ES5117 3 1/2 DVM with
LED Display and Hold
Function Description
1. Analog Common
The COMMON pin is used to set the common-mode voltage for the system which the
input signals are floating. In most of the applications, IN LO, REF LO and COMMON
pins are usually connected. It can remove common-mode voltage concerns. In other
applications, INLO does not connect with COMMON. The ES5117 generates a
common mode voltage, which has the high CMRR (86dB typical). Nevertheless, it
should be care to prevent the output of the integrator form saturation.
The COMMON pin is also used as a voltage reference. It outputs a voltage, which
is around 2.9 volts below the positive supply. The COMMON voltage has a low output
impedance of 15Ω typically.
The analog COMMON is connected internally to a NMOS, which can sink 30mA.
This NMOS will hold the COMMON 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 10uA, so it is easy to pull COMMON voltage to a more negative
voltage.
When the total supply voltage is large enough to cause the zener to regulate (>7V),
the COMMON voltage will have a low temperature coefficient less than 60ppm/℃
typically. The voltage can be used to generate the reference voltage.
2. Reference Voltage
For a 1000 counts reading, the input signal must be equal to the reference voltage. As a
result, it requires the input signal be twice the reference voltage for a 2000 counts full-
scale reading. Thus, for the 200.0mV and 2.000V full-scale, the reference voltage
should equal 100.0mV and 1.000V. In some applications the full-scale input voltage
may be different to 200mV or 2.000V. For example, in the 600mV full-scale
applications, the reference voltage should be set to 300mV.
The differential reference should be used during the measurement of resistor by
the ratio-metric method and when a digital reading of zero is desired for Vin≠0, a
compensating offset voltage can be applied between COMMON and IN LO, and the
voltage of being measured is connected between COMMON and IN HI.
5
03/07/21
CYRUSTEK [ Cyrustek corporation ]
