13 FN7491.5 August 28, 2012 FIGURE 34. Choice of Feedback Resistor and Gain Bandwidth Product For gains greater than 1, the feed" />
參數(shù)資料
型號: EL5178ISZ
廠商: Intersil
文件頁數(shù): 5/17頁
文件大?。?/td> 0K
描述: IC DRVR TWISTED SGL 700MHZ 8SOIC
標準包裝: 97
放大器類型: 差分
電路數(shù): 1
輸出類型: 差分
轉換速率: 850 V/µs
增益帶寬積: 350MHz
-3db帶寬: 700MHz
電流 - 輸入偏壓: 14µA
電壓 - 輸入偏移: 1900µV
電流 - 電源: 12.5mA
電流 - 輸出 / 通道: 100mA
電壓 - 電源,單路/雙路(±): 4.75 V ~ 11 V,±2.38 V ~ 5.5 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 8-SOIC(0.154",3.90mm 寬)
供應商設備封裝: 8-SOIC
包裝: 管件
EL5178, EL5378
13
FN7491.5
August 28, 2012
FIGURE 34.
Choice of Feedback Resistor and Gain
Bandwidth Product
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 EL5178 and EL5378 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 the gains other than 1, optimum response is
obtained with RF between 500Ω to 1kΩ.
The EL5178 and EL5378 have a gain bandwidth product of
350MHz for RLD = 1kΩ. For gains ≥5, its bandwidth can be
predicted by Equation 3:
Driving Capacitive Loads and Cables
The EL5178 and EL5378 can drive a 23pF differential capacitor
in parallel with 200
Ω differential load with less than 5dB of
peaking at gain of 2. If less peaking is desired in applications, a
small series resistor (usually between 5
Ω 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
2, 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 EL5378 only)
The EL5378 can be disabled and its outputs placed in a high
impedance state. The turn-off time is about 1.2s and the turn-
on time is about 130ns. When disabled, the amplifier's supply
current is reduced to 1.7A for IS+ and 120A for IS- typically,
thereby effectively eliminating the power consumption. The
amplifier's power-down can be controlled by standard CMOS
signal levels at the EN pin. The applied logic signal is relative to
the 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 the EN pin is above VS+ - 0.5V.
Output Drive Capability
The EL5178 and EL5378 have internal short circuit protection. Its
typical short circuit current is ±60mA. 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 EL5178 and EL5378, 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 Equation 4:
Where:
TJMAX = Maximum junction temperature
TAMAX = Maximum ambient temperature
θJA = Thermal resistance of the package
The maximum power dissipation actually produced by an IC is
the total quiescent supply current times the total power supply
voltage, plus the power in the IC due to the load, or as expressed
in Equation 5:
Where:
VSTOT = Total supply voltage = VS+ - VS-
ISMAX = Maximum quiescent supply current per channel
ΔVO = Maximum differential output voltage of the application
RLD = Differential load resistance
ILOAD = Load current
i = Number of channelsBy setting the two PDMAX equations
equal to each other, we can solve the output current and RLD to
avoid the device overheat.
VO+
FBP
RG
RF2
IN+
IN-
REF
FBN
VIN+
VIN-
VREF
RF1
VO-
Gain
BW
300MHz
=
×
(EQ. 3)
PD
MAX
T
JMAX
T
AMAX
Θ
JA
---------------------------------------------
=
(EQ. 4)
(EQ. 5)
PD
i
V
STOT
I
SMAX
×
V
(
STOT
ΔV
O )
ΔV
O
R
LD
------------
×
+
×
=
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