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參數(shù)資料
| 型號： | LM2984 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Microprocessor Power Supply System |
| 中文描述： | 微機電源系統(tǒng) |
| 文件頁數(shù)： | 13/16頁 |
| 文件大小： | 398K |
| 代理商： | LM2984 |
Application Hints
(Continued)
This watchdog circuitry continuously monitors a pin on the
μP that generates a positive going pulse during normal op-
eration. The period of this pulse is typically on the order of
milliseconds and the pulse width is typically on the order of
10’s of microseconds. If this pulse ever disappears, the
watchdog circuitry will time out and a RESET low will be sent
to the μP. The time out period is determined by two external
components, R
t
and C
mon
, according to the formula:
T
window
= 0.82 R
t
C
mon
(seconds)
The width of the RESET pulse is set by C
mon
and an internal
resistor according to the following:
RESET
pw
= 2000 C
mon
(seconds)
A square wave signal can also be monitored for errors by fil-
tering the C
input such that only the positive edges of the
signal are detected. Figure 2 is a schematic diagram of a
typical circuit used to differentiate the input signal. Resistor
R
and capacitor C
pass only the rising edge of the square
wave and create a short positive pulse suitable for the μP
monitor input. If the incoming signal continues in a high state
or in a low state for too long a period of time, a RESET low
will be generated.
The threshold voltage and input characteristics of this pin are
compatible with nearly all logic families.
There is a limit on the width of a pulse that can be reliably de-
tected by the watchdog circuit. This is due to the output re-
sistance of the transistor which discharges C
when a high
state is detected at the input. The minimum detectable pulse
width can be determined by the following formula:
PW
min
= 20 C
mon
(seconds)
DS011252-14
FIGURE 2. Monitoring Square Wave μP Signals
13
www.national.com
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| LM2984CT | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動電壓（最大值）:307 mV 輸出電流:1 A 負載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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