EL2257CN 데이터 시트보기 (PDF) - Elantec -> Intersil

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EL2257CN

125 MHz Single Supply, Clamping Op Amps

Elantec -> Intersil 

EL2257C/EL2357C

125 MHz Single Supply, Clamping Op Amps

Output Voltage Clamp

The EL2257C/EL2357C amplifiers have an output volt-

age clamp. This clamping action is fast, being activated

almost instantaneously, and being deactivated in < 7 ns,

and prevents the output voltage from going above the

preset clamp voltage. This can be very helpful when the

EL2257C/EL2357C are used to drive an A/D converter,

as some converters can require long times to recover if

overdriven. The output voltage remains at the clamp

voltage level as long as the product of the input voltage

and the gain setting exceeds the clamp voltage. For

example, if the EL2257C/EL2357C is connected in a

gain of 2, and +3V DC is applied to the CLAMP pin, any

voltage higher than +1.5V at the inputs will be clamped

and +3V will be seen at the output. Each amplifier of the

EL2257C have their own CLAMP pin, so individual

clamp levels may be set, whereas a single CLAMP pin

controls the clamp level of the EL2357C.

Figure 1 below is the EL2257C with each amplifier

unity gain connected. Amplifier A is being driven by a 3

Vp-p sinewave and has 2.25V applied to CLAMPA,

while amplifier B is driven by a 3 Vp-p triangle wave

and 1.5V is applied to CLAMPB. The resulting output

waveforms, with their outputs being clamped is shown

in Figure 2.

Figure 2.

Figure 3 shows the output of amplifier A of the same

circuit being driven by a 0.5V to 2.75V square wave as

the clamp voltage is varied from 1.0V to 2.5V, as well as

the unclamped output signal. The rising edge of the sig-

nal is clamped to the voltage applied to the CLAMP pin

almost instantaneously. The output recovers from the

clamped mode within 5–7 ns, depending on the clamp

voltage. Even when the CLAMP pin is taken 0.2V below

the minimum 1.2V specified, the output is still clamped

and recovers in about 11 ns.

Figure 1.

Figure 3.

The clamp accuracy is affected by 1) the CLAMP pin

voltage, 2) the input voltage, and 3) the load resistor.

Depending upon the application, the accuracy may be as

little as a few tens of millivolts up to a few hundred mil-

livolts. Be sure to allow for these inaccuracies when

choosing the clamp voltage. Curves of Clamp Accuracy

vs. VCLAMP and VIN for 3 values of RL are included in

the Typical Performance Curves Section.

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