EL2257C Elantec Semiconductor, EL2257C Datasheet - Page 16

• Manufacturer Part Number: EL2257C
• Description: 125 MHz Single Supply/ Clamping Op Amps
• Manufacturer: Elantec Semiconductor

EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Unlike amplifiers that clamp at the input and are there-
fore limited to non-inverting applications only, the
EL2257C/EL2357C output clamp architecture works for
both inverting and non-inverting gain applications.
There is also no maximum voltage difference limitation
between V
clamped architectures.
The voltage clamp operates for any voltage between
+1.2V above the GND pin, and the minimum output
voltage swing, V
below +1.2V can saturate transistors and should there-
fore be avoided. Forcing the CLAMP pin above V
simply de-activates the CLAMP feature. In other words,
one cannot expect to clamp any voltage higher than what
the EL2257C/EL2357C 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
EL2257C/EL2357C Comparator Application
The EL2257C/EL2357C can be used as a very fast, sin-
gle 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 EL2257C/EL2357C, the maximum output voltage
can be clamped, thus preventing saturation. Figure 4 is
amplifier A of an EL2257C implemented as a compara-
tor. 2.25V 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, 10 MHz triangular wave is applied,
IN
and V
OP
CLAMP
. Forcing the CLAMP pin much
which is common on input
S+
pin.
OP
16
while Figure 6 is a graph of propagation delay vs. over-
drive as a square wave is presented at the input.
Propagation Delay vs Overdrive
EL2257/EL2357 as a Comparator
Figure 4.
Figure 5.
Figure 6.