DS5002FP datasheet(15/29 Pages) DALLAS

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DS5002FP

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DS5002FP CONNECTION TO 64K X 8 SRAM Figure 7

POWER MANAGEMENT

The DS5002FP monitors VCC to provide power-fail reset, early warning power-fail interrupt, and switch

over to lithium backup. It uses an internal band-gap reference in determining the switch points. These are

called VPFW, VCCMIN, and VLI respectively. When VCC drops below VPFW, the DS5002FP will perform an

interrupt vector to location 2Bh if the power-fail warning was enabled. Full processor operation continues

regardless. When power falls further to VCCMIN, the DS5002FP invokes a reset state. No further code

execution will be performed unless power rises back above VCCMIN. All decoded chip enables and the

R/ W signal go to an inactive (logic 1) state. VCC is still the power source at this time. When VCC drops

further to below VLI, internal circuitry will switch to the lithium cell for power. The majority of internal

circuits will be disabled and the remaining nonvolatile states will be retained. Any devices connected

VCCO will be powered by the lithium cell at this time. VCCO will be at the lithium battery voltage less a

diode drop. This drop will vary depending on the load. Low-power SRAMs should be used for this

reason. When using the DS5002FP, the user must select the appropriate battery to match the RAM data

retention current and the desired backup lifetime. Note that the lithium cell is only loaded when VCC <

VLI. The User’s Guide has more information on this topic. The trip points VCCMIN and VPFW are listed in

the electrical specifications.

DS5002FP Datasheet(PDF) 15 Page - Dallas Semiconductor