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参数资料
| 型号： | MAX690RESA-T |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 电源管理 |
| 英文描述： | 3.0V/3.3V Microprocessor Supervisory Circuits |
| 中文描述： | 1-CHANNEL POWER SUPPLY MANAGEMENT CKT, PDSO8 |
| 封装： | 0.150 INCH, PLASTIC, SO-8 |
| 文件页数： | 11/12页 |
| 文件大小： | 281K |
| 代理商： | MAX690RESA-T |
MAX690T/S/R,
704T/S/R,
802T/S/R,
804–806T/S/R
Backup-Battery Switchover
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 VCC
falls.
This family of P supervisors (designed for 3.3V and 3V
systems) doesn’t always connect VBATT to VOUT when
VBATT is greater than VCC. VBATT connects to VOUT
(through a 140
Ω switch) when VCC is below VSW and
VBATT is greater than VCC, or when VCC 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 VCC.
Switchover at VSW (2.40V) ensures that battery-backup
mode is entered before VOUT gets too close to the 2.0V
minimum required to reliably retain data in CMOS RAM.
Switchover at higher VCC voltages would decrease
backup-battery life. When VCC recovers, switchover is
deferred until VCC rises above the reset threshold
(VRST) to ensure a stable supply. VOUT is connected to
VCC through a 3Ω PMOS power switch.
Manual Reset
A logic low on
–
M
—
R
–
asserts reset. Reset remains asserted
while
–
M
—
R
–
is low, and for tWP (200ms) after
–
M
—
R
–
returns
high. This input has an internal 70A pull-up current, so
it can be left open if it is not used.
–
M
—
R
–
can be driven with
TTL or CMOS logic levels, or with open-drain/collector
outputs. Connect a normally open momentary switch
from
–
M
—
R
–
to GND to create a manual-reset function;
external debounce circuitry is not required.
__________Applications Information
These P supervisory circuits are not short-circuit
protected. Shorting VOUT to ground—excluding power-
up transients such as charging a decoupling
capacitor—destroys the device. Decouple both VCC
and VBATT pins to ground by placing 0.1F capacitors
as close to the device as possible.
Using a SuperCap
as a Backup Power Source
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 SuperCap 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 VCC
while VCC is above the reset threshold, there are no
special precautions when using these P supervisors
with a SuperCap.
Operation without a Backup
Power Source
These P supervisors were designed for battery-
backed applications. If a backup battery is not used,
connect both VBATT and VOUT to VCC, or use a
different P supervisor such as the MAX706T/S/R or
MAX708T/S/R.
Replacing the Backup Battery
The backup power source can be removed while VCC
remains valid, if VBATT is decoupled with a 0.1F
capacitor to ground, without danger of triggering
RESET/
–
R
—
E
—
S
—
E
—
T
–
. As long as VCC stays above VSW,
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 Monitoring
an Additional Power Supply section).
If additional noise margin is desired, connect a resistor
between
–
P
—
F
—
O
–
and PFI as shown in Figure 4a. Select
the ratio of R1 and R2 such that PFI sees 1.237V (VPFT)
when VIN falls to its trip point (VTRIP). R3 adds the
hysteresis and will typically be more than 10 times the
value of R1 or R2. The hysteresis window extends both
above (VH) and below (VL) the original trip point (VTRIP).
3.0V/3.3V Microprocessor Supervisory Circuits
8
_______________________________________________________________________________________
SuperCap is a trademark of Baknor Industries.
PIN NAME
STATUS
VOUT
Connected to VBATT through an internal
140
Ω switch
VCC
Disconnected from VOUT
PFI
The power-fail comparator is disabled when
VCC < VSW
–
P
—
F
—
O
–
Logic low when VCC < VSW or PFI < VPFT
WDI
The watchdog timer is disabled
–
M
—
R
–
Disabled
–
R
—
E
—
S
—
E
—
T
–
Low logic
RESET
High impedance
VBATT
Connected to VOUT
Table 1. Input and Output Status in
Battery-Backup Mode
相关PDF资料 |
PDF描述 |
|---|---|
| MAX690SCSA-T | 3.0V/3.3V Microprocessor Supervisory Circuits |
| MAX690SESA-T | 3.0V/3.3V Microprocessor Supervisory Circuits |
| MAX690TCSA-T | 3.0V/3.3V Microprocessor Supervisory Circuits |
| MAX690TESA-T | 3.0V/3.3V Microprocessor Supervisory Circuits |
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX690RMJA | 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 |
| MAX690SC/D | 功能描述:监控电路 3.0V/3.3V Microprocessor Supervisory Circuit with Reset Threshold of 2.925V 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 |
| MAX690SCPA | 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 |
| MAX690SCPA+ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX690SCSA | 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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