What is wrong with TPA3255?

[chermann]

Originally Posted by doctormord

I don't have that Power-Off-Pop feature on my implemenation of TPA32XX, neither 51 nor 55. The Pop comes from a race condition in fall-times of the power rails and can most likely avoided/tuned if the detection level for the voltage-supervisor is set tight to the supply voltage. If the level is to close to "nominal voltage", the amp will mute on high power with a weak supply. The EVMs solution with feed-forward capacitors is more prone to this effect as it kinda boosts dips in supply voltage change.


Using a TPS3802K33DCK, the threshold voltage for the SVS is 2.93V. The resistor divider 27k+3k3 then trips at about 27V.

Trip levels for other voltages:

34.9V: 36k + 3k3
32.2V: 33k + 3k3
30.3V: 30k9 + 3k3
29.6V: 30k + 3k3
27V: 27k + 3k3
24.2V: 24k + 3k3
22.5V: 22k + 3k3
20.7V: 20k + 3k3

So for a 36V system you may try 33k or 36k instead of 27k.

Hi doc

i use 27k , a zener 4Z7 and 28Vpower for the start...... but its not working. VDD is 2,754Volt. then i checked the 3k3 for the divider....its not 3k3 --> 3562R
reset an TPS "ARK" is still 0Volt...ok....i have no 3k3 at home
i try shortly to push 33V into it--> VDD is about 2.945V but the TPS"ARK" is still doing nothing=> Reset is 0V so the pin 18 of the TPA is 0V--> no sound
curious is that the MR of the TPS "ARK" is "open" but its about 2,74Volt??
did i miss something???


thx
chris

[doctormord]

The levels are 2.87 2.93 2.99 (min type avg), so maybe yours not hitting 2.93V exactly. So either increase the 3k3 a bit or decrease the 27k. It's all written in the datasheet (TPS..)

[chermann]

Originally Posted by doctormord

The levels are 2.87 2.93 2.99 (min type avg), so maybe yours not hitting 2.93V exactly. So either increase the 3k3 a bit or decrease the 27k. It's all written in the datasheet (TPS..)

thanks doc..

[chermann]

...thank you Doc...its working


changed R1 to 22kR 1% and at 29,25V the circuit is working
at the R2(3562) its 2,986V...so its in between the tolerance.


the out pop is still audible "loud" compared to the power on plop. in my lab i use a small 4 ohm speaker. will see/hear at my good speakers what happend when the amp is ready...


thx
chris

[doctormord]

Interesting.. i haven't noticed any problems/plop with my amps. So something must be different for the 12V rails on yours.