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Old 3rd January 2003, 09:16 AM   #1
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Default National gone ground happy?

Recently looking into building the lm4651/52 amp and upon examining the schematic I found that they've used the ground symbol in the typical application circuit.... alot.
According to the circuit diagram they give it has the Vee & Vcc connected to ground on both chips. Has this been intentionally left out and expected to be put back in?
Are there any more connections that should be something other than ground that they've missed?
Also the the Vee/Vcc pins of the lm4652 they have one cap in symbol but 2 descriptions. Do they require both caps?
Many Thanks
Matt
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Old 3rd January 2003, 05:14 PM   #2
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I have looked at "Figure 1" of the LM4651 datasheet and what they are doing is:
1) Vcc and Vee power connections are NOT shown, ie they did not draw in the wires running to the approate supply.
2) The capacitor shown at the Vcc and Vee pins are actually two capicitors in parallel, a 1uF tant and a .1.
Note that the capacitor on Vddbyp is actually three caps!

In reality what they are saying here is that this puppy will oscilate in a heartbeat - extreem care should be used in the PCB layout. Look at page 16 -they are recomending specific parts for certain caps.
Have you loked at this page:
http://www.national.com/appinfo/audi...19,133,00.html

johnm
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Old 4th January 2003, 12:02 PM   #3
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Thanks for the advice.
They reccommend a double sided board which I think is a good idea (for simplicities sake )
I'll report when i'm done
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Old 4th January 2003, 12:34 PM   #4
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Default If you can't cut a double sided board

then use the 3M copper tape - adheres very nicely, cuts with scissors or a Xacto knife, and solders well. I am using it in a project with a switched cap successive approximation ADC -- if you don't ground plane correctly the inacuraccies are awful.
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