Arduino Due I2C with Levelshifter doesn't work

Official Hardware Mega Due
1

Hi Folks,

I managed to drive an LTC6904 (Serial Port Programmable Oscillator) with an Arduino Due when connected directly to the SDA (Pin20) and SCL (Pin21). Everything worked smoothly.

As I need to integrate it into 5V Logic I placed a level shifter in between as shown in the following diagram

LTC6904_WithLevelShifter
LTC6904_WithLevelShifter2668×1350 144 KB

Result: Nothing works any more. I unsoldered the 1k5 pullup registers on the Due and replaced them with 4k7 restistor as shown in the diagram. I tried also with/without the pull ups on the 5V side.

Has anybody got an idea what's wrong?
Any ideas welcome

2

Have you got an oscilloscope? Are the grounds connected. Data sheet for level shifter

3

You probably need to use the open drain type of level shifter.

But why a level shifter in the first place, I thought the LTC6904 was good down to 2.7V ?

Do other 3.3V level sensors or boadrs work on the changed I2C on the DUE ?

4

I need to do it with 5V supply because there's a existing and complex logic board driven with 5Volts

5

Yes, I've got an oscilloscope and Yes, the grounds are connected. Here is more info about the LevelShifter I use:
datasheet.TXB0108.pdf (294.9 KB)

TXB0108Image
TXB0108Image1572×669 129 KB

6

This works with I2C:

7

Oh, you think I've got the wrong level shifter for I2C. Hmm might be the cause

8

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