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TPS54201: Analog dimming vs PWM dimming

Tsugumi Murata
Prodigy 250 points
Part Number: TPS54201

Hello, 

What are the advantages and disadvantages of using PWM dimming vs analog dimming? 

Based on my test with the eval board (TPS54201EVM-818), I found out that analog dimming is much more efficient, no audible noise since frequency is higher, and has much more linear relationship between the current and pwm duty. In what occasions are PWM dimming useful over the analog dimming? 

  • 0
    TI__Genius 13001 points

    Hi,

    Comparing to analog dimming, PWM dimming has better linearity and accuracy especially for low brightness. But analog dimming has no low frequency audible noise and better efficiency since the current amplitude is varied while PWM dimming has constant current amplitude.

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 250 points

    Hello, 

    Thanks for the reply. 

    Can you clarify on what you mean by low brightness? The analog dimming has linearity curve on the datasheet, and also based on experiment i see good linearity for analog dimming at low current. Also do you have any graph for efficiency vs pwm duty and current linearity vs pwm duty for pwm dimming similar to the analog dimming? (DS 9.2.1.3 Figure 22 and Figure 29) 

  • 0 in reply to Tsugumi Murata
    TI__Genius 13001 points

    Hi,

    It's not easy to control small current for IC, so the linearity is not good when small current with analog dimming. But for PWM dimming, you can utilize larger current amplitude and low duty cycle to achieve small equivalent current, and larger current amplitude's accuracy is better.

    What I explain is a general knowledge of analog/PWM dimming. As for TPS54201, since the reference voltage is different(200mV for analog dimming, 100mV for PWM dimming), it's possible that analog dimming has better linearity and accuracy.

    Sorry that I don't such graph on my hand.

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 250 points

    Hi, 

    For PWM dimming efficiency, how were these computed? 

    Was it calculated by Vrms x Irms for square wave?

  • +1 in reply to Tsugumi Murata
    TI__Genius 13001 points

    Hello Tsugumi,

    The efficiency is related with system efficiency and calculated by output power/input power. For PWM dimming, the current amplitude is constant, which means you need set high current amplitude even you just want small current. And high current amplitude brings lower efficiency.

    Robin