LM3410: Unstable behaviour

Hello Michel,

Basically have over 0.47 uF or greater on the output.

What is the input voltage this occurs at?

Is the input voltage stable?  Is the LED near the output of the driver circuit?

You can try changing R762 to 100 ohm.

Best Regards,

Dear Irwin,

Thanks for your quick answer.

The problem occurs at any voltage between 3.5V and 4V.

The input voltage is stable, but with a 100mV ripple due to the pulsed current of the converter. (We have a Li-Ion battery + 500µF ceramic)

Output capacitor (4.7µF) is close to the LM3410. Leds are at 10cm ( inside the display module).

I tried already to change R762 to 100 ohms and 0 ohm. No change.

What I really need is a theoretical analysis of the stability of a design around the LM3410 and how to calculate the phase margin.

A SPICE model would also be helpfull.

Best regards

Michel

Hello Michel,

Unfortunately we don't have a spice model for this part.  If you have a method to sweep the loop you can do that across R762.

You can search the e2e forum as well.  There's a post about increasing the output capacitor and possibly adding some capacitance to the fb pin.

Have you tried a larger inductor value, i noticed you are using the LM3410 'Y' part.

Best Regards,

Thanks Irwin,

Increasing the inductance is a problem for us, because we use dimming input at a frequency higher than 15KHz (to avoid audible noise).

So, if inductance + output caps are too high, the dimming doesn't work because of too long rising time.

Of course, I can swipe the loop, but the best would be to have some information about the "internal loop compensation" inside the IC or better a note that gives some theoretical informations.

Regards

Michel

Hello,

Sorry, we don't have that information.  Have you considered the 'X' part?

Best Regards,