参数资料
| 型号： | MC74HC4538AFG |
| 厂商： | ON Semiconductor |
| 文件页数： | 3/16页 |
| 文件大小： | 0K |
| 描述： | IC MULTIVIBRATOR DUAL 16-SOEIAJ |
| 产品变化通告： | Product Discontinuation 30/Sept/2011 |
| 标准包装： | 50 |
| 系列： | 74HC |
| 逻辑类型： | 单稳态 |
| 独立电路： | 2 |
| 施密特触发器输入： | 是 |
| 传输延迟： | 30ns |
| 输出电流高，低： | 5.2mA，5.2mA |
| 电源电压： | 2 V ~ 6 V |
| 工作温度： | -55°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.209"，5.30mm 宽） |
| 供应商设备封装： | 16-SOEIAJ |
| 包装： | 管件 |
MC74HC4538A
http://onsemi.com
11
When Cx charges up to the reference voltage of the upper
reference circuit (#17), the output of the upper reference
circuit goes low (#18). This causes the output latch to toggle,
taking the Q output of the HC4538A to a low state (#19), and
completing the timeout cycle.
POWERDOWN CONSIDERATIONS
Large values of Cx may cause problems when powering
down the HC4538A because of the amount of energy stored
in the capacitor. When a system containing this device is
powered down, the capacitor may discharge from VCC
through the input protection diodes at pin 2 or pin 14.
Current through the protection diodes must be limited to 30
mA; therefore, the turnoff time of the VCC power supply
must not be faster than t = VCC
Cx/(30 mA). For example,
if VCC = 5.0 V and Cx = 15
mF, the VCC supply must turn off
no faster than t = (5.0 V)
(15 mF)/30 mA = 2.5 ms. This is
usually not a problem because power supplies are heavily
filtered and cannot discharge at this rate.
When a more rapid decrease of VCC to zero volts occurs,
the HC4538A may sustain damage. To avoid this possibility,
use an external damping diode, Dx, connected as shown in
Figure 11. Best results can be achieved if diode Dx is chosen
to be a germanium or Schottky type diode able to withstand
large current surges.
RESET AND POWER ON RESET OPERATION
A low voltage applied to the Reset pin always forces the
Q output of the HC4538A to a low state.
The timing diagram illustrates the case in which reset
occurs (#20) while Cx is charging up toward the reference
voltage of the upper reference circuit (#21). When a reset
occurs, the output of the reset latch goes low (#22), turning
on transistor M1. Thus Cx is allowed to quickly charge up to
VCC (#23) to await the next trigger signal.
On power up of the HC4538A the poweron reset circuit
will be high causing a reset condition. This will prevent the
triggercontrol circuit from accepting a trigger input during
this state. The HC4538A’s Q outputs are low and the Q not
outputs are high.
RETRIGGER OPERATION
When used in the retriggerable mode (Figure 12), the
HC4538A may be retriggered during timing out of the
output pulse at any time after the triggercontrol circuit
flipflop has been reset (#24), and the voltage across Cx is
above the lower reference voltage. As long as the Cx voltage
is below the lower reference voltage, the reset of the
flipflop is high, disabling any trigger pulse. This prevents
M3 from turning on during this period resulting in an output
pulse width that is predictable.
The amount of undershoot voltage on RxCx during the
trigger mode is a function of loop delay, M3 conductivity,
and VDD. Minimum retrigger time, trr (Figure 7), is a
function of 1) time to discharge RxCx from VDD to lower
reference voltage (Tdischarge); 2) loop delay (Tdelay); 3)
time to charge RxCx from the undershoot voltage back to the
lower reference voltage (Tcharge).
Figure 13 shows the device configured in the
nonretriggerable mode.
For additional information, please see Application Note
(AN1558/D) titled Characterization of Retrigger Time in
the HC4538A Dual Precision Monostable Multivibrator.
DX
CX
VCC
Q
RESET
A
B
Figure 13. Discharge Protection During Power Down
RX
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MC74HC4538AFL1 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| MC74HC4538AFL2 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| MC74HC4538AFR1 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| MC74HC4538AFR2 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| MC74HC4538AN | 功能描述:单稳态多谐振荡器 3-6V Dual Precision RoHS:否 制造商:Texas Instruments 每芯片元件:1 逻辑系列:LVC 逻辑类型:Monostable Multivibrator 封装 / 箱体:SSOP-8 传播延迟时间:18.6 ns 高电平输出电流:- 32 mA 低电平输出电流:32 mA 电源电压-最大:5.5 V 电源电压-最小:1.65 V 最大功率耗散: 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装:Reel |
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