Lt8491 I2C not connecting issue

Hi cwae ,

If you see the I2C traffic with a logic analyzer, then the bus is enabled.

Check these two things first:

1. SDA goes to SDA, SCL goes to SCL (check from datasheets, not from schematics symbols).

2. SDA and SCL lines have pull-up resistors (in range of 1k..10k).

Cheers, heke

Hi, Heke 

I have double checked that the locations are right and then I used a logic analyzer to check the bus. I added a secondary slave to the bus, and I am able to see it but not able to see the LT8491.

I have gotten rid of all the components except for the required ones in the image below based on the block diagram. Would you have any thoughts on why I still can't see the chip?

Hi cwae ,

With the shown CA pin connection, the chip should ACK on 0x29H address. Wondering if you could capture the I2C waveform while addressing 0x29 << 1?

In the stripped down circuit you should not leave RT and MODE pins floating. Also VIN should probably be properly connected to a supply (or alternatively the EXTVCC) as some internal supplies are powered from it (also it may be that then the LDO33 pin undervoltage lock-out may disable I2C).

Kindly share your observations.

Cheers, heke

So, I tied mode to GND and RT to a 287K resistor to gnd. Then supplied voltage through VIN and looked at the output of LDO33. I tried with 2 different chips and got 6.4V and 1.4V as an output. Which is very weird. As for the waveform, I can see that there is no acknowledgement. The orange is clk and the red is data

0x29 << 1

0x29

Hi cwae ,

Cool. That LDO33 output is indeed weird. As it is an output of an LDO, it is mandatory to have a capacitor from the pin to ground, as otherwise the regulator is unstable. (if any chance, measure the LDO33 pin voltage using an oscilloscope. That may show if there is a stability issue). Place a  4.7uF or larger capacitor from the LDO33 to ground. Does it help?

Cheers, heke