ADA4896, ADA4897 input bias current direction.

Hello,

In the datasheet of ADA4896/ADA4897 bias current is specified as -11uA (typ.). What "-" sign signifies? At first I assumed it signifies the direction of current flow as in "-" signifies current flowing out of the input pin and "+" signifies current flowing into the input pin. Can you please confirm that?

When I try to simulate bias current, the bias current flows into the input pin which is not what I expected. Could you also clarify that?

Thanks!

  • This is a unique one.  For decades, the input bias current on a data sheet was stated without a sign,

    and we knew if it was an NPN input, the current flowed into the part, and if it was a PNP input, it flowed

    out of the part.  But the ADA4896 data sheet must have been done by a new grad that didn't know the convention

    of leaving the sign off.  The ADA4896 really does have a PNP front end.  The original spice model used

    NPNs and the beta was negative.   This did not work for some spice simulators.  I just looked at the spice model,

    and the front end doesn't use any transistors at all.  Fairly complex, I don't have time to reverse engineer,

    but the short answer to your posting is the spice model is bad.

    Harry

  • Thank you for your response.

    As you said ada4896 does have pnp input as it's shown in figure.44 in the datasheet. :D