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參數(shù)資料
| 型號(hào)： | OPA4650 |
| 英文描述： | Wideband, Low Power, Quad Voltage Feedback OPERATIONAL AMPLIFIER |
| 中文描述： | 寬帶，低功耗，四路電壓反饋運(yùn)算放大器 |
| 文件頁(yè)數(shù)： | 10/13頁(yè) |
| 文件大?。?/td> | 235K |
| 代理商： | OPA4650 |
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10
OPA4650
FREQUENCY RESPONSE COMPENSATION
Each channel of the OPA4650 is internally compensated to
be stable at unity gain with a nominal 60
°
phase margin.
This lends itself well to wideband integrator and buffer
applications. Phase margin and frequency response flatness
will improve at higher gains. Recall that an inverting gain of
–1 is equivalent to a gain of +2 for bandwidth purposes, i.e.,
noise gain = 2. The external compensation techniques devel-
oped for voltage feedback op amps can be applied to this
device. For example, in the non-inverting configuration,
placing a capacitor across the feedback resistor will reduce
the gain to +1 starting at f = (1/2
π
R
F
C
F
). Alternatively, in the
inverting configuration, the bandwidth may be limited with-
out modifying the inverting gain by placing a series RC
network to ground on the inverting node. This has the effect
of increasing the noise gain at high frequencies, thereby
limiting the bandwidth for the inverting input signal through
the gain-bandwidth product.
At higher gains, the gain-bandwidth of this voltage feedback
topology will limit bandwidth according to the open-loop
frequency response curve. For applications requiring a wider
bandwidth at higher gains, consider the quad current feed-
back model, OPA4658. In applications where a large feed-
back resistor is required (such as photodiode transimpedance
circuits), precautions must be taken to avoid gain peaking
due to the pole formed by the feedback resistor and the
summing junction capacitance. This pole can be compen-
sated by connecting a small capacitor in parallel with the
feedback resistor, creating a cancelling zero term. In other
high-gain applications, use of a three-resistor “T” connec-
tion will reduce the feedback network impedance which
reacts with the parasitic capacitance at the summing node.
PULSE SETTLING TIME
High speed amplifiers like the OPA4650 are capable of
extremely fast settling time with a pulse input. Excellent
frequency response flatness and phase linearity are required
to get the best settling times. As shown in the specifications
table, settling time for a
±
1V step at a gain of +1 for the
OPA4650 is extremely fast. The specification is defined as
the time required, after the input transition, for the output to
settle within a specified error band around its final value. For
a 2V step, 1% settling corresponds to an error band of
±
20mV, 0.1% to an error band of
±
2mV, and 0.01% to an
error band of
±
0.2mV. For the best settling times, particu-
larly into an ADC capacitive load, little or no peaking in the
frequency response can be allowed. Using the recommended
R
ISO
for capacitive loads will limit this peaking and reduce
the settling times. Fast, extremely fine scale settling (0.01%)
requires close attention to ground return currents in the
supply decoupling capacitors. For highest performance, con-
sider the OPA642 which isolates the output stage decoupling
from the rest of the amplifier.
THERMAL CONSIDERATIONS
The OPA4650 will not require heatsinking under most
operating conditions. Maximum desired junction tempera-
ture will limit the maximum allowed internal power dissipa-
tion 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 a com-
bination of the total quiescent power for all channels (P
DQ
)
and the sum of the powers dissipated in each of the output
stages (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 a fixed
dc voltage equal to 1/2 of either supply voltage (assuming
equal bipolar supplies). Under this condition, P
DL
= V
S2
/
(4R
L
) where R
L
includes feedback network loading. Note
that it is the power dissipated in the output stage and not in
the load that determines internal power dissipation. As an
example, compute the maximum T
J
for an OPA4650U at
A
V
= +2, R
L
= 100
, R
FB
= 402
,
±
V
S
=
±
5V, with all 4
outputs at |V
S
/2|, and the specified maximum T
A
= +85
°
C.
P
D
= 10V35mA + 4(5
2
)/(4(100
||804
)) = 631mW.
Maximum T
J
= +85
°
C + 0.641W75
°
C/W = 133
°
C.
DRIVING CAPACITIVE LOADS
The OPA4650’s output stage has been optimized to drive
low resistive loads. Capacitive loads will decrease phase
margin which may result in high frequency oscillations or
peaking. Capacitive loads greater than 10pF should be iso-
lated by connecting a small resistance (15
to 30
) in series
with the output as shown in Figure 4. This is especially
important when driving the capacitive input of high-speed
A/D converters. Increasing the gain from +1 will improve
the capacitive load drive due to increased phase margin.
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/ft for RG-58) will not load the amplifier when
the cable is source and load terminated in its characteristic
impedance.
FIGURE 4. Driving Capacitive Loads.
OPA4650
C
L
R
L
R
ISO
(R
ISO
typically 5
to 20
)
25
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| OPA4650P | Wideband, Low Power, Quad Voltage Feedback OPERATIONAL AMPLIFIER |
| OPA4650U | Wideband, Low Power, Quad Voltage Feedback OPERATIONAL AMPLIFIER |
| OPA4684ID | Quad, Low-Power, Current-Feedback OPERATIONAL AMPLIFIER |
| OPA4684 | Wideband, Low-Power, Current Feedback Operational Amplifier |
| OPA4684IPWR | Quad, Low-Power, Current-Feedback OPERATIONAL AMPLIFIER |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| OPA4650P | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| OPA4650U | 制造商:BB 制造商全稱(chēng):BB 功能描述:Wideband, Low Power, Quad Voltage Feedback OPERATIONAL AMPLIFIER |
| OPA4658 | 制造商:BB 制造商全稱(chēng):BB 功能描述:Quad Wideband, Low Power Current Feedback OPERATIONAL AMPLIFIER |
| OPA4658P | 功能描述:高速運(yùn)算放大器 Quad Wideband RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補(bǔ)償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| OPA4658U | 功能描述:高速運(yùn)算放大器 Quad Wideband RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補(bǔ)償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
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