ST7265X datasheet(35/166 Pages) STMICROELECTRONICS

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ST7265x

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POWER SUPPLY MANAGEMENT (Cont’d)

6.4.2.2 Switching from USB Mode to Stand-

Alone Mode

In USB Mode, when the user unplugs the USB ca-

ble, the voltage level drops on the USBVDD line.

The on-chip Power Supply Manager generates a

PLG interrupt when USBVDD reaches USBVIT-.

The user program then can finish the current

processing, and MUST generate a software RE-

SET.

Caution: Care should be taken as during this peri-

od the microcontroller clock is provided from the

PLL output. Functionality in this mode is not guar-

anteed for voltages below VPLLmin.

Software must ensure that the software RESET is

generated before VDD. drops below VPLLmin. Fail-

ing to do this will cause the clock circuitry to stop,

freezing the microcontroller operations.

Once the user program has executed the software

reset, the microcontroller goes into reset state and

all I/O ports go into floating input mode.

During and after this (software induced) reset

phase, the USBEN pin is put in high impedance by

hardware. It causes the USB SWITCH to be

turned OFF, so USBVDD is disconnected from

VDD. The PLL is automatically stopped and the in-

ternal frequency is provided by a division of the

crystal frequency. Refer to Figure 25.

The microcontroller is still powered by the residual

USBVDD voltage (higher than step-up converter

set output level). This VDD voltage decreases dur-

ing the reset phase until it reaches the step-up

converter set output voltage. At that time, step-up

converter resumes operation, and powers the ap-

plication.

Caution: In order to avoid applying excessive volt-

age to the Storage Media, a minimum delay must

be ensured during (and after if needed) the reset

phase, prior to switching ON the external STOR-

AGE switch. See Figure 26 and Figure 27.

ST7265X Datasheet(PDF) 35 Page - STMicroelectronics

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