_max: the sum of the maximum forward voltage of each LED in the LED string at your maximum target output current
      3. R_UVP1, R_UVP2: Please refer to the below figure.
    3. Please do not design R_UVP1 and R_UVP2 with too small values. You can refer to this E2E thread for the reason. A rule of thumb is that you can design the sum of R_UVP1 and R_UVP2 to be around 1Mohm or 2Mohm and this normally would be a good start point. You can then adjust the values based on your test results.
    4. The UVP pin has an internal pull-up to the VCC pin. If you do not need "LED- short to PGND" fault protection and CV mode, you can leave the UVP pin floating.