| Electronics > Beginners |
| XR2206 timing current formula |
| (1/1) |
| marekpasek:
Hello, I have a problem deriving the formula which would descripe the relationship between Vin and output frequency on xr2206. The datasheet says that f =1/RC, where C mean the timing capacity and R means the resistance between pins 3 and 12. Therefore I derived that f = dVin/3RC, where dVin means the voltage difference across resistor with given resistance R and C mean timing capacity. Nevertheless the datasheet also says that f = 320000I/C. Certainly both formulae cannot be correct therefore... where is the mistake Thanks |
| ledtester:
Well, dVin/R = I, right? So the only difference is in the constant - you have 1/3 and the datasheet has 3200000. How are you deriving your 1/3? Could it just be you are using different units? Note that 1/3 = .333333... which is close to 320000 if you multiply by 10^6. |
| marekpasek:
Correct. The voltage on pin 7 (sorry, I was misled and I thought it was pin 3) with reference to pin 12 equals 3v and is constant. Therefore 1/V equals 0.33333. There is a difference only in that. Nevertheless it makes a serious variance in the output frequency. I want to construct a device on whose precision I could rely, so I need to be capable of predicting the output frequency accurately. |
| ledtester:
Two things... 1. If you want to have an RC timing circuit produce a specific fixed frequency you need to make one of the components adjustable (i.e. either a variable resistor or variable capacitor) and use a frequency counter to tune that component to the desired frequency. 2. Below is the formula I found in the XR2206 datasheet. Note that "I measured in mA" is I*1000 and "C measured in microfarads" is C*1000000, so the frequency formula is: --- Code: --- f = 320 * (I*1000) / (C * 1000000) = 0.320 * I / C --- End code --- XR2206 datasheet: https://www.sparkfun.com/datasheets/Kits/XR2206_104_020808.pdf |
| schmitt trigger:
If you are building your own XR2206 based generator, I would suggest to watch this very informative video: |
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