TPS54201: How about the input impedance/current of PWM pin of TPS54201?

John11513

Part Number: TPS54201

Hi team,

As you know the PWM input of TPS54201 is multifunction, it is used for PWM/analog dim input, and also for PWM/analog dim mode configuration. To keep the device operate in PWM mode the amplitude of PWM signal should be within 1.0V to 2.07V. However the PWM signal from controller is 0V to 5V. To meet the requirement of TPS54201 the 0V/5V pwm signal has to be divided down. However TPS54201 datasheet does not specify the input impedance of PWM pin which is must to design the value of divider. Could anyone provide the spec?

Thank you,

John

over 7 years ago

0 Sean Zhou over 7 years ago

TI__Mastermind 22745 points

Hi John,
I will check with our designer tomorrow, I will reply you the answer tomorow. Thanks
Sean

0 Sean Zhou over 7 years ago

TI__Mastermind 22745 points

Hi John,

I have checked with our designer, The input impedance of PWM pin is about 800k, So please be careful with the resistor division.

Sean

0 John11513 over 7 years ago in reply to Sean Zhou

TI__Expert 5720 points

Thank you Sean.
I am curious why this part was designed in this way, how can customer benefit from this kind of design?
But the drawback is obvious, most of MCU can only provide 3.3V/5V TTL/CMOS PWM out, which cannot directly i/f to TPS54201.
Though a simple resistor divider can easily adapt the MCU PWM output to 54201, however you know most of MCU does not accurately specify its GPIO output level. For example, if the MCU output is specified 2.4V (MIN), 5V (MAX), how should they design the divider?

Thank you,
John

0 Sean Zhou over 7 years ago in reply to John11513

TI__Mastermind 22745 points

Hi John,
I'm sorry for your question, We will improve this in our next generation. Thanks for your suggestion.
Sean

0 John11513 over 7 years ago in reply to Sean Zhou

TI__Expert 5720 points

Thank you Sean.

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TPS54201: How about the input impedance/current of PWM pin of TPS54201?