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AD5522 : trouble with MEASOUT voltage range

Question asked by Marc_2 on Mar 10, 2015
Latest reply on Mar 16, 2015 by Marc_2

I am in the process of qualifying the AD5522 for use into a new product.

I use the evaluation board EVAL-AD55222EBDZ (whose accompanying PC software is rather , but this is another question) and I am into trouble.

 

Here are the test conditions :

  • AVDD = +12 V
  • AVSS = -12 V
  • DVCC = +5 V
  • VREF = +5 V
  • FVMI mode, current range ±2 mA
  • OFFSET DAC = A492hex
  • MEASOUT = VSENSE
  • AGND connected to DGND
  • DUTGND2 and DUTGND are connected to AGND
  • DUTGND/channel is disabled
  • GUARD is disabled
  • MEASVH2 connected to FOH2
  • current clamped to ±440 µA (CLL X1 = 7000hex, CLH X1 = 9000hex)
  • Voltage set to +4 V
  • MEASOUT gain = 1
  • MEASVH2, FOH2 voltage swept by HP Agilent Keysight's B2901A SMU from -10 to +10 V
  • MEASOUT2 is observed on an oscilloscope channel.

 

What I see is that the voltage at MEASOUT2 follows the voltage on MEASVH2, but will not go below -5 V.

If I change the Voltage setting to +6 V, MEASOUT2 will not go below -3 V, etc : there seem to be a maximum difference of 9 V between the Voltage setting and MEASOUT2 (so if Voltage is set below -3V, the restriction phenomenon will not show).

On the positive side, there is no such capping effet.

 

With MEASOUT gain = 0.2 the same voltage restriction seem to exist but (of course) at a different scale.

 

The phenomenon seems unrelated to AVSS, the current range, the current clamping, the Guard setting, the DUTGND/channel setting, the 10k resistor setting. It is slightly (not proportionally) related to AVDD.

 

I did not found anything on this in the datasheet. Any hint would be appreciated

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