AnsweredAssumed Answered

AD8436 OBUFOUT offset

Question asked by towheedm on Oct 22, 2013
Latest reply on Oct 30, 2013 by towheedm

While waiting on the AD8436 to arrive, I've tried some simulations using the macro model provided.  The sims were done on LTSpice.

 

I'm using the AD8436 with single supply but noticed that the OBUFOUT has a 104.6mV offset.  This does not happen if I use dual supplies where the offset is around 90uV.  I've tried with several test configurations: OBUFIN- connected to OBUFOUT and OBUFIN+ grounded directly or through a 16K resistor, with OBUFIN- grounded and OBUFIN+ grounded directly or through a 16K resistor.  All configuration gives the same result.

 

I've gone through the datasheet several times, but no mention is made of this.  Is this a problem with the model, or does OBUFOUT behave like this on the physical device also?

 

I'm thinking it's a model error since leaving IBUFV+ and/or OBUFV+ disconnected (if not being used) generates a 'floaring node' error.

 

This is the error log from LTSPICE:

 

Circuit: * C:\Program Files\LTC\LTspiceIV\Draft1.asc

 

WARNING: Node NC_02 is floating.

 

WARNING: Less than two connections to node N009.  This node is used by R:U1:16.

WARNING: Less than two connections to node N004.  This node is used by R:U1:14.

Direct Newton iteration for .op point succeeded.

Singular matrix:  Check node nc_02

   Iteration No. 1

Fatal Error: Singular matrix:  check node nc_02

   Iteration No. 1

 

This circuit has floating nodes.

 

Is this model compatible with LTSpice?

 

Note that I've successfully simulated the AD736 and AD737 using the provided models on LTSpice.

 

Any help on this is greatly appreciated while I await the AD8436.

Outcomes