LPC11C24 CAN supply

[lpcware]

Content originally posted in LPCWare by munoa9 on Tue Jun 07 01:59:35 MST 2016
Hello,

I would like to clarify an issue about the CAN I/O supply pin VDD_CAN, I hope someone can help.
In the datasheet says this pin operates between 2.8 and 5.5 V, but they also say that it has to be connected to microcontroller's VDD pin which is 1.8 to 3.6V. This makes me confused. I don't see why these pins have different supply ranges if they should be connected together.

In order to find some examples, I have purchased a dev kit from Olimex and they connect VDD_CAN to 5V. I didn't have any problems so far, but I wonder if this design is robust.
https://www.olimex.com/Products/ARM/NXP/LPC-P11C24/

On the other hand, I see in the LPCXpresso LPC11C24 dev kit, that pin is connected to 3.3V.
http://www.embeddedartists.com/sites/default/files/docs/schematics/LPCXpressoLPC11C24revB.pdf

Does someone have more information about this pin? Is it fine to connect VDD to 3.3V and VDD_CAN to 5V?

Thank you in advance.

Best regards,
Jon

[alexandreturrel]

Hello,

You say that VDD_CAN should be connected to 5V but in your lpcexpresso board design (LPCXpresso LPC11C24 REV B) you connect it to 3.3V ! 

It is really confusing...

We have circuit to design and it is really important to us to know if VDD_CAN can be powered by 3.3V to gain space on PCB by removing 5V to 3.3V regulator and use only a single regulator. Thanks 

[lpcware]

bump

[lpcware]

Content originally posted in LPCWare by starblue on Tue Jun 07 11:21:03 MST 2016
Near the end of the LPC11Cxx data sheet is a diagram showing that VDD_CAN should be connected to 3V (or any voltage in the lower range I presume).

The integrated CAN transceiver is a TJA1051:
https://www.lpcware.com/content/forum/electrical-specification-canrxd-and-cantxd

[lpcware]

Content originally posted in LPCWare by munoa9 on Tue Jun 07 05:49:37 MST 2016
OK, thank you.

I see pins TXD_CAN and RXD_CAN of the microcontroller are 5V tolerant, so I guess there won't be any problems with that.

Jon

[lpcware]

Content originally posted in LPCWare by R2D2 on Tue Jun 07 04:18:21 MST 2016

---

Quote: munoa9
Then, VDD_CAN need to be connected to 3.3V or could be 5V?

---

LPC11C24 is obviously an 'old' chip and including a 5V transceiver. We always decided to use VDD_CAN = 3.3V because we use 3.3V transceiver networks (from TI). There are no informations about I/O level differences and problems with mixed transceiver networks (there shouldn't arise interoperability problems)...

See also: http://www.ti.com/lit/an/slla337/slla337.pdf

[lpcware]

Content originally posted in LPCWare by munoa9 on Tue Jun 07 03:44:23 MST 2016
Hi,

Thank you for the response.

I see in this thread that they discuss about CAN supply, but it looks like they mainly focus on VCC pin, referred to CAN transceiver. This is pretty clear to me that need to be 5V. In fact, in both dev kit mentioned above and datasheet state like that.

My concern is related to VDD_CAN. I have seen in some notes that VDD and VDD_CAN must be connected together, however, according to the datasheet, these pins have different operating voltage range (1.8 < VDD < 3.6 and 2.8 < VDD_CAN < 5.5). Also, some designs connect both pins to different supplies (VDD=3.3 and VDD_CAN=5) and seem to work well.

Names could be a bit confusing...

VDD           = Microcontroller supply
VDD_CAN  = CAN IO supply
VCC           = CAN transceiver supply

Let's say VDD is 3.3V and VCC is 5V. Then, VDD_CAN need to be connected to 3.3V or could be 5V? Right now I have a design working at VDD_CAN = 5V, but I am not sure if I am operating out of specifications ot I could have reliability problems. From the information I found, I don't see a clear answer.

Thank you.

Jon

[lpcware]

Content originally posted in LPCWare by R2D2 on Tue Jun 07 02:09:40 MST 2016
See:

https://www.lpcware.com/content/forum/lpc11c24-on-chip-can-bus-problem