參數(shù)資料
型號(hào)： MAX819M
廠商： Maxim Integrated Products, Inc.
英文描述： +5V Microprocessor Supervisory Circuits
中文描述： +5V微處理器監(jiān)控電路
文件頁數(shù)： 13/16頁
文件大?。?/td> 114K
代理商： MAX819M
M
+5V Mic roproc essor S upervisory Circ uits
______________________________________________________________________________________
13
Watc hdog Input Current
The MAX817/MAX818 WDI inputs are internally driven
through a buffer and series resistor from the watchdog
counter (Figure 1). When WDI is left unconnected, the
watchdog timer is serviced within the watchdog timeout
period by a low-high-low pulse from the counter chain.
For minimum watchdog input current (minimum overall
power consumption), leave WDI low for the majority of the
watchdog timeout period, pulsing it low-high-low once
within
7
/
8
of the watchdog timeout period to reset the
watchdog timer. If instead WDI is externally driven high for
the majority of the timeout period, up to 150μA can flow
into WDI.
Using a S uperCap as a
Bac kup Power S ourc e
SuperCaps are capacitors with extremely high capaci-
tance values (on the order of 0.47F) for their size. Since
BATT has the same operating voltage range as V
CC
, and
the battery switchover threshold voltages are typically
±30mV centered at V
BATT
, a SuperCap and simple
charging circuit can be used as a backup power source.
Figure 11 shows a SuperCap used as a backup source.
If V
CC
is above the reset threshold and V
BATT
is 0.5V
above V
CC
, current flows to OUT and V
CC
from BATT
until the voltage at BATT is less than 0.5V above V
CC
.
For example, if a SuperCap is connected to BATT
through a diode to V
CC
, and V
CC
quickly changes from
5.4V to 4.9V, the capacitor discharges through OUT
and V
CC
until V
BATT
reaches 5.1V typical. Leakage cur-
rent through the SuperCap charging diode and the
internal power diode eventually discharges the
SuperCap to V
CC
. Also, if V
CC
and V
BATT
start from
0.1V above the reset threshold and power is lost at
V
CC
, the SuperCap on BATT discharges through V
CC
until V
BATT
reaches the reset threshold. Battery-backup
mode is then initiated and the current through V
CC
goes to zero.
Operation Without a
Bac kup Power S ourc e
The MAX817/MAX818/MAX819 were designed for bat-
tery-backed applications. If a backup battery is not
used, connect V
CC
to OUT, and connect BATT to
ground.
Replac ing the Bac kup Battery
The backup power source can be removed while V
CC
remains valid, without danger of triggering a reset
pulse, if BATT is decoupled with a 0.1μF capacitor to
ground. As long as V
CC
stays above the reset thresh-
old, battery-backup mode cannot be entered.
Adding Hysteresis to the Power-Fail
Comparator (MAX 817/MAX 819)
The power-fail comparator has a typical input hystere-
sis of 4mV. This is sufficient for most applications where
a power-supply line is being monitored through an
external voltage divider (see Monitoring an Additional
Supply).
For additional noise margin, connect a resistor between
PFO
and PFI, as shown in Figure 12. Select the ratio of
R1 and R2 such that PFI sees V
PFT
when V
IN
falls to the
Figure 11. Using a SuperCap as a Backup Power Source
with a +5V ±10% Supply
SuperCap is a trademark of Baknor Industries.
BATT
V
CC
OUT
RESET
GND
TOSTATIC RAM
TO
μ
P
0.1F
MAX817
MAX818
MAX819
+5V
100k
Figure 12. Adding Hysteresis to the Power-Fail Comparator
V
CC
GND
TO
μ
P
PFI
PFO
R1
R2
R3
*OPTIONAL
C1*
V
IN
+5V
R1
+ R2
R1
( )
R2
V
H
= 1.25V
V
TRIP
= 1.25V
+
+
||
R2
R3
MAX817
MAX819
PFO
0V
+5V
V
H
V
L
0V
V
TRIP
V
IN
( )
R1
V
L
- 1.25
R3
5
- 1.25
=
R2
1.25
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX819MCPA 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)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
MAX819MCPA+ 功能描述:監(jiān)控電路 5V MPU Supervisor RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)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
MAX819MCSA 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)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
MAX819MCSA+ 功能描述:監(jiān)控電路 5V MPU Supervisor RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)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
MAX819MCSA+T 功能描述:監(jiān)控電路 5V MPU Supervisor RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)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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