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SP791 数据表(PDF) 13 Page - Sipex Corporation |
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SP791 数据表(HTML) 13 Page - Sipex Corporation |
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13 / 19 page  13 SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over © Copyright 2000 Sipex Corporation PIN NAME STATUS 1VBATT Supply current is 1 µA maximum When V CC < VBATT-1.2V 2VOUT VOUT is connected to VBATT through an Internal PMOS switch. 3VCC Battery-switchover comparator monitors VCC for active switchover. V CC is disconnected from VOUT 4 GND GND-0V reference for all signals. 5 BATT ON Logic high. The open-circuit output is equal to VOUT. 6 PFO The power-fail comparator is disabled PFO is forced low. 7 PFI The power-fail comparator is disabled 8 SWT SWT is Ignored. 9 MR MR is ignored. 10 LOWLINE Logic low. 11 WDI WDI is ignored, and goes high impedance. 12 CE OUT Logic high. The open-circuit output voltage is equal to VOUT. 13 CE IN High Impedance. 14 WDO Logic high. The open-circuit output voltage is equal to VOUT. 15 RESET Logic low. 16 WDPO Logic high. The open-circuit output voltage is equal to VOUT. INPUT SUPPLY VOLTAGE The Input Supply Voltage (VCC) should be a regulated +5V source. VCC connects to VOUT via a parallel diode and a large PMOS switch (Figure 10). The switch carries the entire current load for currents less than 250mA. The parallel diode carries any current in excess of 250mA. The maximum continuous current is 250mA, but power-on transients may reach a maximum of 1A. BACKUP-BATTERY INPUT The Backup-Battery Input (VBATT) is similar to VCC, except the PMOS switch and parallel diode are much smaller. Continuous current should be limited to 25mA and peak currents (only during power-up) limited to 250mA. The reverse leakage of this input is less than 1 µA over temperature and supply voltage. OUTPUT SUPPLY VOLTAGE The Output Supply Voltage (VOUT) supplies all the current to the external system and internal circuitry. All open-circuit outputs will, for ex- ample, assume the VOUT voltage in their high states rather than the VCC voltage. At the maxi- mum source current of 250mA, VOUT will typi- cally be 200mV below VCC. VOUT should be decoupled with 0.1 µF capacitor. BATTERY-BACKUP MODE The SP791 requires two conditions to switch to battery-backup mode: 1) VCC must be below the reset threshold; 2) VCC must be below VBATT. Table 1 lists the status of the inputs and outputs in battery-backup mode. BATTERY ON OUTPUT The Battery On Output (BATT ON) indicates the status of the internal VCC/battery-switchover comparator, which controls the internal VCC and VBATT switches. For VCC greater than VBATT (ignoring the small hysteresis effect), BATT ON is a logic low. For VCC less than VBATT, BATT ON is a logic high. Use BATT ON to indicate battery-switchover status or to supply base drive to an external pass transistor for higher-current applications (see Typical Operating Circuit). Figure 10. VCC and VBATT-to-VOUT Switch To enter the Battery-Backup mode, V CC must be less than the Reset threshold and less than V BATT. Table 1. Input/Output states in Battery-Backup mode Corporation VBATT Vcc 2 VOUT 0.1 µF INPUT/OUTPUT STATES IN BATTERY-BACKUP MODE |
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