TPA3255 - all about DIY, Discussion, Design etc

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#724
I use MCP120 with good results in my TPA3251 amp. Resistors should be adjusted according to PVDD voltage used. I currently use 10k and 1k to switch amp on at approx. 32V. There is almost none click/pop during switching on/off and it takes about 0.5s to turn on (unmute).
 

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#726
Sorry for the typo, i meant TPS3801. This is already implemented on the board (EVM and "1HL Chinaboard")


If it doesn't work like intented, you may modify it like so:


Finally got it right:

attachment.php


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Values are meant for 25V threshold.
 

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#727
DarkOne said:
I use MCP120 with good results in my TPA3251 amp. Resistors should be adjusted according to PVDD voltage used. I currently use 10k and 1k to switch amp on at approx. 32V. There is almost none click/pop during switching on/off and it takes about 0.5s to turn on (unmute).
Click to expand...

Great, this looks simple to implement & I am feeding TPA3250 at similar PVDD 31~32V as well.

Some amateurish questions:

1# Power dissipation requirements:
BZX84C4V7 is rated for 1/4w.
So can i use lowest dissipation /smallest package on MCP120, BZX84C4V7?
ie. MCP120T(T092/SOT23)

2# Confirm of Trip point voltage:
~ MCP120 for 3.0v, right?
~ Can any 4.7v zener diode be use instead?
 
#728
doctormord said:
Sorry for the typo, i meant TPS3801. This is already implemented on the board (EVM and "1HL Chinaboard")

Values are meant for 25V threshold.
Click to expand...

Thks Doctor for the great sharing, pardon my amateurish questions here:

- you used TPS3801 or TPS3802K33DCKR? what trip voltage, at 3.3V?
- which resistor to modify if my PVDD is heading 31~32V？
- any power dissipation requirements on the component package: 1/4w?
 
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#729
forestsgump said:
Great, this looks simple to implement & I am feeding TPA3250 at similar PVDD 31~32V as well.

Some amateurish questions:

1# Power dissipation requirements:
BZX84C4V7 is rated for 1/4w.
So can i use lowest dissipation /smallest package on MCP120, BZX84C4V7?
ie. MCP120T(T092/SOT23)

2# Confirm of Trip point voltage:
~ MCP120 for 3.0v, right?
~ Can any 4.7v zener diode be use instead?
Click to expand...

1- That zener is just for protection of MCP120 which has absolute maximum voltage of 7V. There are no requirements on power and you can feel free to not use it. Its just for piece of mind.

2- Its 3V version of MCP120. Don't substitute it with zener, its something completely different.

For 31-32V power supply I would suggest resistors 10k and 1k2. That will unmute TPA at about 28V + 350ms delay.
 
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#731
doctormord said:
If you choose 10k for the upper Resistor, the lower is: 10k/8
485=1.18k so choose 1.2k
Click to expand...


If you choose 10k for the upper Resistor, the lower is: 10k/8.485=1.18k so choose 1.2k.

Powerrating:
PVDD=32V

Current into TPS380X or MCP120 is negligible. We only calculate for the combined voltage divider.

10k+1.2k=11.2k

Current is then:

32V/11.2k=0.0028571429A or 2.86mA

Power follows I^2*R, so for the 10k:

2.86mA^2 * 10k = 82mW -> 1/10W is fine

for the 1.2k:

2.86mA^2 * 1.2k = 9.82mW -> 1/10W is more than fine

Nothing to worry about. The zener conducts only at overvoltage and is then roughly limited to

P_zener = U_zener * ((PVDD - U_zener)/R_upper)

Because differential resistance of the diode is much smaller than R_lower (1.2k) and R_upper (10k)

For 40V overvoltage we have:

P_zener = 4.7V * ((40V-4.7V)/10k) = 17mW

The upper resistor would need a power rating of:

P = ((40V-4.7V)^2)/10k = 125mW = 1/8W

If this overvoltage will occur for long time. If it's just pulses, 1/10W is still fine.

Someone correct me please if I'm wrong.
 
#733
doctormord said:
@forestsgump, may you post a good quality picture/photo of the corresponding section on your board I may use for annotation and posting on my website? I don't have any of these boards on the bench.
Click to expand...

Want to say word of appreciation for Doctormord, also DarkOne -
It is people like you - cared to lend a helpful hand, which kept diyAudio and many enthusiasts going!


Doctormord, after you are done posting, if can could help by sharing a link of your website i can reference exactly what pin to mod? thks.
 

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#735
Thanks for the compliments and pictures. Would be great if you can take them front/back with heatsink removed to see all traces and bias with much (soft) light to keep noise and exposure time low to have it nice and sharp. This amp doesn’t feature a voltage supervisor at all. (Or am i blind?)

Then i will put all annotations in where to patch.

Thanks a lot.
 
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