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LM1085: Maximum Vin for LM1085ISX-3.3?

RAGHUL N M
Intellectual 490 points
Part Number: LM1085

Hi,

We are using LM1085ISX-3.3 voltage regulator for stepping down 24 V dc to 3.3 V dc. 

Even for a load current of 200mA the IC is extremely heating. Is that due to the high drop out voltage (24 - 3.3 =  20.7 V) at the IC?

In the datasheet it is mentioned as "The LM1085 is a regulator with a maximum dropout of 1.5 V at 3 A of load current." 

Can we increase the dropout voltage by reducing the load current?

If this LM1085ISX-3.3 won't work in this case, could you please suggest any other IC for this case.

Thank You for your time. 

  • 0
    TI__Mastermind 23361 points

    Hi Raghul, 

    With a 200mA load current and 20.7V voltage drop from Vin to Vout, the IC is burning more than 4 watts. The KTT package has a RThetaJA value of 40C/W, and the temperature rise could be as high as 160C. If possible, consider using the NDE package, which has a much better RthetaJA of 23C/W; with the same amount of power, the temperature rise could be reduced by 50%. Will you be able to consider the NDE package of this device?

    The dropout value of an LDO is primarily determined by the on-resistance pass-FET device and it's proportional to the load current. 

    Regards, 
    Jason Song