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參數(shù)資料
| 型號(hào)： | MAX804 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 3.0V/3.3V Microprocessor Supervisory Circuits(具有看門狗和支持備用電池,3V高精度復(fù)位器(高電壓復(fù)位)) |
| 中文描述： | 3.0V/3.3V微處理器監(jiān)控電路 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大?。?/td> | 134K |
| 代理商： | MAX804 |
M
Bac kup-Battery S witc hover
In the event of a brownout or power failure, it may be
necessary to preserve the contents of RAM. With a
backup battery installed at VBATT, the devices auto-
matically switch RAM to backup power when V
CC
falls.
This family of μP supervisors (designed for 3.3V and 3V
systems) doesn’t always connect VBATT to V
when
VBATT is greater than V
. VBATT connects to V
(through a 140
switch) when V
is below V
and
VBATT is greater than V
, or when V
falls below
1.75V (typ) regardless of the VBATT voltage. This is
done to allow the backup battery (e.g., a 3.6V lithium
cell) to have a higher voltage than V
CC
.
Switchover at V
(2.40V) ensures that battery-backup
mode is entered before V
gets too close to the 2.0V
minimum required to reliably retain data in CMOS RAM.
Switchover at higher V
voltages would decrease
backup-battery life. When V
recovers, switchover is
deferred until V
rises above the reset threshold
(V
RST
) to ensure a stable supply. V
is connected to
V
CC
through a 3
PMOS power switch.
A logic low on–M—–asserts reset. Reset remains asserted
while–M—–
high. This input has an internal 70μA pull-up current, so
TTL or CMOS logic levels, or with open-drain/collector
outputs. Connect a normally open momentary switch
external debounce circuitry is not required.
is low, and for t
WP
(200ms) after–M—–returns
__________Applic ations Information
These μP supervisory circuits are not short-circuit
protected. Shorting V
to ground—excluding power-
up transients such as charging a decoupling
capacitor—destroys the device. Decouple both V
and VBATT pins to ground by placing 0.1μF capacitors
as close to the device as possible.
Using a S uperCap
as a Bac kup Power S ourc e
SuperCaps are capacitors with extremely high
capacitance values (e.g., order of 0.47F) for their size.
Figure 3 shows two ways to use a SuperCap as a
backup power source. The SuperC ap may be
connected through a diode to the 3V input (Figure 3a)
or, if a 5V supply is also available, the SuperCap may
be charged up to the 5V supply (Figure 3b) allowing a
longer backup period. Since VBATT can exceed V
CC
while V
CC
is above the reset threshold, there are no
special precautions when using these μP supervisors
with a SuperCap.
Operation without a Bac kup
Power S ourc e
These μP supervisors were designed for battery-
backed applications. If a backup battery is not used,
connect both VBATT and V
to V
, or use a
different μP supervisor such as the MAX706T/S/R or
MAX708T/S/R.
Replac ing the Bac kup Battery
The backup power source can be removed while V
remains valid, if VBATT is decoupled with a 0.1μF
capacitor to ground, without danger of triggering
stays above V
SW
,
battery-backup mode cannot be entered.
Adding Hysteresis
to the Power-Fail Comparator
The power-fail comparator has a typical input
hysteresis of 10mV. This is sufficient for most applica-
tions 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
the ratio of R1 and R2 such that PFI sees 1.237V (V
)
when V
falls to its trip point (V
). R3 adds the
hysteresis and will 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
).
3.0V /3.3V Mic roproc essor S upervisory Circ uits
8
_______________________________________________________________________________________
SuperCap is a trademark of Baknor Industries.
PIN NAME
STATUS
V
OUT
Connected to VBATT through an internal
140
switch
Disconnected from V
OUT
The power-fail comparator is disabled when
V
CC
< V
SW
Logic low when V
CC
< V
SW
or PFI < V
PFT
The watchdog timer is disabled
V
CC
PFI
–——O
WDI
–M—–
–————–
Disabled
Low logic
RESET
VBATT
High impedance
Connected to V
OUT
Table 1. Input and Output Status in
Battery-Backup Mode
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX804_C/D | 制造商:MAXIM 制造商全稱:Maxim Integrated Products 功能描述:3.0V/3.3V Microprocessor Supervisory Circuits |
| MAX804_CPA | 制造商:MAXIM 制造商全稱:Maxim Integrated Products 功能描述:3.0V/3.3V Microprocessor Supervisory Circuits |
| MAX804_CSA | 制造商:MAXIM 制造商全稱:Maxim Integrated Products 功能描述:3.0V/3.3V Microprocessor Supervisory Circuits |
| MAX804_EPA | 制造商:MAXIM 制造商全稱:Maxim Integrated Products 功能描述:3.0V/3.3V Microprocessor Supervisory Circuits |
| MAX804_ESA | 制造商:MAXIM 制造商全稱:Maxim Integrated Products 功能描述:3.0V/3.3V Microprocessor Supervisory Circuits |
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