hi,
are there 2 chips inside iso7741? if yes, how can I estimate junction temperature for both chips?
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Hello,
Thank you for your question.
Yes, there are 2 dies inside the ISO7741 and other TI digital isolators as well.
The max junction temperature is listed in the datasheet as shown below (section 7.1 in datasheet):
The Absolute Maximum Ratings listed out in table 7.1 list the conditions that must not be exceeded for device reliability. During device operation, we recommend to limit the device use such that junction temperature doesn't exceed absolute maximum limit.
If you mean, how to estimate the junction temperature for the whole ISO7741 device, you can use the equation found under the safety limiting values table in the datasheet (picture below):
As shown in the picture above, the junction temperature equation is given. The power can be calculated by using the current and supply voltage from the Supply Current Characteristics table in the datasheet that corresponds to your application.
Regards,
Aaditya Vittal
Hello,
Thank you for your reply.
No, there is one thermal resistivity value. Since the thermal resistance from the both dies to air is the same, there is one thermal resistance parameter in the datasheet. In order to find power of each die, use ICC1 and ICC2 (found on supply current characteristics table on datasheet) which depends on your application. Please refer to the equations below:
side 1 die: P1 = VCC1 x ICC1
side 2 die: P2 = VCC2 x ICC2
To find the junction temperature for the whole device (both dies): Ptotal = P1 + P2
The power, ambient temperature(Ta, found on section 7.3 of datasheet) and thermal impedance (R_Theta_ja, found on section 7.4 of datasheet) can be used to calculate the junction temperature: Tj = Ta + P*R_Theta_ja.
Regards,
Aaditya Vittal
Hello,
Both dies are in the same packaging and have the same thermal resistance (R_Theta_ja). Therefore, the junction temperature shown in the datasheet represents the entire isolator device (both dies). This means that the power of side 1 (die 1) and power of side 2 (die 2) can be added together and used as described from my previous post.
Regards,
Aaditya Vittal