CYRUSTEK CO.
ES5108 3 1/2 Digit
ADC with serial output
3
Timing Waveforms
Functional Description
1
Analog Common
The Common pin is used to set the common-mod voltage for the system in which the input signals are floating with
respect to the power supply of the ES5108. In most of the applications, VIN-, VREF- and COMMON pins are tied to
the same point, so that the common mode voltage can be removed from the reference system and the converter. In some
applictions, VIN- may not at the same point with COMMON and thus a common mode voltage exists in the system, The
high CMRR(86db typical) of the ES5108 can take care of this common mode voltage. Nevertheless, it should be care to
prevent the output of the integrator from saturation.
The COMMON pin is also used as a voltage reference. It sets a voltage of around 2.9 volts more negative than the
positive supply. The COMMON voltage of ES5108 has a low output impedance of
typical.
The analog COMMON is tied internally to an N-channel FET capable of sinking 30mA. This FET will hold the COM-
MON voltage at 2.9 volts when an external load attempts to pull the COMMON voltage toward the positive supply.
The source current of COMMON is only 10 A, so it is easy to pull COMMON voltage to a more negative voltage
with respect to the positive supply.
When the total supply voltage is large enough to cause the zener to regulate(>7V), the COMMON voltage will have
a low temperature coefficient typically less than
C. This voltage can be used to generate the ES5108 reference
voltage and anexternal voltage reference will be unnecessary in most cases.
8
July 4, 2002
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