L5973D step down regulator

[Pawe? Flisikowski]

Posted on October 20, 2017 at 14:16

Hi,

I'm repairing an audio power amplifiers from a top model manufacturer like Harman-Kardon, Dynaudio, Bose from cars. And in almost all of models I faceing up with broken regulator L5973. The failure is that the voltage on the output increases to 4-5V causing a damage in connected DSP chips. This is standard application from page 9 from the ST datasheet. Input is 12V output is 3,3V.

What can be a root cause of this behaviour? When I replace for new IC it is working in next coulpe of months ok and again fails.

Maybe somebody had this case and could share some ideas

Regards,

Pawel

[tevet]

Hello, i am repairing a harman kardon with the same IC L5973scheme, i have one for 3,3V and another with 1,2V. The first step (3,3V) is damaged, measuring 4,9V.

I think the problem is age and moisture...

You only replace that IC or broken any more?

Thanks in advance

[ahsrabrifat]

L5973 has a max input voltage of 36V, so a strong spike can cause degradation over time.

Check with an oscilloscope if voltage spikes are exceeding 36V.

Use a TVS diode (like SM8S36A or SM8S33A) on the 12V input to clamp spikes.

Add a low-ESR bulk capacitor (1000µF, 25V or higher) to absorb transients.