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參數(shù)資料
| 型號(hào)： | OP291 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Micropower Single-Supply Rail-to-Rail Input/Output Op Amps |
| 中文描述： | 微功耗單電源軌到軌輸入/輸出運(yùn)算放大器 |
| 文件頁(yè)數(shù)： | 12/20頁(yè) |
| 文件大?。?/td> | 479K |
| 代理商： | OP291 |
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OP191/OP291/OP491
REV. 0
–12–
exceeds approximately 0.6 V. In this condition, current will
flow between the input pins, limited only by the two 5 k
resistors. Being aware of this characteristic is important in
circuits where the amplifier may be operated open-loop, such as
a comparator. Evaluate each circuit carefully to make sure that
the increase in current does not affect the performance.
T he output stage of the OP191 family uses a PNP and an NPN
transistor as do most output stages; however, the output
transistors, Q32 and Q33, are actually connected with their
collectors to the output pin to achieve the rail-to-rail output
swing. As the output voltage approaches either the positive or
negative rail, these transistors begin to saturate. T hus, the final
limit on output voltage is the saturation voltage of these
transistors, which is about 50 mV. T he output stage does have
inherent gain arising from the collectors and any external load
impedance. Because of this, the open-loop gain of the amplifier
is dependent on the load resistance.
Input Overvoltage Protection
As with any semiconductor device, whenever the condition
exists for the input to exceed either supply voltage, attention
needs to be paid to the input overvoltage characteristic. When
an overvoltage occurs, the amplifier could be damaged depend-
ing on the voltage level and the magnitude of the fault current.
Figure 56 shows the characteristic for the OP191 family. T his
graph was generated with the power supplies at ground and a
curve tracer connected to the input. As can be seen, when the
input voltage exceeds either supply by more than 0.6 V, internal
pn-junctions energize allowing current to flow from the input to
the supplies. As described above, the OP291/OP491 does have
5 k
resistors in series with each input, which helps limit the
current. Calculating the slope of the current versus voltage in
the graph confirms the 5 k
resistor.
FUNCT IONAL DE SCRIPT ION
T he OP191/OP291/OP491 are single supply, micropower
amplifiers featuring rail-to-rail inputs and outputs. In order to
achieve wide input and output ranges, these amplifiers employ
unique input and output stages. As the simplified schematic
shows (Figure 55), the input stage is actually comprised of two
differential pairs, a PNP pair and an NPN pair. T hese two
stages do not actually work in parallel. Instead, only one or the
other stage is on for any given input signal level. T he PNP stage
(transistors Q1 and Q2) is required to ensure that the amplifier
remains in the linear region when the input voltage approaches
and reaches the negative rail. On the other hand, the NPN
stage (transistors Q5 and Q6) is needed for input voltages up to
and including the positive rail.
For the majority of the input common-mode range, the PNP
stage is active, as is evidenced by examining the graph of Input
Bias Current vs. Common-Mode Voltage. Notice that the bias
current switches direction at approximately 1.2 volts to 1.3 volts
below the positive rail. At voltages below this, the bias current
flows out of the OP291, indicating a PNP input stage. Above
this voltage, however, the bias current enters the device,
revealing the NPN stage. T he actual mechanism within the
amplifier for switching between the input stages is comprised of
the transistors Q3, Q4, and Q7. As the input common-mode
voltage increases, the emitters of Q1 and Q2 follow that voltage
plus a diode drop. Eventually the emitters of Q1 and Q2 are
high enough to turn Q3 on. T his diverts the 8
μ
A of tail current
away from the PNP input stage, turning it off. Instead, the
current is mirrored through Q4 and Q7 to activate the NPN
input stage.
Notice that the input stage includes 5 k
series resistors and
differential diodes, a common practice in bipolar amplifiers to
protect the input transistors from large differential voltages.
T hese diodes will turn on whenever the differential voltage
Figure 55. Simplified Schematic
Q1 Q2
8
μ
A
5k
Q3
5k
–IN
Q5 Q6
Q11
Q10
Q8
Q7
Q4
Q13
Q15
Q14
Q12
Q9
Q16
Q17
Q18
Q19
Q20
Q21
Q24
Q23
Q22
Q27
Q26
Q30
Q31
Q28
Q25
Q29
Q32
V
OUT
Q33
10pF
+IN
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| OP291GS | Micropower Single-Supply Rail-to-Rail Input/Output Op Amps |
| OP191 | Micropower Single-Supply Rail-to-Rail Input/Output Op Amps |
| OP191GS | Micropower Single-Supply Rail-to-Rail Input/Output Op Amps |
| OP191GBC | Micropower Single-Supply Rail-to-Rail Input/Output Op Amps |
| OP291GBC | Micropower Single-Supply Rail-to-Rail Input/Output Op Amps |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| OP291A | 功能描述:紅外發(fā)射源 Infrared 890nm RoHS:否 制造商:Fairchild Semiconductor 波長(zhǎng):880 nm 射束角:+/- 25 輻射強(qiáng)度: 最大工作溫度:+ 100 C 最小工作溫度:- 40 C 封裝 / 箱體:Side Looker 封裝:Bulk |
| OP291A | 制造商:TT Electronics / OPTEK Technology 功能描述:Infrared LED |
| OP291B | 功能描述:紅外發(fā)射源 Infrared 890nm RoHS:否 制造商:Fairchild Semiconductor 波長(zhǎng):880 nm 射束角:+/- 25 輻射強(qiáng)度: 最大工作溫度:+ 100 C 最小工作溫度:- 40 C 封裝 / 箱體:Side Looker 封裝:Bulk |
| OP291C | 功能描述:紅外發(fā)射源 Infrared 890nm RoHS:否 制造商:Fairchild Semiconductor 波長(zhǎng):880 nm 射束角:+/- 25 輻射強(qiáng)度: 最大工作溫度:+ 100 C 最小工作溫度:- 40 C 封裝 / 箱體:Side Looker 封裝:Bulk |
| OP291GBC | 制造商:AD 制造商全稱:Analog Devices 功能描述:Micropower Single-Supply Rail-to-Rail Input/Output Op Amps |
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