LM2903B-Q1: bias/offset current

Hi Sherry,

the input bias current is always flowing out of the LM2903 because the input stage consists of PNP transistors. And it will be less than 50nA. So the maximum voltage drop across the parallel circuit of R9049 and R9045 will be

90909R x 50nA = 4.5mV

And there's also a leakage current flowing through the zener diode D9010 which will eventually lower the 4.5mV voltage drop a bit.

The input offset current is no additional current but is the imbalance of the both input bias currents. As example, the input bias currents can be -3.5nA and -3.0nA or -3.5nA and -4.0nA, typically.

Keep in mind, that the leakage current through the zener current may heavily increase at voltages even below the 4.3V threshold voltage. It is typical for low voltage zener diodes that their U / I knee is not sharp.

Kai

Hi kai,

Thanks for your reply!

I am a little confused about the definition of input bias current. In my understanding input bias current =1/2((Iin+)+(Iin-)), and input offset current =(Iin+)-(Iin-). Therefore according to bias current/-50nA and offset current/25nA, (In+)=-37.5nA, (In-)=-72.5nA. You mean (In+)=-50nA, (In-)=-50nA according to our datasheet spec?

Thanks & Best Regards,

Sherry