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LT1790 Vout-2.5V

Dear support team, 

I have a few questions regarding LT1790 to output -2.5V. 

  1. In figure 7, R1 is set to 10k for a 3V input. Must we adjust resistor value for higher input voltages (5V input for example)? 
  2. In figure 7 considering RL=20k, Vee=-5V, Vin = 5V. How can we estimate the maximum load on -2.5V output? In LTspice simulation loading -2.5V with a 20k resistor drops -2.5V output ref to -2.14V  

Thank you. 


  • Hi Benoit,

    1. Yes. The purpose of the resistor is to limit the current flowing in, but still biasing some other parts of the system. If you increase the Voltage input and still use 10k resistor, this will cause the pnp transistor from the output pin to turn on.
    2. The equation given seems to be incomplete. The complete equation should be: R=(VEE-Vout)/(125uA+Iout)