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Class D Switching Power Amplifiers and Power D/A conversion

TPA3251d2
TPA3251d2
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Old 11th July 2015, 04:18 PM   #1
Capt Grogg is offline Capt Grogg  United States
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Default TPA3251d2

TI has released TPA3251d2 'AKITA" higher power analog in class D chip with higher order modulator similar to Hypex NCore but with pre filter feedback. First heard about it at CES 3+ years ago. Can be configured as 1,2,3 or 4 channel with 36 volt supply for output stage.
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Old 11th July 2015, 06:44 PM   #2
egra is offline egra  Hungary
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I'm really curious how this chip sounds. Pretty impressive description:

"TPA3251D2 is a high performance class-D power amplifier that enables true premium sound quality with class-D efficiency. It features an advanced integrated feedback design and proprietary high-speed gate driver error correction (PurePath™ Ultra-HD). This technology allows ultra low distortion across the audio band and superior audio quality."

I hope the chinese manufacturers will take the first steps soon.
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"We can hear everything we measure, but we can't measure everything we hear. Let your ears be your guide."
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Old 14th July 2015, 12:57 AM   #3
frammis is offline frammis  United States
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Default TPA3251D2 THD Curves

This is a closed loop part with pre-filter feedback. THD vs power (at 1KHz) & THD vs Frequency curves from June 2015 datasheet attached. I'd like to try a differential input, BTL output implementation.

TI website has samples: TPA3251D2 | Mid/High-Power Class D Amplifiers | Audio | Sample & buy
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Old 15th July 2015, 01:10 AM   #4
doctormord is offline doctormord  Germany
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Yeah, let's make a small board <=10x5cm.
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Old 16th July 2015, 02:47 PM   #5
doctormord is offline doctormord  Germany
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Some short calculation for the required heatsink, worst case:

Rds_on (high/low side): 0.1R
Imax: 14A
Tambient: 30C
Rth_jc(Top): 0.36C/W

Power dissipation per channel:

Pd_channel = IR = Imax*2*Rds_on = 14A*2*0.1R = 196A*0.2R = 39.2W

Power dissipation total:

Pd_total = 2*Pd_channel = 2*39.2W = 78.4W

Tcase = Tjunction - Rth_jc * Pd_Total = 125C - 0.36C/W * 78.4W = 125C - 28.224C = 96.776C

Rth_heatsink = (Tcase - Tambient) / Pd_total = (96.776C - 30C) / 78.4W = 0.85C/W

Rth_heatsink includes thermal conductivity of heatsink grease.

--------------

Lets do the calculation again for Irms (sinus power):

Rds_on (high/low side): 0.1R
Imax: 14A

Tambient: 30C
Rth_jc(Top): 0.36C/W

Power dissipation per channel:

Irms = Imax*sqrt(2) = 14A*0.707 = 9.9A

Pd_channel = IrmsR = Irms*2*Rds_on = 9.9A*2*0.1R = 98A*0.2R = 19.6W

Power dissipation total:

Pd_total = 2*Pd_channel = 2*19.6W = 39.2W

Tcase = Tjunction - Rth_jc * Pd_Total = 125C - 0.36C/W * 39.2W = 125C - 14.112C = 110.888C

Rth_heatsink = (Tcase - Tambient) / Pd_total = (110.888C - 30C) / 39.2W = 2.1C/W

Rth_heatsink includes thermal conductivity of heatsink grease.

Much better.

As music is normally not pure fixed frequency sine wave the maximum temperature will likely not reached even at full power.

----------------------------------------------------------------------
Lastly, for normal use, with an estimated programm factor of 0.5 there will be:

Rds_on (high/low side): 0.1R
Imax: 14A
Music programm factor (mpf): 0.5
Allowed max junction temperatur: 90% from Tj = 0.9*125C = 113C

Tambient: 35C
Rth_jc(Top): 0.36C/W

Power dissipation per channel:

Irms = Imax*sqrt(2) = 14A*0.707 = 9.9A
Iprog = Irms * mpf = 4.45A

Pd_channel = IprogR = Iprog*2*Rds_on = 4.45A*2*0.1R = 19.8A*0.2R = 3.96W

Power dissipation total:

Pd_total = 2*Pd_channel = 2*3.96W = 7.92W

Tcase = Tjunction - Rth_jc * Pd_Total = 113C - 0.36C/W * 7.92W = 113C - 2.85C = 110.15C

Rth_heatsink = (Tcase - Tambient) / Pd_total = (110.15C - 35C) / 7.92W = 9.5C/W
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Old 16th July 2015, 02:49 PM   #6
Buehgemeiste is offline Buehgemeiste
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Quote:
Originally Posted by doctormord View Post
Yeah, let's make a small board <=10x5cm.
Please do that!!!
Most of the commonly used chips are 5+ years old.
Did you see the TAS57xx series with integrated DSP stuff?
If i were an engineer...
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Old 16th July 2015, 04:08 PM   #7
doctormord is offline doctormord  Germany
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Sorry, but i can't find them on the TI page. (With analog inputs)

Last edited by doctormord; 16th July 2015 at 04:11 PM.
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Old 16th July 2015, 04:12 PM   #8
Buehgemeiste is offline Buehgemeiste
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this is one ds:
http://www.ti.com/lit/ds/symlink/tas5756m.pdf

this is the user manual for the software:
http://www.ti.com/lit/ug/slau577a/slau577a.pdf
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Old 16th July 2015, 05:02 PM   #9
doctormord is offline doctormord  Germany
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Thats something totally different. Digital Inputs, less output power, less operating voltage..
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Old 16th July 2015, 05:29 PM   #10
Buehgemeiste is offline Buehgemeiste
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yes
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