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參數(shù)資料
| 型號(hào)： | MAX791 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Microprocessor Supervisory Circuit(微處理器監(jiān)控電路) |
| 中文描述： | 微處理器監(jiān)控電路 |
| 文件頁數(shù)： | 10/20頁 |
| 文件大?。?/td> | 198K |
| 代理商： | MAX791 |
M
dog-timeout period, WDO goes low 70ns after the
falling edge of WDPO and remains low until the next
transition at WDI (Figure 5). A flip-flop can force the
system into a hardware shutdown if there are two suc-
cessive watchdog faults (Figure 6). WDO has a 2 x TTL
output characteristic.
Watc hdog-Pulse Output
As described in the preceding section, WDPO can be
used as the clock input to an external D flip-flop. Upon
the absence of a watchdog edge or pulse at WDI at the
end of a watchdog-timeout period, WDPO will pulse low
for 1ms. The falling edge of WDPO precedes WDO by
70ns. Since WDO is high when WDPO goes low, the
flip-flop’s Q output remains high as WDO goes low
(Figure 5). If the watchdog timer is not reset by a transi-
tion at WDI, WDO remains low and WDPO clocks a
logic low to the Q output, causing the MAX791 to latch
in reset. If the watchdog timer is reset by a transition at
WDI, WDO goes high and the flip-flop’s Q output
remains high. Thus, a system shutdown is only caused
by two successive watchdog faults.
The internal pull-up resistors associated with WDO and
WDPO connect to V
OUT
. Therefore, do not connect
these outputs directly to CMOS logic that is powered
from V
CC
since, in the absence of V
CC
(i.e., battery
mode), excessive current will flow from WDO or
WDPO through the protection diode(s) of the CMOS-
logic inputs to ground.
S elec ting an Alternative Watc hdog
T imeout Period
SWT input controls the watchdog-timeout period.
Connecting SWT to V
OUT
selects the internal 1.6sec
watchdog-timeout period. Select an alternative timeout
period by connecting a capacitor between SWT and
GND. Do not leave SWT floating, and do not connect it
to ground. The following formula determines the watch-
dog-timeout period:
Watchdog Timeout Period = 2.1 x (capacitor value
in nF) ms
This formula is valid for capacitance values between
4.7nF and 100nF (see the Watchdog Timeout vs.
Timing Capacitor graph in the Typical Operating
Characteristics). SWT is internally connected to a
±100nA (typ) current source, which charges and dis-
charges the timing capacitor to create the oscillator fre-
quency that sets the watchdog timeout period (see
C onnecting a Timing C apacitor to SWT in the
Applications Informationsection).
Mic roproc essor S upervisory Circ uit
10
______________________________________________________________________________________
MAX791
CLOCK
D
V
CC
CD4013
V
CC
GND
4
V
OUT
MR
0.1
μ
F
4.7k
*SETS QHIGH ON POWER-UP
VBATT
RESET
WDI
WDPO
WDO
μ
P POWER
μ
P
RESET
I/O
TWO
CONSECUTIVE
WATCHDOG
FAULT
INDICATIONS
Q
Q
SET
RESET V
SS
4
2
15
11
LOWLINE
NMI
INTERRUPT
10
16
1/6 74HC04
14
1
5
3
14
3
2
7
6
*1
μ
F
+5V
1
9
REACTIVATE
+5V
3.6V
Figure 6. Two consecutive watchdog faults latch the system in reset.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX792R | Microprocessor and Non-Volatile Memory Supervisory Circuits(復(fù)位門限2.61V,微處理器和非易失存儲(chǔ)器監(jiān)控電路) |
| MAX792S | Microprocessor and Non-Volatile Memory Supervisory Circuits(復(fù)位門限1.91V,微處理器和非易失存儲(chǔ)器監(jiān)控電路) |
| MAX792T | Microprocessor and Non-Volatile Memory Supervisory Circuits(復(fù)位門限3.06V,微處理器和非易失存儲(chǔ)器監(jiān)控電路) |
| MAX793 | 3.0V/3.3V Adjustable Microprocessor Supervisory Circuits(具有監(jiān)控器、芯片使能和支持備用電池的復(fù)位器) |
| MAX794 | 3.0V/3.3V Adjustable Microprocessor Supervisory Circuits(具有可調(diào)閾值監(jiān)控器、芯片使能和支持備用電池的復(fù)位器) |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX791C/D | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| MAX791CPE | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| MAX791CPE+ | 功能描述:監(jiān)控電路 MPU Supervisor RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| MAX791CSE | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| MAX791CSE+ | 功能描述:監(jiān)控電路 MPU Supervisor RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
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