10

FN7311.6

August 3, 2005

Description of Operation and Application

Information

Product Description

The EL5172 and EL5372 are wide bandwidth, low power

and single/differential ended to single ended output

amplifiers. The EL5172 is a single channel differential to

single ended amplifier. The EL5372 is a triple channel

differential to single ended amplifier. The EL5172 and

EL5372 are internally compensated for closed loop gain of

+1 of greater. Connected in gain of 1 and driving a 500

Ω

load, the EL5172 and EL5372 have a -3dB bandwidth of

250MHz. Driving a 150

Ω load at gain of 2, the bandwidth is

about 50MHz. The bandwidth at the REF input is about

450MHz. The EL5172 and EL5372 is available with a power

down feature to reduce the power while the amplifier is

disabled.

Input, Output, and Supply Voltage Range

The EL5172 and EL5372 have been designed to operate

with a single supply voltage of 5V to 10V or a split supplies

with its total voltage from 5V to 10V. The amplifiers have an

input common mode voltage range from -4.3V to 3.3V for

±5V supply. The differential mode input range (DMIR)

between the two inputs is about from -2.3V to +2.3V. The

input voltage range at the REF pin is from -3.6V to 3.3V. If

the input common mode or differential mode signal is outside

the above-specified ranges, it will cause the output signal

distorted.

The output of the EL5172 and EL5372 can swing from -3.8V

to 3.6V at 500

Ω load at ±5V supply. As the load resistance

becomes lower, the output swing is reduced respectively.

Over All Gain Settings

The gain setting for the EL5172 and EL5372 is similar to the

conventional operational amplifier. The output voltage is

times the gain.

FIGURE 23.

Choice of Feedback Resistor and Gain Bandwidth

Product

For applications that require a gain of +1, no feedback

resistor is required. Just short the OUT pin to FB 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

maximum value that should not be exceeded for optimum

help to reduce the ringing and peaking at the expense of

reducing the bandwidth.

The bandwidth of the EL5172 and EL5372 depends on the

parallel with the load for gains other than +1. As this

combination gets smaller, the bandwidth falls off.

be exceeded for optimum bandwidth performance. For gain

1k

and the frequency response is very flat.

The EL5172 and EL5372 have a gain bandwidth product of

100MHz. For gains

≥5, its bandwidth can be predicted by the

following equation:

Driving Capacitive Loads and Cables

The EL5172 and EL5372 can drive 56pF capacitance in

parallel with 500

Ω load to ground with 4dB of peaking at gain

of +1. If less peaking is desired in applications, a small

series resistor (usually between 5

Ω to 50Ω) can be placed in

series with each output to eliminate most peaking. However,

this will reduce the gain slightly. If the gain setting is greater

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.

Disable/Power-Down

The EL5172 and EL5372 can be disabled and placed its

outputs in a high impedance state. The turn off time is about

1.4µs and the turn on time is about 150ns. When disabled,

V

O

V

(

+

)

1

R

F

R

G

--------

+







×

–

=

-

+

-

+

Σ

G/B

EN

FB

Gain

BW

100MHz

=

×

EL5172, EL5372