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參數(shù)資料
| 型號： | AD8651AR-REEL |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 運(yùn)動控制電子 |
| 英文描述： | 50 MHz, Precision, Low Distortion, Low Noise CMOS Amplifiers |
| 中文描述： | OP-AMP, 1700 uV OFFSET-MAX, 50 MHz BAND WIDTH, PDSO8 |
| 封裝： | MS-012AA, SOIC-8 |
| 文件頁數(shù)： | 15/20頁 |
| 文件大小： | 558K |
| 代理商： | AD8651AR-REEL |
AD8651/AD8652
Input Protection
As with any semiconductor device, if a condition could exist for
the input voltage to exceed the power supply, the device’s input
overvoltage characteristic must be considered. The inputs of the
AD8651 are protected with ESD diodes to either power supply.
Excess input voltage will energize internal PN junctions in the
AD8651, allowing current to flow from the input to the
supplies. This results in an input stage with picoamps of input
current that can withstand up to 4000 V ESD events (human
body model) with no degradation.
Rev. B | Page 15 of 20
Excessive power dissipation through the protection devices will
destroy or degrade the performance of any amplifier. Differen-
tial voltages greater than 7 V will result in an input current of
approximately (|V
CC
– V
EE
| – 0.7 V)/R
I
, where R
I
is the
resistance in series with the inputs. For input voltages beyond
the positive supply, the input current will be approximately (V
I
– V
CC
– 0.7)/R
I
. For input voltages beyond the negative supply,
the input current will be about (V
I
– V
EE
+ 0.7)/R
I
. If the inputs
of the amplifier sustain differential voltages greater than 7 V or
input voltages beyond the amplifier power supply, limit the
input current to 10 mA by using an appropriately sized input
resistor (R
I
), as shown in Figure 54.
+
AD8651
–
(| V
CC
– V
EE
| – 0.7V)
30mA
FOR LARGE | V
CC
– V
EE
|
FOR V
BEYOND
SUPPLY VOLTAGES
+ V
O
R
I
>
R
I
– V
I
+
30mA
(V
I
– V
EE
+ 0.7V)
R
I
>
30mA
(V
I
– V
EE
– 0.7V)
R
I
>
0
Figure 54. Input Protection Method
Overdrive Recovery
Overdrive recovery is defined as the time it takes for the output
of an amplifier to come off the supply rail after an overload
signal is initiated. This is usually tested by placing the amplifier
in a closed-loop gain of 15 with an input square wave of
200 mV p-p while the amplifier is powered from either 5 V or
3 V. The AD8651 has excellent recovery time from overload
conditions (see Figure 31 and Figure 32). The output recovers
from the positive supply rail within 200 ns at all supply voltages.
Recovery from the negative rail is within 100 ns at 5 V supply.
LAYOUT, GROUNDING, AND BYPASSING
CONSIDERATIONS
Power Supply Bypassing
Power supply pins can act as inputs for noise, so care must be
taken that a noise-free, stable dc voltage is applied. The purpose
of bypass capacitors is to create low impedances from the supply
to ground at all frequencies, thereby shunting or filtering most
of the noise. Bypassing schemes are designed to minimize the
supply impedance at all frequencies with a parallel combination
of capacitors of 0.1 μF and 4.7 μF. Chip capacitors of 0.1 μF
(X7R or NPO) are critical and should be as close as possible to
the amplifier package. The 4.7 μF tantalum capacitor is less
critical for high frequency bypassing, and, in most cases, only
one is needed per board at the supply inputs.
Grounding
A ground plane layer is important for densely packed PC
boards to spread the current-minimizing parasitic inductances.
However, an understanding of where the current flows in a
circuit is critical to implementing effective high speed circuit
design. The length of the current path is directly proportional to
the magnitude of parasitic inductances and, therefore, the high
frequency impedance of the path. High speed currents in an
inductive ground return will create an unwanted voltage noise.
The length of the high frequency bypass capacitor leads is
critical. A parasitic inductance in the bypass grounding will
work against the low impedance created by the bypass capacitor.
Place the ground leads of the bypass capacitors at the same
physical location. Because load currents also flow from the
supplies, the ground for the load impedance should be at the
same physical location as the bypass capacitor grounds. For the
larger value capacitors, intended to be effective at lower fre-
quencies, the current return path distance is less critical.
Leakage Currents
Poor PC board layout, contaminants, and the board insulator
material can create leakage currents that are much larger than
the input bias current of the AD8651/AD8652. Any voltage
differential between the inputs and nearby traces will set up
leakage currents through the PC board insulator, for example,
1 V/100 G = 10 pA. Similarly, any contaminants on the board
can create significant leakage (skin oils are a common problem).
To significantly reduce leakages, put a guard ring (shield)
around the inputs and input leads that are driven to the same
voltage potential as the inputs. This ensures that there is no
voltage potential between the inputs and the surrounding area
to set up any leakage currents. To be effective, the guard ring
must be driven by a relatively low impedance source and should
completely surround the input leads on all sides, above and
below, using a multilayer board.
Another effect that can cause leakage currents is the charge
absorption of the insulator material itself. Minimizing the
amount of material between the input leads and the guard
ring will help to reduce the absorption. Also, low absorption
materials, such as Teflon or ceramic, may be necessary in
some instances.
Input Capacitance
Along with bypassing and ground, high speed amplifiers can be
sensitive to parasitic capacitance between the inputs and
ground. A few picofarads of capacitance will reduce the input
impedance at high frequencies, which in turn increases the
amplifier’s gain, causing peaking in the frequency response or
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| AD8651ARZ | 功能描述:IC OPAMP VF CMOS 50MHZ LN 8SOIC RoHS:是 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:DigiTrim® 產(chǎn)品培訓(xùn)模塊:Differential Circuit Design Techniques for Communication Applications 標(biāo)準(zhǔn)包裝:1 系列:- 放大器類型:RF/IF 差分 電路數(shù):1 輸出類型:差分 轉(zhuǎn)換速率:9800 V/µs 增益帶寬積:- -3db帶寬:2.9GHz 電流 - 輸入偏壓:3µA 電壓 - 輸入偏移:- 電流 - 電源:40mA 電流 - 輸出 / 通道:- 電壓 - 電源，單路/雙路(±):3 V ~ 3.6 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-VQFN 裸露焊盤，CSP 供應(yīng)商設(shè)備封裝:16-LFCSP-VQ 包裝:剪切帶 (CT) 產(chǎn)品目錄頁面:551 (CN2011-ZH PDF) 其它名稱:ADL5561ACPZ-R7CT |
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