EL5197C, EL5197AC
Single 200MHz Fixed Gain Amplifier with Enable
Applications Information
particularly for the SO package, should be avoided if
possible. Sockets add parasitic inductance and capaci-
tance which will result in additional peaking and
overshoot.
Product Description
The EL5197C is a current-feedback operational ampli-
fier that offers a wide -3dB bandwidth of 300MHz and a
low supply current of 4mA per amplifier. The EL5197C
works with supply voltages ranging from a single 5V to
10V and they are also capable of swinging to within 1V
of either supply on the output. Because of their current-
feedback topology, the EL5197C does not have the nor-
mal gain-bandwidth product associated with voltage-
feedback operational amplifiers. Instead, its -3dB band-
width to remain relatively constant as closed-loop gain is
increased. This combination of high bandwidth and low
power, together with aggressive pricing make the
EL5197C the ideal choice for many low-power/high-
bandwidth applications such as portable, handheld, or
battery-powered equipment.
Disable/Power-Down
The EL5197AC amplifier can be disabled placing its
output in a high impedance state. When disabled, the
amplifier supply current is reduced to < 150µA. The
EL5197AC is disabled when its CE pin is pulled up to
within 1V of the positive supply. Similarly, the amplifier
is enabled by floating or pulling its CE pin to at least 3V
below the positive supply. For 5V supply, this means
that an EL5197AC amplifier will be enabled when CE is
2V or less, and disabled when CE is above 4V. Although
the logic levels are not standard TTL, this choice of
logic voltages allows the EL5197AC to be enabled by
tying CE to ground, even in 5V single supply applica-
tions. The CE pin can be driven from CMOS outputs.
For varying bandwidth needs, consider the EL5191C
with 1GHz on a 9mA supply current or the EL5192C
with 600MHz on a 6mA supply current. Versions
include single, dual, and triple amp packages with 5-pin
SOT23, 16-pin QSOP, and 8-pin or 16-pin SO outlines.
Capacitance at the Inverting Input
Any manufacturer’s high-speed voltage- or current-
feedback amplifier can be affected by stray capacitance
at the inverting input. For inverting gains, this parasitic
capacitance has little effect because the inverting input is
a virtual ground, but for non-inverting gains, this capac-
itance (in conjunction with the feedback and gain
resistors) creates a pole in the feedback path of the
amplifier. This pole, if low enough in frequency, has the
same destabilizing effect as a zero in the forward open-
loop response. The use of large-value feedback and gain
resistors exacerbates the problem by further lowering
the pole frequency (increasing the possibility of
oscillation.)
Power Supply Bypassing and Printed Circuit
Board Layout
As with any high frequency device, good printed circuit
board layout is necessary for optimum performance.
Low impedance ground plane construction is essential.
Surface mount components are recommended, but if
leaded components are used, lead lengths should be as
short as possible. The power supply pins must be well
bypassed to reduce the risk of oscillation. The combina-
tion of a 4.7µF tantalum capacitor in parallel with a
0.01µF capacitor has been shown to work well when
placed at each supply pin.
The EL5197C has been optimized with a 475Ω feedback
resistor. With the high bandwidth of these amplifiers,
these resistor values might cause stability problems
when combined with parasitic capacitance, thus ground
plane is not recommended around the inverting input pin
of the amplifier.
For good AC performance, parasitic capacitance should
be kept to a minimum, especially at the inverting input.
(See the Capacitance at the Inverting Input section) Even
when ground plane construction is used, it should be
removed from the area near the inverting input to mini-
mize any stray capacitance at that node. Carbon or
Metal-Film resistors are acceptable with the Metal-Film
resistors giving slightly less peaking and bandwidth
because of additional series inductance. Use of sockets,
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