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Hello,
A few questions regarding LM3886. Assume ambient temperature of 60'C.
1) Assume a LM3886 operating at full power output at ambient temperature 60'C. If I want to measure the highest temperature anywhere on the power amp,
where is the best place on or surrounding the power amp to attach an NTC thermocouple ? Would I attach
the thermocouple in the middle of the package itself, output pin 3, or other?
2) The datasheet mentions that the spike protection activates at the internal temperature of 165'C, until releasing again at 155'C.
Using a thermocouple, I am measuring 124'C across the power amp IC package, and am noticing it activating spike protection about every 20 seconds.
Why does a reading of 124'C across the package trigger spike? Should it not be closer to 165'C? Where should I measure temperature?
3) I noticed there are two variants of the LM3866: With isolated, and non-isolated packages. Is there a difference between these two packages in
terms of junction-to-case thermal resistance? Using same thermal paste, can one expect a difference between heat transfer to heatsink for
isolated and non-isolated packages? Where can I find this information? The datasheet is not clear on the distinction.
4) What is the correlation between case temperature and product lifespan in hours. ie: How many hours can LM3886 last if measuring constant
case temperature of 150'C? 125'C? 85'C? 60'C etc..?
Hi Chipset
We can test the case temperature at the central of the package, then to use thermal resistance and power dissipation value to calculate the junction temperature. The protection temperature 165C/155C, are all refer to the junction temperature.
The isolated and non-isolated version doesn't have different thermal performance, they would have same temperature under the same working conditions.
4) What is the correlation between case temperature and product lifespan in hours. ie: How many hours can LM3886 last if measuring constant
case temperature of 150'C? 125'C? 85'C? 60'C etc..?
On Ti.com, the Quality&reliability tab, we can find out the MTBF and FIT data about LM3886 under 55C, as below picture.
You can use the Tool in the below link to check other temperature.
https://www.ti.com/support-quality/reliability/temperature-change-FIT.html
