ISL55002 Datasheet, PDF (9/14 Pages) Intersil Corporation – High Supply Voltage 220MHz Unity-Gain Stable Operational Amplifiers

ISL55002, ISL55004
Product Description
The ISL55002 and ISL55004 are wide bandwidth, low
power, and low offset voltage feedback operational
amplifiers. These devices are internally compensated for
closed loop gain of +1 or greater. Connected in voltage
follower mode and driving a 500Ω load, the -3dB bandwidth
is around a 220MHz. Driving a 150Ω load and a gain of 2,
the bandwidth is about 90MHz while maintaining a 300V/µs
slew rate.
The ISL55002 and ISL55004 are designed to operate with
supply voltage from +15V to -15V. That means for single
supply application, the supply voltage is from 0V to 30V. For
split supplies application, the supply voltage is from ±15V.
The amplifier has an input common-mode voltage range
from 1.5V above the negative supply (V_S- pin) to 1.5V below
the positive supply (V_S+ pin). If the input signal is outside the
above specified range, it will cause the output signal to be
distorted.
The outputs of the ISL55002 and ISL55004 can swing from
-12.75V to +13.4V for V_S = ±15V. As the load resistance
becomes lower, the output swing is lower.
Choice Of Feedback Resistor And Gain Bandwidth
Product
For applications that require a gain of +1, no feedback
resistor is required. Just short the output pin to the inverting
input pin. For gains greater than +1, the feedback resistor
forms a pole with the parasitic capacitance at the inverting
input. As this pole becomes smaller, the amplifier's phase
margin is reduced. This causes ringing in the time domain
and peaking in the frequency domain. Therefore, R_F can't be
very big for optimum performance. If a large value of R_F
must be used, a small capacitor in the few Pico farad range
in parallel with R_F can help to reduce the ringing and
peaking at the expense of reducing the bandwidth. For gain
of +1, R_F = 0 is optimum. For the gains other than +1,
optimum response is obtained with R_F with proper selection
of R_F and R_G (see Figures15 and 16 for selection.)
Video Performance
For good video performance, an amplifier is required to
maintain the same output impedance and the same
frequency response as DC levels are changed at the output.
This is especially difficult when driving a standard video load
of 150Ω, because of the change in output current with DC
level. The dG and dP of this device is about 0.01% and
0.05°, while driving 150Ω at a gain of 2. Driving high
impedance loads would give a similar or better dG and dP
performance.
Driving Capacitive Loads and Cables
The ISL55002 and ISL55004 can drive 47pF loads in parallel
with 500Ω with less than 3dB of peaking at gain of +1 and as
much as 100pF at a gain of +2 with under 3db of peaking. If
less peaking is desired in applications, a small series resistor
(usually between 5Ω to 50Ω) can be placed in series with the
output to eliminate most peaking. However, this will reduce
the gain slightly. If the gain setting is greater than 1, the gain
resistor R_G can then be chosen to make up for any gain loss
which may be created by the additional series resistor at the
output.
When used as a cable driver, double termination is always
recommended for reflection-free performance. For those
applications, a back-termination series resistor at the
amplifier's output will isolate the amplifier from the cable and
allow extensive capacitive drive. However, other applications
may have high capacitive loads without a back-termination
resistor. Again, a small series resistor at the output can help
to reduce peaking.
Output Drive Capability
The ISL55002 and ISL55004 do not have internal short
circuit protection circuitry. They have a typical short circuit
current of 140mA. If the output is shorted indefinitely, the
power dissipation could easily overheat the die or the current
could eventually compromise metal integrity. Maximum
reliability is maintained if the output current never exceeds
±60mA. This limit is set by the design of the internal metal
interconnect. Note that in transient applications, the part is
robust.
Short circuit protection can be provided externally with a
back match resistor in series with the output placed close as
possible to the output pin. In video applications this would be
a 75Ω resistor and will provide adequate short circuit
protection to the device. Care should still be taken not to
stress the device with a short at the output.
Power Dissipation
With the high output drive capability of the ISL55002 and
ISL55004, it is possible to exceed the 150°C absolute
maximum junction temperature under certain load current
conditions. Therefore, it is important to calculate the
maximum junction temperature for an application to
determine if load conditions or package types need to be
modified to assure operation of the amplifier in a safe
operating area.
The maximum power dissipation allowed in a package is
determined according to:
PD_MAX
=
T_{----J---M-----A----X-----–-----}T_{----A---M-----A----X--}
Θ_JA
Where:
• T_JMAX = Maximum junction temperature
• T_AMAX = Maximum ambient temperature
• θ_JA = Thermal resistance of the package
The maximum power dissipation actually produced by an IC
is the total quiescent supply current times the total power
supply voltage, plus the power in the IC due to the load, or:
9
FN7497.1
July 15, 2005