ISL28118_11 Datasheet, PDF (18/28 Pages) Intersil Corporation – 40V Precision Single-Supply, Rail-to-Rail Output, Low-Power

ISL28118, ISL28218
Applications Information
Functional Description
The ISL28118 and ISL28218 are single and dual, 3.2MHz,
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 single-supply applications. The input
stage is able to handle large input differential voltages without
phase inversion, making these amplifiers 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 very low quiescent
current of 850µV, and low temperature drift. Both devices are
fabricated in a new precision 40V complementary bipolar DI
process and are 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 8.
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 12 shows the
common mode input voltage range variation over temperature.
Input Stage Performance
The ISL28118 and ISL28218 PNP input stage has a common
mode input range extending up to 0.5V below ground at +25°C
(Figure 12). Full amplifier performance is guaranteed down for
input voltage down to ground (V-) over the -40°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 62, 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 62. 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 (Figures 31 and 32). With ±15V supplies, this can be
achieved by using feedback resistor values >300kΩ.
The output stage is internally current limited. Output current limit
over temperature is shown in Figures 33 and 34. 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 when driving capacitive loads
(Figures 56 and 57). 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 ISL28118 and ISL28218 are immune to output
phase reversal out to 0.5V beyond the rail (V_{ABS MAX}) limit
(Figure 49).
Single Channel Usage
The ISL28218 is a dual op amp. If the application requires only
one channel, the user must configure the unused channel to
prevent it from oscillating. The unused channel oscillates if the
input and output pins are floating. This results in
higher-than-expected supply currents and possible noise
injection into the channel being used. The proper way to prevent
oscillation is to short the output to the inverting input, and
ground the positive input (Figure 63).
-
+
FIGURE 63. PREVENTING OSCILLATIONS IN UNUSED CHANNELS
18
FN7532.2
May 16, 2011