EL5160_07 INTERSIL [Intersil Corporation], EL5160_07 Datasheet - Page 10
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EL5160_07
Manufacturer Part Number
EL5160_07
Description
200MHz Low-Power Current Feedback Amplifiers
Manufacturer
INTERSIL [Intersil Corporation]
Datasheet
1.EL5160_07.pdf
(17 pages)
Disable/Power-Down
The EL5160 amplifier can be disabled placing its output in a
high impedance state. When disabled, the amplifier supply
current is reduced to < 15µA. The EL5160 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 EL5160 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 EL5160 to be enabled by tying CE
to ground, even in 5V single supply applications. The CE pin
can be driven from CMOS outputs.
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 capacitance (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.)
The EL5160, EL5161, EL5260, EL5261, and EL5360 have
been optimized with a TBDΩ 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.
Feedback Resistor Values
The EL5160, EL5161, EL5260, EL5261, and EL5360 have
been designed and specified at a gain of +2 with R
approximately 806Ω. This value of feedback resistor gives
200MHz of -3dB bandwidth at A
peaking. With A
200MHz of bandwidth with 1dB of peaking. Since the
EL5160, EL5161, EL5260, EL5261, and EL5360 are current-
feedback amplifiers, it is also possible to change the value of
R
Frequency Response for Various R
peaking can be easily modified by varying the value of the
feedback resistor.
Because the EL5160, EL5161, EL5260, EL5261, and
EL5360 are current-feedback amplifiers, their gain-
bandwidth product is not a constant for different closed-loop
gains. This feature actually allows the EL5160, EL5161,
EL5260, EL5261, and EL5360 to maintain about the same -
3dB bandwidth. As gain is increased, bandwidth decreases
slightly while stability increases. Since the loop stability is
improving with higher closed-loop gains, it becomes possible
F
to get more bandwidth. As seen in the curve of
V
= -2, an R
F
10
of approximately TBDΩ gives
V
= 2 with TBDdB of
F
EL5160, EL5161, EL5260, EL5261, EL5360
and R
G
, bandwidth and
F
to reduce the value of R
retain stability, resulting in only a slight loss of bandwidth
with increased closed-loop gain.
Supply Voltage Range and Single-Supply
Operation
The EL5160, EL5161, EL5260, EL5261, and EL5360 have
been designed to operate with supply voltages having a
span of greater than 5V and less than 10V. In practical
terms, this means that they will operate on dual supplies
ranging from ±2.5V to ±5V. With single-supply, the EL5160,
EL5161, EL5260, EL5261, and EL5360 will operate from 5V
to 10V.
As supply voltages continue to decrease, it becomes
necessary to provide input and output voltage ranges that
can get as close as possible to the supply voltages. The
EL5160, EL5161, EL5260, EL5261, and EL5360 have an
input range which extends to within 2V of either supply. So,
for example, on +5V supplies, the EL5160, EL5161, EL5260,
EL5261, and EL5360 have an input range which spans ±3V.
The output range of the EL5160, EL5161, EL5260, EL5261,
and EL5360 is also quite large, extending to within 1V of the
supply rail. On a ±5V supply, the output is therefore capable
of swinging from -4V to +4V. Single-supply output range is
larger because of the increased negative swing due to the
external pull-down resistor to ground.
Video Performance
For good video performance, an amplifier is required to
maintain the same output impedance and the same
frequency response as DC levels are changed at the output.
This is especially difficult when driving a standard video load
of 150Ω, because of the change in output current with DC
level. Previously, good differential gain could only be
achieved by running high idle currents through the output
transistors (to reduce variations in output impedance.)
These currents were typically comparable to the entire 1mA
supply current of each EL5160, EL5161, EL5260, EL5261,
and EL5360 amplifier. Special circuitry has been
incorporated in the EL5160, EL5161, EL5260, EL5261, and
EL5360 to reduce the variation of output impedance with
current output. This results in dG and dP specifications of
0.1% and 0.1°, while driving 150Ω at a gain of 2.
Video performance has also been measured with a 500Ω
load at a gain of +1. Under these conditions, the EL5160 has
dG and dP specifications of 0.1% and 0.1°.
Output Drive Capability
In spite of their low 1mA of supply current, the EL5160,
EL5161, EL5260, EL5261, and EL5360 are capable of
providing a minimum of ±50mA of output current. With a
minimum of ±50mA of output drive, the EL5160 is capable of
driving 50Ω loads to both rails, making it an excellent choice
for driving isolation transformers in telecommunications
applications.
F
below the specified TBDΩ and still
May 7, 2007
FN7387.9