TLV3501: What is frequency equation

elektroboard

Prodigy 105 points

Part Number: TLV3501

Hi.

I built a schematic. I need frequency equation of the circuit? What it is? Thanks

over 1 year ago

0 Chi Nguyen1 over 1 year ago

TI__Genius 11701 points

Hello,

Thanks for reaching out. There is an example of a relaxation oscillator circuit in section 8.2.1 of the TLV3501 datasheet. We also have this app note Relaxation oscillator circuit.

0 elektroboard over 1 year ago in reply to Chi Nguyen1

Prodigy 105 points

Thanks Chi.

I know the equations in these sources. but I could not understand the effect of C2 and R5 in the circuit on mat.equation.

0 Chi Nguyen1 over 1 year ago in reply to elektroboard

TI__Genius 11701 points

Hi,

Sorry I misunderstood your question. I would expect that C2 is now in series with C1 so the total capacitance would need to include both C1 and C2 in the oscillation timing equation. R5 is now also in the resistor divider with R4 so that needs to be included as well.

0 kai klaas69 over 1 year ago

Guru 140200 points

Hi,

as the simulation shows, R5 mainly influences the duty cycle of square wave but has nearly no influence on its frequency:

elektro_tlv3501.TSC

R5 is merely added to improve the symmetry of the square wave. To find the frequency of square wave put the sum of C2 and C1 (33.2nF) the series capacitance of C1 and C2 (199pF) into the formula. The influence of R5 on the frequency is way smaller than the manufacturing tolerances and drifts of C1 and C2 and may be neglected.

Kai

+1 elektroboard over 1 year ago in reply to kai klaas69

Prodigy 105 points

Hi.

I understood R5 thanks for your comment.

But I think C1 and C2 are series. Thats why total capacitance is about 199pF. am I wrong?

0 kai klaas69 over 1 year ago in reply to elektroboard

Guru 140200 points

Oh yes, of course

0 Chi Nguyen1 over 1 year ago in reply to kai klaas69

TI__Genius 11701 points

thank you Kai.

I hope that helps you with your design elektroboard. Let us know if you have any more questions.

0 elektroboard over 1 year ago in reply to kai klaas69

Prodigy 105 points

i calcuted period as t=5/16*199pF*120k. is it true?

0 Chi Nguyen1 over 1 year ago in reply to elektroboard

TI__Genius 11701 points

Hi Elektro,

Using the equations in the app note, I have 0.77 = 2.3 e^(-t/(2*120k * 199pF)) which works out to be t = 2 * 120k * 199pF * ln(0.77/2.3) = ~52us which roughly matches Kai's sim.

0 elektroboard over 1 year ago in reply to Chi Nguyen1

Prodigy 105 points

Thanks Chi and Kai. you helped me a lot. best,

Amplifiers

Amplifiers forum

TLV3501: What is frequency equation