ISL28148 Datasheet, PDF (12/18 Pages) Intersil Corporation – 4.5MHz, Single Dual and Quad Precision Rail-to-Rail Input-Output RRIO Op Amps with Very Low Input Bias Current

ISL28148, ISL28248, ISL28448
Pin Descriptions (Continued)
ISL28148
(6 Ld SOT-23)
ISL28248
(8 Ld SO)
(8 Ld MSOP)
2
4
ISL28448
(14 Ld TSSOP)
11
1
1 (A)
1 (A)
7 (B)
7 (B)
8 (C)
14 (D)
6
8
4
5
-
PIN NAME
FUNCTION
V-
Negative supply
OUT
OUT_A
OUT_B
OUT_C
OUT_D
Output
V+
Positive supply
EN
Chip enable
EQUIVALENT CIRCUIT
V+
CAPACITIVELY
COUPLED
ESD CLAMP
V-
Circuit 2
V+
OUT
Circuit 3
(See circuit 2)
V-
V+
EN
Applications Information
Introduction
The ISL28148, ISL28248 and ISL28448 are single, dual and
quad channel CMOS rail-to-rail input, output (RRIO)
micropower precision operational amplifiers. The parts are
designed to operate from single supply (2.4V to 5.5V) or dual
supply (±1.2V to ±2.75V). The parts have an input common
mode range that extends 0.25V above the positive rail and
100mV below the negative supply rail. The output can swing
within about 3mV of the supply rails with a 100kΩ load.
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 parts achieve input rail-to-rail operation 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 vs the
common-mode voltage range gives us an undistorted
V-
Circuit 4
behavior from typically 100mV below the negative rail and
0.25V higher than the V+ rail.
Rail-to-Rail Output
A pair of complementary MOS 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
devices’ with a 100kΩ load will swing to within 3mV of the
positive supply rail and within 3mV of the negative supply rail.
Results of Overdriving the Output
Caution should be used when overdriving the output for long
periods of time. Overdriving the output can occur in two ways:
1. The input voltage times the gain of the amplifier exceeds the
supply voltage by a large value or
2. The output current required is higher than the output stage
can deliver. These conditions can result in a shift in the Input
Offset Voltage (V_OS) as much as 1µV/hr. of exposure under
these condition.
IN+ and IN- 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. They also contain
back-to-back diodes across the input terminals (“Pin
Descriptions” table - Circuit 1 on page 11). For applications
where the input differential voltage is expected to exceed
12
FN6337.4
September 21, 2010