ST AN676 Application note

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AN676

APPLICATION NOTE

Battery charger using the ST6-REALIZER

INTRODUCTION

Because competition becomes greater and greater it is important to reduce time to market. The ST6 Realizer helps to fullfill this duty. The time needed to realize a design is dramatically reduced. Design of an application takes a few days instead of a few weeks. Users who develop ST6 applications are systems electronics engineers; Often they do not know the assembler well and there are reluctant to use it. The ST6 Realizer allows users to design their applications using symbols known by hardware designers such as comparators, counters, multiplexers. Once the design is over, the ST6 Realizer generates assembly code or executable code for the different ST6 target hardware.

June 2008 Rev 2 1/14

BATTERY CHARGER USING THE ST6-REALIZER

APPLICATION NOTE GOAL

This note aims at introducing the different features of the ST6 Realizer graphic tool. It is also a tutorial to firstly help you get started with ST6 Realizer design, then for you to implement advanced features to optimize your design or to evaluate the target hardware requirements. The application note describes a battery charger because it illustrates the different features of the ST6 Realizer throughout it. The charger implements a simple charging method. Nevertheless charging end points using the negative voltage slope detection method or voltage inflection points can be implemented with this battery charger ST6 board.

HARDWARE SCHEMATICS

The schematics describes the different hardware parts of the application:

The microcontroller connections The power supply The charging indicators The start push button The power command

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BATTERY CHARGER USING THE ST6-REALIZER

Figure 1 : Simple Battery Charger Circuit Schematic

HIGH

POWER SUPPLY

J1 JACK

GND

Battery cell: AA type / 1.2V - 0.5Ah

GND

22MF

C1

VCC

R10

470

R2

LOW

R8

470

T1

CURRENT

VOLTAGE

68 ohms

GND

U1

10 ohms

R4

BATTERY

NiCd BATTERY

BT1

2 ohms

R6

BD236-PNP-45V

GND

T3

7805

IMAX

VCC

GND

MAX CURRENT

ADJUST

RV1

50K-RV

READY

LED_LO

LED_HI

8MHZ-XT-P

GND

C310pF

GND

10pF

XT1

C2

1MF

CHARGE CURRENT

INDICATOR

LD3

LED-RED-5MM

LD2

LD1

GND

470

GND

START PUSH-BUTTON

SW1

R1

470

R2

470

R7

START

C4

VCC

CURRENT

VOLTAGE

ST6210/20 MCU

IMAX

GND

6

7

8

9

10

ST6210

NMI

TEST

RESET/

PB7

PB6

PB5

PB411PB312PB213PB114PB015PA316PA217PA118PA019VSS

START

HIGH

LOW

100K

4

5

OSCOUT

LED_LO

DISCHRG

VCC VDD

1

2

3

U2

TIMER

OSCIN

20

READY

LED_HI

Note that in the circuit diagram the Microcontroller is shown as a simple box. The objective of the ST6 Realizer is to enable you to write the program code for the microcontroller with the same ease and in the same manner as you have drawn the hardware schematic.

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BATTERY CHARGER USING THE ST6-REALIZER

Figure 2 : Functional Diagram

Start

Imax

READY

HIGH

Icharge

Vcharge

The MCU manages all the functions of the application:

At reset the READY LED blinks to indicate that the charger is ready to charge. The user pushes the START button to begin the HIGH charge. The READY LED switches off. The HIGH LED highlights. The LOW charge takes place when the VOLTAGE threshold of 1.5 V is reached. The HIGH LED switches off. The LOW LED switches on. The battery charge is over when the delay of LOW charge is reached. The LOW LED switches off. The READY LED blinks. When the current in the battery is too high, HIGH charge or LOW charge are bypassed.

MCU

LOW

HIGH CHARGE

LOW CHARGE

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Figure 3 : Flow Chart

BATTERY CHARGER USING THE ST6-REALIZER

Start

HIGH charge

Voltage > 1,5V

Yes

LOW charge

Charging time

expired

Yes

No

Current Too High

No

Current Too High

Yes

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