el2150 Intersil Corporation, el2150 Datasheet - Page 15

• Manufacturer Part Number: el2150
• Description: 125mhz Single Supply, Clamping Op Amps
• Manufacturer: Intersil Corporation

Figure 1 below is a unity gain connected EL2157 being
driven by a 3V
CLAMP pin. The resulting output waveform, with its output
being clamped to 2.25V, is shown in Figure 2.
Figure 3 shows the output 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 signal is clamped to the voltage
applied to the CLAMP pin almost instantaneously. The
output recovers from the clamped mode within 5ns - 7ns,
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 11ns.
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 to a few hundred millivolts. Be
sure to allow for these inaccuracies when choosing the
P-P
sinewave, with 2.25V applied to the
FIGURE 1.
FIGURE 2.
FIGURE 3.
15
EL2150, EL2157
clamp voltage. Curves of Clamp Accuracy vs V
V
Performance Curves Section.
Unlike amplifiers that clamp at the input and are therefore
limited to non-inverting applications only, the EL2157 output
clamp architecture works for both inverting and non-inverting
gain applications. There is also no maximum voltage
difference limitation between V
common on input clamped architectures.
The voltage clamp operates for any voltage between +1.2V
above the GND pin, and the minimum output voltage swing,
V
saturate transistors and should therefore be avoided.
Forcing the CLAMP pin above V
CLAMP feature. In other words, one cannot expect to clamp
any voltage higher than what the EL2157 can drive to in the
first place. If the clamp feature is not desired, either let the
CLAMP pin float or connect it to the V
EL2157 Comparator Application
The EL2157 can be used as a very fast, single supply
comparator by utilizing the clamp feature. Most op amps
used as comparators allow only slow speed operation
because of output saturation issues. However, by applying a
DC voltage to the CLAMP pin of the EL2157, the maximum
output voltage can be clamped, thus preventing saturation.
Figure 4 below is the EL2157 implemented as a comparator.
2.5V DC is applied to the CLAMP pin, as well as the IN- pin.
A differential signal is then applied between the inputs.
Figure 5 shows the output square wave that results when a
±1V, 10MHz triangular wave is applied, while Figure 6 is a
graph of propagation delay vs. overdrive as a square wave is
presented at the input.
IN
OP
for 3 values of R
. Forcing the CLAMP pin much below +1.2V can
L
are included in the Typical
FIGURE 4.
FIGURE 5.
IN
OP
and V
simply de-activates the
S
+ pin.
CLAMP
CLAMP
which is
, and