Question regarding ADA4899-1

Question

I have a customer with the following question: 
 
 (1) I am using the SOIC package, which has two –Vs pins. Is it best connect both 4 and 5, or just pin 5 (see figure and data sheet excerpt below)?

(2) Input bias currents can be reduced from -6uA to -0.1uA by tying the ~DISABLE pin to the +5V rail (at the expense of increased wide band noise). My question is does this have any positive or negative affect on the Input Offset current Ios vs temperature specification?, which is specified at 3nA/C (typical)? 
 
 “ ... The SOIC is slightly different with the intent of both isolating the inputs 
 from the supply pins and giving the user the option of using the 
 ADA4899-1 in a standard SOIC board layout with little or no 
 
 modification. Taking the unused Pin 5 and making it a second 
 
 negative supply pin allows for both an input isolated layout and 
 a traditional layout to be supported.”

JinoL · Accepted Answer

Hi Richard, 
 Good Day! 
 1. If you noticed most of our SOIC package High Speed Amplifiers pin outs, pin 5 was allocated as NC or No Connect. Take ADA4857-1 as an example. 
 
 The difference between ADA4899-1 and other HS amplifiers is the modified pin-outs of the latter. In ADA4899-1, pin 5 was designated as another pin for -Vs (negative supply pin) for improvement in the Second Harmonic Distortion performance of the device. 
 
 You have the liberty to either use pin 4 or pin 5 depending on your design requirements. With an enhanced pin-outs of ADA4899-1, you can either use it in Standard SOIC (only pin 4 as the Negative Supply, same as other HS amplifiers pin-outs) or the modified layout (with pin 5 that serves as another Negative Supply for improved HD performance). If you look at EVAL-HSAMP-1 (SO8 single amp evaluation board), it's also compatible with ADA4899-1 which gives you an option to power the device with pin 4 as Negative Supply pin the same as the other HS Amplifiers in SO8 package. 
 2. Connecting pin 8 (DISABLE) to +5V activates the input bias current cancellation circuit of ADA4899-1, thus lowers the input bias current. In this state output-referred offset is minimal but doubles the input-referred current noise. I will have to investigate further for the effect of this configuration on the Input Bias Offset Current Drift of the device. 
 Regards, 
 Jino