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參數(shù)資料
| 型號： | STM1404 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | Security Supervisor with Battery Switchover(帶電池轉(zhuǎn)換功能的安全監(jiān)控器) |
| 中文描述： | 安全監(jiān)控與電池切換（帶電池轉(zhuǎn)換功能的安全監(jiān)控器） |
| 文件頁數(shù)： | 15/36頁 |
| 文件大小： | 362K |
| 代理商： | STM1404 |
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STM1404
Operation
15/36
Operation
Reset input
The STM1404 Security Supervisor asserts a reset signal to the MCU whenever V
CC
goes
below the reset threshold (V
RST
), or when the Push-button Reset Input (MR) is taken low.
RST is guaranteed to be a logic low for 0V < V
CC
< V
RST
if V
BAT
is greater than 1V. Without
a back-up battery, RST is guaranteed valid down to V
CC
=1V.
During power-up, once V
CC
exceeds the reset threshold an internal timer keeps RST low for
the reset time-out period, t
rec
. After this interval RST returns high.
If V
CC
drops below the reset threshold, RST goes low. Each time RST is asserted, it stays
low for at least the reset time-out period (t
rec
). Any time V
CC
goes below the reset threshold
the internal timer clears. The reset timer starts when V
CC
returns above the reset threshold.
Push-button reset input
A logic low on MR asserts reset. Reset remains asserted while MR is low, and for t
rec
(see
Figure 25 on page 25
) after it returns high. The MR input has an internal 40k
Ω
pull-up
resistor, allowing it to be left open if not used. This input can be driven with TTL/CMOS-logic
levels or with open-drain/collector outputs. Connect a normally open momentary switch from
MR to Ground to create a manual reset function; external debounce circuitry is not required.
If MR is driven from long cables or the device is used in a noisy environment, connect a
0.1μF capacitor from MR to V
SS
to provide additional noise immunity. MR may float, or be
tied to V
CC
when not used.
Back-up battery switchover
In the event of a power failure, it may be necessary to preserve the contents of external
SRAM through V
OUT
. With a backup battery installed with voltage V
BAT
, the devices
automatically switch the SRAM to the back-up supply when V
CC
falls.
If back-up battery is not used, connect both V
BAT
and V
OUT
to V
CC
.
This family of Security Supervisors does not always connect V
BAT
to V
OUT
when V
BAT
is
greater than V
CC
. V
BAT
connects to V
OUT
(through a 100
Ω
switch) when V
CC
is below V
SW
(~2.4V) or V
BAT
(whichever is lower). This is done to allow the back-up battery (e.g., a 3.6V
battery) to have a higher voltage than V
CC
.
Assuming that V
BAT
> 2.0V, switchover at V
SO
ensures that battery back-up mode is entered
before V
OUT
gets too close to the 2.0V minimum required to reliably retain data in most
external SRAMs. When V
CC
recovers, hysteresis is used to avoid oscillation around the V
SO
point. V
OUT
is connected to V
CC
through a 3
Ω
PMOS power switch.
The back-up battery may be removed while V
CC
is valid, assuming V
BAT
is adequately
decoupled (0.1μF typ), without danger of triggering a reset.
Note:
Note:
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| STM1404_08 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:3 V FIPS-140 security supervisor with battery switchover |
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| STM1404ARMBQ6F | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:3 V FIPS-140 security supervisor with battery switchover |
| STM1404ARMCQ6F | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:3 V FIPS-140 security supervisor with battery switchover |
| STM1404ARMDQ6F | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:3 V FIPS-140 security supervisor with battery switchover |
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