TPS92515HV: Flicker and Inductor Ringing problem

Gwanyeon Gim

Prodigy 60 points

Part Number: TPS92515HV
Other Parts Discussed in Thread: LM5009, TPS92515,

I made a 3CH LED Driver using TPS92515HV.

It will work by DC 48V.

It was included of 8bit MCU and LM5009, TPS92515, etc.

The MCU was generated 10KHz PWM to control the LED driver.

Below PCB layout

L2 Inductor was making a ringing noise.

LED has flicker sometimes.

CH1 was SW pin, CH2 was PWM CH1.

Where should I fix it to improve?

over 7 years ago

0 Irwin Nederbragt over 7 years ago

TI__Mastermind 28655 points

Hello,

What is your LED stack voltage? If you are using 10 KHz pwm you are probably hearing the 10 KHz. Is this Shunt FET dimming or Enable dimming? What is your switching frequency?

Regards,

0 Gwanyeon Gim over 7 years ago in reply to Irwin Nederbragt

Prodigy 60 points

Led stack is 15ea. led voltage is max 42V. The switching frequency was about 580KHz. pwm prequency is 10KHz.

0 Gwanyeon Gim over 7 years ago in reply to Irwin Nederbragt

Prodigy 60 points

I have to read TPS92515HVEVM-749.

So I write the above schematic. DNP parts are removed.

R5 is changed to 0.15R. R11 is 24K.

0 Irwin Nederbragt over 7 years ago in reply to Gwanyeon Gim

TI__Mastermind 28655 points

Hello Gwanyeon,

That is fine, are you shunt FET dimming? The PWM pin is pulled high and 10 KHz is fairly high PWM frequency so I assume you are shunt FET dimming. If you are the Coff components should be added in so it still switches when the Shunt FET is on. If the inductor is noisy it would be best to try other inductors, some are not as bad as others.

Regards,

0 Gwanyeon Gim over 7 years ago in reply to Irwin Nederbragt

Prodigy 60 points

I did not use the external FET.

Is my schematic shunt FET dimming?

8bit MCU generates 10KHz PWM. PWM is below the yellow wave. red wave is LED voltage.

below picture. Vsw is the yellow line. I_led is the red line.

How I reduce inductor noise? Inductor capacity was 47uH. 100uH?

0 Irwin Nederbragt over 7 years ago in reply to Gwanyeon Gim

TI__Mastermind 28655 points

Hello,

I don't know what you are dimming, there is nothing on the schematic. What have you connected to the schematic to dim? Are you using the PWM test-point? It looks like enable dimming from the oscilloscope picture.

Inductor noise is very common. I would try different manufacturer's inductors. You can also use analog dimming or shunt FET dimming at a higher frequency.

Regards,

0 Irwin Nederbragt over 7 years ago in reply to Irwin Nederbragt

TI__Mastermind 28655 points

I have not heard back from you so I believe you may have solved the issue.
The thread will close now but will reopen if you reply.

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TPS92515HV: Flicker and Inductor Ringing problem