AD825x Supply Rails

Question

Hi, 
 I am looking into using the AD8250,AD8251 or AD8253 devices in a design and I have a few questions. 
 The AD8250/1 will be used to measure a voltage from 0-28V. I plan to supply the device with -1.8V/+32V supplies such that the output can be referenced to ground. 
 Will these devices work with such a supply range? I noticed in the spice model that the /WR input needs to be below -3V for the flip flops. I think this was causing convergence issues with the model. I wonder if this will be a limitation in the real circuit as well? 
 Are these 3 devices similar in this respect?

EZAdministrator · Accepted Answer

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EZ Admin

ADIApproved · Answer

Hi Igor, 
 The AD8250 and AD8251 parts are specified for a power supply operating range of +/-5V to +/-15V. For single-supply configuration it could be from +10V to +30V. However, if you are planning to use a supply voltage of -1.8V/+32V, it is above the specified supply range and too close to the absolute maximum rating of +/-17V. Exposure to absolute maximum rating condition for extended period may affect the device reliability. 
 You can use this Instrumentation Amplifier Operating Range Tool to evaluate your circuit configuration and determine if its within the operating range of the instrumentation amplifier. It can also provide the input common mode vs. output voltage graph, also called as the diamond plot. 
 The AD8250, AD8251 and AD8253 has two gain modes, the latched gain mode and transparent gain mode. What gain mode are you trying to implement? 
 I evaluated the AD8250 and AD8251 spice model, the latched gain mode is working on my simulation using +/-15V and -1.8V/+32V supply . For the transparent gain mode you simply connect the /WR pin to -VS and the voltage levels on A0 and A1 will determine the gain. However, the /WR pin of the spice model requires to connect at a voltage potential of -3V or less. I will test the AD8250/1 in the lab to verify this. I'll get back to you on this. 
 Regards, 
 Jay

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AD825x Supply Rails