Maximum PWM Frequency for MP6541A

Motor Drivers/Sensors
1

Hi,
In the datasheet I can only see frequencies up to 200kHz considered for MP6541A - specifically in the operation current vs PWM frequency plot.

  • Is 200kHz the maximum frequency that should be applied?
  • Are there any internal limitations preventing operation at higher frequencies?

Thank you!

2

Hello Andrea, welcome to the MPS forums!

To answer the following questions you have about the MP6541a:

  1. Yes, 200kHz is the maximum PWM frequency that can be applied in the device.
  2. Some internal and general limitations to applying frequencies higher than the maximum PWM frequency include:

  • Higher frequencies may lead to oscillations leading to unstable operation and hinder Control Loop Stability.

  • Electromagnetic Interference (EMI) can be yielded at higher PWM frequencies which can affect other nearby devices. Filters may be applied to mitigate this but would certainly complicate your design.

  • Switching Losses result when switching occurs too frequently on MOSFETs in your application, leading to decreased efficiency and heat. These FETs are internal, and therefore are a limitation. Choosing a device with external FETs gives you the flexibility in increasing your PWM frequency.

  • Any limitations on Internal Components like capacitors or inductors that are implemented internally in the IC are also limiting factors that narrow down the PWM frequency range.

Hopefully this provided enough insight to your questions.

Best,
Krishan

3

Hi Krishan, Thank you!

  1. Ok understood
  2. Would you know which of these is a limiting factor for MP6541a? Specifically those that affect the device rather than the system (i.e. not EMI)

Best regards,
Andrea

4

Looking at the functional block diagram of the MP6541A, we can take a glimpse at what limits the IC device level as opposed to the system level reasonings I mentioned.

image
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There are the 6 internal N-Channel MOSFETs in this case will have their limits on switching frequency. As you increase the switching frequency beyond their limits, switching losses (conduction losses during on & off transitions) become more significant. This would then lead to system level issues downstream from the device level.

Hopefully this provided further insight on why the PWM frequency is limited.