EL8186 查看數據表（PDF） - Intersil
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EL8186 Datasheet PDF : 9 Pages
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EL8186
Applications Information
Introduction
The EL8186 is a rail-to-rail input and output micro-power
single supply operational amplifier with an enable feature.
The device achieves rail-to-rail input and output operation
and eliminates the concerns introduced by a conventional
rail-to-rail input and output operational amplifier.
Rail-to-Rail Input
The input common-mode voltage range of the EL8186 goes
from negative supply to positive supply without introducing
offset errors or degrading performance associated with a
conventional rail-to-rail input operational amplifier. Many rail-
to-rail input stages use two differential input pairs, a long-tail
PNP (or PFET) and an NPN (or NFET). Severe penalties
have to be paid for this topology. As the input signal moves
from one supply rail to another, the operational amplifier
switches from one input pair to the other causing drastic
changes in input offset voltage and an undesired change in
magnitude and polarity of input offset current.
The EL8186 achieves input rail-to-rail performance without
sacrificing important precision specifications and without
degrading distortion performance. The EL8186's input offset
voltage exhibits a smooth behavior throughout the entire
common-mode input range. The input bias current versus
the common-mode voltage range for the EL8186 gives
consistent behavior from typically 10mV above the negative
rail all the way up to the positive rail.
Input Bias Current Compensation
The input bias currents of the EL8186 are reduced to a
typical 500pA while maintaining excellent bandwidth for a
micro-power operational amplifier. Inside the EL8186 is an
input bias cancelling circuit. The input stage transistors are
still biased with an adequate amount of current for speed but
the cancelling circuit sinks most of the base current, leaving
a small fraction as input bias current. The input bias current
compensation/cancellation operates from typically 10mV
above the negative rail to the positive supply rail.
Rail-to-Rail Output
A pair of complementary MOSFET devices achieves rail-to-
rail output swing. The NMOS sinks current to swing the
output in the negative direction. The PMOS sources current
to swing the output in the positive direction. The EL8186 with
a 100kΩ load will swing to within 3mV of the supply rails.
Enable/Disable Feature
The EL8186 offers an EN pin. The active low enable pin
disables the device when pulled up to at least 2.2V. Upon
disable the part consumes typically 3µA, while the output is
in a high impedance state. The EN also has an internal pull
down. If left open, the EN pin will pull to negative rail and the
device will be enabled by default. The high impedance at
output during disable allows multiple EL8186s to be
connected together as a MUX. The outputs are tied together
in parallel and a channel can be selected by the EN pin.
Typical Applications
R4
R3 10kΩ
R2
K TYPE
THERMOCOUPLE
10kΩ
100kΩ
+ V+
EL8186
- V-
+
5V
410µV/°C
R1
100kΩ
FIGURE 21. THERMOCOUPLE AMPLIFIER
Thermocouples are the most popular temperature-sensing
device because of their low cost, interchangeability, and
ability to measure a wide range of temperatures. The
EL8186 is used to convert the differential thermocouple
voltage into single-ended signal with 10X gain. The
EL8186's rail-to-rail input characteristic allows the
thermocouple to be biased at ground and the converter to
run from a single 5V supply.
7
FN7455.3
June 14, 2005
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