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AD8131 common mode voltage clamped in Spice model

Question asked by PEDALATOR on Oct 15, 2015
Latest reply on Oct 16, 2015 by PEDALATOR

The AD8131 SPICE Macro-model  Revision 2.0 (08/10/2012) Developed by JG/ADI downloaded from ADI website
does not work as expected when driving Vocm pin with an external common mode voltage greater than 2.7V.

 

According to AD8131 DataSheet rev G (page 5 Table 2) we expect that  -Vs=-5V < -3.6 V < Vocm < +3.6V < +Vs=5V

But due to the Spice model bloc "VOCM INPUT RAIL CLIPING"  the Vocm input is clamped to 2.88V +- VDX

therefore when Vocm rises over 2.7V, the output common mode voltage of the AD8131 saturate to 2,93V

and the AD8131 sink too much current at Vocm input

 

See attached Tina simulation schematic with various settings of Vcom input,
showing excess currrent sink on AD8131 input when voltage rise over the input clamp.

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