Output Voltage Problems with Max5033 Buck Converter

Did you have the output loaded? Is this a bread-board, or a real Printed Circuit Board? There are so many questions that would need to be answered before anyone here can be of assistance. There was obviously something wrong with the circuit, but only you are going to be able to find where the error was made, we can try to help, but remote troubleshooting is a difficult task.

Tom

Having looked at the data sheet, if your are following the circuit exactly the only thing I can see that would give you the result you got was, if you have a circuit bridge between the pins 7 and 8.

Like the National Semi versions, these switchmode regulators are pretty straight forward if you follow the datasheet.

Suggest you look at your construction method.

Did you use MAXIMs EESIM online design package?

You should have something like this:-

thanks for comment,

I think I have the following variations from the datasheet circuit:
for some reasons, my Cin is of rating 330uF, 100V, and the fly wheeling diode i can only got is schottky 1N5817 for Vf = 0.45V, other parts are the same.

The output load I tried ranging from a LED running 2mA thru a resistor, and to a resistor of 25ohm, which aimed to run 2xxmA. The shutdown divider should be working properly according to the given formula for R3,4..hpmh.

lastly, I removed the BUSA and all components, rewired by hand onto another DIY PCB... it doesn't help.

For the fixed output parts 5033A/B/C you shouldn't have Rs 3 and 4: just R1 and R2 for shutdown divider:-

The only Application diagram I can find with R3 and R4 is for the variable output part 5033D. The pot is used to set the voltage at the feedback pin:-

was an typo error. R1 and R2 are the divider and my R3 is short and R4 left open for fixed 5V version

sorry for misconfuse

This afternoon I gone through the datasheet and your inputs.. thanks all.
I finally put aside the scope and started on some mechanical work and explore the chip....

I worry that "chuck of copper in the middle" and "attempt to work" mentioned by Andy is refering to my photo which taken under a microscope 2 minutes before....

THE 5033 BUSA mark is still recognizable after N-time soldering works...

Are you saying that it was a forgery, or just that you have not only dismantled the chip (in some drastic way) and it now is as good as being a forgery, eg. it does not work anymore?

Have you managed to get your power supply working with a new chip?

our team purchaser bought 10 pcs NEW BUSA from a "IC supplier" thru a web.

I totally tried 3 out of the 10, and my colleague suggested me to dismantle one of the 3 failures... The photo is showing the 2nd one I tried.

The copper inside now... some how difficult to make me to beleive it is a chip / semiconductor..., the package was too brittle too. And the VCC->GND Resistance show 384k ohms for the rest of the 10.. , which seems to be normal.

I think i need to handle with our purchaser before I can get a "new" and "functionable" chip..... f

So you appear to have been sold forgeries.

I am pleased that my comments appear to have been helpful to you fixing the problems.......

Sad in a way for you though at the same time that the help was even needed.... forgeries have become really big business all over the world...Up to now I have been lucky.....

HI all~

Lesson. Our team exchanged 3 new pcs of IC from the vendor and then I got back my on-board low-voltage-facility working properly .~ The orignal aim is to reduce one ext DC source and make the board more handy.

With your supports and vendor's free lecture, I gone thru. a review on SMPS buck design, flywheel diode selection, even layout basics and exp. in working whom selling forgeries.

Finally, some figures here:
Ultimate load is 16x8mA TTL loadings, which to turn on some ICs which 50V, and 1N5817 works fine yet for the load current.

Good luck All~

I can sincerely say that all were very happy to help you and we are also glad that your vendor replaced the chip forgeries with proper chips.....and that everything now works.

You did all the hard work, we only made suggestions.

Have a great day.....