ISL28258FBZ Intersil, ISL28258FBZ Datasheet - Page 13

• Manufacturer Part Number: ISL28258FBZ
• Description: IC OPAMP RRIO PREC 68UA 8-SOIC
• Manufacturer: Intersil

Specifications of ISL28258FBZ

• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 0.1 V/µs
• Gain Bandwidth Product: 200kHz
• -3db Bandwidth: 420kHz
• Current - Input Bias: 1pA
• Voltage - Input Offset: 3.1µV
• Current - Supply: 68µA
• Current - Output / Channel: 30mA
• Voltage - Supply, Single/dual (±): 2.4 V ~ 5.5 V, ±1.2 V ~ 2.75 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

external series resistor must be used to ensure the input
currents never exceed 5mA (Figure 47).
Enable/Disable Feature
The ISL28158 offers an EN pin that disables the device
when pulled up to at least 2.0V. In the disabled state (output
in a high impedance state), the part consumes typically 10µA
at room temperature. By disabling the part, multiple
ISL28158 parts can be connected together as a MUX. In this
configuration, the outputs are tied together in parallel and a
channel can be selected by the EN pin. The loading effects
of the feedback resistors of the disabled amplifier must be
considered when multiple amplifier outputs are connected
together. Note that feed through from the IN+ to IN- pins
occurs on any Mux Amp disabled channel where the input
differential voltage exceeds 0.5V (e.g., active channel
V
implementation is best suited for small signal applications. If
large signals are required, use series IN+ resistors, or large
value R
minimize the impact on the active channel. See “Limitations
of the Differential Input Protection” on page 13 for more
details. The EN pin also has an internal pull-down. If left
open, the EN pin will pull to the negative rail and the device
will be enabled by default. When not used, the EN pin should
either be left floating or connected directly to the -V pin.
Limitations of the Differential Input Protection
If the input differential voltage is expected to exceed 0.5V, an
external current limiting resistor must be used to ensure the
input current never exceeds 5mA. For non-inverting unity
gain applications, the current limiting can be via a series IN+
resistor, or via a feedback resistor of appropriate value. For
other gain configurations, the series IN+ resistor is the best
choice, unless the feedback (R
resistors are both sufficiently large to limit the input current to
5mA.
OUT
= 1V, while disabled channel V
F
V
, to keep the feed through current low enough to
IN
FIGURE 47. INPUT CURRENT LIMITING
R
IN
+
-
13
F
) and gain setting (R
R
IN
L
= GND), so the mux
V
OUT
ISL28158, ISL28258
G
)
Large differential input voltages can arise from several
sources:
1) During open loop (comparator) operation. Used this way,
the IN+ and IN- voltages don’t track, so differentials arise.
2) When the amplifier is disabled but an input signal is still
present. An R
the varying IN+ signal creates a differential voltage. Mux
Amp applications are similar, except that the active channel
V
3) When the slew rate of the input pulse is considerably
faster than the op amp’s slew rate. If the V
with the IN+ signal, a differential voltage results, and visible
distortion occurs on the input and output signals. To avoid
this issue, keep the input slew rate below 0.1V/µs, or use
appropriate current limiting resistors.
Large (>2V) differential input voltages can also cause an
increase in disabled I
Using Only One Channel
The ISL28258 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
will oscillate if the input and output pins are floating. This will
result 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
negative input and ground the positive input (as shown in
Figure 48).
Current Limiting
These devices have no internal current-limiting circuitry. If
the output is shorted, it is possible to exceed the Absolute
Maximum Rating for output current or power dissipation,
potentially resulting in the destruction of the device.
OUT
FIGURE 48. PREVENTING OSCILLATIONS IN UNUSED
determines the voltage on the IN- terminal.
L
CHANNELS
or R
G
CC
to GND keeps the IN- at GND, while
.
+
-
OUT
can’t keep up
August 29, 2008
FN6377.3