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| 型号： | MAX703ESA-T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 5/9页 |
| 文件大小： | 0K |
| 描述： | IC MPU SUPERVISORY CIRCUIT 8SOIC |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 备用电池电路 |
| 监视电压数目： | 1 |
| 输出： | 推挽式，图腾柱 |
| 复位： | 低有效 |
| 复位超时： | 最小为 140 ms |
| 电压 - 阀值： | 4.65V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOIC |
| 包装： | 带卷 (TR) |
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
Detailed Description
RESET Output
A μP ’s reset input starts the μP in a known state.
Whenever the μP is in an unknown state, it should be
held in reset. The MAX703/MAX704 assert reset when
V CC is low, preventing code-execution errors during
power-up, power-down, or brownout conditions.
When V BATT is 2V or more, RESET is always valid, irre-
spective of V CC . On power-up, as V CC rises, RESET
remains low. When V CC exceeds the reset threshold,
an internal timer holds RESET low for a time equal to
the reset pulse width (typically 200ms); after this inter-
val, RESET goes high (Figure 2). If a power-fail or
applied to V BATT (Figure 3). During this time, diode D1
(between V BATT and the substrate) conducts current
from V BATT to V CC if V BATT ≥ (V CC + 0.6V).
When the battery-backup mode is activated, V BATT
connects to V OUT . In this mode, the substrate connects
to V BATT and internal circuitry is powered from the bat-
tery (Figure 3). Table 1 shows the status of the MAX703/
MAX704 inputs and outputs in battery-backup mode.
When V CC is below, but within, 1V of V BATT , the internal
switchover comparator draws about 30μA. Once V CC
Table 1. Input and Output Status in
Battery-Backup Mode
brownout condition occurs (i.e., V CC drops below the
reset threshold), RESET is asserted. As long as V CC
remains below the reset threshold, the internal timer is
continually restarted, causing the RESET output to
remain low. Thus, a brownout condition that interrupts a
previously initiated reset pulse causes an additional
200ms delay from the end of the last interruption.
Power-Fail Comparator
The PFI input is compared to an internal reference. If
PFI is less than 1.25V, PFO goes low. The power-fail
comparator can be used as an undervoltage detector
to signal a failing power supply. In the Typical
Operating Circuit, an external voltage-divider at PFI is
used to monitor the unregulated DC voltage from which
the regulated +5V supply is derived.
The voltage-divider can be chosen so the voltage at
PFI falls below 1.25V just before the +5V regulator
SIGNAL
V CC
V OUT
V BATT
RESET
PFI
PFO
MR
V BATT
STATUS
Disconnected from V OUT .
Connected to V BATT through an internal 80 ?
p-channel MOSFET switch.
Connected to V OUT . Supply current is < 1μA when
V CC < (V BATT - 1V).
Logic-low.
Power-fail comparator is disabled.
Logic-low.
Disabled.
V CC
drops out. PFO is then used as an interrupt to prepare
the μP for power-down.
S1
S2
MAX703
MAX704
S3
S4
To conserve power, the power-fail comparator is turned
D1
D2
off and PFO is forced low when the MAX703/MAX704
enter battery-backup mode.
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 V BATT , the MAX703/
MAX704 automatically switch RAM to backup power
when V CC fails.
SUBSTRATE
D3
V OUT
As long as V CC exceeds the reset threshold, V CC con-
nects to V OUT through a 5 ? p-channel MOSFET power
switch. Once V CC falls below the reset threshold,
RESET goes low and V CC or V BATT (whichever is high-
er) switches to V OUT . Note that V BATT switches to V OUT
through an 80 ? switch only if V CC is below the reset-
threshold voltage and V BATT is greater than V CC . When
CONDITION
V CC > Reset Threshold
V CC < Reset Threshold and
V CC > V BATT
V CC < Reset Threshold and
V CC < V BATT
S1/S2
Open
Open
Closed
S3/S4
Closed
Closed
Open
V CC exceeds the reset threshold, it is connected to the
MAX703/MAX704 substrate, regardless of the voltage
Figure 3. Battery-Switchover Block Diagram
_______________________________________________________________________________________
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX703-MAX704 | 制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:Low-Cost レP Supervisory Circuits with Battery Backup |
| MAX703MJA | 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 |
| MAX704 | 制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:Low-Cost レP Supervisory Circuits with Battery Backup |
| MAX704_C/D | 制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:3.0V/3.3V Microprocessor Supervisory Circuits |
| MAX704_CPA | 制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:3.0V/3.3V Microprocessor Supervisory Circuits |
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