LME49600: Paralleling Devices

Leo A.

Part Number: LME49600

Hello,

I need more than 250mA of current than the LME49600 provides, what is the best way to parallel the devices to get more current.

Thanks;

Leo

over 6 years ago

0 Ivan Salazar over 6 years ago

TI__Guru** 103055 points

Hi Leo,

The following blog post might be helpful for your question: e2e.ti.com/.../paralleling-op-amps-is-it-possible

Best regards,
-Ivan Salazar
Applications Engineer - Low Power Audio & Actuators

0 Leo A. over 6 years ago in reply to Ivan Salazar

Intellectual 545 points

The LME49600 is not an opamp. I don't see how that article applies.

I plan to use multiple units inside the feedback look of a single opamp.

0 kai klaas69 over 6 years ago in reply to Leo A.

Guru 140200 points

Hi Leonid,

the article discusses the master-slave-method which is also valid for unity gain buffers like the LME49600.

Can you show us a schematic of your planned circuit?

Kai

0 Leo A. over 6 years ago in reply to kai klaas69

Intellectual 545 points

Something like this but with 12 of them in parallel to be able to drive the 4 ohm load. I need super low output impedance so that damping factor can be very high.

I have found mulitple implementations online whch do not use resistors to prevent the divices from driving each other, like this one:

http://forum.zelfbouwaudio.nl/viewtopic.php?t=17844

How do they do it then without the resistors? Is this possible due to the internal output resistance of the device?

0 Leo A. over 6 years ago in reply to Leo A.

Intellectual 545 points

please respond.

0 kai klaas69 over 6 years ago in reply to Leo A.

Guru 140200 points

Hi Leonid,

with a low overall gain the circuit is unstable:

But with a high overall gain it looks much better:

Even a high capacitive load can be driven:

And the output resistances can be increased:

The circuit should still be simulated with real loads, though.

leonid.TSC

Kai

0 Leo A. over 6 years ago in reply to kai klaas69

Intellectual 545 points

Is 10mohn enogh to separate the devices. That would be great as 10mohm / 12 will be a very low output impedance.

I will review simulation and get back to you, if I have more questions.

Is there an NDA that we can sign because I actually have a different design for the feedback, but I dont want to share it publicly.

0 kai klaas69 over 6 years ago in reply to Leo A.

Guru 140200 points

Hi Leonid,

please take the TNIA-TI file I gave you and make your own simulations. Then you will notice, that the simulation does not run with output resistances smaller than 10mR. That's the actual reason, why I have put 10mR resistors at the output.

Please note, that this simualtion might not show realistic results as it assumes totally identical LME49800. So, I personally would never run this circuit without output resistances.

Please also note that I'm not a TI employee. :-)

Kai

0 Leo A. over 6 years ago in reply to kai klaas69

Intellectual 545 points

Please take a look at this simulation, the LME49600 is exhibiting some interesting behavior when being driven to the rail. Is this a simulation artifact or will this happen in reality?

I have tried different feedback typologies and nothing seems to fix it.

Transistor_Amp_Tina.TSC

0 kai klaas69 over 6 years ago in reply to Leo A.

Guru 140200 points

Hi Leonid,

yes, the LME49600 behaves that way when its output is clipping. This cannot be prevented. Just keep the input amplitude low enough so that the output of LME49600 cannot clip.

Kai

0 Leo A. over 6 years ago in reply to kai klaas69

Intellectual 545 points

Guess I will have to clamp the input to ensure that behavior does not happen.

0 kai klaas69 over 6 years ago in reply to Leo A.

Guru 140200 points

Hi Leonid,

if you only reproduce music from a CD or DVD, an additional input clamping might not be needed, because the maximum output voltage of such a playback device is automatically limited. Just provide some headroom for the input signal to safely prevent output clipping. If the output signal is not high enough for your application, increase the supply voltage.

Kai

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LME49600: Paralleling Devices