TMP175: TMP175 : I2C NACK issue when sending the address

Hi Othmane,

Welcome to the E2E forums.

I see the NACK you are receiving, it looks to me that your addressing is correct based on your description. To start troubleshooting, can you verify the TMP175 is receiving power, and share the relevant part of your schematic? 

Also, i see several instances where the SCL goes low and SDA changes at what appears to be the same time, this is shown as t_(HDDAT) on the TMP175 timing diagram. 

Can you zoom into one of these edges? The TMP175 has a minimum t_(HDDAT) of 4ns, the device can have communication issues if that timing is violated. 

Best Regards,
Brandon Fisher

hi Brandon,

thank you for your answer, I have already checked:
- THDDAT: 360 ns Falling edge
- TSUDAT: 5us
- Different timing requirements
- different addresses
- The TMP175 is powered (3.3V)
- I2C speed is at 100kHz (in Fast Mode)

THDDAT :                                                                                   TSUDAT :                                                                 

Schematic : ( 5k pullup SCL & SDA  next to master ) :

best regards

othmane

Hi Othmane,

Your timing looks good to me. It does look like you are tying the address pin to ground via a 100kOhm resistor. I know this method works on some of our other temp sensors to register a float, but it may not be reliable since this isn't the intended setup of that pin. I also haven't done it myself with the TMP175 before. 

I see that you tried different addresses, does that include the 0x48 (A0-A2 -> GND) address? If possible, I would also suggest either removing or shorting R62 to see if the address detection on that pin is the cause.

Best Regards,
Brandon Fisher

Hi Brandon,

Indeed I have already tried to put A0 to gnd directly, to Vcc and floating. I removed the R62 to get floating.

I also change IC to make sure it is not an IC trouble

Best regards

Othmane

Hi Othmane,

Do you have other devices on the bus that are communicating successfully? Also, are you taking these logic analyzer captures at the pins of the TMP175?

Based on what you've checked so far, the most likely culprit is that something is disconnected or shorted somewhere in the layout or the rest of the schematic. If you see the SDA and SCL signals at the device pins then this is less likely. 

Best Regards,
Brandon Fisher

Hi Brandon,

I already have other devices on the I2C bus that are communicating successfully and the signals were captured at the SDA and SCL pins of Tmp175.

Best regards,

Othmane