ImperfectSeven
New Member
Hi there, I am trying to use a PWM as a DAC to set a reference voltage for my high voltage boost converter. Through my own research I have gathered what information I think is critical to this:
The PWM clock is 24 MHz
I want each bit to represent a 1V increase on the high voltage side and after some math found that I need 2268 bits.
This gives me a PWm frequency of 24 MHz/2268 bits = 10.58 kHz
From what I understand I need my low pass filter's 3dB point to be around 2 kHz
Also I have concluded that decreasing the ripple is more important than the settling time.
The ripple can be no more than 2 mV peak to peak as anything more will cause my high voltage to change.
With these conditions in mind I need to design an RC low pass filter, but my problem comes in that I don't know how to select the values for R and C.
So far I am using a 2nd order ladder configuration and I know that R[SUB]1[/SUB] >> R[SUB]2[/SUB] and that R[SUB]1[/SUB]C[SUB]1[/SUB]=R[SUB]2[/SUB]c[SUB]2[/SUB]
At this point however it seems to be a guess and check game to figure out the values of R and C, is this true?
The PWM clock is 24 MHz
I want each bit to represent a 1V increase on the high voltage side and after some math found that I need 2268 bits.
This gives me a PWm frequency of 24 MHz/2268 bits = 10.58 kHz
From what I understand I need my low pass filter's 3dB point to be around 2 kHz
Also I have concluded that decreasing the ripple is more important than the settling time.
The ripple can be no more than 2 mV peak to peak as anything more will cause my high voltage to change.
With these conditions in mind I need to design an RC low pass filter, but my problem comes in that I don't know how to select the values for R and C.
So far I am using a 2nd order ladder configuration and I know that R[SUB]1[/SUB] >> R[SUB]2[/SUB] and that R[SUB]1[/SUB]C[SUB]1[/SUB]=R[SUB]2[/SUB]c[SUB]2[/SUB]
At this point however it seems to be a guess and check game to figure out the values of R and C, is this true?