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Class D Switching Power Amplifiers and Power D/A conversion

TI TPA3255EVM
TI TPA3255EVM
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Old 6th October 2017, 08:53 AM   #1
Kay Pirinha is offline Kay Pirinha  Germany
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Default TI TPA3255EVM

Does anybody know why the supply voltage limit is set to 53.5 V instead of, e.g., 53 V or 54 V? Does the supply need to be regulated, or mustn't the supply limit be exceeded at full output power only?

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Last edited by Kay Pirinha; 6th October 2017 at 08:55 AM.
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Old 6th October 2017, 03:37 PM   #2
doctormord is offline doctormord  Germany
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You need to make sure, your rails wont hit any limit specified in the datasheet. Your rails aren't just PVDD set by the supply (i.e. 50V) it also includes pumping effects and overshoot.

With a bad/unregulated supply you may experience some sag which might get modulated by connection wire inductance and bulk capacitance. This need to/should be measured directly at the chip pins.
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Old 6th October 2017, 04:02 PM   #3
DPH is offline DPH  United States
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Quote:
Originally Posted by Kay Pirinha View Post
Does anybody know why the supply voltage limit is set to 53.5 V instead of, e.g., 53 V or 54 V? Does the supply need to be regulated, or mustn't the supply limit be exceeded at full output power only?

Best regards!
Add to that many people are running theirs at 48V due to the ease of SMPS with that voltage.
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Old 6th October 2017, 04:06 PM   #4
Kay Pirinha is offline Kay Pirinha  Germany
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But with only 48V supply voltage power output won't reach the specified 315 W/channel, will it?

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Old 6th October 2017, 04:11 PM   #5
DPH is offline DPH  United States
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Of course not. It's a trade-off between ease of completion and squeezing the last bits out of the system. With the added question of how much you truly benefit from that last few watts before having the police called on you. I'm probably going to pick a couple 3255's up and run it as 4x SE + 2 BTL in an active system. Massive overkill, but hard to justify not going for the 3255's over the 3251's at the same cost.
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Old 6th October 2017, 04:13 PM   #6
doctormord is offline doctormord  Germany
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So you hear the difference between 280 and 315W? Beside that, 315W is meant for pure resistive load without any additional connection resistance or complex impedance.
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Old 6th October 2017, 04:52 PM   #7
2wice is offline 2wice  South Africa
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If I wanted to limit the output to less than 170W, how can I calculate power required?
Bloody less than sign keeps chopping my post.

Last edited by 2wice; 6th October 2017 at 05:18 PM.
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Old 6th October 2017, 05:17 PM   #8
doctormord is offline doctormord  Germany
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You can use the current limit programming resistor.

Approximation of datasheet values for CB3C:

TI TPA3255EVM-tpa3255_cb3c-png

170Wrms is about 340Wpk so at 4R there will be:

SQRT(340Wpk/4R) = 9.2A -> 41kOhms -> 39kOhms choosen to have some headroom.
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Last edited by doctormord; 6th October 2017 at 05:20 PM.
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Old 6th October 2017, 05:19 PM   #9
2wice is offline 2wice  South Africa
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Can't I just reduce the input voltage?
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Old 6th October 2017, 05:31 PM   #10
doctormord is offline doctormord  Germany
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Of course,

SQRT(170W*4R) = 26.1Vrms

26.1Vrms *1.41 = 36.8V

38-40V should be fine.
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