PWM Driver duty cycle

RE: PWM Driver duty cycle

Karl Ylvisaker — Fri, 04 Jun 2021 09:43:07 GMT

[quote user="ColorPen"]Thank you Karl.[/quote]

No problem at all! :)

[quote user="ColorPen"]I'll try to modify my hardware design and firmware.[/quote]

Great! I look forward to hearing if you achieve the desired functionality.

Best regards,
Karl

RE: PWM Driver duty cycle

Taylor — Fri, 04 Jun 2021 09:05:48 GMT

Thank you Karl.

I'll try to modify my hardware design and firmware.

RE: PWM Driver duty cycle

Karl Ylvisaker — Thu, 03 Jun 2021 15:58:08 GMT

[quote user="ColorPen"]Thank for your reply.[/quote]

No problem at all, I am happy to help!

[quote user="ColorPen"]Should I add second-order RC filter on hardware?[/quote]

There are many good guides on how you can proceed to use a filter to smoothen a PWM waveform into a somewhat continuous voltage level.
Exactly which filter you end up using depends on the needs of your application, but if you just need a smoothened average you can achieve this with a simple low-pass filter, for instance.

[quote user="ColorPen"]

My power system is 3.3V, and I need 1.0V or 2.5V to control the driver chip.So, I set the duty cycle as 30%(1.0V avg) and

75%(2.5V avg). Is that correct?

[/quote]

This looks correct to me, but I would advice you to always try this out and scope the output before applying it to a sensitive sensor/driver chip, to avoid accidentally damaging it, since this is a risk if anything does not go as expected in the code.

[quote user="ColorPen"]How can I set the IO output low(0V) after I handle my application? 3.3V(avg) is not allowed to happen.[/quote]

Remove the " | NRF_DRV_PWM_PIN_INVERTED " part of the pin configuration, and you should see the polarity revert back to the default (non-inverted).

Best regards,
Karl

RE: PWM Driver duty cycle

Taylor — Thu, 03 Jun 2021 09:38:38 GMT

Hi Karl,

Thank for your reply.

I want to use PWM to control motor driver chip which have a VREF pin to set limit current.

My power system is 3.3V, and I need 1.0V or 2.5V to control the driver chip.So, I set the duty cycle as 30%(1.0V avg) and

75%(2.5V avg). Is that correct? Should I add second-order RC filter on hardware?

[quote userid="87869" url="~/f/nordic-q-a/75813/pwm-driver-duty-cycle/313320#313320"]You are using the NRF_DRV_PWM_PIN_INVERTED option when configuring your PWM pin. This will inverse its polarity, and set its idle state to high.[/quote]

How can I set the IO output low(0V) after I handle my application? 3.3V(avg) is not allowed to happen.

Thanks!

RE: PWM Driver duty cycle

Karl Ylvisaker — Thu, 03 Jun 2021 09:14:26 GMT

Hello,

Thank you for your patience with this.

[quote user=""]The voltage will change when button is pushed,but the voltage is not accurate.Is there a better way?[/quote]

Could you please elaborate more on what behavior you are currently seeing?
How are you measuring the voltages, and how is it currently behaving? What do you mean when you say that it is not accurate?
The nRF52810 does not have a DAC module, so unfortunately there is no better way to synthesize lower voltages on an output.

What will you use these modulated voltages levels for? Please keep in mind that PWM only toggles between VDD and GND, so while the average voltage of a PWM waveform can be changed, there is still only VDD and GND present on the pin - so you need to make sure that whatever is on the receiving end is ok with this.

[quote user=""]BTW, I need the IO to output low after reached a certain voltage value.So I used nrf_drv_pwm_uninit(&m_pwm0), but the IO output high.[/quote]

You are using the NRF_DRV_PWM_PIN_INVERTED option when configuring your PWM pin. This will inverse its polarity, and set its idle state to high.

Best regards,
Karl