SN74LVC1G07: Power Dissipation

Anurag Hosamani

Part Number: SN74LVC1G07
Other Parts Discussed in Thread: TXU0104, SN74AUP1G08, TXB0104, TMP1075, SN74LV244A

As per the standard power dissipation calculation using the Tj and Rtja, the values are more than the power consumption itself. In this case, how do I calculate/consider the power dissipation.

For example, as per datasheet Tj=150°C, Rtja=278°C/W and I have considered Ta=55°C. So using the formula Pd=(Tj-Ta)/Rtja gives Pd=341.73mW.

But the power consumption of this device itself is about 50uW. Can you clarify how can the dissipation be more than the consumption? Or Am I missing something?

I have this same question on similar buffers like SN74AUP1G08, SN74LV244A and on the TXB0104/TXU0104 Level translators and TMP1075 temperature sensors.

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 272340 points

Tj specifies the maximum allowed temperature. Your calculation shows that to reach that temperature, the device would need to dissipate 341 mW. In other words, you are allowed to dissipate up to 341 mW.

If the device actually dissipates less power, then the actual junction temperature will be lower. Which is a good thing.

0 Anurag Hosamani over 2 years ago in reply to Clemens Ladisch

Prodigy 60 points

Hi Clemens,

Thank you. I understand that this gives me the maximum allowed Pd.

But my question is how do I consider the Pd since the calculation is giving me more Pd than the actual consumption.

Let me clarify my question, I am calculating the Pd for the thermal analysis of the board. Since, the calculation is giving the Pd which is more than the consumption, in this case what value should I consider/take for my thermal analysis.

This same question applies to other devices that I have mentioned in the first post.

0 Clemens Ladisch over 2 years ago in reply to Anurag Hosamani

Guru 272340 points

Whether you call it "consumption" or "dissipation" does not matter.

What matters is that one is the maximum allowed value, and the other is the actual value. You always want the actual value. (But it must never exceed the maximum.)

0 Anurag Hosamani over 2 years ago in reply to Clemens Ladisch

Prodigy 60 points

Let's say the consumption and dissipation does not matter.

Since it is a low power device, how do you calculate the dissipation in this case? I do not have the assembled PCB to check it physically, and I am not sure how to calculate the actual value.

0 Clemens Ladisch over 2 years ago in reply to Anurag Hosamani

Guru 272340 points

I_CC is the idle power consumption. It does not include the power dissipated in the output transistors when a current flows through the output pin into or out of the load.

See [FAQ] How do I Calculate Power Consumption or Current Consumption for my CMOS Logic Device?

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SN74LVC1G07: Power Dissipation