ST AN1529 Application note

AN1529

APPLICATION NOTE

EXTENDING THE CURRENT & VOLTAGE CAPABILITY ON THE ST7265 VDDF SUPPLY

by Microcontroller Division Applications

INTRODUCTION

The ST7265 features a VDDF pin to make it easier to interface between the its own MCU supply (VDD) and external devices with a lower voltage supply. This VDDF pin can be used as a selectable 2.4 to 3.6V power supply to external devices and to supply some of the ST7265 I/Os: consequently, a device supplied by the VDDF pin can interface with the ST7265 directly without any electrical voltage adaptation.

In some cases, the programmable voltage values or the current capability of the embedded regulator may not match the application needs. An alternative solution is required.

This application note describes two such solutions, based on practical implementations: A 3.3V/500mA power supply for driving a Microdrive Storage media on the ST7265x_EVAL/MS “5in1” USB Mass Storage evaluation board from STMicroelectronics.

AN1529/0201

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EXTENDING THE CURRENT & VOLTAGE CAPABILITY

1 FEATURE OVERVIEW

Two implementations are described in this application note, covering two different requirements:

–The required voltage value is outside the range of the embedded programmable regulator

–Higher current capability

Both solutions feature a low power mode to meet the USB suspend mode specification.

1.1 REPLACING THE EMBEDDED REGULATOR

An external regulator can be used to obtain an output voltage that is outside the range of the embedded programmable regulator. This solution can also be a way to bypass the output current limitations. A dedicated MCU I/O pin is needed to reduce the consumption of the external circuitry to typically 50µA when in suspend mode.

1.2 ADDING A CURRENT AMPLIFIER

This solution is a cost-effective way to extend the output current capability of the internal regulator. This solution involves a voltage follower which is referenced on the VDDF output from the internal regulator. Zero consumption is reached by turning off the VDDF output from the embedded regulator.

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