9

FN7385.6

March 2, 2009

EL5152 Product Description

The EL5152, EL5153, EL5252, and EL5455 are wide

bandwidth, low power, low offset voltage feedback

operational amplifiers capable of operating from a single or

dual power supplies. This family of operational amplifiers are

internally compensated for closed loop gain of +1 or greater.

Connected in voltage follower mode, driving a 500

Ω load

members of this amplifier family demonstrate a -3dB

bandwidth of about 270MHz. With the loading set to

accommodate typical video application, 150

Ω load and gain

set to +2, bandwidth reduces to about 180MHz with a

600V/µs slew rate. Power down pins on the EL5152 and

EL5252 reduce the already low power demands of this

amplifier family to 17µA typical while the amplifier is

disabled.

Input, Output and Supply Voltage Range

The EL5152 and EL5153 families have been designed to

operate with supply voltage ranging from 5V to 12V. Supply

voltages range from ±2.5V to ±5V for split supply operation.

Of course split supply operation can easily be achieved

using single supplies by splitting off half of the single supply

with a simple voltage divider as illustrated in the application

circuit section.

Input Common Mode Range

These amplifiers have an input common mode voltage

driven beyond this range the output signal will exhibit

distortion.

Maximum Output Swing & Load Resistance

The outputs of the EL5152 and EL5153 families maximum

resistance of 500

Ω. Naturally, as the load resistance

becomes lower, the output swing lowers accordingly; for

instance, if the load resistor is 150

Ω, the output swing

ranges from -3.5V to 3.5V. This response is a simple

application of Ohms law indicating a lower value resistance

results in greater current demands of the amplifier.

Additionally, the load resistance affects the frequency

response of this family as well as all operational amplifiers,

as clearly indicated by the Gain vs Frequency for Various RL

curves clearly indicate. In the case of the frequency

response reduced bandwidth with decreasing load

resistance is a function of load resistance in conjunction with

the output zero response of the amplifier.

Choosing a Feedback Resistor

A feedback resistor is required to achieve unity gain; simply

short the output pin to the inverting input pin. Gains greater

than +1 require a feedback and gain resistor to set the

desired gain. This gets interesting because the feedback

resistor forms a pole with the parasitic capacitance at the

inverting input. As the feedback resistance increases the

position of the pole shifts in the frequency domain, the

amplifier's phase margin is reduced and the amplifier

becomes less stable. Peaking in the frequency domain and

ringing in the time domain are symptomatic of this shift in

pole location. So we want to keep the feedback resistor as

small as possible. You may want to use a large feedback

resistor for some reason; in this case to compensate the shift

of the pole and maintain stability a small capacitor in the few

Pico farad range in parallel with the feedback resistor is

recommended.

For the gains greater than unity, it has been determined a

feedback resistance ranging from 500

Ω to 750Ω provides

optimal response.

Gain Bandwidth Product

The EL5156 and EL5157 families have a gain bandwidth

product of 210MHz for a gain of +5. Bandwidth can be

predicted by the following Equation 1:

Video Performance

For good video performance, an amplifier is required to

maintain the same output impedance and same frequency

response as DC levels are changed at the output; this

characteristic is widely referred to as “diffgain-diffphase”.

Many amplifiers have a difficult time with this especially while

driving standard video loads of 150

Ω, as the output current

has a natural tendency to change with DC level. The EL5152

dG and dP for these families is a respectable 0.006% and

0.04%, while driving 150

Ω at a gain of 2. Driving high

impedance loads would give a similar or better dG and dP

performance as the current output demands placed on the

amplifier lessen with increased load.

Driving Capacitive Loads

The EL5152 and EL5153 families can easily drive capacitive

loads as demanding as 27pF in parallel with 500

Ω while

holding peaking to within 5dB of peaking at unity gain. Of

course if less peaking is desired, a small series resistor

(usually between 5

Ω to 50Ω) can be placed in series with the

output to eliminate most peaking. However, there will be a

small sacrifice of gain which can be recovered by simply

adjusting the value of the gain resistor.

Driving Cables

Both ends of all cables must always be properly terminated;

double termination is absolutely necessary for reflection-free

performance. Additionally, 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.

Gain

BW

GainBandwidthProduct

=

×

(EQ. 1)

EL5152, EL5153, EL5252, EL5455