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參數(shù)資料
| 型號(hào)： | MAX707 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Low-Cost,μP Supervisory Circuits(帶有掉電報(bào)警復(fù)位器,復(fù)位門限4.65V) |
| 中文描述： | 低成本、微處理器監(jiān)控電路 |
| 文件頁數(shù)： | 7/12頁 |
| 文件大?。?/td> | 129K |
| 代理商： | MAX707 |
Power-Fail Comparator
The power-fail comparator can be used for various pur-
poses because its output and noninverting input are
not internally connected. The inverting input is internal-
ly connected to a 1.25V reference.
To build an early-warning circuit for power failure, con-
nect the PFI pin to a voltage divider (see Typical
Operating Circuit. Choose the voltage divider ratio so
that the voltage at PFI falls below 1.25V just before the
+5V regulator drops out. Use PFO to interrupt the μP
so it can prepare for an orderly power-down.
__________Applic ations Information
Ensuring a V alid RES ET
Output Down to V
CC
= 0V
When V
CC
falls below 1V, the MAX705-MAX708 RESET
output no longer sinks current—it becomes an open cir-
cuit. High-impedance CMOS logic inputs can drift to
undetermined voltages if left undriven. If a pull-down
resistor is added to the RESET pin as shown in Figure 5,
any stray charge or leakage currents will be drained to
ground, holding RESET low. Resistor value (R1) is not
critical. It should be about 100k
, large enough not to
load RESET and small enough to pull RESET to ground.
Monitoring V oltages Other T han the
Unregulated DC Input
Monitor voltages other than the unregulated DC by
connecting a voltage divider to PFI and adjusting the
ratio appropriately. If required, add hysteresis by con-
necting a resistor (with a value approximately 10 times
the sum of the two resistors in the potential divider net-
work) between PFI and PFO. A capacitor between PFI
and GND will reduce the power-fail circuit’s sensitivity
to high-frequency noise on the line being monitored.
RESET can be asserted on other voltages in addition to
the +5V V
CC
line. Connect PFO to MR to initiate a RESET
pulse when PFI drops below 1.25V. Figure 6 shows the
MAX705-MAX708 configured to assert RESET when the
+5V supply falls below the reset threshold, or when the
+12V supply falls below approximately 11V.
Monitoring a Negative V oltage
The power-fail comparator can also monitor a negative
supply rail (Figure 7). When the negative rail is good (a
negative voltage of large magnitude), PFO is low, and
when the negative rail is degraded (a negative voltage
of lesser magnitude), PFO is high. By adding the resis-
tors and transistor as shown, a high PFO triggers reset.
As long as PFO remains high, the MAX705-
MAX708/MAX813L will keep reset asserted (RESET =
low, RESET = high). Note that this circuit’s accuracy
depends on the PFI threshold tolerance, the V
CC
line,
and the resistors.
M
Low-Cost, μP S upervisory Circ uits
_______________________________________________________________________________________
7
t
WP
t
WD
t
WD
t
WD
+5V
0V
WDI
+5V
0V
WDO
+5V
0V
RESET
+5V
0V
(RESET)
t
RS
( ) ARE FOR MAX813L ONLY.
RESET EXTERNALLY
TRIGGERED BY MR
Figure 3. MAX705/MAX706/MAX813L Watchdog TIming
Figure 4. MAX705/MAX706 RESET, MR, and WDO Timing with
WDI Three-Stated. The MAX707/MAX708/MAX813L RESET
output is the inverse of RESET shown.
t
RS
t
RS
+5V
0V
RESET
WDO
+5V
0V
MR
t
MR
MR EXTERNALLY DRIVEN LOW
+5V
0V
V
CC
V
RT
V
RT
t
MD
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX707 | μP Supervisory Circuits(μP監(jiān)控電路) |
| MAX708 | μP Supervisory Circuits(μP監(jiān)控電路) |
| MAX711 | 3.3V/5V or Adjustable, Step-Up/Down DC-DC Converters |
| MAX710 | 3.3V/5V or Adjustable, Step-Up/Down DC-DC Converters |
| MAX710ESE | 3.3V/5V or Adjustable, Step-Up/Down DC-DC Converters |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX707/D | 制造商:MAXIM 制造商全稱:Maxim Integrated Products 功能描述:?P Supervisory Circuits |
| MAX707C/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 |
| MAX707CPA | 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 |
| MAX707CPA+ | 功能描述:監(jiān)控電路 Single uPower 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 |
| MAX707CSA | 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 |
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