6 channel LME49830 power amp

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cuibono

cuibono

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Like Cce in this image (from AN-1645)?
 

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cuibono

cuibono

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This is from the app note for the LME49830, an-1850. It shows two resistors, Rbo1 and Rbo2, but doesn't actually use them - in other designs, like the LME49810 and LME49811, there are resistors here. Why?

SpittinLlama, where are you? :bawling:
 

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cuibono

cuibono

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Hooray, I didn't kill the board - the power plug had come loose. :rolleyes:

So I retried using 200ohms for Rg and still no luck with the ringing on the square wave. Inspecting it, it looks like its ringing at about 143kHz. I found a number of other oscillations looking at the noise floor. Hmmm. The search continues. I'm still wondering about those Rbo resistors - why aren't they used in AN-1850, when so many others use them?
 
cuibono

cuibono

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Also, I set the scope into XY mode, and compared the input to output, looking for phase shift. 20Hz showed some (I'd guess less than 20deg?), and then again some at 150kHz (maybe 30deg?). Would the shift around 150kHz have anything to do with the ringing at about 143kHz? Or with the LPF on the input of the LME chip, which is set to 130kHz?
 
fab

fab

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fabaudio.online
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cuibono said:
...I'm still wondering about those Rbo resistors - why aren't they used in AN-1850, when so many others use them?
Click to expand...

My guest is that they are there on the layout for test point purpose.... and/or maybe put zener diode there to limit the voltage during initial test to avoid destructing the expensive mosfets...

What values other use?
I think that the LME49810 for bjt has resistors there...

On my PCB - bought on the net - for LME49830 I have no Rbo resistors and it shows no sign of oscillation... but I use LAteral mosfet - I did not use the vertical ones.
 
cuibono

cuibono

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Thanks for your input! I've been looking at a lot of other LME chip family designs, and they almost always have resistors between the the gate drive lines (even the LME49830 pdf has them - often the value is around 12k total). Interesting that yours don't. Where did you get them?
 
fab

fab

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cuibono said:
Thanks for your input! I've been looking at a lot of other LME chip family designs, and they almost always have resistors between the the gate drive lines (even the LME49830 pdf has them - often the value is around 12k total). Interesting that yours don't. Where did you get them?
Click to expand...

The schematics I have from http://www.chp-pcb.cn/ has protection diodes (zener in series with 1N4148) instead of the 12k resistors. This schematics is propriatery of this company so I suppose I can not put it here. This is standard practice to protect mosfet. However, this web site is off-line since a few days...
 
cuibono

cuibono

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So I've tried a number of things: I heated and pulled off all the copper on the pcb that was filling unused space. Tested that. Then I cut off the output section and re-did it point to point on the heatsink. Tested that. The results? No difference in the square wave ringing. So I doubt the layout has anything to do with it.

I tried adding 6.8k resistors in the Rbo positions - didn't do anything.

I tried different values of compensation caps (going from 20pF to 22 then 27). Didn't do anything.

What else could I try? :smash:
 
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