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LM385-ADJ model problems

Prodigy 10 points

Replies: 1

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I was using the supplied model and noticed a strange operation.

 

The LM385-ADJ data sheet (National Semiconductor DS005250) page 2 defines the output voltage equation as:

Vout = 1.24V*(R3/R2 + 1) where R2 connects from output pin (+) to FB pin and R3 connects from FB pin to pin (-).

The schematic diagram on page 9 indicates the reference is from the output pin (+) and FB pin which corresponds to the equation.

 

When simulating with the model I used R1=249K, R2=249K and R3=750K to get 5V out. The simulation did not work.

If I reverse the resistors R2 and R3, then the simulation works correctly.

It appears that the model is incorrectly using a reference between the FB pin and pin (-) which is opposite to the datasheet and is similar to the TL431A.

 

Could you verify the operation and advise if this model is correct.

Larry

1 Reply

  • Hi Larry,

    I was able to replicate what you are seeing and we are looking into this. We will get back shortly.

    Thanks,

    Nikhil Gupta | EDA Development (Machine Learning)                                                                                                                                                    

     

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