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Newbee: howto make device with 2 GND pins

Former Member

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?

 

 

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  • Chuck Huber wrote:

    On 04/26/2010 04:22 AM, Joern Paschedag wrote:

    ...

    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.

     

    Don't forget thermal considerations.  Each pin will carry some heat away

    from the die.  So connecting these externally is essential if you expect

    to meet the theta-ja specs.

     

    Enjoy,

        - Chuck

     

    Yes, I can not envision a situation where I would not want to connect

    "redundant" pins in an actual layout.  They generally don't add extra

    pins just for the hell if it.  Usually it is to lower inductance,

    increase current carrying capacity, or for thermal considerations.

     

Reply

  • Chuck Huber wrote:

    On 04/26/2010 04:22 AM, Joern Paschedag wrote:

    ...

    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.

     

    Don't forget thermal considerations.  Each pin will carry some heat away

    from the die.  So connecting these externally is essential if you expect

    to meet the theta-ja specs.

     

    Enjoy,

        - Chuck

     

    Yes, I can not envision a situation where I would not want to connect

    "redundant" pins in an actual layout.  They generally don't add extra

    pins just for the hell if it.  Usually it is to lower inductance,

    increase current carrying capacity, or for thermal considerations.

     

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