ISL28408_14 Datasheet, PDF (21/34 Pages) Intersil Corporation – 40V Precision Single Supply Rail-to-Rail Output Low Power Operational Amplifiers

ISL28108, ISL28208, ISL28408
Applications Information
Functional Description
The ISL28108, ISL28208, and ISL28408 are single, dual and
quad, 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 temperature drift ranging from
1.1µV/°C for the ISL28208 and ISL28408 in the SOIC package to
1.4µV/°C for the ISL28208 in the TDFN package and the ISL28408
in the SOIC package (see Figures 11 through 20). All 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 10.
Input Stage Performance
The PNP input stage has a common mode input range extending
up to 0.5V below ground at +25°C (see Figures 23 and 24). 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 65, 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 65. 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 31 and 32). 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 65)
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 is internally current limited. Output current limit
over-temperature is shown in Figures 37 and 38. The amplifiers
can withstand a short circuit to either rail as long as the power
dissipation limits are not exceeded. This applies to only one
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 60 and 61). 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. These devices are immune to output phase reversal, out
to 0.5V beyond the rail (V_{ABS MAX}) limit (see Figure 40).
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FN6935.5
March 4, 2014