MAX5033CASA DC-DC converter not providing correct output voltage

Thread Starter

Cristian M

Joined Sep 14, 2017
7
Hello! I'm using MAX5033CASA DC-DC converter to generate 12V/500mA from a 48V voltage. My schematic is attached to the message.

The input voltage to the converter is 30V (I will need to figure out why) and the problem is that the converter generated 5V output, when it should be 12V.

My schematic is the same as that provided in the datasheet. Does anybody encountered this problem? Is there a problem with the schematic? If so, can it be resolved?

Thank you!
 

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crutschow

Joined Mar 14, 2008
30,105
It sounds like you have the MAX5033B version instead of the MAX5033C version of the converter.

If so you should be able to increase the voltage to 12V by adding a voltage divider between the output and the FB input.
For example try adding a 1kΩ resistor from the FB pin to common and a 1.4kΩ resistor from the output to the FB pin.
Because the value of the FB pin input resistance is not given, you may have to tweak the value of the 1.4kΩ resistor to get exactly 12V out.
 

AlbertHall

Joined Jun 4, 2014
12,070
The input voltage to the converter is 30V (I will need to figure out why) and the problem is that the converter generated 5V output, when it should be 12V.
Look at the input to the converter with a scope.
I suspect the problem may be an interaction between the POE chip and the converter chip with the POE repeatedly switching its output on and off. What you measure as 30V may in fact not be a DC voltage but more like a PWM signal.

[EDIT] Or connect the 48V input direct to the DC-DC converter and see what voltage you get.
 

Thread Starter

Cristian M

Joined Sep 14, 2017
7
Look at the input to the converter with a scope.
I suspect the problem may be an interaction between the POE chip and the converter chip with the POE repeatedly switching its output on and off. What you measure as 30V may in fact not be a DC voltage but more like a PWM signal.

[EDIT] Or connect the 48V input direct to the DC-DC converter and see what voltage you get.
Thank you! I will try that.
 

Thread Starter

Cristian M

Joined Sep 14, 2017
7
I connected the PG output of the PD chip to the ON/!OFF input of the converter and it generates 12V, but the problem is that the voltage does not maintain. I will ask this in another thread, as this is a different problem.
 
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