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参数资料
| 型号： | MAX817LEPA+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/16页 |
| 文件大小： | 0K |
| 描述： | IC SUPERVISOR MPU 5V 8-DIP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 类型： | 备用电池电路 |
| 监视电压数目： | 1 |
| 复位： | 低有效 |
| 复位超时： | 最小为 140 ms |
| 电压 - 阀值： | 4.65V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 8-DIP（0.300"，7.62mm） |
| 供应商设备封装： | 8-PDIP |
| 包装： | 管件 |
+5V Microprocessor Supervisory Circuits
Watchdog 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 SuperCap? as a
Backup Power Source
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
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
Backup Power Source
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.
Replacing the Backup 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 (MAX817/MAX819)
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
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
R1
V IN
PFI
+5V
V CC
MAX817
MAX819
+5V
R2
C1*
R3
PFO
V CC
BATT
OUT
MAX817
MAX818
MAX819 RESET
TO STATIC RAM
TO μ P
+5V
PFO
TO μ P
GND
*OPTIONAL
(
)
100k
0.1F
GND
0V
0V
R2
V TRIP = 1.25V R1 + R2
V L
V TRIP
V IN
V H
V H = 1.25V
(
R2 || R3
R1 + R2 || R3
)
Figure 11. Using a SuperCap? as a Backup Power Source
with a +5V ±10% Supply
V L - 1.25
R1
+
5 - 1.25
R3
=
1.25
R2
SuperCap is a trademark of Baknor Industries.
Figure 12. Adding Hysteresis to the Power-Fail Comparator
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX817LEPA+ | 功能描述:监控电路 5V MPU Supervisor RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| MAX817LESA | 功能描述:监控电路 RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| MAX817LESA+ | 功能描述:监控电路 5V MPU Supervisor RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| MAX817LESA+T | 功能描述:监控电路 5V MPU Supervisor RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| MAX817LESA-T | 功能描述:监控电路 RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
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