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參數資料
| 型號： | LMV821M5 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 運算放大器 |
| 英文描述： | Low Voltage, Low Power, R-to-R Output, 5 MHz Op Amps |
| 中文描述： | OP-AMP, 3500 uV OFFSET-MAX, 5 MHz BAND WIDTH, PDSO5 |
| 封裝： | SOT-23, 5 PIN |
| 文件頁數： | 11/24頁 |
| 文件大小： | 1068K |
| 代理商： | LMV821M5 |
APPLICATION NOTE
This application note is divided into two sections: design
considerations and Application Circuits.
1.0 Design Considerations
This section covers the following design considerations:
1. Frequency and Phase Response Considerations
2. Unity-Gain Pulse Response Considerations
3. Input Bias Current Considerations
1.1 Frequency and Phase Response Considerations
The relationship between open-loop frequency response
and open-loop phase response determines the closed-loop
stability performance (negative feedback). The open-loop
phase response causes the feedback signal to shift towards
becoming positive feedback, thus becoming unstable. The
further the output phase angle is from the input phase angle,
the more stable the negative feedback will operate. Phase
Margin (
φ
) specifies this output-to-input phase relationship
at the unity-gain crossover point. Zero degrees of phase-
margin means that the input and output are completely in
phase with each other and will sustain oscillation at the unity-
gain frequency.
The AC tables show
φ
for a no load condition. But
φ
m
changes with load. The Gain and Phase margin vs Fre-
quency plots in the curve section can be used to graphically
determine the
φ
for various loaded conditions. To do this,
examine the phase angle portion of the plot, find the phase
margin point at the unity-gain frequency, and determine how
far this point is from zero degree of phase-margin. The larger
the phase-margin, the more stable the circuit operation.
The bandwidth is also affected by load. The graphs of Figure
1 and Figure 2 provide a quick look at how various loads af-
fect the
φ
and the bandwidth of the LMV821/822/824 family.
These graphs show capacitive loads reducing both
φ
and
bandwidth, while resistive loads reduce the bandwidth but in-
crease the
φ
. Notice how a 600
resistor can be added in
parallel with 220 picofarads capacitance, to increase the
φ
m
20(approx.), but at the price of about a 100 kHz of band-
width.
Overall, the LMV821/822/824 family provides good stability
for loaded condition.
1.2 Unity Gain Pulse Response Considerations
A pull-up resistor is well suited for increasing unity-gain,
pulse response stability. For example, a 600
pull-up resis-
tor reduces the overshoot voltage by about 50%, when driv-
ing a 220 pF load. Figure 3 shows how to implement the
pull-up resistor for more pulse response stability.
Higher capacitances can be driven by decreasing the value
of the pull-up resistor, but its value shouldn’t be reduced be-
yond the sinking capability of the part. An alternate approach
is to use an isolation resistor as illustrated in Figure 4 .
Figure 5shows the resulting pulse response from a LMV824,
while driving a 10,000pF load through a 20
isolation
resistor.
DS100128-60
FIGURE 1. Phase Margin vs Common Mode Voltage for
Various Loads
DS100128-61
FIGURE 2. Unity-Gain Frequency vs Common Mode
Voltage for Various Loads
DS100128-41
FIGURE 3. Using a Pull-up Resistor at the Output for
Stabilizing Capacitive Loads
DS100128-43
FIGURE 4. Using an Isolation Resistor to Drive Heavy
Capacitive Loads
www.national.com
11
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LMV821M5/NOPB | 功能描述:運算放大器 - 運放 Low Volt Sgl Op Amp RoHS:否 制造商:STMicroelectronics 通道數量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV821M5/NOPB | 制造商:Texas Instruments 功能描述:Operational Amplifier (Op-Amp) IC |
| LMV821M5NOPB | 制造商:Texas Instruments 功能描述: |
| LMV821M5X | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV821M5X/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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