TPS92512: PWM Noise

Diego Bernardi

Part Number: TPS92512

Hi all!

I'm new to the forum, so I hope everything I'm posting is correct :-)

I'm using a TPS92512 to drive a led channel made by 6 Cool White led ( CREE XP-G2 ); this is the schematic: so all ok, it works and I'm able to change the current intensity via PWM 8 bit @ 100Hz ;

the problem starts here, there's a lot of noise when dimming the led..what am I doing wrong? maybe some components value?

Thank you!

over 8 years ago

0 Clinton Jensen over 8 years ago

TI__Mastermind 25500 points

Hello Diego,

Do you mean audible noise during PWM dimming? If so it is a common problem. You can refer to this post for what is hopefully some useful insight for you.

Regards,

Clint

LM3409: PWM dimming audible ringing - Power management forum - Power management - TI E2E support for...

e2e.ti.com

Part Number: LM3409 When I am operating the driver under normal operation the system is quiet. On my PWM dimming circuit, i get audible ringing, I am PWM dimming

0 Diego Bernardi over 8 years ago in reply to Clinton Jensen

Prodigy 40 points

Hello Clint,

thank you for your reply.

Yes , I mean audible noise when PWM dimming, even if I change PWM frequency. I'll take a look at your link!

Thanks

0 Diego Bernardi over 8 years ago in reply to Diego Bernardi

Prodigy 40 points

Hello Clint,

so change the inductor with higher DCR, a lower Irms/Isat could decrease noise?

Thank you

0 Clinton Jensen over 8 years ago in reply to Diego Bernardi

TI__Mastermind 25500 points

Hello Diego,

It may or may not. The thing with inductors if they are making the noise is that any seemingly minor differences could change how they behave with respect to audible noise. If that is your noise source it will just take some experimenting trying different inductors until you find one that doesn't buzz at your PWM dimming frequency.

Regards,

Clint

0 Diego Bernardi over 8 years ago in reply to Clinton Jensen

Prodigy 40 points

Hello Clint,

the problem hasn't been solved yet; so what about changing the value of the inductor?

0 Clinton Jensen over 8 years ago in reply to Diego Bernardi

TI__Mastermind 25500 points

Hello Diego,

Changing the inductor value may help. But I am curious as to whether something else might be going on if you tried different inductors and none of the helped. Do you have the noise at all PWM duty cycles or just at low duty cycles? Could you provide the LED current and PH voltage waveforms during PWM dimming when you are hearing the noise? Could you try increasing the input voltage or decreasing the LED stack voltage by one or two LEDs to see if it goes away? This part likes to have a lot of headroom when PWM dimming to avoid potential BOOT UVLO issues and I'm wondering if you are seeing that.

Thanks,

Clint