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参数资料
| 型号： | EL2008CT |
| 英文描述： | 55 MHz 1 Amp Buffer Amplifier |
| 中文描述： | 55兆赫1安培缓冲放大器 |
| 文件页数： | 10/12页 |
| 文件大小： | 446K |
| 代理商： | EL2008CT |
7
EL2008C
55 MHz 1 Amp Buffer Amplifier
E
L
20
08
C
they have a series resistance of about 20
. If the output
of the EL2008C is accidentally shorted it is possible that
some devices driving the EL2008C's input could be
damaged or destroyed driving the EL2008C's load
through the diodes while the EL2008C is unaffected. In
such cases a resistor in series with the input of the
EL2008C can limit the current.
Source Impedance
The EL2008C has good input to output isolation. Open
loop, capacitive and resistive sources up to 100 k
present no oscillation problem driving resistive loads as
long as care is used in board layout to minimize output
to input coupling and the supplies are properly bypassed.
When driving capacitive loads in the 100 pF to 1000 pF
region source resistances above 25
can cause peaking
and oscillation. Such problems can be eliminated by
placing a capacitor from the EL2008C's input to ground.
The value should be about 1/4 the load capacitance. In a
feedback loop there is a speed penalty and a possibility
of oscillation when the EL2008C is driven with a source
impedance of 200
or more. Significant phase shift can
occur due to the EL2008C's 25 pF input capacitance.
Inductive sources can cause oscillations. A series resis-
tor of a few hundred ohms to 1 k
will usually solve the
problem.
Current Limit
The EL2008C has internal current limiting to protect the
output transistors. The current limit is about 1.5A at
room temperature and decreases with junction tempera-
ture. At 150°C junction temperature it is above 1A.
Heat Sinking
A suitable heat sink will be required for most applica-
tions. The thermal resistance junction to case for the TO-
220 package is 4°C per watt. No voltage appears at the
heat sink tab so no precautions need to be taken to avoid
shorting the tab to a supply voltage or ground. As there
is a small parasitic capacitance between the tab and the
buffer circuitry, it is recommended that the tab be con-
nected to AC ground (either supply voltage or DC
ground). The center lead is internally connected to the
tab so the connection can be made at the tab or the center
lead.
Parallel Operation
If more than 1A is required or if heat management is a
problem, several EL2008Cs may be paralleled together.
The result is as through each device was driving only
part of the load. For example, if two units are paralleled
then a 5
load looks like 10 to each EL2008C. Of
course, parallel operation reduces both the input and out-
put impedance and increases bias current. But there is no
increase in offset voltage. Three units in parallel can
drive a 3
load ±10V at 2500 V/s. The output imped-
ance will be about 0.33
.
Resistive Loads
The DC gain of the EL2008C is the product of the
unloaded gain (0.999) and the voltage divider formed by
the device output resistance and the load resistance.
AV = 0.999* (RL/RL + ROUT)
The high frequency response varies with the load resis-
tance as shown by the characteristic curves. Both gain
and phase are shown. If the 80 MHz peaking is undesir-
able when driving load resistors greater than 50
, an RC
snubber circuit can be used from output to ground. The
capacitive load section discusses snubber usage in more
detail.
Capacitive Loads
The EL2008C is not stable driving purely capacitive
loads between 100 pF and 500 pF. Purely capacitive
loads from 500 pF to 1000 pF will also have excessive
peaking as shown in the characteristic curves. The
squarewave response will have large overshoots and
ring for hundreds of nanoseconds.
When driving capacitive loads, stability can be achieved
and peaking and ringing can be minimized either by add-
ing a 50
(or less) load in parallel with the capacitive
load or by an RC snubber circuit from output to ground.
The snubber values can be found empirically by observ-
ing a squarewave or the frequency response. First just
put a resistor alone from the output to ground until the
desired response is achieved. The gain will be reduced
due to the output resistance of the EL2008C and power
consumption will be high. Then put a capacitor in series
with the resistor to restore gain at low frequencies and
eliminate the DC current. Start with a small capacitor
and increase until the response is optimum. The figure
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