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LM2676-ADJ Problems

Chris Desmond

Prodigy 30 points

Hello:

I'm designing a 15V and 3.3V SMPS using the LM2676-ADJ. I'm using the evaluation board with the recommended components from the data sheet. The 15V version exhibits a 200mV p-p sawtooth wave @ 400 Hz with light loads and poor load step response. The 3.3v version exhibits an odd pulse-type waveform @ 10 kHz on the output when loaded at 0.5A when the input voltage is raised above 14V and also shows poor load step responds. Please help.

-Chris

over 11 years ago

0 Denislav Petkov over 11 years ago

TI__Mastermind 19891 points

Hello Chris,

If possible, could you please attach some scope shots of what you are seeing. Please include the SW node, input and output voltage.

Also, what output capacitor (part number) are you using and can you confirm your inductor values?

Regards,

Denislav

0 Chris Desmond over 11 years ago in reply to Denislav Petkov

Prodigy 30 points

For the 3.3v Design: L = 24uH Pulse Engineering PE-53933SNL, Cout = 470uF Panasonic EEE-FP0J471AP

Vout:

V SW Node:

15V Design: L = 77uH Pulse Engineering PE-54038SNLT, Cout = 47uF, kemet T495D476K020ATE100

Vout:

V SW Node:

Thanks;

-Chris

0 Chris Desmond over 11 years ago in reply to Chris Desmond

Prodigy 30 points

For some reason, the pictures did not show-up in the above post.

-Chris