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參數(shù)資料
| 型號： | MAX794 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 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) |
| 中文描述： | 3.0V/3.3V可調(diào)、微處理器監(jiān)控電路 |
| 文件頁數(shù)： | 18/20頁 |
| 文件大?。?/td> | 211K |
| 代理商： | MAX794 |
M
Adding Hysteresis to the Power-Fail
Comparator (MAX 793/MAX 794)
The power-fail comparator has a typical input hystere-
sis of 10mV. This is sufficient for most applications
where a power-supply line is being monitored through
an external voltage divider (see the section Monitoring
an Additional Power Supply).
If additional noise margin is desired, connect a resistor
between PFO and PFI as shown in Figure 16a. Select
the ratio of R1 and R2 such that PFI sees V
PFT
when
V
IN
falls to its trip point (V
TRIP
). R3 adds the additional
hysteresis and should typically be more than 10 times
the value of R1 or R2. The hysteresis window extends
both above (V
H
) and below (V
L
) the original trip point
(V
TRIP
).
Connecting an ordinary signal diode in series with R3,
as shown in Figure 16b, causes the lower trip point (V
L
)
to coincide with the trip point without hysteresis (V
TRIP
),
so the entire hysteresis window occurs above V
TRIP
.
This method provides additional noise margin without
compromising the accuracy of the power-fail threshold
when the monitored voltage is falling. It is useful for
accurately detecting when a voltage falls past a thresh-
old. The current through R1 and R2 should be at least
1μA to ensure that the 25nA (max over temperature)
PFI input current does not shift the trip point. R3 should
be larger than 82k
so it does not load down the PFO
pin. Capacitor C1 is optional, and adds noise rejection.
Monitoring an Additional Power S upply
These μP supervisors can monitor either positive or
negative supplies using a resistor voltage divider to
PFI. PFO can be used to generate an interrupt to the
μP or to cause reset to assert (Figure 12).
Interfac ing to μPs with
Bidirec tional Reset Pins
Since the RESET output is open drain, the MAX793/
MAX794/MAX795 interface easily with μPs that have
bidirectional reset pins, such as the Motorola 68HC11.
Connecting the RESET output of the μP supervisor
directly to the RESET input of the microcontroller with a
single pull-up resistor allows either device to assert
reset (Figure 17).
Negative-Going V
CC
T ransients
These supervisors are relatively immune to short-dura-
tion negative-going V
CC
transients (glitches) while issu-
ing resets to the μP during power-up, power-down, and
brownout conditions. Therefore, resetting the μP when
V
CC
experiences only small glitches is usually not rec-
ommended.
Figure 18 shows maximum transient duration vs. reset-
comparator overdrive, for which reset pulses are
not
generated. The graph was produced using negative-
going V
CC
pulses, starting at 3.3V and ending below
the reset threshold by the magnitude indicated (reset
comparator overdrive). The graph shows the maximum
pulse width a negative-going V
CC
transient can typically
3.0V /3.3V Adjustable Mic roproc essor
S upervisory Circ uits
18
______________________________________________________________________________________
100
0
10 20
RESET COMPARATOR OVERDRIVE, V
RST
- V
CC
(mV)
30
100
10
20
30
80
90
M
M
μ
s
40
50
60 70
80
90
60
40
50
70
Figure 18. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive
START
SET WDI
HIGH
RETURN
PROGRAM
CODE
Subroutine or
ProgramLoop
SET WDI LOW
Figure 19. Watchdog Flow Diagram
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX794CPE | 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 |
| MAX794CPE+ | 功能描述:監(jiān)控電路 3/3.3/AdjV 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 |
| MAX794CSE | 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 |
| MAX794CSE+ | 功能描述:監(jiān)控電路 3/3.3/AdjV 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 |
| MAX794CSE+T | 功能描述:監(jiān)控電路 3/3.3/AdjV 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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