LME49810 - a new cousin for LM4702

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glennb

Member
Joined 2004
home.pacific.net.au/~gnb/audio/
#1
Hi chip heads,

LME49810 is a new audio power amp driver chip which appears in National Semiconductor's latest Analog Product Guide (2Q2007), available at http://www.national.com/whatsnew/files/national_analog_product_selguide.pdf (88 pages, 1.7MB)

The product folder is at http://www.national.com/pf/LM/LME49810.html and the PDF data sheet (22 pages) can be downloaded from there.

Its been briefly mentioned in the LM4702 thread http://www.diyaudio.com/forums/showthread.php?s=&postid=1222529 but I thought a new thread should be started.

The LME49810 is a 'single' cousin of the 'dual' LM4702, although its output current is about ten times that of the LM4702 and new features have been added like soft clamping and dedicated bias pins for the Vbe multiplier. The power supply rails are up to +/- 100V, slew up to 50 V/uS.

My samples have just gone into 'shipped' status from Singapore, so the first prototype amp is not far away....
 
#2
About 10 minutes after that post the nice UPS guy knocked on the front door. Ripping into the package and pulling out the camera....

The LME49810 is in the middle, with a ruler for scale. It is flanked by a LM4702 and LM4780 also for scale. It has tiny pins like the LM4780, but at least they don't have to pass the full speaker output current! 2mm pin spacing on the left and 4mm pin spacing on the right.
 

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#5
Yes, I too have taken notice of this chip. 🙂 I would say it is much better suited for a FET amp than the 4702 is. And I have my samples and will be testing that scenario with IRFP240 and IRFP9240 very soon.

The bias arrangement and Baker clamp, which basically helps keep the amp stable into clipping if I understand correctly, make this chip much more robust than the 4702. I just want to see how it sounds first, and the MOSFET arrangement here could not be simpler.

Here is a brief explanation of a Baker Clamp from on old TI doc:
What is the function of a Baker Clamp?
The collector current of the power transistor in a switching regulator is proportional to variable output load current. Normally, with bipolar transistors the fixed base drive current is optimized for a maximum output load current. This can result in unacceptably large storage time at light load, because the transistor will be driven into deep saturation. The baker clamp prevents deep transistor saturation by providing a path for excessive base drive current. Many applications, such as flyback and forward converters, are utilizing this technique. The baker clamp diode must have a fast reverse recovery time.
Click to expand...
Cheers!
Russ
 
#8
I've put up a web page for this chip at http://home.pacific.net.au/~gnb/audio/lme49810.html, to sit along-side my pages for the LM4702 and LM4780. More information will be added as experimentation with the chip proceeds. Feel free to send me comments, corrections, ideas.

The LM4702 would still be preferred for lower power stereo amps, but for high power mono blocks the LME49810 looks better.
 
#12
jackinnj said:


It's two channels, so less real estate consumption.
Click to expand...

Sure, but that does not carry much weight...

Also to get the same capability you would need to add more parts to the LM4702 (clamp and drivers etc) which would probably take more space than two 49810s.

Not saying the 4702 is bad, but I think the 49810 is better (on paper as I still have to hear it) in my book.

Cheers!
Russ
 
#13
for DIY it's a small consideration -- for a manufacturer of high end products heeding National's guidelines there's the need for localized decoupling and storage at the power pins of either chip --

a hint for both chips -- mount the decoupling caps on the underside of the PCB -- and if possible use polypropylene devices -- you want the legs on the decoupling caps to the as short as possible.
 
#15
jackinnj said:
for DIY it's a small consideration -- for a manufacturer of high end products heeding National's guidelines there's the need for localized decoupling and storage at the power pins of either chip --
Click to expand...

Hmm I thought this was DIY aduio.... 🙂

But just to play along, I am sure other factors important to commercial applications are:

- Overdrive stability
- Flexible drive capability
- Wider range of power device choices

I don't see how it would be any more difficult to produce a great stereo amp with the mono chip. In fact it would probably be less expensive to use it if you matched feature for feature.

It may be an apples/oranges comparison.

The 4702 simply does not have the same capabilities on its own. Thats the main point.
 
#16
I am thinking about the difference between LM4702 and LME49810. Is there possibility that these two chips are made using same die and configured (enable/ disable certain circuits such as Baker clamp) according to their own specs. For memory devices, it is common practice, not sure if it is the same in the analog world.

Has anyone opened these two chips to see the difference of the die itself?
 
#17
ozonek said:
I am thinking about the difference between LM4702 and LME49810. Is there possibility that these two chips are made using same die and configured (enable/ disable certain circuits such as Baker clamp) according to their own specs. For memory devices, it is common practice, not sure if it is the same in the analog world.

Has anyone opened these two chips to see the difference of the die itself?
Click to expand...

The chip design of the 49810 is probably based on half a 4702, with improved slew rate, added baker clamp, clip flag, higher current output transistors. Neither are listed on http://www.national.com/packaging/parts/DIE.html

I have yet to have the misfortune of letting the blue smoke out of a 4702 or 49810, but if I do, it would be worth trying to expose the die.
 
#18
glennb said:


The chip design of the 49810 is probably based on half a 4702, with improved slew rate, added baker clamp, clip flag, higher current output transistors. Neither are listed on http://www.national.com/packaging/parts/DIE.html

I have yet to have the misfortune of letting the blue smoke out of a 4702 or 49810, but if I do, it would be worth trying to expose the die.
Click to expand...


I think you are right. It is base on the 4702 but not the same die. Their slew rate and some other spec are different, should be another design.
 
#19
All you have to do is ask....

I called National. It is a different die. It is in fact a significantly different bias scheme. Though National will not give away the farm. 😉

According to the nice gentleman I spoke with there are more new devices on the way as well... Could it be a new dual part coming based on the 49810? Hmmmmm that would be sweet. 🙂

Cheers!
Russ
 
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