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參數(shù)資料
| 型號： | AD8565 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 16 V Rail-to-Rail Operational Amplifiers |
| 中文描述： | 16 V的軌到軌運(yùn)算放大器 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大小： | 152K |
| 代理商： | AD8565 |
AD8565/AD8566/AD8567
–
8
–
REV. A
APPLICATIONS
Theory of Operation
The AD856x family is designed to drive large capacitive loads in
LCD applications. It has high output current drive, rail-to-rail
input/output operation and is powered from a single 16 V supply.
It is also intended for other applications where low distortion and
high output current drive are needed.
Figure 1 illustrates a simplified equivalent circuit for the AD856x.
The rail-to-rail bipolar input stage is composed of two PNP
differential pairs, Q4
–
Q5 and Q10
–
Q11, operating in series with
diode protection networks, D1
–
D2. Diode network D1
–
D2
serves as protection against large transients for Q4
–
Q5, to
accommodate rail-to-rail input swing. D5
–
D6 protect Q10
–
Q11
against zenering. In normal operation, Q10
–
Q11 are off and their
input stage is buffered from the operational amplifier inputs by
Q6
–
D3 and Q8
–
D4. Operation of the input stage is best understood
as a function of applied common-mode voltage: When the inputs
of the AD856x are biased midway between the supplies, the
differential signal path gain is controlled by resistive loads (Via R9,
R10) Q4
–
Q5. As the input common-mode level is reduced toward
the negative supply (V
NEG
or GND), the input transistor current
sources, I1 and I2, are forced into saturation, thereby forcing the
Q6
–
D3 and Q8
–
D4 networks into cutoff; However, Q4
–
Q5 remain
active, providing input stage gain. Inversely, when common-mode
input voltage is increased toward the positive supply, Q4
–
Q5 are
driven into cutoff, Q3 is driven into saturation, and Q4 becomes
active, providing bias to the Q10
–
Q11 differential pair. The point
at which Q10
–
Q11 differential pair becomes active is approximately
equal to (V
POS
–
1 V).
R1
R3
R4
D1
D2
Q4
Q3
BIAS LINE
V
–
D3
D4
Q5
Q4
R5
R6
Q10
Q11
C1
C2
D5
D6
Q8
Q6
R9
R10
FOLDED
CASCADE
V+
I1
I2
V
NEG
V
POS
Figure 1. AD856x Equivalent Input Circuit
The benefit of this type of input stage is low bias current. The
input bias current is the sum of base currents of Q4
–
Q5 and
Q6
–
Q8 over the range from (V
NEG
+ 1 V) to (V
POS
–
1 V). Outside
of this range, input bias current is dominated by the sum of base
current of Q10
–
Q11 for input signals close to V
NEG
and of Q6
–
Q8
(Q10
–
Q11) for signal close to V
POS
. From this type of design,
the input bias current of AD856x not only exhibits different
amplitude, but also exhibits different polarities. Figure 2 provides
the characteristics of the input bias current versus common-mode
voltage. It is important to keep in mind that the source impedances
driving the AD856x inputs are balanced for optimum dc and ac
performance.
INPUT COMMON-MODE VOLTAGE
–
V
1,000
–
1,0000
16
2
I
–
4
6
8
10
12
14
800
200
–
200
–
600
–
800
600
400
0
–
400
V
S
= 16V
T
A
= 25 C
Figure 2. AD856x Input Bias Current vs. Common-Mode
Voltage
In order to achieve rail-to-rail output performance, the AD856x
design uses a complementary common-source (or gmRL) output.
This configuration allows output voltages to approach the power
supply rails, particularly if the output transistors are allowed to
enter the triode region on extremes of signal swing which are
limited by V
GS
, the transistor sizes, and output load current.
Also, this type of output stage exhibits voltage gain in an open-loop
gain configuration. The amount of gain depends on the total
load resistance at the output of the AD856x.
Input Overvoltage Protection
As with any semiconductor device, whenever the input exceeds
either supply voltages, attention needs to be paid to the input
overvoltage characteristics. As an overvoltage occurs, the amplifier
could be damaged, depending on the voltage level and the magnitude
of the fault current. When the input voltage exceeds either supply
by more than 0.6 V, internal pn junctions will allow current to
flow from the input to the supplies.
This input current is not inherently damaging to the device as
long as it is limited to 5 mA or less. If a condition exists using
the AD856x where the input exceeds the supply more than 0.6 V,
a series external resistor should be added. The size of the resistor
can be calculated by using the maximum overvoltage divided by
5 mA. This resistance should be placed in series with either input
exposed to an overvoltage.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AD8565AKS | 16 V Rail-to-Rail Operational Amplifiers |
| AD8566 | 16 V Rail-to-Rail Operational Amplifiers |
| AD8566ARM | 16 V Rail-to-Rail Operational Amplifiers |
| AD8567 | 16 V Rail-to-Rail Operational Amplifiers |
| AD8567ACP | 16 V Rail-to-Rail Operational Amplifiers |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD8565_06 | 制造商:AD 制造商全稱:Analog Devices 功能描述:16 V Rail-to-Rail Operational Amplifiers |
| ad8565001aksz-rl7 | 制造商:Analog Devices 功能描述: |
| AD8565AKS | 制造商:AD 制造商全稱:Analog Devices 功能描述:16 V Rail-to-Rail Operational Amplifiers |
| AD8565AKS-R2 | 制造商:Analog Devices 功能描述:OP Amp Single GP R-R I/O 16V 5-Pin SC-70 T/R 制造商:Analog Devices 功能描述:OP AMP SGL GP R-R I/O 16V 5PIN SC-70 - Tape and Reel |
| AD8565AKS-REEL7 | 制造商:Analog Devices 功能描述:OP Amp Single GP R-R I/O 16V 5-Pin SC-70 T/R 制造商:Analog Devices 功能描述:OP AMP SGL GP R-R I/O 16V 5PIN SC-70 - Tape and Reel 制造商:Rochester Electronics LLC 功能描述:SINGLE 16V 35MA CBCMOS AMPLIFIER - Tape and Reel 制造商:Analog Devices 功能描述:AMPLIFIER IC NUMBER OF CIRCUITS:1 |
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