ISL28236 Datasheet, PDF (10/13 Pages) Intersil Corporation – 5MHz, Dual Precision Rail-to-Rail Input-Output (RRIO) Op Amp

ISL28236
Pin Descriptions
ISL28236
(8 Ld SOIC)
(8 Ld MSOP)
PIN NAME
2 (A)
6 (B)
IN-
IN-_A
IN-_B
FUNCTION
inverting input
EQUIVALENT CIRCUIT
V+
IN-
IN+
3 (A)
5 (B)
4
IN+
IN+_A
IN+_B
V-
Non-inverting input
Negative supply
1 (A)
7 (B)
OUT
OUT_A
OUT_B
Output
8
V+
Positive supply
Applications Information
Introduction
The ISL28236 is a dual channel Bi-CMOS rail-to-rail input,
output (RRIO) micropower precision operational amplifier.
The part is designed to operate from single supply (2.4V to
5.5V) or dual supply (±1.2V to ±2.75V). The ISL28236 has
an input common mode range that extends 0.25V above the
positive rail and down to the negative supply rail. The output
operation 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. Thus causing drastic changes in input offset voltage
and an undesired change in magnitude and polarity of input
offset current.
The ISL28236 solves this problem using an internal
charge-pump to provide a voltage boost to the V+ supply rail
driving the input differential pair. This results in extending the
input common voltage rails to 0.25V beyond the V+ positive
10
V-
Circuit 1
See Circuit 1
V+
CAPACITIVELY
COUPLED
ESD CLAMP
V-
Circuit 2
V+
OUT
V-
Circuit 3
See Circuit 2
rail. The input offset voltage exhibits a smooth behavior
throughout the extended common-mode input range. The
input bias current versus the common-mode voltage range
gives an undistorted behavior from the negative rail to 0.25V
higher than the positive rail.
Power Supply Decoupling
The internal charge pump operates at approximately 27MHz
and oscillator ripple doesn’t show up in the 5MHz bandwidth
of the amplifier. Good power supply decoupling with 0.01µF
capacitors at each device power supply pin, is the most
effective way to reduce oscillator ripple at the amplifier
output. Figure 36 shows the electrical connection of these
capacitors using split power supplies. For single supply
operation with V- tied to a ground plane, only a single 0.01µF
capacitor from V+ is needed. When multiple ISL28236
op amps are used on a single PC board, each op amp will
require a 0.01µF decoupling capacitor at each supply pin
Rail-to-Rail Output
The rail-rail output stage uses CMOS devices that typically
swing to within 3mV of the supply rails with a 100kΩ load.
The NMOS sinks current to swing the output in the negative
direction. The PMOS sources current to swing the output in the
positive direction.
FN6921.0
June 18, 2009