DS5002FP datasheet(23/25 Pages) DALLAS

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DS5002FP Secure Microprocessor Chip

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Figure 14. Connection to 64k x 8 SRAM

POWER MANAGEMENT

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

lithium backup. It uses an internal bandgap 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 is 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 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 is at the lithium battery voltage minus

approximately 0.45V (less a diode drop). This drop varies 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

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

in the electrical specifications.

DS5002FP Datasheet(PDF) 23 Page - Dallas Semiconductor