Issue with MAX17502H DC-DC Converter – 3.3 V Output Not Regulating at 5 V Input

[akshayakumar]

Hi everyone,


I'm using the MAX17502H step-down DC-DC converter to convert 5 V input to a 3.3 V output. Based on the design calculations, the required inductor value came out to be approximately 24.75 μH. However, due to component availability, I used a 22 μH inductor instead.


The issue I'm facing is that the output voltage is not regulating when the input is exactly 5 V. The converter only starts generating the expected 3.3 V output when the input voltage is increased above approximately 5.3 V.


I’m trying to understand whether this behaviour is due to the lower inductor value, the dropout voltage of the converter, or something else. According to the datasheet, the device should support 5 V to 3.3 V conversion, so I’m unsure why it's failing at 5 V input.


Has anyone experienced similar behaviour or can suggest what might be causing this? Any help would be appreciated!
please find attached schematic below
View attachment 199061

Thanks in advance!

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[FvM]

You didn't report what's the observed output voltage at 5V input, below or above 3.3V?

Attaching a schematic somehow failed, please try again.

 

[mtwieg]

One common pitfall to look out for:
When the MAX17502H tries to start up, it may want to draw a relatively large inrush current from Vin. If the source is not capable of supporting the inrush, then Vin might drop low enough that the MAX17502H stops operating. Then Vin will rise up, the MAX17502 will try and start again, and the cycle might continue indefinitely.

Basically you should look at Vin on a scope and verify it is actually maintaining a nice smooth 5V.