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Voltage Reference technical note
ADCVREF
SENSE
AD9628
ADCVREF
SENSE
GND+1.8V
ADCVREF
SENSE
+1.8V
ADCVREF
SENSE
+1.8V
ADCVREF
SENSE
+1.8V
MASTER ADCVREF generatorSLAVE ADC
VREF LOAD
INTERNAL ADC VREF SOLUTION
To GND =VREF int. generatorTo +1.8V = external VREF
Internal Voltage Reference considerations
Typical drift characteristics of the internal reference modeError is from -20 to +60degrees about 5 mV on 1 Volt
LOAD CURRENT (5 ADC)
7.5 Kohm x 5 ADCLOAD IS 1.5 KohmThe current from VREF master ADC is 0.6 mAAbout -0.2% or -2mV on 1V
External Reference generator
ADCVREF
SENSEADCVREF
SENSE
+1.8V+1.8V
ADCVREF
SENSE
+1.8V
ADCVREF
SENSE
+1.8V
ADCVREF
SENSE
+1.8V
SLAVE ADCVREF 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 thaninternal 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