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參數(shù)資料
| 型號： | LT1886CS8 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 運動控制電子 |
| 英文描述： | Dual 700MHz, 200mA Operational Amplifier |
| 中文描述： | DUAL OP-AMP, 5000 uV OFFSET-MAX, 530 MHz BAND WIDTH, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SO-8 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大小： | 331K |
| 代理商： | LT1886CS8 |
12
LT1886
APPLICATIU
For example, reducing R
BT
by a factor of n = 4, and with an
amplifer gain of (1 + R
F
/R
G
) = 10 requires that R
P2
/R
P1
=12.3.
Note that the overall gain is increased:
W
U
U
V
V
R
+
R
(
R
R
[
n
R
R
R
(
R
o
i
P
P
P
F
G
P
P
P
=
+
)
(
)
(
)
[
]
+
)
]
2
2
1
1
2
1
1 1
1
/
/
/
/
/
A simpler method of using positive feedback to reduce the
back-termination is shown in Figure 8. In this case, the
drivers are driven differentially and provide complemen-
tary outputs. Grounding the inputs, we see there is invert-
ing gain of –R
F
/R
P
from –V
o
to V
a
V
a
= V
o
(R
F
/R
P
)
and assuming R
P
>> R
L
, we require
V
a
= V
o
(1 – 1/n)
solving
R
F
/R
P
= 1 – 1/n
So to reduce the back-termination by a factor of 3 choose
R
F
/R
P
= 2/3. Note that the overall gain is increased to:
V
o
/V
i
= (1 + R
F
/R
G
+ R
F
/R
P
)/[2(1 – R
F
/R
P
)]
ADSL Driver Requirements
The LT1886 is an ideal choice for ADSL upstream (CPE)
modems. The key advantages are:
±
200mA output drive
with only 1.7V worst-case total supply voltage headroom,
high bandwidth, which helps achieve low distortion, low
quiescent supply current of 7mA per amplifier and a
space-saving, thermally enhanced SO-8 package.
An ADSL remote terminal driver must deliver an average
power of 13dBm (20mW) into a 100
line. This corre-
sponds to 1.41V
RMS
into the line. The DMT-ADSL peak-to-
average ratio of 5.33 implies voltage peaks of 7.53V into
the line. Using a differential drive configuration and trans-
former coupling with standard back-termination, a trans-
former ratio of 1:2 is well suited. This is shown on the front
page of this data sheet along with the distortion perfor-
mance vs line voltage at 200kHz, which is beyond ADSL
requirements. Note that the distortion is better than
–73dBc for all swings up to 16V
P-P
into the line. The gain
of this circuit from the differential inputs to the line voltage
is 10. Lower gains are easy to implement using the
compensation techniques of Figure 5. Table 2 shows the
drive requirements for this standard circuit.
The above design is an excellent choice for desktop
applications and draws typically 550mW of power. For
portable applications, power savings can be achieved by
reducing the back-termination resistor using positive feed-
back as shown in Figure 9. The overall gain of this circuit
is also 10, but the power consumption has been reduced
to 350mW, a savings of 36% over the previous design.
Note that the reduction of the back-termination resistor
has allowed use of a 1:1 transformer ratio.
+
–
1886 F07
R
F
R
BT
R
P2
R
P1
R
G
V
i
V
a
V
P
V
o
R
L
R
F
R
G
1 +
(
R
L
n
(
=
V
o
V
i
= 1 –
–
1
n
FOR R
BT
=
)
R
F
R
G
1 +
(
)
R
P1
R
P1
+ R
P2
R
P1
R
P2
+ R
P1
R
P2
/(R
P2
+ R
P1
)
1 + 1/n
)
Figure 7. Back-Termination Using Positive Feedback
–
+
R
BT
R
F
R
G
R
P
R
P
R
G
R
L
R
L
–V
i
V
a
–V
a
V
i
–V
o
V
o
–
+
R
BT
1886 F08
R
F
R
L
n
=
V
o
V
i
n =
1 –
(
2
FOR R
BT
=
R
F
R
P
R
F
R
P
)
+
R
F
R
G
1 +
1 –
R
F
R
P
1
Figure 8. Back-Termination Using Differential Positive Feedback
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| LT1886CS8#PBF | 功能描述:IC OPAMP DUAL 200MA 700MHZ 8SOIC RoHS:是 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標準包裝:100 系列:- 放大器類型:通用 電路數(shù):1 輸出類型:- 轉(zhuǎn)換速率:0.2 V/µs 增益帶寬積:- -3db帶寬:- 電流 - 輸入偏壓:100pA 電壓 - 輸入偏移:30µV 電流 - 電源:380µA 電流 - 輸出 / 通道:- 電壓 - 電源，單路/雙路(±):±2 V ~ 18 V 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:8-SO 包裝:管件 |
| LT1886CS8#TR | 功能描述:IC OPAMP DUAL 200MA 700MHZ 8SOIC RoHS:否 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標準包裝:100 系列:- 放大器類型:通用 電路數(shù):1 輸出類型:- 轉(zhuǎn)換速率:0.2 V/µs 增益帶寬積:- -3db帶寬:- 電流 - 輸入偏壓:100pA 電壓 - 輸入偏移:30µV 電流 - 電源:380µA 電流 - 輸出 / 通道:- 電壓 - 電源，單路/雙路(±):±2 V ~ 18 V 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:8-SO 包裝:管件 |
| LT1886CS8#TRPBF | 功能描述:IC OPAMP DUAL 200MA 700MHZ 8SOIC RoHS:是 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標準包裝:100 系列:- 放大器類型:通用 電路數(shù):1 輸出類型:- 轉(zhuǎn)換速率:0.2 V/µs 增益帶寬積:- -3db帶寬:- 電流 - 輸入偏壓:100pA 電壓 - 輸入偏移:30µV 電流 - 電源:380µA 電流 - 輸出 / 通道:- 電壓 - 電源，單路/雙路(±):±2 V ~ 18 V 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:8-SO 包裝:管件 |
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