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参数资料
| 型号： | MAX704CPA |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 7/9页 |
| 文件大小： | 0K |
| 描述： | IC MPU SUPERVISORY CIRCUIT 8-DIP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 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： | 4.4V |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 8-DIP（0.300"，7.62mm） |
| 供应商设备封装： | 8-PDIP |
| 包装： | 管件 |
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
Ensuring a Valid RESET Output
Down to V CC = 0V
When V CC falls below 1V, the MAX703/MAX704 RESET
output no longer sinks current; it becomes an open cir-
cuit. High-impedance CMOS logic inputs can drift to
undetermined voltages if left as open circuits. If a pull-
down resistor is added to the RESET pin as shown in
Figure 6, any stray charge or leakage currents will flow
to ground, holding RESET low. Resistor value R1 is not
critical. It should be about 100k ? , which is large
enough not to load RESET and small enough to pull
RESET to ground.
Replacing the Backup Battery
The backup battery can be removed while V CC remains
valid without triggering a reset. As long as V CC stays
above the reset threshold, battery-backup mode cannot
be entered. This is an improvement on switchover ICs
that initiate a reset when V CC and V BATT are at or near
the same voltage level (regardless of the reset thresh-
old voltage). If the voltage on the unconnected V BATT
pin floats up toward V CC , this condition alone cannot
initiate a reset when using the MAX703/MAX704.
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
V IN is near the power-fail comparator trip point. Figure 7
shows how to add hysteresis to the power-fail com-
parator. Select the ratio of R1 and R2 so that PFI sees
1.25V when V IN 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 current
through R1 and R2 should be at least 1μA to ensure
that the 25nA (max) PFI input current does not shift the
V CC
MAX703
V OUT
trip point. R3 should be larger than 10k ? to prevent it
from loading down the PFO pin. Capacitor C1 adds
additional noise rejection.
V BATT
MAX704
RESET
Monitoring a Negative Voltage
The power-fail comparator can be used to monitor a
Figure 6. RESET Valid to Ground Circuit
V IN
+5V
R1
V CC
R1
negative supply voltage using Figure 8’s circuit. When
the negative supply is valid, PFO is low. When the neg-
ative supply voltage droops, PFO goes high. This cir-
cuit ’s accuracy is affected by the PFI threshold
tolerance, the V CC voltage, and resistors R1 and R2.
+5V
R1
V CC
PFI
PFI
PFO
R2
R3
C1*
PFO
MAX703
MAX704
GND
*OPTIONAL
R2
MAX703
MAX704
GND
+5V
PFO
TO μ P
+5V
PFO
V-
0V
0V
V L
V TRIP
V H
0V
V TRIP = 1 . 25 ? 1 2 ?
V H = 1 . 25 / ? ?
? R + R ?
? R 2 ?
? R 2 | | R 3 ?
? R 1 + R 2 | | R 3 ?
V IN
V L ? 1 . 25 5 ? 1 . 25 1 . 25
+ =
R 1 R 3 R 2
5 ? 1 . 25 1 . 25 ? V TRIP
=
R 1 R 2
NOTE: V TRIP IS NEGATIVE
V TRIP
V-
0V
Figure 7. Adding Hysteresis to the Power-Fail Comparator
Figure 8. Monitoring a Negative Voltage
_______________________________________________________________________________________
7
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX704CPA+ | 功能描述:监控电路 MPU Supervisor 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 |
| MAX704CSA | 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 |
| MAX704CSA+ | 功能描述:监控电路 MPU Supervisor 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 |
| MAX704CSA+T | 功能描述:监控电路 MPU Supervisor 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 |
| MAX704CSA-T | 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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