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AD7124: AIN15 Out of Range using +/-1.8V Supplies

Question asked by anaber on Jun 14, 2018
Latest reply on Jun 19, 2018 by JellenieR

Hello,

 

I'm using the Eval-AD7124-8SDZ board with the Eval-SDP-CB1Z communication board, and I'm having trouble getting any readings. I'm trying to perform bipolar measurements with a split power supply, and I receive the following error whenever I try to start acquisition:

 

"AIN15 is outside of limits. The analog input limits are (AVSS-0.1)-(AVDD+0.1) when buffers are enabled and Gain=1, or (AVSS-0.05)-(AVDD+0.05) under all other conditions."

 

I have verified the supply voltages. Since AIN15 can be used as REFIN2-, I tried tying it to AVSS directly with no effect. Switching between the internal and external references (LK4 and in the register settings) also does not appear to fix the problem. Attached is the register configuration I'm using for reference. Is there some configuration setting I am missing (the input is currently disabled) or an incorrect switch setting? Thank you for your time.

 

Physical Setup:

9V wall wart connected to J5
-1.8V connected between GND and AVSS on J7

LK1: Pos B (1.8V to Avdd)
LK2: Pos B (Barrel Jack)
LK3: Inserted (Refin- to Avss)
LK4: Pos B (Internal Ref.)
LK5: Disconnected
LK6: Inserted

SL2: Pos A (Barrel Jack)
SL3: Pos B (1.8V)
SL5: Pos B
SL7: Pos B (1.8V)
AVDD to AVSS: Disconnected (R49-R52)
SDPGND to AGND: Connected (R58,R59,R61,R62)

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