EL8176 INTERSIL [Intersil Corporation], EL8176 Datasheet - Page 10

• Manufacturer Part Number: EL8176
• Description: Micropower Single Supply Rail-to-Rail Input-Output Precision Op Amp
• Manufacturer: INTERSIL [Intersil Corporation]

Applications Information
Introduction
The EL8176 is a rail-to-rail input and output micro-power
precision 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 I/O operational amplifier as
discussed below.
Rail-to-Rail Input
The input common-mode voltage range of the EL8176 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 circuit 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 EL8176 achieves input rail-to-rail without sacrificing
important precision specifications and without degrading
distortion performance. The EL8176'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 EL8176 gives us an
undistorted behavior from typically 10mV above the negative
rail all the way up to the positive rail.
10
EL8176
Input Bias Current Compensation
The input bias currents as low as 500pA are achieved while
maintaining an excellent bandwidth for a micro-power
operational amplifier. Inside the EL8176 is an input bias
canceling circuit. The input stage transistors are still biased
with an adequate current for speed but the canceling circuit
sinks most of the base current, leaving a small fraction as
input bias current. The input bias current
compensation/cancellation is stable from -40°C to +125°C
and operates from typically 10mV 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 EL8176 with a 100kΩ load
will swing to within 3mV of the supply rails.
Enable/Disable Feature
The EL8176 offers an EN pin. The active low EN pin
disables the device when pulled up to at least 2.0V. When
disabled, the output is in a high impedance state and the part
consumes typically 3µA. When disabled, the high
impedance output allows multiple parts to be MUXed
together. When configured as a MUX, the outputs are tied
together in parallel and a channel can be selected by pulling
the EN pin to 0.8V or lower.The EN pin has an internal
pull-down. If left open or floating, the EN pin will internally be
pulled low, enabling the part by default.
October 26, 2006
FN7436.6