Mitsubishi DS5000TK manual Power Supply Slew Rate ±1, Battery Attach Procedure, Battery Lifetime

USER'S GUIDE

POWER SUPPLY SLEW RATE Figure 6±1

40 μs, 130 μs

VCC

VCCMIN

VLI

LITHIUM

CURRENT

Each time VCC is restored, the lithium backed functions will remain as they were left. A result is that many of these values are not altered on a reset condition except for the `no battery reset'. In the documentation, this is referred to as `No VLI reset'. This will occur after the first time VCC is applied to the microprocessor. The `no bat- tery reset' state is documented in the section on resets. A module user will never see the `no battery reset' condi- tion as it was cleared during assembly and test prior to leaving the factory.

BATTERY ATTACH PROCEDURE

This section applies to microprocessor chips only, not modules. When a microprocessor is received from the factory, it is completely uninitialized. All nonvolatile func- tions are absent since there is no backup source con- nected to the chip. As mentioned above, the micropro- cessor must place circuits in a low power state to prepare for lithium backup. If a battery were attached to an uninitialized chip, the backup current would be unpredictable. For this reason, the following battery attach procedure must be followed.

1.Apply VCC to the microprocessor.

2.Attach the lithium cell to the VLI input.

3.Configure and program the device as normal. (Optional at this time.)

4.Power down the microprocessor (remove VCC) using the guidelines discussed above while leaving

the battery attached.

The first time a battery is attached to the microprocessor is a special event. When power is applied in the absence of a lithium cell, the device performs a No VLI Reset. This allows the microprocessor to initialize control bits that are ordinarily nonvolatile and unaffected by a reset. The microprocessor will never be completely in this state again unless all power (including battery) is removed by the user. In order to provide the extremely low back up currents (<75 nA), the circuits must config- ure themselves for lithium backup. This is done when VCC is removed from the chip. That is, the microproces- sor IS NOT CONFIGURED FOR LITHIUM BACKUP when it is received. Therefore, the battery should be attached with VCC at +5V. This will prevent the micropro- cessor from placing a load on the lithium cell until VCC is removed. At this time, the microprocessor performs its power down procedure and prepares for ultra low power data retention. Attaching the battery to an unpowered microprocessor places an unknown load on the lithium cell. This may drain the cell excessively and should not be done.

BATTERY LIFETIME

The calculations of data retention lifetime are helpful for chip or module users. They can serve as design and system reliability guidelines. All lithium backed micro- controller modules are rated for better than 10 years of data retention in the absence of VCC at 25°C. Following these guidelines, similar performance can be achieved using chips. It is also not difficult to achieve better than

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