ST7265X datasheet(37/166 Pages) STMICROELECTRONICS

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ST7265x

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POWER SUPPLY MANAGEMENT (Cont’d)

6.4.3 Storage Media Interface I/Os

The microcontroller is able to drive Storage Media

through an interface operating at a different volt-

age from the rest of the circuit.

This is achieved by powering the Storage Media

interface I/O circuitry through a specific supply rail

connected to VDDF pin. The VDDF pin can be used

either as an input or output.

If the on-chip voltage regulator is off, power to the

interface I/Os should be provided externally to the

VDDF pin. This should be the case when in Stand-

Alone Mode, or in USB mode when the current re-

quired to power the Storage Media is above the

current capacity of the on-chip regulator.

If the on-chip voltage regulator is on, it powers the

interface I/Os, and VDDF pin can supply the Stor-

age Media. This is recommended in USB Mode,

when the current required to power the Storage

Media is within the capacity of the on-chip regula-

tor.

Application Example:

Stand-Alone Mode

– The Storage Media interface supply is powered

by VDD enabled by an external switch (see Fig-

ure 26) which connects VDD to VDDF. This switch

can be driven by any True Open Drain I/O pin

and controlled by user software.

– The on-chip voltage regulator must be disabled

to avoid any conflict and to decrease consump-

tion (reset the REGEN bit in the PCR register).

USB Mode

– In this case the core of the microcontroller is run-

ning from the USB bus power or the self power

supply. VDD and USBVDD pins are supplied with

a voltage from 4.0 to 5.5V.

– The Storage Media Interface can be powered

through the on-chip regulator (providing power to

the I/O pins and output on pin VDDF) if the current

requirement is within the output capacity of the

on chip regulator.

– The regulator output voltage can be pro-

grammed to 2.8V, 3.3V, 3.4V or 3.5 Volts, de-

pending on the Storage Media specifications.

(see VSET[1:0] bits in PCR register description)

– Should the current requirement for the Storage

Media be higher than the current capacity of the

on chip regulator, an external regulator should be

used (See Figure 27). Thus the on-chip voltage

regulator must be disabled to avoid any conflict

(reset the REGEN bit in the PCR register).

Caution: The user should ensure that VDD does

not exceed the maximum rating specified for the

Storage Media VDDF max when switching STOR-

AGE switch on.

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