Newbee: howto make device with 2 GND pins

On 4/26/2010 2:13 PM, Michael Sansom wrote:

Joern Paschedag wrote:

Am 25.04.2010 20:41, schrieb Rens:

Like SOT223 a device having 2 pins internally connected in the device.

Sot224 pin 2 and 4(cooling pad) are the same.

I supposed that connecting one pin it is also connected to the other.

However, on the board a airwire still remains. This is also true for a

sot223 device from the library.

I tried the mailto:GND@1 etc. naming, but seems not to work.

What am I doing wrong?

 

 

 

Eagle does not know internal connections. So the rule is one pin for

one pad. Some SO8 transistors have four drains which are internally

connected. They are named D, D@1, d@2, D@3 in the library in this

example. It would be ok, if you connect just one of these pins in the

schematic and eagle would do the same in board.

BUT, why should a manufactorer add more pads, if one is enough?

Because the chip is connected to the pads with bonding wires and one

wire is not thick enough to carry the amount of current specified in

the data sheet. So two or more connections are used in parallel to

carry the current. So you should see that all equal named pins are

connected externally to avoid a "slow blowing fuse" device.

 

 

What is the significance (if any) of using the "@" symbol in the example

above.

 

BTW, what I do in this situation is have GND1, GND2, GND3, .... as pin

names on the symbol and then connect them all independently to "GND" on

the schematic. Works well.

 

The part following the '@' is not shown so that each looks like the same

label pin.

On 4/26/2010 2:13 PM, Michael Sansom wrote:

Joern Paschedag wrote:

Am 25.04.2010 20:41, schrieb Rens:

Like SOT223 a device having 2 pins internally connected in the device.

Sot224 pin 2 and 4(cooling pad) are the same.

I supposed that connecting one pin it is also connected to the other.

However, on the board a airwire still remains. This is also true for a

sot223 device from the library.

I tried the mailto:GND@1 etc. naming, but seems not to work.

What am I doing wrong?

 

 

 

Eagle does not know internal connections. So the rule is one pin for

one pad. Some SO8 transistors have four drains which are internally

connected. They are named D, D@1, d@2, D@3 in the library in this

example. It would be ok, if you connect just one of these pins in the

schematic and eagle would do the same in board.

BUT, why should a manufactorer add more pads, if one is enough?

Because the chip is connected to the pads with bonding wires and one

wire is not thick enough to carry the amount of current specified in

the data sheet. So two or more connections are used in parallel to

carry the current. So you should see that all equal named pins are

connected externally to avoid a "slow blowing fuse" device.

 

 

What is the significance (if any) of using the "@" symbol in the example

above.

 

BTW, what I do in this situation is have GND1, GND2, GND3, .... as pin

names on the symbol and then connect them all independently to "GND" on

the schematic. Works well.

 

The part following the '@' is not shown so that each looks like the same

label pin.