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參數(shù)資料
| 型號： | ADG749BKS |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 運動控制電子 |
| 英文描述： | CMOS Low Voltage 2.5ohm SPDT Switch In SC70 Package |
| 中文描述： | 1-CHANNEL, SGL POLE DOUBLE THROW SWITCH, PDSO6 |
| 封裝： | PLASTIC, MO-203AB, SC-70, 6 PIN |
| 文件頁數(shù)： | 7/8頁 |
| 文件大?。?/td> | 126K |
| 代理商： | ADG749BKS |
ADG749
–7–
REV. 0
APPLICATIONS INFORMATION
The ADG749 belongs to Analog Devices’ new family of
CMOS switches. This series of general purpose switches have
improved switching times, lower on resistance, higher band-
widths, low power consumption and low leakage currents.
ADG749 Supply Voltages
Functionality of the ADG749 extends from 1.8 V to 5.5 V single
supply, which makes it ideal for battery powered instruments,
where important design parameters are power efficiency and
performance.
It is important to note that the supply voltage effects the input
signal range, the on resistance and the switching times of the
part. By taking a look at the typical performance characteristics
and the specifications, the effects of the power supplies can be
clearly seen.
For V
DD
= 1.8 V operation, R
ON
is typically 40
over the tem-
perature range.
On Response vs. Frequency
Figure 1 illustrates the parasitic components that affect the ac
performance of CMOS switches (the switch is shown surrounded
by a box). Additional external capacitances will further degrade
some performance. These capacitances affect feedthrough,
crosstalk and system bandwidth.
C
DS
S
V
IN
R
ON
C
D
C
LOAD
R
LOAD
D
V
OUT
Figure 1. Switch Represented by Equivalent Parasitic
Components
The transfer function that describes the equivalent diagram of
the switch (Figure 1) is of the form (A)s shown below.
A
(
s
)
=
R
T
s
(
R
ON
C
DS
)
+
1
s
(
R
T
R
ON
C
T
)
+
1
where:
R
T
=
R
LOAD
/(
R
LOAD
+
R
ON
)
C
T
=
C
LOAD
+
C
D
+
C
DS
The signal transfer characteristic is dependent on the switch
channel capacitance, C
DS
. This capacitance creates a frequency
zero in the numerator of the transfer function A(s). Because the
switch on resistance is small, this zero usually occurs at high
frequencies. The bandwidth is a function of the switch output
capacitance combined with C
DS
and the load capacitance. The
frequency pole corresponding to these capacitances appears in
the denominator of A(s).
The dominant effect of the output capacitance, C
D
, causes the
pole breakpoint frequency to occur first. Therefore, in order to
maximize bandwidth a switch must have a low input and output
capacitance and low on resistance. The On Response vs. Fre-
quency plot for the ADG749 can be seen in TPC 7.
Off Isolation
Off isolation is a measure of the input signal coupled through an
off switch to the switch output. The capacitance, C
DS
, couples
the input signal to the output load, when the switch is off as
shown in Figure 2.
C
DS
S
V
IN
C
D
C
LOAD
R
LOAD
D
V
OUT
Figure 2. Off Isolation Is Affected by External Load Resis-
tance and Capacitance
The larger the value of C
DS
, larger values of feedthrough will be
produced. The typical performance characteristic graph of TPC
5 illustrates the drop in off isolation as a function of frequency.
From dc to roughly 200 kHz, the switch shows better than
–
95 dB isolation. Up to frequencies of 10 MHz, the off isolation
remains better than
–
67 dB. As the frequency increases, more and
more of the input signal is coupled through to the output. Off
isolation can be maximized by choosing a switch with the small-
est C
DS
as possible. The values of load resistance and capacitance
affect off isolation also, as they contribute to the coefficients of the
poles and zeros in the transfer function of the switch when open.
A
(
s
)
=
s
(
R
LOAD
C
DS
)
s
(
R
LOAD
)(
C
LOAD
+
C
D
+
C
DS
)
+
1
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相關代理商/技術參數(shù) |
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|---|---|
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| ADG749BKS-REEL7 | 制造商:Analog Devices 功能描述:Analog Switch Single SPDT 6-Pin SC-70 T/R 制造商:Analog Devices 功能描述:IC SWITCH SPDT SINGLE CMOS |
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| ADG749BKSZ-R2 | 制造商:Analog Devices 功能描述:Analog Switch Single SPDT 6-Pin SC-70 T/R 制造商:Analog Devices 功能描述:SINGLE SPDT, PB FREE - Tape and Reel |
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