LM1085: Potentiometer getting fumed and burned as powering IC

Anurag Kumar20

Intellectual 810 points

Part Number: LM1085

I have followed referenced design as described in datasheet.

Only, difference I am using 100 Ohm resistor instead of 121 Ohm (Although, I believe it shouldn't affect it).

One 10uF electrolytic at input and another same value, but tantalum at output.

As Input I am providing 24V and as trying to move pot towards one end it starts burning.

I am not able to debug it, as I believe it may be because of high heat dissipation.

I have tried changing input Voltage, but still no luck.

over 5 years ago

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Anurag,

keep the connections of components as short as possible. Try the circuit shown in figure 14 of datasheet.

Kai

0 Anurag Kumar20 over 5 years ago in reply to kai klaas69

Intellectual 810 points

Hey Kai,

I tried that circuit, but still R2 is getting heated.
Any other reason??

0 kai klaas69 over 5 years ago in reply to Anurag Kumar20

Guru 140200 points

Hi Anurag,

everything connected to the right pins? Have you increased the caps at input and output? Have you mounted the protection diode?

Does it work when you replace the pot with a 1k resistor?

Can you take a fresh LM1085?

Kai

0 Ryan Eslinger over 5 years ago in reply to kai klaas69

TI__Guru 55940 points

Hi Anurag,

In addition to the questions raised by kai klaas69, could you also provide a multi channel scopeshot showing Vin, Vout, and Iout? This will help us better understand the relationship between these rails.

Could you also tell us about your capacitors for your application as these are not shown on your schematic?

Very Respectfully,
Ryan

0 Anurag Kumar20 over 5 years ago in reply to Ryan Eslinger

Intellectual 810 points

The issue seems to be resolved, after I tried a brand new IC and fresh component.

I believe, IC was damaged because of few components and in return was damaging resistors and pot.

Thanks for replying.
Anurag

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LM1085: Potentiometer getting fumed and burned as powering IC