NS LM478x series chips with pins that say "no connect". - diyAudio
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Old 7th November 2004, 05:47 PM   #1
captain is offline captain  United States
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Default NS LM478x series chips with pins that say "no connect".

I'm curious about how people are dealing with the "unsued pins"...the ones marked "No Connect" on the LM4780, 81, and 82 chips.

I am laying out a board with PCB software and I want to cut off one of the pins to make room for a trace. All the others I'll leave alone. I was just going to solder them to isolated pads...not connected to ground or V+ or V-.

But I've noticed that some of the PCB layouts shown in this forum have these pins either connected to Ground or one of the Rails.

The Datasheets don't seem to shed any light...(unless I glossed over it).

Help...
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Old 7th November 2004, 06:30 PM   #2
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These pins are often really connected to nothing but in my professional work I regard these pin as "do not connect" meaning let them be unconnected.
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Old 8th November 2004, 12:38 AM   #3
garbage is offline garbage  Singapore
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IIRC, there was a thread sometime back regarding this... some one also did tests and verified that internally, the chips are indeed not connected.
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Old 8th November 2004, 05:07 AM   #4
richv is offline richv  Netherlands
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In the LM4780 application information sheet at the bottem on the reference pcb layout the NC pins 13, 23, 24 and 26 are connected with the Ground pins 12 and 19 and then to the star ground. NC pins 1 and 3 are running on V- Power and the other NC pin 6 is really not connected - orphaned. So it does not seem to matter however it makes me wander why they went thru the trouble of connecting four of them (13-23-24-26) to ground consuming valuable space on the pcb.
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Old 8th November 2004, 06:23 AM   #5
digi01 is offline digi01  China
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Quote:
Originally posted by richv
In the LM4780 application information sheet at the bottem on the reference pcb layout the NC pins 13, 23, 24 and 26 are connected with the Ground pins 12 and 19 and then to the star ground. NC pins 1 and 3 are running on V- Power and the other NC pin 6 is really not connected - orphaned. So it does not seem to matter however it makes me wander why they went thru the trouble of connecting four of them (13-23-24-26) to ground consuming valuable space on the pcb.
REALLY,the NC pins is no connect.
I use the same way to deal with my 3886igc Ver#2.the tracks looks clean and sexy.
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