qustion on LTC3873-5 IC

[high voltage]

hi all
i am going to use LTC3873-5 ic on my design of fly-back converter…how can i calculate its parameter…u may say use its data sheet….but actually i don’t now how to use it???? plus i also need to knw how ltc3873-5 generate the PWM..
thnx in advance

 

[mtwieg]

The datasheet gives as much detail as you need to design with it. Its method of generating PWM is implied in the block diagram it shows you. It's a current mode controller. Its output is controlled by a latch which is set (output goes high) by the oscillator at the beginning of each cycle. From then on, it compares the current sense voltage to the error voltage (with some offsets and slope compensation thrown in) and uses the result to reset the latch (output goes low). It stays low until the next oscillator cycle sets it again. That's how current mode controllers usually work.

If you're new to designing SMPS, then starting off with a fancy chip from Linear may not be a good idea. Linear tech parts often perform well, but they are much more complicated than basic controllers. The upside is that their datasheets often provide detailed design procedures. If you read through it a few times thoroughly, it should be enough to do a design. If not, feel free to ask some specific questions.