ISL28108 Datasheet, PDF (15/25 Pages) Intersil Corporation – 40V Precision Single Supply Rail-Rail Output Low Power Operational Amplifiers

ISL28108, ISL28208
Applications Information
Functional Description
The ISL28108 and ISL28208 are single and dual, 1.2MHz, single
supply rail-to-rail output amplifiers with a common mode input
voltage range extending to a range of 0.5V below the V- rail. Their
input stages are optimized for precision sensing of ground
referenced signals in low voltage, single supply applications. The
input stage has the capability of handling large input differential
voltages without phase inversion making them suitable for high
voltage comparator applications. Their bipolar design features
high open loop gain and excellent DC input and output
temperature stability. These op amps feature low quiescent
current of 165µA, and a maximum low temperature drift of only
1.1µV/°C for the SOIC package and 1.4µV/°C for the TDFN
package (see Figures 7 and 8). Both devices are fabricated in a
new precision 40V complementary bipolar DI process and
immune from latch-up.
Operating Voltage Range
The devices are designed to operate over the 3V (±1.5V) to 40V
(±20V) range and are fully characterized at ±5V and ±15V. Both DC
and AC performance remain virtually unchanged over the ±5V to
±15V operating voltage range. Parameter variation with operating
voltage is shown in the “Typical Performance Curves” beginning on
page 6.
Input Stage Performance
The ISL28108 and ISL28208 PNP input stage has a common
mode input range extending up to 0.5V below ground at +25°C
(see Figures 11 and 12). Full amplifier performance is guaranteed
down to ground (V-) over the -40°C to +125°C temperature range.
For common mode voltages down to -0.5V the amplifiers are fully
functional, but performance degrades slightly over the full
temperature range. This feature provides excellent CMRR, AC
performance and DC accuracy when amplifying low level ground
referenced signals.
The input stage has a maximum input differential voltage equal
to a diode drop greater than the supply voltage (max 42V) and
does not contain the back-to-back input protection diodes found
on many similar amplifiers. This feature enables the device to
function as a precision comparator by maintaining very high
input impedance for high voltage differential input comparator
voltages. The high differential input impedance also enables the
device to operate reliably in large signal pulse applications
without the need for anti-parallel clamp diodes required on
MOSFET and most bipolar input stage op amps. Thus, input
signal distortion caused by nonlinear clamps under high slew
rate conditions are avoided.
In applications where one or both amplifier input terminals are at
risk of exposure to voltages beyond the supply rails, current
limiting resistors may be needed at each input terminal (see
Figure 53 R_IN+, R_IN-) to limit current through the power supply
ESD diodes to 20mA.
R_F
V+
V_IN-
R_IN-
-
V_IN+
R_IN+ ₊
R_L
R_G
V-
FIGURE 53. INPUT ESD DIODE CURRENT LIMITING
Output Drive Capability
The bipolar rail-to-rail output stage features low saturation levels
that enable an output voltage swing to less than 10mV when the
total output load (including feedback resistance) is held below
50µA (Figures 19 and 20). With ±15V supplies this can be
achieved by using feedback resistor values >300kΩ. The low input
bias and offset currents (-43nA and ±3nA +25°C max
respectively) minimize DC offset errors at these high resistance
values. For example, a balanced 4 resistor gain circuit (Figure 53)
with 1MΩ feedback resistors (R_F, R_G) generates a worst case
input offset error of only ±3mV. Furthermore, the low noise
current reduces the added noise associated with high feedback
resistance.
The output stage can swing at moderate levels of output current
(Figures 21 and 22) and the output stage is internally current
limited. Output current limit over-temperature is shown in
Figures 25 and 26. The amplifiers can withstand a short circuit to
either rail as long as the power dissipation limits are not
exceeded. This applies to only 1 amplifier at a time for the dual
op amp. Continuous operation under these conditions may
degrade long term reliability.
The amplifiers perform well driving capacitive loads (Figures 48
and 49). The unity gain, voltage follower (buffer) configuration
provides the highest bandwidth, but is also the most sensitive to
ringing produced by load capacitance found in BNC cables. Unity
gain overshoot is limited to 30% at capacitance values to 0.33nF.
At gains of 10 and higher, the device is capable of driving more
than 10nF without significant overshoot.
Output Phase Reversal
Output phase reversal is a change of polarity in the amplifier
transfer function when the input voltage exceeds the supply
voltage. The ISL28108 and ISL28208 are immune to output
phase reversal, out to 0.5V beyond the rail (V_{ABS MAX}) limit (see
Figure 28).
15
FN6935.1
March 17, 2011