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LT1009: ADJ Pin

Ray Vincent Aranzaso
Genius 16295 points
Part Number: LT1009

Hi,

Good Day.

The LT1009 data sheet says: "A third terminal (ADJ) allows the reference voltage to be adjusted ±5% to eliminate system errors."

I cannot find any documentation or technical paper that explains how to use the ADJ (trim) pin. I see that you can tie a variable resistor to the ADJ pin but that does not explain how the ADJ pin works and what the resistance calculations are. How large of a resistor is needed? Is it tied to the ground or to the positive rail?

Please advise. Thank you very much.

Best Regards,

Ray Vincent

  • 0
    TI__Prodigy 170 points

    Hello Ray, 

    I'm going to discuss this internally so that I can give you an accurate answer. I'll reach out again within 24 hours to help you with this.

    Sincerely,

    Alex

  • 0
    TI__Prodigy 170 points

    Hello again Ray,

    You are correct about the ADJ pin being connected to the variable pin of a variable resistor.

    We recommend that this variable resistor has a total resistance from anode to cathode pins of 10kOhms. For the pins of the variable resistor, one should be connected to the anode, the other should be connected to the cathode, and the variable pin of the variable resistor should be connected to the ADJ pin. While we don't have any specific documentation on how the specific resistance values impact the V_KA voltage, I hope this PSpice model can help you understand the relationship.

    This model was created from the internal schematic in the datasheet (shown below), where we simply assumed I_B for each BJT to be 0 for simplicity. Because Q11 and Q13 are diode connected we simply replaced them with voltage sources of 0.6V (for explanation).

     

    The TL1009 has an initial tolerance of 0.2%, and the ADJ pin can be used to ensure that V_KA is at exactly 2.5V, or could be used to increase or decrease this output by 5%.

    I hope this helps you understand how to use this component. If you need me to clarify anything please let me know.

    Best,

    Alex