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 (V
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, th e programm able voltage v alues or the current capability of the emb edded
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.
) and external devices with a lower voltage suppl y. This VDDF pin can be used as
DD
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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 regu lator. Ze ro cons umpti on is r eached by turning o ff th e V DD F outpu t from the
embedded regulator.
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