I am using an AD7124-8 and switching the 50uA current source on and off. How long do I have to wait before the current source is stable?
May I know what is your application? Does it really requires switching the current sources on/off? How often do you turn in on/off? Currently, we don't have data for stability over time, the excitation current may power up quickly but it may not have completely settled before the ADC begins conversion. However, if a ratio metric configuration is used whereby the
the RTD measurements for example is referred to a voltage across a precision reference resistor that is driven with the same current source, any variations or errors in the current sources are removed. Therefore, in this type of application the excitation current does not need to be completely settled. One important consideration while using the excitation current is the output compliance, the AD7124 IOUT has an output compliance of AVSS-0.05V to AVDD-0.37V for 50uA/100uA/250uA/500uA and AVSS-0.05V to AVDD-0.48V for 750uA/1000uA current sources. These specifications must be meet.
Good to hear you have solved the issue. But you are right any capacitors connected to the ADC that are in the path of the excitation currents will need some extra time to charge. So, the time required to charge the external caps sets the settling time.
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