National Semiconductor – LME49811

The LME49811 from National Semiconductor / TI

Greetings!

Class D amplifiers and drivers are becoming so popular that some of the largest IC manufacturers are no longer focusing on class AB or A driver chips.  This is certainly the case for TI and sub group National Semiconductor.  Of course some of us don’t like class D.  What about our firm favourites: LME49xxx series or the LM4702?

According to a lot of feedback on the net, this chip is now EOL.  Here’s a result from the TI forum pages and the Elektor forum.  There is no result from the RS Components website and it is believed shipping was only until the end of March 2017.

LME49811 - end of line
LME49811 – end of life

Whilst this puts most DIYer types in a spot, especially when it comes to building the Q-watt designed by the Elektor team, all is not lost.

The LM4702 is a major player in the high voltage VAS and power driver market.  Tech specs from TI here.

TI: “The LM4702 is a high fidelity audio power amplifier driver
designed for demanding consumer and pro-audio applications.
Amplifier output power may be scaled by changing the
supply voltage and number of output devices. The LM4702
is capable of delivering in excess of 300 watts per channel
single ended into an 8 ohm load in the presence of 10% high
line headroom and 20% supply regulation”.

An interesting point here is that the LME49811 is used to drive one complementary Darlington output pair, the LM4702 is a stereo equivalent.

Read here from Texas Instruments engineer Toyojiro Naokawa about the LME49811 / LM4702 relationship.

But wait, a surprise is in store….. as in Digi-Key

LM4702C - obsolete as well?
LM4702C – obsolete as well?
LM4702 - Mouser
LM4702 – Mouser

For supplier requests and stock of the LM4702 series refer to http://www.digchip.com/ – also try eBay but do check credentials.

The problem with our electronics industry today is that it’s a case of here today and gone tomorrow.  Class-D is certainly the way things are moving and this is where we should be focusing.  In my own opinion stick to audio with discrete components.  IMO there is no reason why with modern ultra fast switching technology that the class-D amplifier should be no worse than the the older AB class. If you do need class AB or A, use available ICs such as the TDA7293/94 for the mid and high frequencies, D for the bass.

Class AB MOSFET amplifiers can use less components than a BJT amplifier for the same output, this is inherent in the nature of driving high gain transistors which are charge plate devices.  Driving the gates with too high a voltage is a problem though.  The DMOS TDA7293 /  7294 are quality chips in my mind.

Further reading:

The DIY Audio forum has a lot of information on chip amplifiers, not necessarily as drivers.

 

 

 

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