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ADM8691ARN Fiches technique(PDF) 5 Page - Analog Devices |
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ADM8691ARN Fiches technique(HTML) 5 Page - Analog Devices |
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5 / 16 page  ADM8690–ADM8695 REV. 0 –5– PIN CONFIGURATIONS 1 2 3 4 8 7 6 5 TOP VIEW (Not to Scale) ADM8690 ADM8692 ADM8694 VOUT PFO WDI RESET VBATT VCC GND PFI 14 13 12 11 16 15 10 9 8 1 2 3 4 7 6 5 TOP VIEW (Not to Scale) ADM8691 ADM8693 ADM8695 VBATT CEIN WDO RESET RESET VOUT VCC GND PFO WDI CEOUT BATT ON LOW LINE OSC IN OSC SEL PFI CIRCUIT INFORMATION Battery Switchover Section The battery switchover circuit compares VCC to the VBATT input, and connects VOUT to whichever is higher. Switchover occurs when VCC is 50 mV higher than VBATT as VCC falls, and when VCC is 70 mV greater than VBATT as VCC rises. This 20 mV of hysteresis prevents repeated rapid switching if VCC falls very slowly or remains nearly equal to the battery voltage. VCC VBATT VOUT BATT ON (ADM8690, ADM8695) 100 mV 700 mV INTERNAL SHUTDOWN SIGNAL WHEN VBATT > (VCC + 0.7V) GATE DRIVE Figure 1. Battery Switchover Schematic During normal operation, with VCC higher than VBATT, VCC is internally switched to VOUT via an internal PMOS transistor switch. This switch has a typical on-resistance of 0.7 Ω and can supply up to 100 mA at the VOUT terminal. VOUT is normally used to drive a RAM memory bank which may require instanta- neous currents of greater than 100 mA. If this is the case then a bypass capacitor should be connected to VOUT. The capacitor will provide the peak current transients to the RAM. A capaci- tance value of 0.1 µF or greater may be used. If the continuous output current requirement at VOUT exceeds 100 mA, or if a lower VCC–VOUT voltage differential is desired, an external PNP pass transistor may be connected in parallel with the internal transistor. The BATT ON output (ADM8691/ ADM8693/ADM8695) can directly drive the base of the exter- nal transistor. A 7 Ω MOSFET switch connects the V BATT input to VOUT dur- ing battery backup. This MOSFET has very low input-to-out- put differential (dropout voltage) at the low current levels required for battery back up of CMOS RAM or other low power CMOS circuitry. The supply current in battery back up is typi- cally 0.4 µA. The ADM8690/ADM8691/ADM8694/ADM8695 operates with battery voltages from 2.0 V to 4.25 V, and the ADM8692/ ADM8693 operates with battery voltages from 2.0 V to 4.0 V. High value capacitors, either standard electrolytic or the farad size double layer capacitors, can also be used for short-term memory backup. A small charging current of typically 10 nA (0.1 µA max) flows out of the V BATT terminal. This current is useful for maintaining rechargeable batteries in a fully charged condition. This extends the life of the backup battery by com- pensating for its self discharge current. Also note that this cur- rent poses no problem when lithium batteries are used for backup since the maximum charging current (0.1 µA) is safe for even the smallest lithium cells. If the battery switchover section is not used, VBATT should be connected to GND and VOUT should be connected to VCC. PRODUCT SELECTION GUIDE Part Nominal Reset Nominal VCC Nominal Watchdog Battery Backup Base Drive Chip Enable Number Time Reset Threshold Timeout Period Switching Ext PNP Signals ADM8690 50 ms 4.65 V 1.6 s Yes No No ADM8691 50 ms or ADJ 4.65 V 100 ms, 1.6 s, ADJ Yes Yes Yes ADM8692 50 ms 4.4 V 1.6 s Yes No No ADM8693 50 ms or ADJ 4.4 V 100 ms, 1.6 s, ADJ Yes Yes Yes ADM8694 200 ms 4.65 V 1.6 s Yes No No ADM8695 200 ms or ADJ 4.65 V 100 ms, 1.6 s, ADJ Yes Yes Yes |
Numéro de pièce similaire - ADM8691ARN |
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Description similaire - ADM8691ARN |
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