Voltage Reference technical note ADC VREF SENSE AD9628 ADC VREF SENSE GND+1.8V ADC VREF SENSE +1.8V ADC VREF SENSE +1.8V ADC VREF SENSE +1.8V MASTER ADC VREF generator SLAVE ADC VREF LOAD INTERNAL ADC VREF SOLUTION To GND =VREF int. generator To +1.8V = external VREF

Internal Voltage Reference considerations Typical drift characteristics of the internal reference mode Error is from -20 to +60degrees about 5 mV on 1 Volt LOAD CURRENT (5 ADC) 7.5 Kohm x 5 ADC LOAD IS 1.5 Kohm The current from VREF master ADC is 0.6 mA About -0.2% or -2mV on 1V

External Reference generator ADC VREF SENSE ADC VREF SENSE +1.8V ADC VREF SENSE +1.8V ADC VREF SENSE +1.8V ADC VREF SENSE +1.8V SLAVE ADC VREF LOAD Precision zener diode Precision resistors V out 1V Example of solution

Conclusions Internal ADC generator for the common reference is a solution with very low thermal drift and the error for the load current (five ADC) is about 0.5 % (5mV on 1V) The solution with external generator must have better features than internal generator and the circuit should be appropriate and stable. The proposed external circuit solution requires an appropriate thermal exscursion test. However, a solution with external generator could be provided and not mounted on the board. Voltage reference is very important for the precision of analog conversion