How to Interface 4 TMP112 devices on a single bus?

Hi Vijay,

Please see the comment below.

1. How ADD0 pin works when 4 devices are connected onto single bus, how ADD0 pin differentiates SCL and SDA lines when it is connected to them?

Reply -> TMP112 is capable of configuring the address up to 4 addresses, but it has a base address of 0x48. The lower two bits (bit1 and bit0) can be programmed via ADD0 pin as shown in attached picture, so you can attach four TMP112 devices in one single master of I2C with different unique address. When the device is powered up, the address is determined based on the ADD0 pin connect to GND, VDD, SDA or SCL then one of the address is chosen.

When the ADD0 connects to SCL or SDA lines, TMP112 compares the inputs of ADD0 with SDA and SCL to determine if it’s shorted together. Once it’s completed, it sets the address internally based on the result of the comparison.

I reviewed your schematic. It is a good practice to organize your schematic so that it would be easier to debug whenever the circuit isn’t working. I provided example diagram. I realized that you have 8 TMP112s in your schematic; therefore, you might need a second master in order to communicate the other 4 devices since TMP112 can only configured up to 4 devices. It looks like that you wanted to monitor the ALERT pin through one of the GPIO pin; there will be a delay whenever you want to read the ALERT pin because you have to switch from part-to-part. Overall, I don’t see any problem.

Just curious, what kind of application you are planning to use with 8 TMP112s?

2. Is there any dimension constraints for resistor and capacitor used in the schematic?

Reply -> No, you can use any dimension of the resistor or capacitor as long as it meets desired value.

Aaron