EL5171 查看數據表（PDF） - Intersil
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EL5171 Datasheet PDF : 14 Pages
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EL5171, EL5371
The gain setting for EL5371 is:
VODM
=
(
VIN
+
–
VI
N
-
)
×
⎛
⎜
⎝
1
+
-R----F----1-R---+--G---R-----F---2- ⎠⎟⎞
VODM
=
(
VIN
+
–
VI
N
-
)
×
⎛
⎜
⎝
1
+
-2-R--R---G--F- ⎠⎟⎞
VOCM = VREF
Where:
• RF1 = RF2 = RF
RF1
VIN+
RG
VIN-
VREF
FBP
IN+
IN-
REF
FBN
RF2
VO+
VO-
FIGURE 24.
Choice of Feedback Resistor and Gain Bandwidth
Product
For applications that require a gain of +1, no feedback
resistor is required. Just short the OUT+ pin to FBP pin and
OUT- pin to FBN pin. For gains greater than +1, the
feedback resistor forms a pole with the parasitic capacitance
at the inverting input. As this pole becomes smaller, the
amplifier's phase margin is reduced. This causes ringing in
the time domain and peaking in the frequency domain.
Therefore, RF has some maximum value that should not be
exceeded for optimum performance. If a large value of RF
must be used, a small capacitor in the few Pico farad range
in parallel with RF can help to reduce the ringing and
peaking at the expense of reducing the bandwidth.
The bandwidth of the EL5171 and EL5371 depends on the
load and the feedback network. RF and RG appear in parallel
with the load for gains other than +1. As this combination gets
smaller, the bandwidth falls off. Consequently, RF also has a
minimum value that should not be exceeded for optimum
bandwidth performance. For gain of +1, RF = 0 is optimum.
For the gains other than +1, optimum response is obtained
with RF between 500Ω to 1kΩ.
The EL5171 and EL5371 have a gain bandwidth product of
100MHz for RLD = 1kΩ. For gains ≥5, its bandwidth can be
predicted by the following equation:
Gain × BW = 100MHz
Driving Capacitive Loads and Cables
The EL5171 and EL5371 can drive 50pF differential
capacitor in parallel with 1kΩ differential load with less than
5dB of peaking at gain of +1. If less peaking is desired in
applications, a small series resistor (usually between 5Ω to
50Ω) can be placed in series with each output to eliminate
most peaking. However, this will reduce the gain slightly. If
the gain setting is greater than 1, the gain resistor RG can
then be chosen to make up for any gain loss which may be
created by the additional series resistor at the output.
When used as a cable driver, double termination is always
recommended for reflection-free performance. For those
applications, a back-termination series resistor at the
amplifier's output will isolate the amplifier from the cable and
allow extensive capacitive drive. However, other applications
may have high capacitive loads without a back-termination
resistor. Again, a small series resistor at the output can help
to reduce peaking.
Disable/Power-Down (for EL5371 only)
The EL5371 can be disabled and placed its outputs in a high
impedance state. The turn off time is about 0.95µs and the
turn on time is about 215ns. When disabled, the amplifier's
supply current is reduced to 1.7µA for IS+ and 120µA for IS-
typically, thereby effectively eliminating the power
consumption. The amplifier's power down can be controlled
by standard CMOS signal levels at the ENABLE pin. The
applied logic signal is relative to VS+ pin. Letting the EN pin
float or applying a signal that is less than 1.5V below VS+ will
enable the amplifier. The amplifier will be disabled when the
signal at EN pin is above VS+ - 0.5V.
Output Drive Capability
The EL5171 and EL5371 have internal short circuit
protection. Its typical short circuit current is ±90mA for
EL5171 and ±70mA for EL5371. If the output is shorted
indefinitely, the power dissipation could easily increase such
that the part will be destroyed. Maximum reliability is
maintained if the output current never exceeds ±60mA. This
limit is set by the design of the internal metal
interconnections.
Power Dissipation
With the high output drive capability of the EL5171 and
EL5371. It is possible to exceed the 135°C absolute maximum
junction temperature under certain load current conditions.
Therefore, it is important to calculate the maximum junction
temperature for the application to determine if the load
conditions or package types need to be modified for the
amplifier to remain in the safe operating area.
The maximum power dissipation allowed in a package is
determined according to:
PDMAX = T----J---M-----A----X-Θ----–-J---A-T----A---M-----A----X--
10
FN7307.6
October 30, 2006
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