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參數(shù)資料
| 型號(hào)： | DM74LS221SJX |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 諧振器 |
| 英文描述： | Monostable Multivibrator |
| 中文描述： | LS SERIES, DUAL MONOSTABLE MULTIVIBRATOR, PDSO16 |
| 封裝： | 5.30 MM, EIAJ TYPE2, SOP-16 |
| 文件頁數(shù)： | 2/8頁 |
| 文件大?。?/td> | 108K |
| 代理商： | DM74LS221SJX |
www.fairchildsemi.com
2
D
Functional Description
The basic output pulse width is determined by selection of
an external resistor (R
X
) and capacitor (C
X
). Once trig-
gered, the basic pulse width is independent of further input
transitions and is a function of the timing components, or it
may be reduced or terminated by use of the active low
CLEAR input. Stable output pulse width ranging from 30 ns
to 70 seconds is readily obtainable.
Operating Rules
1. An external resistor (R
X
) and an external capacitor
(C
X
) are required for proper operation. The value of C
X
may vary from 0 to approximately 1000
μ
F. For small
time constants high-grade mica, glass, polypropylene,
polycarbonate, or polystyrene material capacitor may
be used. For large time constants use tantalum or spe-
cial aluminum capacitors. If timing capacitor has leak-
ages approaching 100 nA or if stray capacitance from
either terminal to ground is greater than 50 pF the tim-
ing equations may not represent the pulse width the
device generates.
2. When an electrolytic capacitor is used for C
X
a switch-
ing diode is often required for standard TTL one-shots
to prevent high inverse leakage current. This switching
diode is not needed for the DM74LS221 one-shot and
should not be used.
Furthermore, if a polarized timing capacitor is used on
the DM74LS221, the positive side of the capacitor
should be connected to the
“
C
EXT
”
pin (Figure 1).
3. For C
X
>>
1000 pF, the output pulse width (t
W
) is
defined as follows:
t
W
=
KR
X
C
X
where [R
X
is in k
]
[C
X
is in pF]
[t
W
is in ns]
K
≈
Ln2
=
0.70
4. The multiplicative factor K is plotted as a function of C
X
for design considerations: (See Figure 4).
5. For C
X
<
1000 pF see Figure 3 for t
W
vs. C
X
family
curves with R
X
as a parameter.
6. To obtain variable pulse widths by remote trimming,
the following circuit is recommended: (See Figure 2).
7. Output pulse width versus V
CC
and temperatures: Fig-
ure 5 depicts the relationship between pulse width vari-
ation versus V
CC
. Figure 6 depicts pulse width variation
versus temperatures.
8. Duty cycle is defined as t
W
/T
×
100 in percentage, if it
goes above 50% the output pulse width will become
shorter. If the duty cycle varies between LOW and
HIGH values, this causes output pulse width to vary, or
jitter (a function of the R
EXT
only). To reduce jitter, R
EXT
should be as large as possible, for example, with
R
EXT
=
100k jitter is not appreciable until the duty cycle
approaches 90%.
9. Under any operating condition C
X
and R
X
must be kept
as close to the one-shot device pins as possible to min-
imize stray capacitance, to reduce noise pick-up, and
to reduce I-R and Ldi/dt voltage developed along their
connecting paths. If the lead length from C
X
to pins (6)
and (7) or pins (14) and (15) is greater than 3 cm, for
example, the output pulse width might be quite different
from values predicted from the appropriate equations.
A non-inductive and low capacitive path is necessary to
ensure complete discharge of C
X
in each cycle of its
operation so that the output pulse width will be accu-
rate.
10. Although the DM74LS221's pin-out is identical to the
DM74LS123 it should be remembered that they are not
functionally identical. The DM74LS123 is a retrigger-
able device such that the output is dependent upon the
input transitions when its output
“
Q
”
is at the
“
High
”
state. Furthermore, it is recommended for the
DM74LS123 to externally ground the C
EXT
pin for
improved system performance. However, this pin on
the DM74LS221 is not an internal connection to the
device ground. Hence, if substitution of an DM74LS221
onto an DM74LS123 design layout where the C
EXT
pin
is wired to the ground, the device will not function.
11. V
CC
and ground wiring should conform to good high-
frequency standards and practices so that switching
transients on the V
CC
and ground return leads do not
cause interaction between one-shots. A 0.01
μ
F to 0.10
μ
F bypass capacitor (disk ceramic or monolithic type)
from V
CC
to ground is necessary on each device. Fur-
thermore, the bypass capacitor should be located as
close to the V
CC
-pin as space permits.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| DM74LS221SJ | Dual Non-Retriggerable One-Shot with Clear and Complementary Outputs |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| DM74LS22J | 制造商:Rochester Electronics LLC 功能描述: |
| DM74LS240N | 功能描述:緩沖器和線路驅(qū)動(dòng)器 Oct 3-STATE Bf/Ln Dr RoHS:否 制造商:Micrel 輸入線路數(shù)量:1 輸出線路數(shù)量:2 極性:Non-Inverting 電源電壓-最大:+/- 5.5 V 電源電壓-最小:+/- 2.37 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Reel |
| DM74LS240SJ | 功能描述:緩沖器和線路驅(qū)動(dòng)器 Oct 3-STATE Bf/Ln Dr RoHS:否 制造商:Micrel 輸入線路數(shù)量:1 輸出線路數(shù)量:2 極性:Non-Inverting 電源電壓-最大:+/- 5.5 V 電源電壓-最小:+/- 2.37 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Reel |
| DM74LS240SJX | 功能描述:緩沖器和線路驅(qū)動(dòng)器 Oct 3-STATE Bf/Ln Dr RoHS:否 制造商:Micrel 輸入線路數(shù)量:1 輸出線路數(shù)量:2 極性:Non-Inverting 電源電壓-最大:+/- 5.5 V 電源電壓-最小:+/- 2.37 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Reel |
| DM74LS240WM | 功能描述:緩沖器和線路驅(qū)動(dòng)器 Oct 3-STATE Bf/Ln Dr RoHS:否 制造商:Micrel 輸入線路數(shù)量:1 輸出線路數(shù)量:2 極性:Non-Inverting 電源電壓-最大:+/- 5.5 V 電源電壓-最小:+/- 2.37 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Reel |
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