Direction of AD790A bias current

Question

Hi, 
 The AD790A bias current is 2.5(Typ)/5(Max) according to the data sheet. I suppose the AD790A bias current flows into the device as with any simple NPN differential input stage. Is that right? 
 Best regards, 
 Nikkee

FormerMember · Accepted Answer

Nikkee, 
 Unusual question. Why does it matter in your system? What are you doing? 
 IVR in spec table implies PNP input stage, so current flows out. 
 Harry

FormerMember · Answer

Nikkee, 
 Most data sheets for op amps, comparators, etc. for offset voltage, input bias current, etc. simply 
 have a number with no + or - sign. For offset voltage, 1 mV means +/-1 mV. For bias current, 
 IF there is only one input diff pair, the current will be in one direction, but is usually not speciifed, 
 so 1 uA could be + or -. 
 For rail to rail input op amps, such as the OP291, it can actually reverse, depending on which input 
 pair is working. See figure 12 on the OP291 data sheet. 
 Why is the direction inportant? Must be an unusual circuit.... 
 Harry

EZAdministrator · Answer

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