AN2269 datasheet(18/25 Pages) STMICROELECTRONICS

18 / 25 page

ST8024 Application Hardware Guidelines

AN2269 - Application Note

18/25

4.1

Power Supply Optimization

The ST8024 can drive both 3V and 5V cards by the supply voltage selector pin 5/3V (pin 3)

as shown in

Figure 1 on page 1. If the 5/3V pin is connected to GND, the VCC voltage is 3V,

and if the 5/3V is connected to VDD, the VCC voltage is 5V.

A step-up converter supplied by VDDP is used for the VCC voltage generation. It doubles the

input voltage VDDP or follows it, depending on the 5/3V and VDDP values:

●

5/3V=H and VDDP > 5.8 V; voltage follower

●

5/3V=H and VDDP < 5.7 V; voltage doubler

●

5/3V=L and VDDP > 4.1 V; voltage follower

●

5/3V=L and VDDP < 4.0 V; voltage doubler

The S1 and S2 pins are used for duplicating the supply voltage VDDP by using the 100nF

pumping capacitor (C4). The charge pump output pin (VUP) has to be connected to a 100nF

storage capacitor (C5) to stabilize the voltage.

Figure 16.

Step-up Converter Block Diagram

ON/OFF

PGND

100nF

VUP

VCC

Regulator

PVCC

EN2

ST8024

OUTPUT

Step-up

Mode

Selector

AI11894

AN2269 Datasheet(PDF) 18 Page - STMicroelectronics