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TPS61165: Low PWM settings

Cameron Perl
Expert 5385 points
Part Number: TPS61165

Hey team,

I have a few questions regarding the TPS61665 which will be driving 16V @ 40mA max current. The LEDs are comprised of 2 parallel strings of 5 LEDs (Vf=3.2V) w/ 20mA passing through each string. They need to be able to dim the backlight leds.

Their PWM output is a 3.3V level signal at 133Hz, not the 1.8V signal in the circuit above. The dimming is changed by the modulation of the PWM duty cycle.

1. Can this part be used with a 3.3V drive at 133Hz

2. If so, what would that circuit topology look like

3. What would be the performance tradeoffs? (Noise / efficiency / etc),

Additional questions:

  • What is the "d" shown in figure 16 of the datasheet in the equation for LED current?
  • Are there any simulation tools for this device?
    • I see there is a transient p-spice model

Thanks,

Cameron

  • +1
    TI__Genius 9630 points

    Hi Cameron,

    I think you are checking the configuration with external PWM dimming, shown in Fig 16 . So for your questions

    1 can be used with 3.3V, 133Hz

    2. the basic topology is pretty much the same as the given one in Fig. 16, but need to tune resistor values to let the brightness change linearly by duty cycle. Also notice to add zener diode at output in case there is open condition. For more detailed information, you can refer to the AN and calculation tool.

    AN: 

    8054.slva471.pdf

    tool: in tps61165 product main page https://www.ti.com/product/TPS61165

    3.The voltage level and frequency will not impact too much on the performance. Just notice to tune RC filter if low frequency
    pin, this is bad to efficiency and system stability.

    Additional: 1. d represents duty cycle of PWM input

                      2. Yes, the simulation tool can be got oh the main page as well