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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  
Watchdog Input  
As discussed in the Reset section, the Watchdog input is  
used to monitor microprocessor activity. It can be used to  
insure that the microprocessor is in  
a continually  
responsive state by requiring that the WDI pin be toggled  
every second. If the WDI pin is not toggled within the 1.6  
second window (minimum tWD + tRS), a reset pulse will be  
asserted to return the microprocessor to the initial  
start-up state. Pulses as short as 50ns can be applied to  
the WDI pin. If this feature is not used, the WDI pin  
should be open circuited or the logic placed into a high-  
impedance state to allow the pin to float.  
Backup-Battery Switchover  
A power loss can be made less severe if the system RAM  
contents are preserved. This is achieved in the  
ASM690/692/ 802/805 by switching from the failed VCC to  
an alternate power source connected at VBATT when VCC  
is less than the reset threshold voltage (VCC < VRT), and  
VCC is less than VBATT. The VOUT pin is normally  
connected to VCC through a 2Ω PMOS switch but a  
Table 1. Pin Connections in Battery Backup Mode  
Pin  
Connection  
Connected to VBATT through internal  
PMOS switch  
VOUT  
VBATT  
Connected to VOUT  
Disabled  
PFI  
brown-out or loss of VCC will cause a switchover to VBATT  
Logic-LOW  
by means of a 20Ω PMOS switch. Although both  
PFO  
RESET  
WDI  
Logic-LOW (except on ASM805 where  
it is HIGH)  
conditions (VCC < VRT and VCC <VBATT) must occur for  
the switchover to VBATT to occur, VOUT will be switched  
back to VCC when VCC exceeds VRT irrespective of the  
voltage at VBATT. It should be noted that an internal  
device diode (D1 in Figure 3) will be forward biased if  
VBATT exceeds VCC by more than a diode drop when VCC  
is switched to VOUT. Because of this it is recommended  
that VBATT be no greater than VRT +0.6V.  
Watchdog timer disabled  
During the backup power mode, the internal circuitry of  
the supervisory circuit draws power from the battery  
supply. While VCC is still alive, the comparator circuits  
remain alive and the current drawn by the device is  
typically 35µA. When VCC drops more than 1.1V below  
VBATT, the internal switchover comparator, the PFI  
comparator and WDI comparator will shut off, reducing  
the quiescent current drawn by the IC to less than 1µA.  
Condition  
SW1/SW2  
Open  
SW3/SW4  
Closed  
Closed  
Open  
VCC > Reset Threshold  
VCC < Reset Threshold  
VCC > VBATT  
Open  
Backup Power Sources - Batteries  
Battery voltage selection is important to insure that the  
battery does not discharge through the parasitic device  
diode D1 (see Figure 3) when VCC is less than VBATT and  
VCC >VRT.  
VCC < Reset Threshold  
VCC < VBATT  
Closed  
ASM690A/802A/805L Reset Threshold = 4.65V  
ASM692A /ASM802M Reset Threshold = 4.4V  
µP Power Supply Supervisor With Battery Backup Switch  
4 of 15  
Notice: The information in this document is subject to change without notice.