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IMP805L Datasheet(PDF) 7 Page - A1 PROs co., Ltd. |
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IMP805L Datasheet(HTML) 7 Page - A1 PROs co., Ltd. |
7 / 10 page 7 IMP690A IMP690A , 692A , 692A , 802L, 802M, 805L , 802L, 802M, 805L Application Information Backup Power Sources - SuperCapTM Capacitor storage, with very high values of capacitance, can be used as a back-up power source instead of batteries. SuperCapTM are capacitors with capacities in the fractional farad range. A 0.1 farad SuperCapTM would provide a useful backup power source. Like the battery supply, it is important that the capacitor voltage remain below the maximum voltages shown in Table 2. Although the circuit of Figure 5 shows the most simple way to connect the SuperCapTM, this circuit cannot insure that an overvoltage condi- tion will not occur since the capacitor will ultimately charge up to VCC. To insure that an overvoltage condition does not occur, the circuit of Figure 6 is preferred. In this circuit configuration, the diode-resistor pair clamps the capacitor voltage at one diode- drop below VCC. VCC itself should be regulated within ±5% of 5V for the IMP692A/802M or within ±10% of 5V for the IMP690A/802L/805L to insure that the storage capacitor does not achieve an overvoltage state. Note: SuperCapTM is a trademark of Baknor Industries Figure 5. Capacitor as a backup power source Figure 6. Capacitor as back-up Power Source - Voltage clamped to 0.5V below VCC 690A_08.eps +5V GND IMP692A IMP802M ( ) IMP805L 100k + 0.1F VBATT VCC To µP To Static RAM RESET VOUT + 690A_07.eps +5V GND ( ) IMP805L 0.1F VBATT VCC To µP To Static RAM RESET (RESET) VOUT Operation Without a Backup Power Source When operating without a back-up power source, the VBATT pin should be connected to GND and VOUT should be connected to VCC, since power source switchover will not occur. Connecting VOUT to VCC eliminates the voltage drop due to the ON-resistance of the PMOS switch. 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 volt- age 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 7. Figure 7. Simple Voltage divider sets PFI trip point 5 1 25 2 1 2 R R R V + < . 5 1 25 2 1 2 R R R V + > . 690A_09.eps +5V GND 0V PFO +5V A A B B IMP690A IMP692A IMP802L IMP802M IMP805L R2 PFI VCC PFO R1 |
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