TLE2062 short circuit current

Hello Shihab,

Graph 20 in the TLE2026 data sheet is applicable to all the packages, but note that the T_A is specified as 25 C on the graph. The most important factor in a short circuit condition is that the junction temperature (Tj) of the output device doesn't exceed its maximum rating; that is providing the output can safely provide the current in that condition. The TLE2026 doesn't state the maximum Tj_MAX , but for nearly all TI devices and processes Tj_MAX is rated at 150 C. Then it comes down to the thermal resistance of the package being selected as to what Tj will be attained in the short-circuit condition.

The TLE2026 data sheet lists the thermal resistance, junction to case (Θja), as 97.1 °C/W for the D (SO-8) package, and 84.6 °C/W for the P (8 pin DIP) package. It doesn'y list the ceramic JG; so I looked on line for a number and found it  listed as 110 °C/W. Therefore, the JG package is the worst-case thermal condition.

The junction temperature is calculated from:

Tj = T_A + P_D Θja

P_D = P_{Quiesent_MAX} + P_{OUT_XSTR}

P_Quiesent = [(Vs+) +|Vs-|]  (I_{Quiescent_MAX}) = (30 V) ( 350 uA) = 10.5 mW

P_{OUT_XSTR} = V_{OUT_XSTR} (I_SC) = (15 V) (50 mA) = 750 mW     For a short to ground, 0 V,  and I_SC = 50 mA from the graph

P_D = 10.5 mW + 750 mW = 760.5 mW

If T_A = 25 °C, then:

Tj = 25 °C + (760.5 mW) (110 °C/W) = 108 °C

Increasing T_A to 85 °C:

Tj = 85°C + (760.5 mW) (110 °C/W) = 168.7 °C

Therefore, the maximum Tj would be exceeded. For the same conditions Tj calculates to 158.8 °C for the SO-8, and 149.3 °C for the 8-pin PDIP.

If the output is shorted to one of the supplies the condition is worse because the output transistor would have 30 V across it. It is not a good idea to leave the output shorted for any longer than necessary. Also, do not short more than one output at a time, or the device may be damaged.

For more information about the subject of operational amplifier power dissipation, see my recent Precision Hub blogs:

http://e2e.ti.com/blogs_/b/precisionhub/archive/2014/07/30/top-2-questions-on-op-amp-power-dissipation-part-1.aspx

http://e2e.ti.com/blogs_/b/precisionhub/archive/2014/08/08/top-2-questions-on-op-amp-power-dissipation-part-2.aspx

Regards, Thomas

PA - Linear Applications Engineering 

Thank you Thomas,

Can you tell me how the elapsed time is calculated. I am interested to understand how much time it will take the Tj to reach Tjmax=150degC. Because unlike normal operation, during short circuit a transient short circuit current will be flown and it will take sometime for the Tj to reach Tjmax. This will help me in defining the maximum circuit turn off time from the event of an output short circuit.

Regards,

Shihab.

Hello Shihab,

The TLE2062 thermal calculations I provded were for a steady-state Tj condition. The thermal path from ambient to the device junction involves a series of the thermal impedances - resistances and capacitances - having individual time constants. Initially, Tj may actually rise quickly during a short-circuit condition and then drop to a lower steady-state level once the dwell time has exceeded all the thermal time constants. The heat at that pont is being transferred to the ambient environment via conduction and radiation.  

I don't have any unique insight into the TLE2062 Short-circuit Output Current vs. time graph, but it appears to be straightforward in its intended meaning. The short-circuit is applied at t = 0 and measured as the time progresses to 60 seconds. The graph indicates that the short-circuit current is limited initially to about +/-60 mA, and then deceases to about +/-50 mA over the 60 seconds. Indeed the device is self heating during this time but the internal design is such that it limits the current to the +/-50 mA rather than increasing.

The TLE2062 is a high output current op amp. Amplifiers having that capability almost always have output current limiting to prevent them from being damaged should an output short-circuit occur.

Regards, Thomas

PA - Linear Applications Engineering