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OPA551: DDPAK/TO-263 package question - pin 4?

David Sandler
Intellectual 1910 points
Part Number: OPA551

Hi,

I have some questions relative to OPA551 amplifier.

 

We are attempting to heat sink the device by connecting the DPAK package TAB to -15VDC (so tab connected to same potential as pin 4), and I stumbled on this note – see below.  In our present setup, the pin 4 (negative supply input) and TAB are both connected directly to negative rail.

                                                                                                     

Assuming that pin 4 is already connected to negative supply, is it acceptable to connect the TAB of the OPA551 to negative power supply rail without any loss in performance?  If not can the TABs of multiple OPA551 devices be connected to each-other (in this case electrically isolated from negative supply… basically a standalone copper pour used to heat sink multiple devices).  

 

Thanks,

David

 

 

  • 0
    TI__Guru* 93105 points
    Hi David,

    Pin 4 and the DDPAK tab of the OPA551 are internally connected, but as the Section 9.1, on datasheet Pg 17 states, "The tab of the DDPAK/TO-263 package is electrically connected to the negative supply (V–). However, this connection must not be used to carry current. For best thermal performance, solder the tab directly to the PCB copper area." Since pin 4 is being relied upon to carry the return curent, and not the tab, connecting them together to Vs- assures maximum performance. The caution makes sure that the user doesn't float pin 4 and use the tab only for the V- return. The tab connection to V- has some small resistance that gets shorted when it is connected directly to pin 4.

    The tabs of several DDPAK devices can be tied together to a separate copper pour, but because they are tied internally to the OPA551 V- potential they will reside at that potential anyway. I would simply connect all of the tabs and pin 4 connection to the same V- copper pour and that shorts that small tab connection resistance I mentioned.

    Regards, Thomas
    Precision Ampifiers Applicaitons Engineering