參數(shù)資料
型號： 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)： 15/20頁
文件大?。?/td> 198K
代理商： MAX791
Using S uperCaps or MaxCaps
with the MAX 791
VBATT has the same operating voltage range as V
CC
,
and the battery-switchover threshold voltages are typi-
cally ±30mV centered at VBATT, allowing use of a
SuperCap and a simple charging circuit as a backup
source (Figure 12).
If V
CC
is above the reset threshold and VBATT is 0.5V
above V
CC
, current flows to V
OUT
and V
CC
from VBATT
until the voltage at VBATT is less than 0.5V above V
CC
.
For example, with a SuperCap connected to VBATT
and through a diode to V
CC
, if V
CC
quickly changes
from 5.4V to 4.9V, the capacitor discharges through
V
OUT
and V
CC
until VBATT reaches 5.3V typical.
Leakage current through the SuperCap charging diode
and MAX791 internal power diode eventually dis-
charges the SuperCap to V
CC
. Also, if V
CC
and VBATT
start from 0.5V above the reset threshold and power is
lost at V
CC
, the SuperCap on VBATT discharges
through V
CC
until VBATT reaches the reset threshold;
the MAX791 then switches to battery-backup mode and
the current through V
CC
goes to zero (Figure 10).
Using S eparate Power S upplies
for V BAT T and V
CC
If using separate power supplies for V
CC
and VBATT,
VBATT must be less than 0.3V above V
CC
when V
CC
is
above the reset threshold. As described in the previous
section, if VBATT exceeds this limit and power is lost at
V
CC
, current flows continuously from VBATT to V
CC
via
the VBATT-to-V
OUT
diode and the V
OUT
-to-V
CC
switch
until the circuit is broken (Figure 10).
Alternative Chip-Enable Gating
Using memory devices with CE and CE inputs allows
the MAX791 CE loop to be bypassed. To do this, con-
nect CE IN to ground, pull up CE OUT to V
OUT
, and
connect CE OUT to the CE input of each memory
device (Figure 13). The CE input of each part then con-
nects directly to the chip-select logic, which does not
have to be gated by the MAX791.
Adding Hysteresis to the
Power-Fail Comparator
Hysteresis adds a noise margin to the power-fail com-
parator and prevents repeated triggering of PFO when
VIN is near the power-fail comparator trip point. Figure
14 shows how to add hysteresis to the power-fail com-
parator. Select the ratio of R1 and R2 such that PFI
sees 1.25V when VIN falls to the desired trip point
(V
TRIP
). Resistor R3 adds hysteresis. It will typically be
an order of magnitude greater than R1 or R2. The cur-
rent through R1 and R2 should be at least 1μA to
ensure that the 25nA (max) PFI input current does not
shift the trip point. R3 should be larger than 10k
to
prevent it from loading down the PFO pin. Capacitor C1
adds additional noise rejection.
M
Mic roproc essor S upervisory Circ uit
______________________________________________________________________________________
15
MAX791
V
CC
GND
PFI
*OPTIONAL
R2
R3
R1
VIN
+5V
C1*
TO
μ
P
PFO
TRIP
= 1.25 R1 + R2
V
H
= 1.25 / R2
||
R R3 R1 R3 R2
V
PFO
+5V
0V
0V
V
H
V
TRIP
V
IN
V
L
Figure 14. Adding Hysteresis to the Power-Fail Comparator
相關PDF資料
PDF描述
MAX792R Microprocessor and Non-Volatile Memory Supervisory Circuits(復位門限2.61V,微處理器和非易失存儲器監(jiān)控電路)
MAX792S Microprocessor and Non-Volatile Memory Supervisory Circuits(復位門限1.91V,微處理器和非易失存儲器監(jiān)控電路)
MAX792T Microprocessor and Non-Volatile Memory Supervisory Circuits(復位門限3.06V,微處理器和非易失存儲器監(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位器)
MAX794 3.0V/3.3V Adjustable Microprocessor Supervisory Circuits(具有可調閾值監(jiān)控器、芯片使能和支持備用電池的復位器)
相關代理商/技術參數(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 人工復位:Resettable 監(jiān)視器:No Watchdog 電池備用開關:No Backup 上電復位延遲（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 人工復位:Resettable 監(jiān)視器:No Watchdog 電池備用開關:No Backup 上電復位延遲（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 人工復位:Resettable 監(jiān)視器:No Watchdog 電池備用開關:No Backup 上電復位延遲（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 人工復位:Resettable 監(jiān)視器:No Watchdog 電池備用開關:No Backup 上電復位延遲（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 人工復位:Resettable 監(jiān)視器:No Watchdog 電池備用開關:No Backup 上電復位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel
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