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ASM802LCSAF 参数 Datasheet PDF下载

ASM802LCSAF图片预览
型号: ASM802LCSAF
PDF下载: 下载PDF文件 查看货源
内容描述: 微处理器电源监控器,备用电池切换 [μP Power Supply Supervisor With Battery Backup Switch]
分类和应用: 电池微处理器监控
文件页数/大小: 15 页 / 344 K
品牌: PULSECORE [ PulseCore Semiconductor ]
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ASM690A/692A  
ASM802L/802M  
ASM805L  
April 2008  
rev 1.7  
reasonable and should be larger than 10kΩ to avoid  
Power-Fail Comparator  
The Power Fail feature is an independent voltage  
monitoring function that can be used for any number of  
monitoring activities. The PFI function can provide an  
early sensing of power supply failure by sensing the  
voltage of the unregulated DC ahead of the regulated  
supply sensing seen by the backup-battery switchover  
circuitry. The PFI pin is compared to a 1.25V internal  
reference. If the voltage at the PFI pin is less than this  
reference voltage, the PFO pin goes low. By sensing the  
voltage of the raw DC power supply, the microprocessor  
system can prepare for imminent power-loss, especially if  
the battery backup supply is not enabled. The input  
voltage at the PFI pin results from a simple resistor  
voltage divider as shown in Figure 6.  
excessive loading on the PFO pin. The calculations for  
the correct values of resistors to set the hysteresis  
thresholds are given in Figure 7. A capacitor can be  
added to offer additional noise rejection by low-pass  
filtering.  
Power Fail Hysteresis  
A noise margin can be added to the simple monitoring  
circuit of Figure 6 by adding positive feedback from the  
PFO pin. The circuit of Figure 7 adds this positive  
“latching” effect by means of an additional resistor R3  
connected between PFO and PFI which helps in pulling  
PFI in the direction of PFO and eliminating an indecision  
at the trip point. Resistor R3 is normally about 10 times  
higher in resistance than R2 to keep the hysteresis band  
Monitoring Capabilities Of The Power-fail Input:  
Although designed for power supply failure monitoring,  
the PFI pin can be used for monitoring any voltage  
condition that can be scaled by means of a resistive  
divider. An example is the negative power supply monitor  
configured in Figure 8. In this case a good negative  
supply will hold the PFI pin below 1.25V and the PFO pin  
µP Power Supply Supervisor With Battery Backup Switch  
6 of 15  
Notice: The information in this document is subject to change without notice.