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LM337L: FB resistance

Hirotaka Matsumoto
Guru 27585 points
Part Number: LM337L

Hi all

Would you mind if we ask LM337L?

Our customer tries to use follow conditions;
-120ohm / 560ohm Vout=-7V
-1.2kohm / 5.6kohm Vout=-7V

On the datasheet P1, the resistance value is R1=240ohm and R2=ADJ.
So, in case of kohm unit, if there is some effect, could you let us know?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Guru 55940 points

    Hi Hirotaka,

    The output voltage for a linear regulator will be equal to the internal reference gained by the resistor divider ratio.  As such, as long as the ratio between R1 and R2 remains consistent, you can increase or decrease the total resistance in the divider (R1 + R2) to change the divider current and therefore the overall efficiency of the application. 

    It is important to recognize that the adjustment pin current will impact the output voltage as well.  The full equation for calculating Vout for LM337L is:

    Vout = Vref x (1 + (R2 / R1)) - Iadj x R2

    Since Iadj is 50 uA (typ), the equation is can be simplified when using smaller resistors as  (Iadj x R2) becomes negligible.  As long as you can accept the change in voltage caused by (Iadj x R2), there is no issue with increasing the resistor sizes.

    Very Respectfully,

    Ryan