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參數(shù)資料
| 型號： | SNJ54LV221AW |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 諧振器 |
| 英文描述： | LV/LV-A/LVX/H SERIES, DUAL MONOSTABLE MULTIVIBRATOR, CDFP16 |
| 封裝： | GREEN, CERAMIC, DFP-16 |
| 文件頁數(shù)： | 2/23頁 |
| 文件大?。?/td> | 662K |
| 代理商： | SNJ54LV221AW |
SN54LV221A, SN74LV221A
DUAL MONOSTABLE MULTIVIBRATORS
WITH SCHMITT TRIGGER INPUTS
SCLS450G DECEMBER 1999 REVISED APRIL 2005
10
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
caution in use
To prevent malfunctions due to noise, connect a high-frequency capacitor between VCC and GND, and keep
the wiring between the external components and Cext and Rext/Cext terminals as short as possible.
power-down considerations
Large values of Cext can cause problems when powering down the ’LV221A because of the amount of energy
stored in the capacitor. When a system containing this device is powered down, the capacitor can discharge
from VCC through the protection diodes at pin 2 or pin 14. Current through the input protection diodes must be
limited to 30 mA; therefore, the turn-off time of the VCC power supply must not be faster than
t = VCC × Cext/30 mA. For example, if VCC = 5 V and Cext = 15 pF, the VCC supply must turn off no faster than
t = (5 V)
× (15 pF)/30 mA = 2.5 ns. Usually, this is not a problem because power supplies are heavily filtered
and cannot discharge at this rate. When a more rapid decrease of VCC to zero occurs, the ’LV221A can sustain
damage. To avoid this possibility, use external clamping diodes.
output pulse duration
The output pulse duration, tw, is determined primarily by the values of the external capacitance (CT) and timing
resistance (RT). The timing components are connected as shown in Figure 2.
VCC
RT
CT
To Rext/Cext
Terminal
To Cext
Terminal
Figure 2. Timing-Component Connections
The pulse duration is given by:
tw
+ K
R
T
C
T
if CT is ≥ 1000 pF, K = 1.0
or
if CT is < 1000 pF, K can be determined from Figure 7
where:
tw = pulse duration in ns
RT = external timing resistance in k
CT = external capacitance in pF
K
= multiplier factor
Equation 1 and Figure 3 or 4 can be used to determine values for pulse duration, external resistance, and
external capacitance.
(1)
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