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TPS92513 Analog Dimming - Getting to 10%?

Duncan MacGregor
Intellectual 470 points
Other Parts Discussed in Thread: TPS92513

We have a new design based on the TPS92513. Using the TPS92513-EVM we have not been able to achieve the 10:1 analog dimming turn-down ratio. With the default EVM set up (1.0 Amp max current) we have only been able to achieve a minimum current using analog dimming of ~160 mA. A 10K trim pot was used to generate the IADJ voltage input. Even with the IADJ tied to GND we get the same results. This behavior does not agree with Figure 5. Output Current vs. IADJ Voltage in the EVM User's Guide which implies that we should be able get a bit below 100 mA.

As we are close to finalizing our board design we would appreciate some suggestions so we can achieve the full 10:1 analog dimming range.

Thanks - Duncan

  • 0
    TI__Mastermind 25500 points
    It can depend on the input voltage used, the LED stack voltage, and the switching frequency. If there is a large differential between the input voltage and the LED stack you may run into minimum switch off time and the current cannot reduce further. For those kinds of applications you can still get 10:1 but it may require reducing the switching frequency so the minimum on time results in a lower minimum duty cycle.
  • 0 in reply to Clinton Jensen
    Intellectual 470 points

    Thanks. We have some supply versus LED voltage headroom so we can work with that.

    From what I can tell the TPS92513 is the best choice for true analog dimming control. We need both analog and PWM dimming for our application. The devices that convert an analog input to PWM dimming won't work for us. Is the TPS92513 the best option that TI has for analog dimming?


    Really appreciate your help - Duncan

  • 0 in reply to Duncan MacGregor
    TI__Mastermind 25500 points

    All of our buck converters with analog dimming do well with it and can achieve 10:1, but the TPS92513 is one of the most cost effective at this current level so it is a very good choice.