參數(shù)資料
型號: ADA4891-1ARZ
廠商: Analog Devices Inc
文件頁數(shù): 10/24頁
文件大小: 0K
描述: IC OPAMP GP RR CMOS 220MHZ 8SOIC
標準包裝: 98
放大器類型: 通用
電路數(shù): 1
輸出類型: 滿擺幅
轉換速率: 210 V/µs
-3db帶寬: 240MHz
電流 - 輸入偏壓: 2pA
電壓 - 輸入偏移: 2500µV
電流 - 電源: 4.4mA
電流 - 輸出 / 通道: 125mA
電壓 - 電源,單路/雙路(±): 2.7 V ~ 5.5 V,±1.35 V ~ 2.75 V
工作溫度: -40°C ~ 125°C
安裝類型: 表面貼裝
封裝/外殼: 8-SOIC(0.154",3.90mm 寬)
供應商設備封裝: 8-SO
包裝: 管件
ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4
Data Sheet
Rev. E | Page 18 of 24
TERMINATING UNUSED AMPLIFIERS
Terminating unused amplifiers in a multiamplifier package is
an important step in ensuring proper operation of the functional
amplifier. Unterminated amplifiers can oscillate and draw
excessive power. The recommended procedure for terminating
unused amplifiers is to connect any unused amplifiers in a
unity-gain configuration and to connect the noninverting input
to midsupply voltage. With symmetrical bipolar power supplies,
this means connecting the noninverting input to ground, as
08054-
064
–VS
+VS
ADA4891
Figure 59. Terminating Unused Amplifier with
Symmetrical Bipolar Power Supplies
In single power supply applications, a synthetic midsupply
source must be created. This can be accomplished with a simple
resistive voltage divider. Figure 60 shows the proper connection
for terminating an unused amplifier in a single-supply
configuration.
08054-
065
2.5k
+VS
ADA4891
Figure 60. Terminating Unused Amplifier with Single Power Supply
DISABLE FEATURE (ADA4891-3 ONLY)
The ADA4891-3 includes a power-down feature that can be
used to save power when an amplifier is not in use. When an
amplifier is powered down, its output goes to a high impedance
state. The output impedance decreases as frequency increases;
this effect can be observed in Figure 34. With the power-down
function, a forward isolation of 40 dB can be achieved at
50 MHz. Figure 46 shows the forward isolation vs. frequency
data. The power-down feature is asserted by pulling the PD1,
PD2, or PD3 pin low.
Table 7 summarizes the operation of the power-down feature.
Table 7. Disable Function
Power-Down Pin Connection (PDx)
Amplifier Status
>VTH or floating
Enabled
<VTH
Disabled
SINGLE-SUPPLY OPERATION
The ADA4891 can also be operated from a single power supply.
Figure 61 shows the ADA4891-3 configured as a single 5 V
supply video driver.
The input signal is ac-coupled into the amplifier via
Capacitor C1.
Resistor R2 and Resistor R4 establish the input midsupply
reference for the amplifier.
Capacitor C5 prevents constant current from being drawn
through the gain set resistor (RG) and enables the ADA4891-3
at dc to provide unity gain to the input midsupply voltage,
thereby establishing the output voltage at midsupply.
Capacitor C6 is the output coupling capacitor.
The large-signal frequency response obtained with single-
supply operation is identical to the bipolar supply operation
(Figure 18 shows the large-signal frequency response).
Four pairs of low frequency poles are formed by R2/2 and C2,
R3 and C1, RG and C5, and RL and C6. With this configuration,
the 3 dB cutoff frequency at low frequency is 12 Hz. The
values of C1, C2, C5, and C6 can be adjusted to change the low
frequency 3 dB cutoff point to suit individual design needs.
For more information about single-supply operation of op amps,
see the Analog Dialogue article “Avoiding Op Amp Instability
Problems in Single-Supply Applications” (Volume 35, Number 2)
08054-
086
C2
1F
R2
50kΩ
R4
50kΩ
R3
100kΩ
C1
22F
R1
50Ω
C6
22F
RL
150Ω
RG
453Ω
RF
453Ω
C5
22F
ADA4891-3
+5V
VOUT
VIN
–VS
C3
10F
C4
0.01F
+5V
Figure 61. Single-Supply Video Driver Schematic
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