参数资料
| 型号： | AD8659ARZ-RL |
| 厂商： | Analog Devices Inc |
| 文件页数： | 14/24页 |
| 文件大小： | 0K |
| 描述： | IC OPAMP RRIO 18V CMOS 14SOIC |
| 标准包装： | 2,500 |
| 放大器类型： | 通用 |
| 电路数： | 4 |
| 输出类型： | 满摆幅 |
| 转换速率： | 0.07 V/µs |
| 增益带宽积： | 200kHz |
| 电流 - 输入偏压： | 5pA |
| 电压 - 输入偏移： | 350µV |
| 电流 - 电源： | 18µA |
| 电流 - 输出 / 通道： | 12mA |
| 电压 - 电源，单路/双路(±)： | 2.7 V ~ 18 V，±1.35 V ~ 9 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 14-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 14-SO |
| 包装： | 带卷 (TR) |
Data Sheet
AD8657/AD8659
Rev. B | Page 21 of 24
COMPARATOR OPERATION—AD8657
An op amp is designed to operate in a closed-loop configuration
with feedback from its output to its inverting input. Figure 72
shows the AD8657 configured as a voltage follower with an input
voltage that is always kept at midpoint of the power supplies.
The same configuration is applied to the unused channel. A1 and
A2 indicate the placement of ammeters to measure supply current.
ISY+ refers to the current flowing from the upper supply rail to
the op amp, and ISY refers to the current flowing from the op
amp to the lower supply rail. As shown in Figure 73, as expected
in normal operating condition, the total current flowing into the
op amp is equivalent to the total current flowing out of the op amp,
AD8657
1/2
A1
100k
ISY+
+VSY
VOUT
–VSY
ISY–
A2
08804-
066
Figure 72. Voltage Follower
0
5
10
15
20
25
30
35
40
0
2
4
6
8
10
12
14
16
18
I SY
P
E
R
DUA
L
A
MPL
IF
IER
(
A
)
VSY (V)
ISY–
ISY+
08804-
067
Figure 73. Supply Current vs. Supply Voltage (Voltage Follower)
In contrast to op amps, comparators are designed to work in an
open-loop configuration and to drive logic circuits. Although
op amps are different from comparators, occasionally an unused
section of a dual op amp is used as a comparator to save board
space and cost; however, this is not recommended.
Figure 74 and Figure 75 show the AD8657 configured as a com-
parator, with 100 k resistors in series with the input pins. Any
unused channels are configured as buffers with the input voltage
have input devices that are protected from large differential
input voltages by Diode D1 and Diode D2 (refer to Figure 68).
These diodes consist of substrate PNP bipolar transistors, and
conduct whenever the differential input voltage exceeds approxi-
mately 600 mV; however, these diodes also allow a current path
from the input to the lower supply rail, thus resulting in an
increase in the total supply current of the system. As shown in
Figure 76, both configurations yield the same result. At 18 V of
power supply, ISY+ remains at 36 μA per dual amplifier, but ISY
increases to 140 μA in magnitude per dual amplifier.
AD8657
1/2
A1
100k
ISY+
+VSY
VOUT
–VSY
ISY–
A2
08804-
068
Figure 74. Comparator A
AD8657
1/2
A1
100k
ISY+
+VSY
VOUT
–VSY
ISY–
A2
08804-
069
Figure 75. Comparator B
0
20
40
60
80
100
120
140
160
0
2
4
6
8
10
12
14
16
18
I SY
p
E
R
DUA
L
A
MPL
IF
IER
(
A
)
VSY (V)
ISY–
ISY+
08804-
070
Figure 76. Supply Current vs. Supply Voltage (AD8657 as a Comparator)
Note that 100 k resistors are used in series with the input of
the op amp. If smaller resistor values are used, the supply current of
the system increases much more. For more details on op amps as
comparators, refer to the AN-849 Application Note Using Op
Amps as Comparators.
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