Thermal area required for LT3083

The application is to use LT3083 as constant current source of 1A. If I have 1 oz 4 layer PCB, which thermal considerations I need to take care. In terms of Copper area, thermal vias etc...

Can you please provide the calculations to get best optimum PCB area required for LT3083 as 1A constant current source. The input voltage will constant 5 V.

  • 0
    •  Analog Employees 
    on Aug 19, 2020 3:51 PM 6 months ago

    What is the voltage of your load?  The power dissipation of your LT3083 depends on the IN to OUT voltage.

    Your pcb may be 1 ounce starting copper thickness on all layers, but after plating the pcb may be 1 ounce inner copper and 2 ounce finished outer copper - I would double-check to make sure.  

    The Thermal Considerations sections for the LT308X datasheets publish hand-measured thermal resistances from junction to ambient for the different package options and different amounts of top-side copper.  If you are using a 2-layer pcb, use the thermal resistances from the LT3080 datasheet.  If you are using a 4-layer pcb, use the thermal resistances from the LT3083 datasheet.  I show the Thermal Considerations datasheet sections for both the LT3080 and LT3083 in the images below, with the 2-layer and 4-layer text highlighted.

    The LT308X demonstration circuits - DC1585A in the case of the LT3083 - are good resources for the thermal design of pcbs.  Within the LT308X lineup there are demonstration circuits for different package options.

    LT3080 DS p14 comp_1.png

    LT3083 DS p15 comp_1.png

  • Hi all,


    We are planning to design constant current source with LT3083.


    Vin: 5 V

    Iout (constant current)= 1A………R1=1Ohm

    Pout = (Vin-Vout) * Iout

    Pout= (5V – 1V) * 1A

    Pout = 4 W


    è I need external heat sink size calculations for LT3083 with T package (TO220) to dissipate 4 W of power.


    Awaiting for your reply please…….

    LT3083 as constant current source