ISL28288_07 Datasheet, PDF (10/13 Pages) Intersil Corporation – Dual and Quad Micropower Single Supply Rail-to-Rail Input and Output (RRIO) Op-Amp

ISL28288, ISL28488
Pin Descriptions (Continued)
ISL28288
ISL28488
EQUIVALENT
(10 LD MSOP) (16 LD QSOP) PIN NAME CIRCUIT
DESCRIPTION
10
OUT_C
Circuit 3 Amplifier C output
11
IN-_C
Circuit 1 Amplifier C inverting input
12
IN+_C
Circuit 1 Amplifier C non-inverting input
14
IN+_D
Circuit 1 Amplifier D non-inverting input
15
IN-_D
Circuit 1 Amplifier D inverting input
16
OUT_D
Circuit 3 Amplifier D output
8, 9
NC
-
No internal connection
IN-
CIRCUIT 1
V+
IN+
V-
LOGIC
PIN
V+
V-
CIRCUIT 2
V+
OUT
V-
CIRCUIT 3
V+
CAPACITIVELY
COUPLED
ESD CLAMP
V-
CIRCUIT 4
Applications Information
Introduction
The ISL28288 and ISL28488 are dual and quad CMOS
rail-to-rail input, output (RRIO) micropower operational
amplifiers. These devices are designed to operate from a
single supply (2.4V to 5.0V) or dual supplies (±1.2V to
±2.5V) while drawing only 120μA of supply current. This
combination of low power and precision performance makes
these devices suitable for solar and battery power
applications.
Rail-to-Rail Input
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 ISL28288 achieves input rail-to-rail without sacrificing
important precision specifications and degrading distortion
performance. The devices’ input offset voltage exhibits a
smooth behavior throughout the entire common-mode input
range. The input bias current versus the common-mode
voltage range gives us an undistorted behavior from typically
100mV below the negative rail and 10% higher than the V+
rail (0.5V higher than V+ when V+ equals 5V).
Input Protection
All input terminals have internal ESD protection diodes to both
positive and negative supply rails, limiting the input voltage to
within one diode beyond the supply rails. There is an
additional pair of back-to-back diodes across the input
terminals. For applications where the input differential voltage
is expected to exceed 0.5V, external series resistors must be
used to ensure the input currents never exceed 5mA.
Rail-to-Rail Output
A pair of complementary MOSFET devices are used to achieve
the 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 ISL28288 with
a 100kΩ load will swing to within 4mV of the positive supply rail
and within 3mV of the negative supply rail.
Enable/Disable Feature
The ISL28288 offers an EN pin that disables the device
when pulled up to at least 2.0V. In the disabled state (output
in a high impedance state), the part consumes typically 4µA.
By disabling the part, multiple ISL28288 parts can be
connected together as a MUX. In this configuration, the
outputs are tied together in parallel and a channel can be
selected by the EN pin. The loading effects of the feedback
resistors of the disabled amplifier must be considered when
multiple amplifier outputs are connected together. The EN
pin also has an internal pull down. If left open, the EN pin will
pull to the negative rail and the device will be enabled by
default.
Using Only One Channel
The ISL28288 is a dual op amp. If the application only
requires one channel, the user must configure the unused
channel to prevent it from oscillating. The unused channel
will oscillate if the input and output pins are floating. This will
result in higher than expected supply currents and possible
10
FN6339.1
June 28, 2007