# heat generation by semiconductors

I am trying to do a power analysis of an IC. It is an I2C isolator. Now, there are 2 I2C buses (hence bidirectional). I want to analyse the effects of its working on the temperature. The ambient temp is 25Degrees celcius.

Now, I am connecting it between an MCU and a temp sensor (for eg).

The current rating is as shown below -

Now, this IC is being run at 3.3V Vcc.The Iol1 and Iol2 are the current that is supplied from the source .

MCU <---> I2C1 <----> Isolator <----> I2C2 <----> Sensor.

So, the current sourced by the Iol1/2 as 3.5mAmps is nothing but the current sourced/sunk by the MCU/sensor. Now, suppose the data is coming via the SDA line from the MCU. Then probably the MCU sends a very low current. The I2C ASIC then sends a max of 3.5mAmps to the sensor, right ?

Now, the logic high is 3.3, which implies Power = 3.3*0.0035 =11mW. This is for the data lines. Likewise for clock. So merely doubling it would give me the power consumption of the said IC.

But, then a small current is needed for the IC to work. Provide power to the logic inside. How much is that ? Is it not the quiscent current ? That info is not given.

Now, I want to calculate the temperature aspect. Now, Vout =3.3 and I = 3.5mAmps.

Power = 11mW per pin (SDA). Power total = 22mW (power and clock).

Theta-ja = 117C/W.

Temperature = 0.022*117 = 2.577 Degrees C.

The temp of the IC = 25(ambient) + 2.5 = approx 27.5 Degrees Celcius.

Is my analysis accurate ?

• What exactly are you trying to do here? You seem to have skipped over the I2C pull-up resistors entirely. Which devices are you calculating power consumption for? Do you have a schematic of the actual system you want to analyze? – user2943160 Jul 13 '16 at 4:08
• I am trying to see the impact on temperature due to the working of this IC. Only this IC. There might be passives that are around. I merely want to analyse this IC. – Board-Man Jul 13 '16 at 4:10
• Did you see section 7.5 yet? – Ignacio Vazquez-Abrams Jul 13 '16 at 4:29
• It gives almost the same value of approx 3.5mAmps. But my doubt pertains more to the impact on temperature. – Board-Man Jul 13 '16 at 4:36