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LM567 vs LM567CN

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Uljabaan

New Member
Hi there,

I am trying to configure my LM567CN to respond to frequencies of about 19kHz using the following formula: F = 1 / (1.1 * R1 * C1), but the chip responds to completely different frequencies. The datasheets I've found mention LM567 and LM567C. Is it possible that the formula will be different for LM567CN?

thanks
 
What values of R and C did you choose? The N suffix just describes the PDIP package.
Show the complete circuit.
 
Here's the values I used, I will post pictures of the complete circuit later when I get back home.

R = 470Ω
C = 0.1μF

Using the formula from datasheet, this should give me 19342.36 Hz.

thanks
 
I think you got the equation wrong. It is f=1.1/(RC) which gives me 23.4 kHz.
 
From the "old" National Semi datasheet:
upload_2015-10-25_9-28-37.png


I guess it depends on the voltage at which it switches: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capchg.html

John
 

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Here's the values I used, I will post pictures of the complete circuit later when I get back home.

R = 470Ω
C = 0.1μF

Using the formula from datasheet, this should give me 19342.36 Hz.

thanks

Yes that is what I also Calculate using that formula.
This is the Formula shown in my 1982, National Data Book.
I will prototype it a little later and check it out.

But Looking at the Data Sheet, QUOTE.


11.2.1.2.1 Timing Components

To calculate the timing components for an approximated desired central detection frequency (f0), the timing
capacitor value (C1) should be stated in order to calculate the timing resistor value (R1). Typically for most
applications, a 0.1-µF capacitor is used.


1.1
fo = -----
R1 C1

This is the Formula that is now shown in the Online PDF.
So, Which is Correct?

I will Check it out today.
 
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Do you use the output and loop filters mentioned in the datasheet?
I don't know what restrictions there are for the R value, but I think it should not be too low.
Try a few kohms for it.

Edit: I found a Philips datasheet, where R is recommended between 2 and 20 kohm
 
Last edited:
The Correct Formula is:

1
------------------
( R1 C1)
------------
1.1

C1 in uF
R1 in K Ohms

Calculate the (R1 C1)
Divided by the 1.1 First.
Than Divide that answer by the 1.
 
The Correct Formula is:

1
------------------
( R1 C1)
------------
1.1

C1 in uF
R1 in K Ohms

Calculate the (R1 C1)
Divided by the 1.1 First.
Than Divide that answer by the 1.

How is that different than simply:

1.1
-------
(R1C1)

That is, the TI datasheet.

Oops, you edited while I was writing and changed the units. I believe TI uses Farads and Ohms.

John
 
Do you use the output and loop filters mentioned in the datasheet?
I don't know what restrictions there are for the R value, but I think it should not be too low.
Try a few kohms for it.

Edit: I found a Philips datasheet, where R is recommended between 2 and 20 kohm

Yes, I use both:

PIN1 (Output filter) = 0.02μF
PIN2 (Loop filter) = 0.007μF
 
Okay, it got a bit more confusing now that we have two conflicting datasheets...

I've changed both R1 and C1:

R1 (timing resistor) = 568.7Ω
C1 (timing capacitor) = 0.1μF

so that using the 1.1 / R1C1 formula, this should result in the centre frequency of about 19.3kHz.
However, the output at PIN 8 is always high. I tested it for frequencies between 10 and 24kHz.
 
LM567-Formula.png


CORRECTION, R1 is Meg Ohms

This has been Tested on a Bread Board and is Correct.
 
Algebraically, your formula is no different than the TI formula. Did you miss that point?

I didn't mention before, because my purpose was to point out that there were two formulas from the two manufacturers. In theory, the multiplier could be changed depending on the comparator threshold set; however by analogy to the 555, I suspect the TI formula is the correct one.

John
 
Here's the values I used, I will post pictures of the complete circuit later when I get back home.

R = 470Ω
C = 0.1μF

Using the formula from datasheet, this should give me 19342.36 Hz.

thanks

Based on these Values, your Frequency will be 23.419Khz.
 
Algebraically, your formula is no different than the TI formula. Did you miss that point?

I didn't mention before, because my purpose was to point out that there were two formulas from the two manufacturers. In theory, the multiplier could be changed depending on the comparator threshold set; however by analogy to the 555, I suspect the TI formula is the correct one.

John

Ti is Different.

Ti Formula Multiplies the C1 R1 result by the 1.1
Mine Divides it by the 1.1.
 
If you can post your R1 and C1, and the centre frequency you got, I will try to replicate your exact values to make sure that there are no other issues with my circuit.

I Used a .1 uf Cap but with Various Resistance Values and got Correct Frequencies on my Frequency Counter.

If you use a .01 Cap and a 5.8K resistor, you will come Close to your 19Khz.
Remember that Just because a Cap is Marked .01, Does Not mean it is that Exact Value.
Possibly use a 5K6 resistor in series with a 500 Ohm trimpot to Get the Exact Frequency of 19Khz.

Note the Supply Voltage MUST be Regulated at 5 Volts.
Or the Frequency will Change with Supply voltage changes.
 
Last edited:
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