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# LT3743 control compensation

Hi

We've been using the LT3743 for several years now. I'm reviewing the circuit design, and I noticed that the formula on p.20 of the datasheet doesn't work - or maybe I'm misreading it somehow.

Rc = fs * L * 1000V / (Vo * Rs) (I tried to copy/paste from the PDF file, but the result was unreadable; the next couple lines are copy/paste)

where fS is the switching frequency, L is the inductance
value, VIN is the input voltage and RS is the sense resistor.

I assumed "1000V" meant 1000 * VIN, If I plug in values from the top line of Table 6, I get 450kohms, but the table says 47.5kohms. So it's off by an order of magnitude. Is there a typo in the formula?

Thanks!

## Top Replies

The given equations are used for calculating the starting value of the compensation components. They are not meant to be used for calculating the exact values. After finding the starting point, you should do some bench tests to tune and optimize your compensation network.

Regards,

Peter Pham

• • I'm sorry, Peter, but how is being high by a factor of 10 a "good starting point?"

My setup is not on Table 6, so the previous engineer apparently just used the vlaues on the demo board. Considering we're using a 24V supply, and running at 1MHz, that might be wrong.

• If you plug the top-line values into the equation, you will get: Rc =0.5*10^6*1.5*10^-6*1000/(4*0.005) = 37.5k, which is only 10k off from the recommended value. This is very normal.

• I see where I got confused. The "V" in the equation is NOT Vin. Leaving that "V" off would have been a lot clearer. So the input voltage doesn't enter the equation at all.