8

FN6200.3

November 3, 2009

Product Description

The ISL55001 is a wide bandwidth, low power, and low

offset voltage feedback operational amplifier. This device

is 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 ISL55001 is 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

outside the above specified range, it will cause the output

signal to be distorted.

The outputs of the ISL55001 can swing from -12.75V to

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

used, a small capacitor in the few Pico Farad range in

peaking at the expense of reducing the bandwidth. 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 ISL55001 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

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 ISL55001 does not have internal short circuit

protection circuitry. It has 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 ISL55001, 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 Equation 1:

Where:

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: For sourcing use Equation 2:

PD

MAX

T

JMAX

T

AMAX

–

Θ

JA

---------------------------------------------

=

(EQ. 1)

PD

MAX

(V

V

–

I

SMAX

V

V

OUTi

–

()

i1

=

n

∑

V

OUTi

R

LOADi

---------------------

×

+

×

=

(EQ. 2)

ISL55001