LMR16006: Design instable in Webbench

Hi Jan,

Did customer test the circuit and found unstable issue?

What's voltage rating of the output cap customer used? it should be 35V or higher.

B R

Andy 

Hi Andy, 

you find the ratings in the pdf I attached 

Regards 

Jan

Hi Jan,

Pls provide below info:

Vin range

Vout

Load current

IC is LMR16006X

I will check the circuit design accordingly.

B R

Andy

WBDesign4 (9) (1).pdf

Hi Jan,

I simulate the design. Cout 6.8uF is too small. the loop is stable with Cout =15uF or bigger

B R

Andy

Hi Andy, 

the customer figured out that as well. Now the question is, why the formula in the datasheet is not correct. Have you calculated it with the formula under 9.2.2.3 in the datasheet. If I take formula 5 

and set in the values: 

Cout>2*0.165A/(7000000Hz *9.3V)=5.069e-08F

But I'm not sure if fsw must be in kHz or in Hz

Regards 

Jan 

Hi Andy, 

my customer also ask how to choose the resistors for SHD-Pin if he uses the enable thresholds?

Thanks 

Jan 

Hi Jan

Change inductor to 100uH will improve the loop stability with Cout=6.8uF

For the SHDN resistor design, pls refer to LMR14030 data sheet---8.3.6 Enable and Adjustable Under-voltage Lockout  section.

B R

Andy