ISL28118M Datasheet, PDF (14/22 Pages) Intersil Corporation – 40V Extended Temperature Range, Precision Single-Supply, Rail-to-Rail Output

ISL28118M
Applications Information
Functional Description
The ISL28118M is a 3.2MHz, single-supply, rail-to-rail output
amplifier with a common mode input voltage range extending to
a range of 0.5V below the V- rail. The input stage is optimized for
precision sensing of ground-referenced signals in single-supply
applications. The input stage is able to handle large input
differential voltages without phase inversion, making this
amplifier suitable for high-voltage comparator applications. The
bipolar design features high open loop gain, excellent DC
input/output temperature stability with a low quiescent current
of 850µV, and low temperature drift. The op amp is fabricated in
a new precision 40V complementary bipolar DI process and is
immune from latch-up.
Operating Voltage Range
The op amp is designed to operate over a single supply range of 3V
to 40V or a split supply voltage range of +1.8V, -1.2V to +/-20V.
The device is fully characterized at 10V (±5V) and 30V (±15V). Both
DC and AC performance remain virtually unchanged over the
complete operating voltage range. Parameter variation with
operating voltage is shown in the “Typical Performance Curves”
beginning on page 6.
The input common mode voltage to the V+ rail (V+ -1.8V over the
full temperature range) may limit amplifier operation when
operating from split V+ and V- supplies. Figure 6 shows the
common mode input voltage range variation over temperature.
Input Stage Performance
The ISL28118M PNP input stage has a common mode input range
extending up to 0.5V below ground at +25°C (Figure 6). Full
amplifier performance is guaranteed with input voltage down to
ground (V-) over the -55°C to +125°C temperature range. For
common mode voltages down to -0.5V below ground (V-), 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 is 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 52, 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 49. 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 15mV when the
total output load (including feedback resistance) is held below
50µA. With ±15V supplies, this can be achieved by using feedback
resistor values >300kΩ.
The output stage is internally current limited. The amplifiers can
withstand a short circuit to either rail as long as the power
dissipation limits are not exceeded. Continuous operation under
these conditions may degrade long-term reliability.
The amplifiers perform well when driving capacitive loads
(Figures 45 and 46). 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 35% 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 ISL28118M is immune to output phase reversal for
input voltage to 0.5V beyond the rail (V_{ABS MAX}) limit (Figure 38).
Power Dissipation
It is possible to exceed the +150°C maximum junction
temperatures under certain load and power supply conditions. It
is therefore important to calculate the maximum junction
temperature (T_JMAX) for all applications to determine if power
supply voltages, load conditions, or package type need to be
modified to remain in the safe operating area. These parameters
are related using Equation 1:
T_JMAX = T_MAX + θ_JAxPD_MAXTOTAL
(EQ. 1)
where
• P_DMAXTOTAL is the sum of the maximum power dissipation of
each amplifier in the package (PD_MAX)
• T_MAX = Maximum ambient temperature
• Θ_JA = Thermal resistance of the package
14
FN7858.0
May 11, 2011