What is the operating ambient temperature and junction temperature of the 16Channel ADC part number :AD7490BCPZ
Yes, Suresh, you understand correctly. However, be aware that the device will probably function more near the limits of the specification at +85 deg than it does at +25 deg.
On page 6 of the AD7490 datasheet, the Absolute Maximum rating table, it was shown that the junction temperature is 150C and operating range is from -40C to +85C, typically ambient temperature is at 25C.
Operating temperature is mentioned as -40deg to 85deg, it is Ambient temperature of the component or junction temperature of the component. if it is ambient temperature of the component means, what is the operating junction temperature of the component.
AD7490 specification for ambient temperature (Ta) is at 25C.
What is the operating junction temperature?
Junction Temp would be around ~49C. That is the theta(ja) x power dissipation which is 108.2 C/W x 450mW.
The difference between junction temp and external temp(25C) is around 23.69C.
Please dont confuse me, if possible please provide correct answer.
This is going to be a very long answer, but I am trying to be very complete and very clear about a subject that my many years as an analog applications engineer has taught me that many, many people do not understand. Please do not consider me as "talking down" to you. I just want to be completely clear.
I think that the confusion here is a very common one. First of all, let's define some things. Ambient temperature means the temperature in which the device finds itself operating. This is the temperature within the enclosure where the part is used. The junction temperature means the temperature of the die itself. It is called "junction temperature' because, going back to bipolar technology, the die dissipates power in the PN junctions on the die. It is more appropriately called "die temperature" today.
ICs are "generally" specified for operation within what is called an ambient temperature range, which is -40°C to +85°C for the AD7490BCPZ. However, when manufacturers do their testing at these temperature extreme, they use fast test machines that test so quickly that the die does not have a chance to increase in temperature very much as would be the case after operating in your system for a while. There is usually no problem at cold temperatures because the die warms up with use. But if the operating ambient temperature is at the +85°C limit, the die temperature can increase above this limit in normal operation (due to self-heating) and the device may or may not function as you expect. This is not a problem with the AD7490, as we will see in a moment.
To determine how much the die temperature will increase, multiply the die power consumption by the junction to ambient thermal resistance (theta j-a). In the case of the AD7490, the theta j-a is shown on in the Absolute Maximum Ratings Table on data sheet page 6 to be 108.2°C/W for the LFCSP and 97.9°C/W for the TSSOP. Since the AD7490BCPZ is in the LFCSP, we use the 108.2°C/W, which must be multiplied by the power consumption in watts (not milliwats) to get the die temperature rise above ambient. Power requirements are shown on page 4 of the data sheet to be 12.5mW at 5V and a 20MHz clock. (Do NOT use the 450 mW shown in the Absolute Maximum Rating table as this is the package power capability and is NOT the actual die power consumption.) We find that 12.5mW = 0.0125W and the die temperature is 0.0125W x 108.2°C/W = 1.3525°C. So, with an ambient temperature of 85°C, the die temperature will only be higher than ambient temperature by a little more than one degree. This is because of the low power consumption of the AD7490.
So, the answer to your questions are:
Die temperature is less than 1.5°C above ambient temperature
Ambient temperature is whatever environment your design provides and must be between -40°C and +85°C.
Here is a little more information: ICs are usually completely specified at 25°C ONLY. the -40°C to 85°C range (or whatever the range is for a given product) is where the device is guaranteed to FUNCTION, but MAY or MAY NOT perform to published specifications, except for those specifications that are expressly called out to be over the entire operating temperature range. In the case of the AD7490, the heading of the electrical specifications table (page 3 of data sheet) and the timing specification table (page 5 of data sheet) both say "TA = TMIN to TMAX, unless otherwise noted". Note, however, that "Typical" numbers are almost universally meant to indicate what you can expect at 25°C ONLY and are NOT GUARANTEED, but are typical at 25°C.This means that, unless a given specification says otherwise, the specifications in the table are good over the entire -40°C and +85°C temperature range. I see no exceptions in either of these tables, indicating that all specifications are guaranteed over the entire temperature range.
Furthermore, the "Absolute Maximum Ratings" table give the limiting values beyond which there might result permanent, irreversible damage to the device. To put things such as Ambient Temperature and Thermal Resistance in this table, then, is not quite right, in my opinion. Such things more properly belong in an "Operating Ratings" table, which ADI does not use. I suppose their lack of an Operating Ratings table is why I suppose they put these things in the Abs Max table.
Thank you for your brief explanation,
1.As per your explanation the Temperature range (-40deg to 85deg) mentioned in the data sheet is ambient.
2.If the component is operated in ambient temperature of 85 deg the junction temperature will rise up to 86.325 deg only , at this junction temperature the device characteristics will not affected.
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