CC2540 layout

John WALKER2

Other Parts Discussed in Thread: CC2540

Hi, hand built 3 transmitters using CC2540. Three because I thought I had a short from pin 40 to pin 41, the ground pad on the ic base. It was only when I checked on an unsoldered CC2540 that pin 40 is connected to the ground plane. On all the application schematics there is nothing to show that pin 40 is connected to pin 41. On the schematic pin 40 is shown with a 1uf decoupler to ground. Can anyone confirm that this is the case i.e. that pin 40 is connected to pin 41 on the die and if so why the 1uf decoupler. Also - T.I. an explanation on the schematic would be helpful to save hours of frustration and wasted time.

over 12 years ago

0 John WALKER2 over 12 years ago

Intellectual 265 points

Problem solved. Unfortunately I have laid out the symbol mirror image, hence my confusion with pin numbers. It would. in my opinion, to print bottom view using larger font size and in BOLD. It would also be helpful to put top view and bottom view alongside each other to avoid any confusion; useful when you are working 'blind' without a sample. Luckily, however, still in the prototyping stage.

0 Fredrik K over 12 years ago

TI__Guru** 106705 points

Hi John,

In all our schematics pin 40 is labeled "DCOUPL", I am not sure why you would think this is the same as ground. If you do want to know what I certain pin does, I recommend refering to the datasheet. The table on page 17 says this about the DCOUPL pin: "1.8-V digital power-supply decoupling. Do not use for supplying external circuits."

In other words, pin 40 is connected to the output of the internal 1.8V LDO used to power the internal digital circuitry. It is connected to an external pin because it needs a big decoupling cap.

Cheers,

Fredrik

0 John WALKER2 over 12 years ago in reply to Fredrik K

Intellectual 265 points

Hi Fredrik, thanks for the reply. The confusion arose because I laid out the chip in mirror image. Luckily still prototyping so no great financial consideration. I did reply to my original thread along the same lines. I think it would be helpful if the data sheet displayed the top view of the component alongside the bottom view. Also to make the font size larger for 'bottom view' and in bold

0 Fredrik K over 12 years ago in reply to John WALKER2

TI__Guru** 106705 points

Hi John,

Your second post was not shown before now, strange.

Good to hear that you solved your problem! I guess wether one should display both top view and bottom view, or one of those only is a matter of opinion. Personally I prefer top view only to avoid confusion :-)

If you have any other questions, do not hesitate to ask!

Cheers,

Fredrik

0 patrick nefos over 11 years ago in reply to Fredrik K

Expert 1850 points

Hi Fredrik,

I also have a layout/schematic question.

Inside swrr071b.zip, the CC2540Keyfob_SCHEMATIC.pdf, What is Pin2 of the debug header connected to?

Otherwise, the schematic makes sense to me.

Thanks,

Patrick

0 John WALKER2 over 11 years ago in reply to patrick nefos

Intellectual 265 points

Hi Patrick, pin 2 is connected to the Vcc (battery) of the CC2540. Look at the top right hand corner of the schematic above C311 and you'll see the Vcc symbol.

John

0 patrick nefos over 11 years ago in reply to John WALKER2

Expert 1850 points

Thanks John,

Sorry I was misleading. I mean PIN2 on the 10 pin Debug header.

That symbol does not have VCC, but perhaps an omission.

Patrick

0 Fredrik K over 11 years ago in reply to patrick nefos

TI__Guru** 106705 points

Hi Patrick,

It is Vcc, the text is just missing from the symbol.

Cheers,
Fredrik

0 John WALKER2 over 11 years ago in reply to patrick nefos

Intellectual 265 points

Hi Patrick, pin 2 on the SoC/debug shows the peculiar symbol, a bit like pi which is the CC2540 Vcc. Look at the schematic and you will see the same symbol above C311 clearly marked Vcc.

John

0 patrick nefos over 11 years ago in reply to John WALKER2

Expert 1850 points

Thanks John, this is clear now.

Patrick

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CC2540 layout