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參數(shù)資料
| 型號： | OP496 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Micropower, Rail-to-Rail Input and Output Operational Amplifiers(微功耗,滿幅度輸入輸出四運放) |
| 中文描述： | 微功耗，軌到軌輸入和輸出運算放大器（微功耗，滿幅度輸入輸出四運放） |
| 文件頁數(shù)： | 12/16頁 |
| 文件大?。?/td> | 242K |
| 代理商： | OP496 |
OP196/OP296/OP496
REV. A
–12–
APPLICAT IONS INFORMAT ION
Functional Description
T he OP196 family of operational amplifiers are single-supply,
micropower, rail-to-rail input and output amplifiers. Input off-
set voltage (V
OS
) is only 300
μ
V maximum, while the output will
deliver
±
5 mA to a load. Supply current is only 50
μ
A, while
bandwidth is over 450 kHz and slew rate is 0.3 V/
μ
s. Figure 36
is a simplified schematic of the OP196—it displays the novel
circuit design techniques used to achieve this performance.
Input Overvoltage Protection
T he OPx96 family of op amps uses a composite PNP/NPN
input stage. T ransistor Q1 in Figure 36 has a collector-base
voltage of 0 V if +IN = V
EE
. If +IN then exceeds V
EE
, the junc-
tion will be forward biased and large diode currents will flow,
which may damage the device. T he same situation applies to
+IN on the base of transistor Q5 being driven above V
CC
. T here-
fore, the inverting and noninverting inputs must not be driven
above or below either supply rail unless the input current is
limited.
Figure 37 shows the input characteristics for the OPx96 family.
T his photograph was generated with the power supply pins con-
nected to ground and a curve tracer’s collector output drive
connected to the input. As shown in the figure, when the input
voltage exceeds either supply by more than 0.6 V, internal pn-
junctions energize and permit current flow from the inputs to
the supplies. If the current is not limited, the amplifier may be
damaged. T o prevent damage, the input current should be lim-
ited to no more than 5 mA.
10
0%
100
90
8
6
4
2
0
–2
–4
–6
–8
–1.5
–1 –0.5
INPUT VOLTAGE – Volts
0
0.5
1
1.5
I
Figure 37. Input Overvoltage I-V Characteristics of the
OPx96 Family
Output Phase Reversal
Some other operational amplifiers designed for single-supply
operation exhibit an output voltage phase reversal when their
inputs are driven beyond their useful common-mode range.
T ypically for single-supply bipolar op amps, the negative supply
determines the lower limit of their common-mode range. With
these common-mode limited devices, external clamping diodes
are required to prevent input signal excursions from exceeding
the device’s negative supply rail (i.e., GND) and triggering out-
put phase reversal.
T he OPx96 family of op amps is free from output phase reversal
effects due to its novel input structure. Figure 38 illustrates the
performance of the OPx96 op amps when the input is driven
beyond the supply rails. As previously mentioned, amplifier
input current must be limited if the inputs are driven beyond
the supply rails. In the circuit of Figure 38, the source amplitude
is
±
15 V, while the supply voltage is only
±
5 V. In this case, a
2 k
source resistor limits the input current to 5 mA.
10
0%
100
90
V
S
=
±
5V
A
V
= 1
5V
1ms
5V
0
0
V
IN
V
OUT
V
TIME – 1ns/DIV
Figure 38. Output Voltage Phase Reversal Behavior
Input Offset Voltage Nulling
T he OP196 provides two offset adjust terminals that can be
used to null the amplifier’s internal V
OS
. In general, operational
amplifier terminals should never be used to adjust system offset
voltages. A 100 k
potentiometer, connected as shown in Fig-
ure 39, is recommended to null the OP196’s offset voltage. Off-
set nulling does not adversely affect T CV
OS
performance,
providing that the trimming potentiometer temperature coeffi-
cient does not exceed
±
100 ppm/
°
C.
6
7
2
3
V–
V+
OP196
100k
4
1
5
Figure 39. Offset Nulling Circuit
Driving Capacitive Loads
OP196 family amplifiers are unconditionally stable with capaci-
tive loads less than 170 pF. When driving large capacitive loads
in unity-gain configurations, an in-the-loop compensation
technique is recommended, as illustrated in Figure 40.
OP296
C
F
V
IN
R
G
R
F
R
X
C
L
V
OUT
R
X
= R
O
= OPEN-LOOP OUTPUT RESISTANCE
F
O
R
G
C
F
=
[
I+
(
)
]
(
)
C
L
R
O
A
CL
|
I
R
F
+ R
G
R
F
Figure 40. In-the-Loop Compensation Technique for
Driving Capacitive Loads
A Micropower False-Ground Generator
Some single supply circuits work best when inputs are biased
above ground, typically at 1/2 of the supply voltage. In these
cases, a false-ground can be created by using a voltage divider
buffered by an amplifier. One such circuit is shown in Figure 41.
T his circuit will generate a false-ground reference at 1/2 of the
supply voltage, while drawing only about 55
μ
A from a 5 V
supply. T he circuit includes compensation to allow for a 1
μ
F
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