ISL28166_0808 Datasheet, PDF (10/13 Pages) Intersil Corporation – 39μA Micropower Single and Dual Rail-to-Rail Input-Output Low Input Bias Current (RRIO) Op Amps

ISL28166, ISL28266
Applications Information
Introduction
The ISL28166 is a single BiMOS rail-to-rail input, output
(RRIO) operational amplifier with an enable feature. The
ISL28266 is a dual version without the enable feature. Both
devices are designed to operate from single supply (2.4V to
5.0V) or dual supplies (±1.2V to ±2.5V) while drawing only
39µA of supply current per amplifier. This combination of low
power and precision performance makes this device suitable
for a variety of low power applications including battery
powered systems.
Rail-to-Rail Input/Output
These devices feature bi-polar inputs which have an input
common mode range that extends to the rails, and CMOS
outputs that can typically swing to within about 4mV of the
supply rails with a 100kΩ load. The NMOS sinks current to
swing the output in the negative direction. The PMOS sources
current to swing the output in the positive direction.
Input Protection
All input terminals have internal ESD protection diodes to both
positive and negative supply rails, limiting the input voltage to
within one diode beyond the supply rails. They also contain
back-to-back diodes across the input terminals. For
applications where the input differential voltage is expected to
exceed 0.5V, external series resistors must be used to ensure
the input currents never exceed 5mA (Figure 34).
-
R_IN
V_IN
+
R_L
V_OUT
FIGURE 34. INPUT CURRENT LIMITING
Enable/Disable Feature
The ISL28166 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. By disabling the part, multiple ISL28166 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 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.
The loading effects of the feedback resistors of the disabled
amplifier must be considered when multiple amplifier outputs
are connected together.
Using Only One Channel
The ISL28266 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 35).
-
+
FIGURE 35. PREVENTING OSCILLATIONS IN UNUSED
CHANNELS
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.
Power Dissipation
It is possible to exceed the +125°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 in 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)
• PD_MAX for each amplifier can be calculated using
Equation 2:
PD_MAX
=
2*V_S × I_SMAX + (V_S
-
V_OUTMAX
)
×
V_{-----O----U----T----M-----A----X--}
R_L
(EQ. 2)
where:
• T_MAX = Maximum ambient temperature
• θ_JA = Thermal resistance of the package
• PD_MAX = Maximum power dissipation of 1 amplifier
• V_S = Supply voltage
• I_MAX = Maximum supply current of 1 amplifier
• V_OUTMAX = Maximum output voltage swing of the
application
• R_L = Load resistance
10
FN6155.4
August 29, 2008