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OPA2211A output short circuit and thermal performance

Guru 20090 points

Replies: 3

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Hello,

I have some questions aboout opa2211A.
Our customer use OPA2211AIDDA.

(1)thermal performance
Please let me know calculation of Tj.
I understood that Tj=Ta+(Pd*θja).
But this device has θjp.
Please let me know calculation of TJ by θjp.

And should we use which thermal resistance value ?
θJa or θJp?


(2)Output Short-Circuit of ABSOLUTE MAXIMUM RATINGS
I can see the Output Shout-Circuit rating as "Continuous" in the datasheet.
I think that we can connect OUTpin to V-pin directly, we can connect OUTpin to V+pin directly.
But it is an opamp only in the dual package.

Is my understanding correct?

Best Regards,
Ryuji Asaka

  • Ryuji,

    OPA2211AIDDA has power pad for better power dissipation, thus the thermal resistance,θjp, is given between the junction and power pad instead of junction to ambient, θja. Assuming that you will solder the power pad to PCB (minimizing θpb), in order to calculate a junction temperature,Tj, you also need to know the thermal resistance between your PCB (heat sink) and ambient, θba. Therefore, the full Tj equation is as follow:

    Tj=Ta+[Pd*(θjp+θpb+θba)]  where

    Ta - ambient temperature
    Pd - power dissipation in the package

    θjp - junction to pad thermal resistance
    θpb - pad to board thermal resistance (minimized by soldering thermal pad to PCB, (θpb=~0)
    θba - board to ambient thermal resistance


    If you do not solder the thermal pad to the PCB, use θja for your worst case calculation (based on high-k board).


    OPA2211 short-circuit function is only for protection of the IC from damage in case of accidental shorting of the output and thus shoud never be used intentionally - prolong exposure of IC to short-circuit condition will lead to degradation of IC performance and shortening life of the product.

     

    OPA211 (single) may be left in short-circuit condition for prolong time without damaging the part BUT in case of the dual version ONLY one channel (at any given time) is allowed in short-circuit condition - see note(2) above - placing both channels of the dual package in short-circuit condition would result in doubling power dissipation in the package, which may lead to the violation of the absolute maximum junction temperature, Tj_max=200C (see table above). 

    Marek Lis, MGTS
    Sr Application Engineer
    Precision Analog - TI Tucson

  • Guru 20090 points

    In reply to Marek Lis:

    Hello Marek san,
     
    Thank you for the information.
    By the way, how do I get the θba ?
    If we can't get θba , should we calculate by θja for worst case?
     
    Best Regards,
    Ryuji Asaka
  • In reply to Ryuji:

    Ryuji,

    The board to ambient thermal resistance, θba, depends on the physical PCB board layout of the (V-) plane connected to the thermal pad of OPA2211 package; for that reason, you should ask the board manufacturer to help you to calculate its value based on the actual size and shape of the (V-) metal layer.  In case you cannot obtain θba, a prudent (conservative) approach would be, in fact, to use θja number for your worst case thermal analysis. 

     

    Marek Lis, MGTS
    Sr Application Engineer
    Precision Analog - TI Tucson

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