M25P40 datasheet(35/53 Pages) STMICROELECTRONICS

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M25P40

Power-up and Power-down

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Power-up and Power-down

At Power-up and Power-down, the device must not be selected (that is Chip Select (S) must

follow the voltage applied on VCC) until VCC reaches the correct value:

●

VCC(min) at Power-up, and then for a further delay of tVSL

●

VSS at Power-down

A safe configuration is provided in Section 3: SPI modes.

To avoid data corruption and inadvertent write operations during power-up, a Power On

Reset (POR) circuit is included. The logic inside the device is held reset while VCC is less

than the Power On Reset (POR) threshold voltage, VWI – all operations are disabled, and

the device does not respond to any instruction.

Moreover, the device ignores all Write Enable (WREN), Page Program (PP), Sector Erase

(SE), Bulk Erase (BE) and Write Status Register (WRSR) instructions until a time delay of

tPUW has elapsed after the moment that VCC rises above the VWI threshold. However, the

correct operation of the device is not guaranteed if, by this time, VCC is still below VCC(min).

No Write Status Register, Program or Erase instructions should be sent until the later of:

●

tPUW after VCC passed the VWI threshold

●

tVSL after VCC passed the VCC(min) level

These values are specified in Table 9.

If the delay, tVSL, has elapsed, after VCC has risen above VCC(min), the device can be

selected for READ instructions even if the tPUW delay is not yet fully elapsed.

At Power-up, the device is in the following state:

●

The device is in the Standby Power mode (not the Deep Power-down mode).

●

The Write Enable Latch (WEL) bit is reset.

●

The Write In Progress (WIP) bit is reset.

Normal precautions must be taken for supply rail decoupling, to stabilize the VCC supply.

Each device in a system should have the VCC rail decoupled by a suitable capacitor close to

the package pins. (Generally, this capacitor is of the order of 100 nF).

At Power-down, when VCC drops from the operating voltage, to below the Power On Reset

(POR) threshold voltage, VWI, all operations are disabled and the device does not respond

to any instruction. (The designer needs to be aware that if a Power-down occurs while a

Write, Program or Erase cycle is in progress, some data corruption can result.)

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