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參數(shù)資料
| 型號： | OPA644 |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | Low Distortion Current Feedback Operational Amplifier(低失真電流反饋運算放大器) |
| 中文描述： | 低失真電流反饋運算放大器（低失真電流反饋運算放大器） |
| 文件頁數(shù)： | 10/13頁 |
| 文件大?。?/td> | 143K |
| 代理商： | OPA644 |
OPA644
10
INPUT PROTECTION
Static damage has been well recognized for MOSFET de-
vices, but any semiconductor device deserves protection
from this potentially damaging source. The OPA644 incor-
porates on-chip ESD protection diodes as shown in Figure 3.
This eliminates the need for the user to add external protec-
tion diodes, which can add capacitance and degrade AC
performance.
All pins on the OPA644 are internally protected from ESD
by means of a pair of back-to-back reverse-biased diodes to
either power supply as shown. These diodes will begin to
conduct when the input voltage exceeds either power supply
by about 0.7V. This situation can occur with loss of the
amplifier’s power supplies while a signal source is still
present. The diodes can typically withstand a continuous
current of 30mA without destruction. To insure long term
reliability, however, diode current should be externally lim-
ited to 10mA or so whenever possible.
The OPA644 utilizes a fine geometry high speed process
that withstands 500V using the Human Body Model and
100V using the machine model. However, static damage can
cause subtle changes in amplifier input characteristics with-
out necessarily destroying the device. In precision opera-
tional amplifiers, this may cause a noticeable degradation of
offset voltage and drift. Therefore, static protection is strongly
recommended when handling the OPA644.
OUTPUT DRIVE CAPABILITY
The OPA644 has been optimized to drive 75
and 100
resistive loads. The device can drive 2Vp-p into a 75
load.
This high-output drive capability makes the OPA644 an
ideal choice for a wide range of RF, IF, and video applica-
tions. In many cases, additional buffer amplifiers are un-
needed.
Many demanding high-speed applications such as
ADC/DAC buffers require op amps with low wideband
output impedance. For example, low output impedance is
essential when driving the signal-dependent capacitances at
the inputs of flash A/D converters. As shown in Figure 4,
the OPA644 maintains very low closed-loop output imped-
ance over frequency. Closed-loop output impedance in-
creases with frequency since loop gain is decreasing with
frequency.
THERMAL CONSIDERATIONS
The OPA644 does not require a heat sink for operation in
most environments. At extreme temperatures and under full
load conditions a heat sink may be necessary.
The internal power dissipation is given by the equation
P
D
= P
DQ
+ P
DL
, where P
DQ
is the quiescent power dissipa-
tion and P
DL
is the power dissipation in the output stage due
to the load. (For
±
V
CC
=
±
5V, P
DQ
= 10V
x
26mA = 260mW,
max). For the case where the amplifier is driving a grounded
load (R
L
) with a DC voltage (
±
V
OUT
) the maximum value of
P
DL
occurs at
±
V
OUT
=
±
V
CC
/ 2, and is equal to P
DL
, max
= (
±
V
CC
)
2
/4R
L
. Note that it is the voltage across the output
transistor, and not the load, that determines the power
dissipated in the output stage.
The short-circuit condition represents the maximum amount
of internal power dissipation that can be generated. The
variation of output current with temperature is shown in the
Typical Performance Curves.
CAPACITIVE LOADS
The OPA644’s output stage has been optimized to drive low
resistive loads. Capacitive loads, however, will decrease the
amplifier’s phase margin which may cause high frequency
peaking or oscillations. Capacitive loads greater than 5pF
should be buffered by connecting a small resistance, usually
5
to 25
, in series with the output as shown in Figure 5.
This is particularly important when driving high capacitance
loads such as flash A/D converters.
100
10
1
0.1
0.01
0.001
10K
100K
1M
10M
100M
Frequency (Hz)
O
)
A
V
= +2V/V
FIGURE 4. Closed-Loop Output Impedance vs Frequency.
FIGURE 5. Driving Capacitive Loads.
OPA644
C
L
R
L
R
S
(R
S
typically 5
to 25
)
402
External
Pin
+V
CC
–V
CC
Internal
Circuitry
FIGURE 3. Internal ESD Protection.
ESD Protection diodes internally
connected to all pins.
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| OPA644U | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| OPA644UB | 制造商:BB 制造商全稱:BB 功能描述:Low Distortion Current Feedback OPERATIONAL AMPLIFIER |
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| OPA646 WAF | 制造商:Texas Instruments 功能描述: |
| OPA646U | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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