But I have checked everything
Please tell your detail results to allow a meaningful discussion. It would be also interesting how you actually measure PWM linearity.
A photo may help too. Never underestimate the power of bad layout and wiring.:wink:why dont you post your circuit ???
that will help solving your problem
Thanks, but what's wanted is your circuit, not a copy of a circuit from the datasheet.Please find the attached circuit for your reference
One way is to use negative feedback. You filter the PWM output to generate the average DC voltage and feed that back as negative feedback to an op amp that also has the DC control voltage as an input. With proper scaling of the voltage, the op amp output voltage to the PWM modulator will be such as to correct for any non-linearity in the modulator. Some form of that feedback circuit is typically used in PWM switching voltage regulators to regulate the output voltage.........................
By seeing all your answers, I am still unclear as how to make Pulse width linear to DC voltage.
To measure PWM linearity, I was just measuring the width in oscilloscope. I was expecting a proportional change in width with respect to a DC voltage. My VIN goes upto 8V. My triangular peak is at 9V. By seeing all your answers, I am still unclear as how to make Pulse width linear to DC voltage.
That doesn't say much without a linearity number. You also didn't mention the PWM frequency.I did plot the graph between Input DC voltage and output pulse width measured value and the equation of the graph is order 2.
What do you want to achieve? Highest pwm linearity can be achieved with a pure digital pwm controller, you don't need to take a DDS triangle generator detour. The said "agilent wave generator" is a DDS design, I assume. Depending on the triangle frequency, limited output filter bandwidth affects triangle linearity however, something that can be easily calculated.Same is the case with Duty cycle. Now can I use a DDS chip ? will it give me high accuracy triangle wave?
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