ISL28117_1110 Datasheet, PDF (19/33 Pages) Intersil Corporation – 40V Precision Low Power Operational Amplifiers

ISL28117, ISL28217, ISL28417
Applications Information
Functional Description
The ISL28117, ISL28217 and ISL28417 are single, dual and
quad, low noise precision op amps. Both devices are fabricated
in a new precision 40V complementary bipolar DI process. A
super-beta NPN input stage with input bias current cancellation
provides low input bias current (180pA typical), low input offset
voltage (13µV typical), low input noise voltage (8nV/√Hz), and
low 1/f noise corner frequency (~8Hz). These amplifiers also
feature high open loop gain (18kV/mV) for excellent CMRR
(145dB) and THD+N performance (0.0005% @ 3.5V_RMS, 1kHz
into 2kΩ). A complimentary bipolar output stage enables high
capacitive load drive without external compensation.
Operating Voltage Range
The devices are designed to operate over the 4.5V (±2.25V) to
40V (±20V) range and are fully characterized at 10V (±5V) and
30V (±15V). The Power Supply Rejection Ratio typically exceeds
140dB over the full operating voltage range and 120dB
minimum over the -40°C to +125°C temperature range. The
worst case common mode input voltage range over temperature
is 2V to each rail. With ±15V supplies, CMRR performance is
typically >130dB over-temperature. The minimum CMRR
performance over the -40°C to +125°C temperature range is
>120dB for power supply voltages from ±5V (10V) to ±15V (30V).
Input Performance
The super-beta NPN input pair provides excellent frequency
response while maintaining high input precision. High NPN beta
(>1000) reduces input bias current while maintaining good
frequency response, low input bias current and low noise. Input
bias cancellation circuits provide additional bias current
reduction to <1nA, and excellent temperature stabilization.
Figures 11 through 18 show the high degree of bias current
stability at ±5V and ±15V supplies that is maintained across the
-40°C to +125°C temperature range. The low bias current TC
also produces very low input offset current TC, which reduces DC
input offset errors in precision, high impedance amplifiers.
The +25°C maximum input offset voltage (V_OS) for the “B” grade is
50µV and 100µV for the “C” grade. Input offset voltage temperature
coefficients (V_OSTC) are a maximum of ±0.6µV/°C for the “B” and
±0.9µV/°C for the “C” grade. Figures 3 through 6 show the typical
gaussian-like distribution over the ±5V to ±15V supply range and over
the full temperature range. The V_OS temperature behavior is smooth
(Figures 7 through 10) maintaining constant TC across the entire
temperature range.
Input ESD Diode Protection
The input terminals (IN+ and IN-) have internal ESD protection
diodes to the positive and negative supply rails, series connected
500Ω current limiting resistors and an anti-parallel diode pair
across the inputs (Figure 53).
V+
- ^500Ω
V_IN
+ ^500Ω
V_OUT
R_L
V-
FIGURE 53. INPUT ESD DIODE CURRENT LIMITING- UNITY GAIN
The series resistors limit the high feed-through currents that can
occur in pulse applications when the input dV/dT exceeds the
0.5V/µs slew rate of the amplifier. Without the series resistors, the
input can forward-bias the anti-parallel diodes causing current to
flow to the output resulting in severe distortion and possible diode
failure. Figure 48 provides an example of distortion free large signal
response using a 4V_P-P input pulse with an input rise time of <1ns.
The series resistors enable the input differential voltage to be equal
to the maximum power supply voltage (40V) without damage.
In applications where one or both amplifier input terminals are at
risk of exposure to high voltages beyond the power supply rails,
current limiting resistors may be needed at the input terminal to
limit the current through the power supply ESD diodes to
20mA max.
Output Current Limiting
The output current is internally limited to approximately ±45mA
at +25°C and 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. Figures 27 and 28 show the current limit variation with
temperature.
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 ISL28117, ISL28217 and ISL28417 are immune to
output phase reversal, even when the input voltage is 1V beyond
the supplies.
Unused Channels
The ISL28217 is a dual op-amp. If the application only requires
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 this oscillation is
to short the output to the inverting input and ground the positive
input, as shown in Figure 54.
-
+
FIGURE 54. PREVENTING OSCILLATIONS IN UNUSED CHANNELS
19
October 13, 2011
FN6632.8