Maximum PWM frequency for MP6551 to achieve 12-Bits

[elgordo]

Hi,

I wish to use the maximum switching frequency I can with the MP6551. My application requires 12-Bit resolution. How can I determine this frequency?

[mpsnow.bryan]

The minimum pulse the MP6551 can support is about 1us. If you want to achieve 12-bit accuracy (4096 distinct PWM duty cycles) you will need at least a 4096us PWM period. I would round that up to 4200us to cover offset and gain errors. So with a required PWM period of 4200us the maximum frequency the MP6551 can support and achieve 12-bit resolution is 1/4200us or 238Hz.

[Luison]

This is not true. It must be the most uninformative post on the forum.
The driver “starts” with a pulse of at least 220ns, but works at 100% with a pulse of at least 320-340ns (the driver makes a clear step on the way up, which is not noticeable on the way down).
On the other hand, the maximum pulse, the minimum time it detects at zero, is only 100ns.
In the rest of the PWM operating range, it detects without any problem variations of 5ns, probably less. I use it at 40KHz with 4050 steps and it detects each and every step, except the 48-65 first, initial step and full activation, and last 40.

Check the photos attached.

Finally, the AI does not recommend using this driver because it indicates that it can only be used at 238Hz, a nonsense comment that has surely made the company lose thousands of euros.

[george.FAE]

Hi Luison,

Thanks for reaching out about the previous answer. To further expound on the information you mentioned, according to the MP6551’s datasheet, the device can support a switching frequency as high as 500 KHz. If a PWM timer must provide this switching frequency with 12 bits of resolution, then the PWM timer frequency must be 500 KHz multiplied by 2^12 which is 2.048 GHz.

Considering most microcontrollers will not operate at these high frequencies, the maximum switching frequency will need to be smaller than 500 KHz. Luckily, motors hardly require such high frequencies, with 200 KHz being at the highest we typically see within the industry. Hence, if in need of such high switching frequency, the resolution would need to be decreased to 10 bits. Alternatively, a 50 KHz switching frequency with 12 bit resolution could be generated with a PWM timer running at 204.8 MHz which is within the realm of possibility.

Thus the max switching frequency is 200kHz with 10 bit resolution or 50kHz with 12 bit resolution.