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ADM8695 Datasheet(PDF) 14 Page - Analog Devices |
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ADM8695 Datasheet(HTML) 14 Page - Analog Devices |
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14 / 20 page  ADM8690/ADM8691/ADM8692/ADM8693/ADM8695 Rev. B | Page 14 of 20 APPLICATION INFORMATION INCREASING THE DRIVE CURRENT If the continuous output current requirements at VOUT exceed 100 mA, or if a lower VCC– VOUT voltage differential is desired, an external PNP pass transistor can be connected in parallel with the internal transistor. The BATT ON output (ADM8691/ ADM8693/ADM8695) can directly drive the base of the external transistor. PNP TRANSISTOR 0.1µF 0.1µF BATTERY VBATT VCC VOUT BATT ON 5V INPUT POWER ADM8691/ ADM8693/ ADM8695 Figure 24. Increasing the Drive Current USING A RECHARGEABLE BATTERY FOR BACKUP If a capacitor or a rechargeable battery is used for backup then the charging resistor should be connected to VOUT because this eliminates the discharge path that would exist during power- down if the resistor is connected to VCC. ADM869x R 0.1µF 0.1µF VBATT VCC VOUT 5V INPUT POWER RECHARGEABLE BATTERY VOUT – VBATT R I = Figure 25. Rechargeable Battery ADDING HYSTERESIS TO THE POWER-FAIL COMPARATOR For increased noise immunity, hysteresis can be added to the power-fail comparator. Because the comparator circuit is noninverting, hysteresis can be added simply by connecting a resistor between the PFO output and the PFI input as shown in Figure 26. When PFO is low, Resistor R3 sinks current from the summing junction at the PFI pin. When PFO is high, the series combination of R3 and R4 sources current into the PFI summing junction. This results in differing trip levels for the comparator. 5V 0V PFO 0V VL VH VIN VH = 1.3V VL = 1.3V ASSUMING R4 < < R3 THEN HYSTERESIS VH – VL = 5V 1+ R1 R2 R1 R3 ) ( + 1+ R1 R2 R1 (5V – 1.3V) R3 (1.3V (R3 + R4)) ) ( – ADM869x 1.3V PFI PFO TO MICROPROCESSOR NMI 5V VCC 7V TO 15V INPUT POWER 7805 R1 R2 R3 R4 R1 R2 ) ( Figure 26. Adding Hysteresis to the Power-Fail Comparator MONITORING THE STATUS OF THE BATTERY The power-fail comparator can be used to monitor the status of the backup battery instead of the power supply, if desired. This is shown in Figure 27. The PFI input samples the battery voltage and generates an active low PFO signal when the battery voltage drops below a chosen threshold. It can be necessary to apply a test load to determine the loaded battery voltage. This is done under processor control using CEOUT. Because CEOUT is forced high during the battery backup mode, the test load is not applied to the battery while it is in use, even if the microprocessor is not powered. ADM869x PFI BATTERY 10M Ω 10M Ω R1 R2 5V INPUT POWER 20k Ω OPTIONAL TEST LOAD LOW BATTERY SIGNAL TO MICROPROCESSOR I/O PIN VBATT VCC CEOUT CEIN PFO FROM MICROPROCESSOR I/O PIN APPLIES TEST LOAD TO BATTERY Figure 27. Monitoring the Battery Status |
Número de pieza similar - ADM8695_15 |
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Descripción similar - ADM8695_15 |
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