EL2176C/EL2276C
70 MHz/1 mA Current Mode Feedback Amp w/Disable
tion should be used, but it should be removed
Applications Information
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 their additional series
inductance. Use of sockets, particularly for the
SO package should be avoided if possible. Sock-
ets add parasitic inductance and capacitance
which will result in some additional peaking and
overshoot.
Product Description
The EL2176C/EL2276C are current-feedback op-
b
erational amplifiers that offer a wide
3 dB
bandwidth of 70 MHz, a low supply current of
1 mA per amplifier and the ability to disable to
0 mA. Both products also feature high output
current drive. The EL2176C can output 100 mA,
while the EL2276C can output 55 mA per ampli-
fier. The EL2176C/EL2276C work with supply
g
voltages ranging from a single 3V to 6V, and
Disable/Power-Down
they are also capable of swinging to with in 1V of
either supply on the input and the output. Be-
cause of their current-feedback topology, the
EL2176C/EL2276C do not have the normal gain-
bandwidth product associated with voltage-feed-
back operational amplifiers. This allows their
The EL2176C/EL2276C amplifiers can be dis-
abled, placing their output in a high-impedance
state. When disabled, each amplifier’s supply cur-
rent is reduced to
0 mA. Each EL2176C/
EL2276C amplifier is disabled when its
ENABLE pin is floating or pulled up to within
0.5V of the positive supply. Similarly, each am-
plifier is enabled by pulling its ENABLE pin at
b
3 dB bandwidth to remain relatively constant
as closed-loop gain is increased. This combina-
tion of high bandwidth and low power, together
with aggressive pricing make the EL2176C/
EL2276C the ideal choice for many low-power/
high-bandwidth applications such as portable
computing, HDSL, and video processing.
g
least 3V below the positive supply. For 5V sup-
plies, this means that an EL2176C/EL2276C am-
plifier will be enabled when ENABLE is at 2V or
less, and disabled when ENABLE is above 4.5V.
Although the logic levels are not standard TTL,
this choice of logic voltages allows the EL2176C/
EL2276C to be enabled by tying ENABLE to
a
ground, even in 3V single-supply applications.
The ENABLE pin can be driven from CMOS
outputs or open-collector TTL.
For Single, Dual and Quad applications without
disable, consider the EL2170C (8-Pin Single),
EL2270C (8-Pin Dual) and EL2470C (14-Pin
Quad). If more AC performance is required, refer
to the EL2180C/EL2186C family which provides
Singles, Duals, and Quads with 250 MHz of
bandwidth while consuming 3 mA of supply cur-
rent per amplifier.
When enabled, supply current does vary some-
what with the voltage applied at ENABLE. For
example, with the supply voltages of the
b
g
EL2176C at 5V, if ENABLE is tied to 5V
(rather than ground) the supply current will in-
crease about 15% to 1.15 mA.
Power Supply Bypassing and Printed
Circuit Board Layout
As with any high-frequency device, good printed
circuit board layout is necessary for optimum
performance. Ground plane construction is high-
ly recommended. Lead lengths should be as short
as possible. The power supply pins must be well
bypassed to reduce the risk of oscillation. The
combination of a 4.7 mF tantalum capacitor in
parallel with a 0.1 mF capacitor has been shown
to work well when placed at each supply pin.
Capacitance at the Inverting Input
Any manufacturer’s high-speed voltage- or cur-
rent-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 capacitance (in
conjunction with the feedback and gain resistors)
creates a pole in the feedback path of the amplifi-
er. 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 feed-
For good AC performance, parasitic capacitance
should be kept to a minimum especially at the
inverting input (see the Capacitance at the In-
verting Input section). Ground plane construc-
10
ELANTEC [ ELANTEC SEMICONDUCTOR ]
