6 channel LME49830 power amp

[cuibono]

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

[cuibono]

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?

[Yuli_35]

Sorry I was not clear enough....

I was thinking about a cap after RGP1 and -VEE. this will do an RC filter ... and the fc will be 1/ (2 x pi x RGP1 x C)

Reference to this drawing :
http://www.diyaudio.com/forums/attac...amp=1241969879

Brgds - Gilles.

[cuibono]

Thanks - your talking about a cap from drain to gate. I'll let you know how it goes....

[Yuli_35]

Sorry to mention that you have to do that on both MOS ! 8-)

[cuibono]

Somewhere between increasing the gate resistors and adding Rbo resistors, I've blown another channel. Sigh....

[cuibono]

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

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]

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]

Originally posted by cuibono
...I'm still wondering about those Rbo resistors - why aren't they used in AN-1850, when so many others use them?

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]

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?