LTC4317 Communications to Honeywell pressure transducer IC (LTC4317IDHC#PBF)

Hi Trevor, 

The captures above don't have voltage levels, but I do see the RC constant changing between an ACK response and the NACK.  

The LTC4317 is not a bus buffer; It is a pass switch only (with the exception when its actively doing a translation). The point to note is that the electrical characteristics of the bus will change when each LTC4317 is enabled or inserted into the I2C bus. That’s because with each LTC4317 there is a 10kΩ pull-up on each OUT segment of the bus (per the schematics above). The additional 10kΩ resistors will need to be driven by the I2C devices and may inadvertently be making a pretty stiff pull-up.

My first suggestion would be to check the low level on the bus at the Honeywell device, and see if logic low may be too high for the device to detect the signal. 

Regards,

Jason 

Jason,

Thanks so much for your prompt reply.  The Honeywell sensor is the HSCMAND060PA3A3.  It looks like the high and low logic levels are 80% and 20% of the supply voltage respectively(3.3V).  

Digital Operating Specifications pg.10

sensing.honeywell.com/index.php

All the scope graphs are 1V/div, 5ms/div.  Do you think it would be worthwhile to increase the value of the pullup resistors?  Do you have any idea what that short first data pulse is in the graph labeled COMS to Honeywell through I2C translator send 0x5F?

Thanks,

Trevor

Jason,

Thanks so much for your prompt reply.  The Honeywell sensor is the HSCMAND060PA3A3.  It looks like the high and low logic levels are 80% and 20% of the supply voltage respectively(3.3V).  

Digital Operating Specifications pg.10

sensing.honeywell.com/index.php

All the scope graphs are 1V/div, 5ms/div.  Do you think it would be worthwhile to increase the value of the pullup resistors?  Do you have any idea what that short first data pulse is in the graph labeled COMS to Honeywell through I2C translator send 0x5F?

Thanks,

Trevor