參數(shù)資料
型號(hào)： OPA658UB
元件分類(lèi)： 運(yùn)算放大器
英文描述： Wideband, Low Power Current Feedback OPERATIONAL AMPLIFIER
中文描述： 寬帶，低功耗電流反饋運(yùn)算放大器
文件頁(yè)數(shù)： 10/13頁(yè)
文件大?。?/td> 215K
代理商： OPA658UB
10
OPA658
402
OPA658
V
AC
402
R
L
+V
S
+V
S
V
S
2
R
OUT
S
2
V
OUT
= V
V
V
AC
A
V
= +2
specified total supply voltage of 11V. Higher supply voltages
can break down internal junctions possibly leading to cata-
strophic failure. Single supply operation is possible as long as
common mode voltage constraints are observed. The com-
mon mode input and output voltage specifications can be
interpreted as a required headroom to the supply voltage.
Observing this input and output headroom requirement will
allow non-standard or single supply operation. Figure 3
shows one approach to single-supply operation.
THERMAL CONSIDERATIONS
The OPA658 will not require heatsinking under most oper-
ating conditions. Maximum desired junction temperature
will set a maximum allowed internal power dissipation as
described below. In no case should the maximum junction
temperature be allowed to exceed 175
°
C.
Operating junction temperature (T
J
) is given by
T
A
+ P
D
θ
JA
. The total internal power dissipation (P
D
) is
the sum of quiescent power (P
DQ
) and additional power
dissipated in the output stage (P
DL
) to deliver load power.
Quiescent power is simply the specified no-load supply
current times the total supply voltage across the part. P
DL
will depend on the required output signal and load but
would, for a grounded resistive load, be at a maximum when
the output is fixed at a voltage equal to 1/2 either supply
voltage (for equal bipolar supplies). Under this condition
P
DL
= V
S2
/(4 R
L
) where R
L
includes feedback network
loading.
Note that it is the power in the output stage and not into the
load that determines internal power dissipation.
As an example, compute the maximum T
J
for an OPA658N
at A
V
= +2, R
L
= 100
, R
FB
= 402
,
±
V
S
=
±
5V, and the
specified maximum T
A
= +85
°
C. P
D
= 10V 8.5mA + 5
2
/
[4 (100
|| 804
)] = 155mW. Maximum T
J
= 85
°
C +
0.155W 150
°
C/W = 108
°
C.
DRIVING CAPACITIVE LOADS
The OPA658’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
10
to 35
, 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.
In general, capacitive loads should be minimized for opti-
mum high frequency performance. Coax lines can be driven
if the cable is properly terminated. The capacitance of coax
cable (29pF/foot for RG-58) will not load the amplifier
when the coaxial cable or transmission line is terminated
with its characteristic impedance.
FIGURE 4. Closed-Loop Output Impedance vs Frequency.
100
10
1
0.1
0.01
0.001
10k
100k
1M
10M
100M
O
)
Frequency (Hz)
G = +2
ESD PROTECTION
ESD static damage has been well recognized for MOSFET
devices, but any semiconductor device deserves protection
from this potentially damaging source. This is particularly
true for very high speed, fine geometry processes.
ESD static damage can cause subtle changes in amplifier
input characteristics without necessarily destroying the de-
vice. In precision operational amplifiers, this may cause a
noticeable degradation of offset voltage and drift. Therefore,
static protection is strongly recommended when handling
the OPA658.
OUTPUT DRIVE CAPABILITY
The OPA658 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 OPA658 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 OPA658 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.
FIGURE 3. Single Supply Operation.
相關(guān)PDF資料
PDF描述
OPA658 Wideband, Low Power Current Feedback OPERATIONAL AMPLIFIER
OPA658N Wideband, Low Power Current Feedback OPERATIONAL AMPLIFIER
OPA658P Wideband, Low Power Current Feedback OPERATIONAL AMPLIFIER
OPA658U Wideband, Low Power Current Feedback OPERATIONAL AMPLIFIER
OPA660AP Wide Bandwidth OPERATIONAL TRANSCONDUCTANCE AMPLIFIER AND BUFFER
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