0
\$\begingroup\$

I have constructed the following 12v in - 3.3v out buck converter circuit using a TL5001 PWM controller based on this document. After etching PCBs and soldering surface mount components the board unfortunately does not do what I expect it to. The output voltage is measured to be about 11.6v rather than 3.3v.

Measuring the output of the TL5001, i would expect a PWM signal however there is just a constant 12v (same as the input voltage). It appears that there is no switching happening in the circuit hence no change in the output voltage. I have double checked all component values and checked for shorts. Fairly certain that the circuit I have built is exactly the same as the one I designed. Have also replaced the MOSFET driver IC, TL5001 and the MOSFET itself to no avail.

This is the first time I have done any PCB layout. I don't think my board layout was very good - the filtering capacitors for the ICs are too spaced out for example. I'm not sure if this might be the problem?

Any ideas what might be wrong?

etched board buck converter PCB schematic

\$\endgroup\$
6
\$\begingroup\$

You have your MOSFET incorrectly connected and the body diode is conducting all the time: -

enter image description here

As you can see from this TI document you have inadvertently swapped source and drain connections: -

enter image description here

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.