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Transcript
Voltage Reference technical note AD9628 INTERNAL ADC VREF SOLUTION To GND =VREF int. generator To +1.8V = external VREF MASTER ADC VREF generator SLAVE ADC VREF LOAD VREF SENSE +1.8V VREF ADC SENSE +1.8V VREF ADC SENSE +1.8V VREF ADC SENSE +1.8V VREF ADC SENSE GND ADC 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 Example of solution Precision zener diode V out 1V Precision resistors SLAVE ADC VREF LOAD VREF SENSE +1.8V VREF ADC SENSE +1.8V VREF ADC SENSE +1.8V VREF ADC SENSE +1.8V VREF ADC SENSE +1.8V ADC Conclusions Voltage reference is very important for the precision of analog conversion 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.
