TPA3255: TPA3255 large ripple

Darren Yang

Expert 2000 points

Part Number: TPA3255

Hi，our customer use TPA3255 design for Trolley audio，now meet encountered 450KHZ running frequency and output large ripple. could you help check it and give some suggestions for us to debug it，tks！

over 7 years ago

0 Justin Bohr over 7 years ago

TI__Mastermind 28020 points

Hi Darren,

Could you send a scope shot of the ripple? If the ripple is at 450kHz, then you are probably looking at the output without a 20 kHz filter. The ~1V ripple at the switching frequency is normal.

Justin

0 Darren Yang over 7 years ago in reply to Justin Bohr

Expert 2000 points

Hi, Justin

if the Fpwm is 450khz , the ripple is normal,however, we find the Fpwm will be changed to 620khz automatic during aging test Instead of 450khz，but the R(FREQ_ADJ) is used 30K ohms，only we use 36K ohms can make the Fpwm change to 450khz again, but the recommended resistance is 29.7K~30.3K ohms,This is a normal phenomenon？if the Fpwm is be changed，it will also increase output ripple. pls help check it and give some suggestions,tks!

0 Justin Bohr over 7 years ago in reply to Darren Yang

TI__Mastermind 28020 points

Hi Darren,

This is not a normal phenomenon, the variance over temperature of the internal oscillator will not vary that much. This seems more like the resistor is changing values significantly, as the 600kHz mode is 10k ohm. Could you describe what the life time testing is? Is there any way that the resistor is changing values during this test due to temperature?

Justin

0 Darren Yang over 7 years ago in reply to Justin Bohr

Expert 2000 points

Hi Justin

we test the resistor is 30k ohms not change during this test, tks!

0 Justin Bohr over 7 years ago in reply to Darren Yang

TI__Mastermind 28020 points

Hi Darren,

Are you able to look at the voltage across the resistor during operation or the stress test? Does the switch to 600 kHz happen immediately when doing large outputs?

Could you share the layout? There is a possibility that the ground layout/connections to the reference passives for the device might not be optimal, which could cause the ground ground noise, changing the references.

Justin

0 Darren Yang over 7 years ago in reply to Justin Bohr

Expert 2000 points

Hi Justin

PCB layout as attachment,tks!200w toplayer.pdf

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TPA3255: TPA3255 large ripple