ISL28190 Datasheet, PDF (9/14 Pages) Intersil Corporation – Single and Dual Ultra-Low Noise, Ultra-Low Distortion, Rail-to-Rail, Op Amp

ISL28190, ISL28290
Applications Information
Product Description
The ISL28190 and ISL28290 are voltage feedback operational
amplifier designed for communication and imaging applications
requiring very low voltage and current noise. Both parts feature
low distortion while drawing moderately low supply current. The
ISL28190 and ISL28290 use a classical voltage-feedback
topology which allows them to be used in a variety of
applications where current-feedback amplifiers are not
appropriate because of restrictions placed upon the feedback
element used with the amplifier.
Enable/Power-Down
The ISL28190 and ISL28290 amplifiers are disabled by
applying a voltage greater than 2V to the ENABLE pin, with
respect to the V- pin. In this condition, the output(s) will be in
a high impedance state and the amplifier(s) current will be
reduced to 13µA/Amp. By disabling the part, multiple parts
can be connected together as a MUX. The outputs are tied
together in parallel and a channel can be selected by the
ENABLE pin. The ENABLE pin also has an internal pull
down. If left open, the ENABLE pin will pull to the negative
rail and the device will be enabled by default.
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. Both parts have
additional back-to-back diodes across the input terminals (as
shown in Figure 25). In pulse applications where the input
Slew Rate exceeds the Slew Rate of the amplifier, the
possibility exists for the input protection diodes to become
forward biased. This can cause excessive input current and
distortion at the outputs. If overdriving the inputs is necessary,
the external input current must never exceed 5mA. An
external series resistor may be used to limit the current as
shown in Figure 25.
-
R
+
FIGURE 253. LIMITING THE INPUT CURRENT TO LESS THAN
5mA
Using Only One Channel
The ISL28290 is a Dual channel op-amp. If the application
only requires one channel when using the ISL28290, the
user must configure the unused channel to prevent it from
oscillating. Oscillation can occur 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 26).
-
+
FIGURE 26. PREVENTING OSCILLATIONS IN UNUSED
CHANNELS
Current Limiting
The ISL28190 and ISL28290 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. This is why output short circuit current is
specified and tested with R_L = 10Ω.
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 as follows:
T_JMAX = T_MAX + (θ_JAxPD_MAXTOTAL)
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 as follows:
PD_MAX
=
2*V_S × I_SMAX + (V_S
-
V_OUTMAX
)
×
V_{-----O----U----T----M-----A----X--}
R_L
whereT_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
9
FN6247.3
April 13, 2007