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參數(shù)資料
| 型號(hào)： | OPA688 |
| 元件分類： | 運(yùn)動(dòng)控制電子 |
| 英文描述： | Unity Gain Stable, Wideband VOLTAGE LIMITING AMPLIFIER |
| 中文描述： | 單位增益穩(wěn)定，寬帶電壓限幅放大器 |
| 文件頁(yè)數(shù)： | 16/16頁(yè) |
| 文件大?。?/td> | 185K |
| 代理商： | OPA688 |
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OPA688
CAPACITIVE LOADS
Capacitive loads, such as the input to ADCs, will decrease
the amplifier’s phase margin, which may cause high fre-
quency peaking or oscillations. Capacitive loads
≥
2pF
should be isolated by connecting a small resistor in series
with the output as shown in Figure 11. Increasing the gain
from +2 will improve the capacitive drive capabilities due
to increased phase margin.
In general, capacitive loads should be minimized for opti-
mum high frequency performance. The capacitance of coax
cable (29pF/foot for RG-58) will not load the amplifier
when the coaxial cable, or transmission line, is terminated
in its characteristic impedance.
capacitance from the inverting input to ground causes peak-
ing or oscillations. To compensate for this effect, connect a
small capacitor in parallel with the feedback resistor. The
bandwidth will be limited by the pole that the feedback
resistor and this capacitor create. In other high gain applica-
tions, use a three resistor “Tee” network to reduce the RC
time constants set by the parasitic capacitances. Be careful
to not increase the noise generated by this feedback network
too much.
PULSE SETTLING TIME
The OPA688 is capable of an extremely fast settling time in
response to a pulse input. Frequency response flatness and
phase linearity are needed to obtain the best settling times.
For capacitive loads, such as an A/D converter, use the
recommended R
S
in the
R
S
vs Capacitive Load
plot. Ex-
tremely fine scale settling (0.01%) requires close attention to
ground return current in the supply decoupling capacitors.
The pulse settling characteristics when recovering from
overdrive are very good.
DISTORTION
The OPA688’s distortion performance is specified for a
500
load, such as an A/D converter. Driving loads with
smaller resistance will increase the distortion as illustrated in
Figure 12. Remember to include the feedback network in the
load resistance calculations.
FIGURE 11. Driving Capacitive Loads.
FIGURE 12. 5MHz Harmonic Distortion vs Load Resistance.
–40
–45
–50
–55
–60
–65
–70
–75
–80
–85
–90
HARMONIC DISTORTION vs LOAD RESISTANCE
Load Resistance (
)
2
50
100
1000
V
O
= 2Vp-p
f
1
= 5MHz
HD2
HD3
OPA688
C
L
R
L
R
S
V
O
R
L
is optional
FREQUENCY RESPONSE COMPENSATION
The OPA688 is internally compensated to be unity-gain
stable, and has a nominal phase margin of 60
°
at a gain of
+2. Phase margin and peaking 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).
Standard external compensation techniques work with this
device. For example, in the inverting configuration, the
bandwidth may be limited without 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, which limits the bandwidth.
To maintain a wide bandwidth at high gains, cascade several
op amps, or use the high gain optimized OPA689.
In applications where a large feedback resistor is required,
such as photodiode transimpedance amplifier, the parasitic
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相關(guān)代理商/技術(shù)參數(shù) |
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| OPA688M | 制造商:TI 制造商全稱:Texas Instruments 功能描述:UNITY-GAIN-STABLE WIDEBAND VOLTAGE LIMITING AMP LIFIER |
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| OPA688P | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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| OPA688U/2K5 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-Feedback Operational Amplifier |
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