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Old 23rd October 2014, 04:33 AM   #1
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Default Class D Amplifier Buck Converter Design

I am designing a high efficiency compact class D amplifier. I am a newbie at class D amplifier design so I have some questions.

1. Can I use the voltage output of a step down dc/dc buck converter as a clock pulse to drive the amp since it's a switched output or would I have to use an external clock circuit?

2. What would be the best buck converter IC for the job? Right now i'm looking at the LTC3440 but if there are any other suggestions I would like to hear them.

Thank you.
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Old 24th October 2014, 01:58 AM   #2
Khron is offline Khron  Romania
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Uhmmm.... Just to clear things up, what exactly ARE you trying to design? A class-D amplifier, or a buck converter?

While it's true, "structurally" there are similarities between the way a (synchronous) buck converter and a class-D amplifier works... I'm sure everyone else is as confused as i am - which may well be a big part of the reason for the silence
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Old 25th October 2014, 03:26 AM   #3
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I apologize for the confusion. My aim is to use a dc/dc buck converter as a supply for a class D amplifier. The class D amplifier that I am wanting to supply power to calls for a clock pulse on the inputs. Can I supply this clock pulse using the buck converter? I know that there is an input for synchronus operation that calls for an external clock pulse, but can I use the output of the buck converter as a clock pulse to drive the class D amplifier without having an external clock pulse generator?
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Old 25th October 2014, 11:07 AM   #4
Khron is offline Khron  Romania
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What exact class-D amplifier would that be, then?

And does it require some lower supply voltage than you have available? I don't really see any other reason for using a buck converter "upstream" of it, otherwise.

"Clock pulse on the inputs", you say? That's starting to sound like some PWM-input power stage...
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Old 25th October 2014, 11:55 AM   #5
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You definitely cannot use the output of the buck converter.
It is not a switched output. The output is a cap which is feed by pulsed currents. The output voltage is mostly DC, only very few switching residual there.

The LTC3440 has no sync out. The only point from where you could
draw something like sync signal is the switching node, pin 4.
With some good luck your class D amp might accept the signal when
you have the LTC running on a frequency which is fine for the class D and feed pick the signal with some signal conditioning (high pass + eventually clamp).
But it is a scrappy solution, if it works at all.
The duty cycle at pin 4 depends on the input voltage and output voltage and will also show all regulation actions of the LTC...
Proper solution would be to use your audio clock and use it to sync the class D amp and the LTC.

P.S.
You seem to work at very low power. What's your application?
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