I2C slave address for given LTC2631 schematic support

Hi Kapil,

The LTC2631 is a pretty straightforward device. Have you verified signal integrity on the SDA/SCL signals? It's always a good idea to check:

• logic low level, which shouldn't be an issue with your 4.7k pullup resistors
• No ringing on falling edges
• "reasonable" rising edges such that all timing requirements are met (too much capacitance will slow down both edges, but the rising edge is usually affected more than falling.)
• And make sure you've got a low-impedance ground connection between the DAC and controller.

Scope shots and a photograph of your circuit would be a big help.

Also, I'm moving this to the precision DAC forum.

-Mark

Hey  mthoren_adi,
Thanks for your suggestion.
I found one issue with my hardware design, I forgot to isolate digital GND (Layer:2) and digital POWER (Layer:3) layers in my 4 layer PCB but as it's different layers and not connected to Analog GND and Power, will it affect TWI communication.

Attaching PCB layout of each layer.

1: Top plane: 

2: Digital GND plane

3: Digital Power Plane

4: Analog GND plane

Maybe layer2 and layer3 creating problems in I2C communication.

If the grounds are disconnected as you suggest, it won't work at all.

You're almost always better starting out with a single ground plane. This article is an excellent reference:

http://www.hottconsultants.com/pdf_files/june2001pcd_mixedsignal.pdf

But for your situation, because this is a fairly low-speed part, just tie the grounds together as well as you can and see if you can at least communicate with it.

-Mark

Yes, both digital GND and digital GND are connected through microcontroller PCB board. 

If it's still not working, then you'll need to probe what's happening on the I2C bus, preferably with an oscilloscope first to verify signal integrity and timing.

I check with the Arduino I2C scanner (playground.arduino.cc/.../) example and it's able to read salve address but when I'm using Nordic Semiconductor nrf52832 SOC it's not working with the similar I2C Scanner example(infocenter.nordicsemi.com/index.jsp

This could very well be a signal integrity issue. Your schematic shows 5V supply and pullup voltage, but it looks like the Nordic chip is 3.3V. Which Arduino are you using? Also note that if you're pulling up SDA/SCL to 5V, and the Nordic chip is powered on 3.3V, you may end up damaging the Nordic chip. There are various level shifters out there that can cleanly translate between different I2C bus voltages - a favorite is LTC4313, but there are other simpler options.

You'll want to reconcile the Vol and Vil, Vih of both devices. Again, getting a good scopeshot of what's going on on the I2C bus should help zero in on the problem.

-Mark

Hi
I used Arduino mega board and tested with both 3.3 as well as 5V supply to DAC, it's able to detect slave address in both cases.

Please find scopeshot of the SDA and SCL signals with the Nordic board.

SCL:

SDA:


  

At first glance your voltage levels look reasonable for a 3.3V bus. Is the LTC2631 powered by 3.3V or 5V in this situation? If 5V, a 3.3V logic level violates the LTC2631 VIH.

The next step would be to grab scope shots with SDA and SCL on the same screen, at a more appropriate vertical scale (like 2V/div, or 1V/div), so that you can clearly see timing relationships and logic levels.

Since you have one case that works (Arduino w/ 3.3V supply) and one case that doesn't work (Nordic), look for differences between the two - for example, if the LTC2631 is powered by 5V always, is the 3.3V supply slightly lower in the Nordic situation? If so, the Arduino may be marginally working.

-Mark