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