0
\$\begingroup\$

I am making a schematic for a project with CC2640 microcontroller. The datasheet provided at TI does not mention any GND pin. However, they say something called "Exposed Ground Pad". Is this the GND pin?

How do I show it (GND) in schematic view in NI Multisim that gives fixed footprint selections in multiples of 2(e.g 8, 16, 32,48), when using component Wizard for component creation . I am currently using 48 pin VQFN Package.

\$\endgroup\$

1 Answer 1

1
\$\begingroup\$

Many ICs have an exposed pad underneath. Sometimes is for grounding, sometimes for heat dissipation, sometimes simply for mechanical support. I've seen one (an IMU) where the exposed pad was supposed to be left unsoldered. The datasheet usually makes it pretty clear.

Your specific part's datasheet, however, isn't so clear. In addition, this part has different grounding methods for each of their different packages.

For the VQFN-48 (7x7mm) and the VQFN-32 (5x5mm) packages, the only ground connection is the exposed pad. But, for the VQFN-32 (4x4mm) package, there are actual Vss pins in addition to the exposed pad.

These signals can be seen in Tables 4-1 through 4-3 of the linked datasheet, but it is confusing that the extra Vss signals would simply seem to be omitted. However, if you look at the example circuits in Figures 7-3 and 7-5, you can verify the intention of the datasheet.

Unfortunately, they don't have an example circuit for the VQFN-48, but comparing the VQFN-32 tables with the VQFN-32 diagrams implies that you can trust the VQFN-48 table.

(note that each image has a Vss pin labelled "33" in a 32-pin package)

Figure 7-3: 5x5mm VQFN-32:

5X5

Figure 7-5: 4x4mm VQFN-32:

4X4


As far as MultiSim goes, there is an answer to your question here at the NI Forum:

Generally thermal pads are added using a the rectangular SMD pin (or custom pad shape if you require a cutout). an example using the custom pad shape already in the database is the QFN40P600X600X80-49N.

...

You should go there to read the whole answer.

\$\endgroup\$
4
  • 1
    \$\begingroup\$ Is there a reason you don't quote the NI Forum answer more extensively? Would be a shame if this answer became trash because NI reshuffled their site and the link broke :/ \$\endgroup\$ Feb 16, 2017 at 3:27
  • \$\begingroup\$ Good point, @ThreePhaseEel. I didn't know if there were copyright (ot similar) issues. I'll look into it later, and edit appropriately :) \$\endgroup\$
    – bitsmack
    Feb 16, 2017 at 5:50
  • \$\begingroup\$ I have mentioned that I am using 48 pin package. Please edit your answer which talks about 32 pin.:-) \$\endgroup\$
    – AAI
    Feb 16, 2017 at 20:43
  • 1
    \$\begingroup\$ @AjeyaAnand - Sorry, I should have been more clear. There is no example for the 48-pin IC. But, the 48-pin IC is documented the same as one of the 32-pin ICs, and so those example circuits show that you can trust the Pin Mapping tables which show the exposed pad as the only grounding connection. I've edited the answer a bit for clarity... \$\endgroup\$
    – bitsmack
    Feb 21, 2017 at 4:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.