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ADM802LM bảng dữ liệu(PDF) 5 Page - Analog Devices |
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ADM802LM bảng dữ liệu(HTML) 5 Page - Analog Devices |
5 / 8 page ADM690A/ADM692A/ADM802L/M/ADM805L/M –5– REV. 0 BATTERY SWITCHOVER RESET GENERATOR WATCHDOG TRANSITION DETECTOR (1.6s) 4.65V* 1.25V *4.4V FOR ADM692A/ADM802M/ADM805M ADM690A ADM692A ADM802L ADM802M ADM805L ADM805M POWER FAIL OUTPUT (PFO) RESET VOUT VBATT VCC WATCHDOG INPUT (WDI) POWER FAIL INPUT (PFI) (RESET) ( ) = ADM805L/M ONLY Figure 7. Functional Block Diagram POWER FAIL RESET, RESET RESET is an active low output which provides a RESET signal to the microprocessor whenever VCC is at an invalid level. When VCC falls below the reset threshold, the RESET output is forced low. The nominal reset voltage threshold is 4.65 V (ADM690A/ ADM802L/ADM805L or 4.4 V ADM692A/ADM802M/ ADM805M. On power-up RESET will remain low for 200 ms after VCC rises above the reset threshold. This allows time for the power supply and microprocessor to stabilize. On power-down, the RESET output remains low with VCC as low as 1 V. This ensures that the microprocessor is held in a stable shutdown condition. The guaranteed minimum and maximum thresholds are as follows: ADM690A/ADM802L/ADM805L: 4.5 V and 4.75 V ADM692A: 4.25 V and 4.5 V. ADM802L: 4.55 V and 4.7 V ADM802M: 4.3 V and 4.45 V The ADM805L and ADM805M contain an active high reset output. This is the complement of RESET and is intended for processors requiring an active high RESET signal. The guaranteed minimum and maximum thresholds for the ADM805 are: ADM805L: 4.5 V and 4.75 V ADM805M: 4.25 V and 4.5 V. Watchdog Timer RESET, RESET The watchdog timer circuit monitors the activity of the micro- processor in order to check that it is not stalled in an indefinite loop. An output line on the processor is used to toggle the Watchdog Input (WDI) line. If this line is not toggled within 1.6 seconds, a RESET pulse is generated. The watchdog timeout period restarts with each transition on the WDI pin. To ensure that the watchdog timer does not time out, either a high-to-low or low-to-high transition on the WDI pin must occur at or less than the minimum timeout period. If WDI remains permanently either high or low, reset pulses will be issued after each timeout period (1.6 s). The watchdog monitor can be deactivated by floating the Watchdog Input (WDI) or by connecting it to midsupply. +5V 0V +5V 0V +5V 0V +5V 0V 0V 3.0V 3.0V tRS VCC VOUT RESET RESET PFO VBATT = PFI = 3.0V Figure 8. Timing Diagram BATTERY SWITCHOVER SECTION During normal operation with VCC higher than the reset threshold, VCC is internally switched to VOUT via an internal PMOS transistor switch. This switch has a typical on-resistance of less than 1 Ω and can supply up to 100 mA at the V OUT terminal. Once VCC falls below the reset threshold, the higher of VCC or VBATT is switched to VOUT. This means that VBATT connects to VOUT only when VCC is below the reset threshold and VBATT is greater than VCC. VOUT is normally used to drive a RAM memory bank which may require instantaneous 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 capacitance value of 0.1 µF or greater may be used. A 9 Ω MOSFET switch connects the V BATT input to VOUT during battery backup. This MOSFET has very low input-to- output differential (dropout voltage) at the low current levels required for battery backup of CMOS RAM or other low power CMOS circuitry. The supply current in battery backup is typically 0.05 µA. Typically 3 V batteries are used as the backup supply. High value capacitors, either standard electrolytic or the farad size double layer capacitors, can also be used for short-term memory back up. A small charging current of typically 10 nA (0.1 µA max) flows out of the VBATT terminal. This current is useful for maintaining rechargeable batteries in a fully charged condition. This extends the life of the back up battery by compensating for its self discharge current. Also note that this current poses no problem when lithium batteries are used for back up 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. |
Số phần tương tự - ADM802LM_15 |
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Mô tả tương tự - ADM802LM_15 |
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