7106_15 Datasheet, PDF (13/18 Pages) Unisonic Technologies – CONVERTERS

7106
CMOS IC
„ DETAILED DESCRIPTION(Cont.)
Reference Capacitor
A 0.1μF capacitor gives good results in most applications. However, where a large common mode voltage exists
(i.e., the REF LO pin is not at analog COMMON)and a 200mV scale is used, a larger value is required to prevent
roll-ovre error. Generally 1μF will hold the roll-over error to 0.5 count in this instance.
Oscillator Components
For all ranges of frequency a 91kΩ resistor is recommended and the capacitor is selected from the equation:
f= 0.45/RC for 48kHz Clock (3 Readings/sec), C=100pF.
Reference Voltage
The analog input required to generate full scale output (2000 counts) is: V_IN=2V_REF.Thus, for the 200mV and 2V
scale, V_REF should equal 100mV and 1V, respectively. However, in many applications where the A/D is connected to
a transducer, there will exist a scale factor other than unity between the input voltage and the digital reading. For
instance, in a weighing system, the designer might like to have a full scale reading when the voltage from the
transducer is 0.662V. Instead of dividing the input down to 200mV, the designer should use the input voltage directly
and select V_REF=0.341V. Suitable values for integrating resistor and capacitor would be 120kΩ and 0.22μF. This
makes the system slightly quieter and also avoids a divider network on the input.
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