Z8 Encore! -Based Battery Charger
Contents
1. the ADC reads the actual values for the converter output voltage the battery volt age and the current The ADC measures the output voltage and output current of the DC DC converter as a feedback to the controller It measures the volt age at the battery terminals as an input to determine the charge termination When the actual values are known they are checked for safety limit compliance The safety routine is responsible for the overall safety features associated with the battery charger The charger ensures safety by comparing the actual converter voltage and battery voltage with the calculated thresholds Crossing these thresholds switches off the PWM output which turns off the converter out putand terminates charging functions Such ter mination protects the batteries in case of a device failure The LED status indicator reflects an unsuc cessful termination If everything is within limits the battery is tested for full charge Full charge is tested using different methods for different batteries see Appendix D Battery Technology on page 15 If the battery is ANO013703 0708 Z8 Encore Based Battery Charger Z ILIA AN l U U fully charged charging terminates and the LED indicators are updated If the battery requires fur ther charging the controller calculates the required duty cycle for maintaining the setpoint at the con verter output The controller implements proportional plus inte gral PI con2. Converter Converter V I ADC Channels attery Voltage Feedback Z8 Encore MCU Batter Selector GPIO as Inpuls Jumper Settings us Indicator LED Port GPIO as Outputs Figure 2 Block Diagram of Battery Charger Hardware In this application the Z8 Encore MCU s Ports E and H are used as GPIO Port B is used as an ADC input Timer is used in PWM mode and the output is tapped at the pin PCl Timerl out ANO013703 0708 Z8 Encore Based Battery Charger The step down DC DC buck converter provides appropriate voltage or current for the set battery type and parameters The buck converter modu lates a higher voltage from the external source with a varying pulse width PWM method to generate a lower voltage The pulse width is con trolled by the control algorithm based on the values obtained from the feedback section The output of the external source is preferably set to twice the value of the converter output voltage Voy The feedback section consists of three differential amplifiers attenuators The corresponding parame ters are the converter voltage VoU battery volt age VBATT and battery current Igarr The battery current and the converter current are the same The battery type is selected by setting one of the four jumpers provided The jumper status 1s read initially and the corresponding routine is selected for charging The charger indicates the charger status via LEDs which a
3. PH1 PH PH x J2 J3 J4 J5 Title Using Z8 Encore as a Battery Charger Select Select Select Select i Nicd NiMH SLA Li Ion Pee Becument Number nons Date Tuesday January 07 2003 Sheet of 5 4 3 2 ANO013703 0708 Figure 9 Feedback Section and Battery Type Selector Jumper Settings Page 12 of 17 Z8 Encore Based Battery Charger Zilog Appendix C Flowcharts The main battery charging routine is displayed in Figure 10 Initialize peripherals Read and verify battery type Get the battery parameters Calculate safety limits and thresholds for charging and termination Read feedback values for battery voltage current and converter voltage Within safety limits Is the battery charged Terminate Calculate the duty cycle Figure 10 Flowchart for the Main Routine ANO013703 0708 Page 13 of 17 Z8 Encore Based Battery Charger Zilog The ISR return routine is displayed in Figure 11 Start ISR Reload PWM Value Update charge ending data every 10 seconds Return from ISR Figure 11 Flowchart for the ISR Return Routine ANO013703 0708 Page 14 of 17 Appendix D Battery Technology The four mainstream battery chemistries discussed in this Application Note feature different charging and discharging characteristics Long term battery life and performance are critically dependent upon how batteries are charged Therefore it is impor tant to charge batteries wi
4. omae rame OO q e s cs D Time in minutes lout in mAmps Vbatt Vout in mVolts Figure 6 NiMH Charging Profile The charging profiles for NiCd and NIMH batteries demonstrate constant current outputs of 270 mA and 150 mA respectively These are equal to their rated battery capacity measured in mAh The Page 7 of 17 charging times for NiCd and NiMH are 1 hour 45 minutes and 1 hour 25 minutes respectively Because the SLA and Li Ion batter ies follow similar charging constant voltage with limited current and ter mination profiles absolute voltage only the SLA battery was charged The results are provided in this document gt Note Summary This Application Note demonstrates the use of Z8 Encore in a battery charger implementation Ordi nary battery chargers can charge batteries of a par ticular type and of a particular voltage The Z8 Encore based hardware software provides flexi bility such that batteries of different types can be charged with the same charger The Z8 Encore 10 bit ADC ensures accurate charge termination facilitating faster recharge Such termination avoids overcharging and prolongs battery life The flexibility of the PWM mode allows for accurate DC DC buck step down converter implementation with excellent line load regulation The test results clearly demonstrate the charging and termination mechanisms used by the charger to successfully charge different batte
5. Application Note AN013703 0708 Abstract This Application Note demonstrates Zilog s Z8 Encore based battery charger that charges various rechargeable batteries in a fast efficient and safe manner All the important rechargeable battery types Sealed Lead Acid SLA Nickel Cadmium NiCd Nickel Metal Hydride NiMH and Lithium Ion Li Ion are addressed in this Application Note The Z8 Encore based charger manages each bat tery type according to its individual charging pro file gt Note 7e source code file associated with this application note ANO137 SCO1 zip is available for down load at www zilog com Product Overview Z8 Encore products are based on the new 8 bit eZ8 CPU and introduce Flash memory to Zilog s extensive line of 8 bit microcontrollers unit MCU The Flash in circuit programming capabil ity allows for faster development time and program changes in the field The new eZ8 core maintains backward compatibility with Zilog s popular zi MCU Featuring Zilog s high performance register to reg ister based architecture eZ8 the new Z8 Encore MCUS combine a fast 20 MHz core up to 64 KB of Flash memory up to 4 KB of linear register SRAM and an extensive array of on chip peripher als These peripherals make Z8 Encore suitable for a variety of applications including motor con trol security systems home appliances personal electronic devices and sensors J Z8 Encore Based Battery Ch
6. G4 3 4 PEO leno 2 PEO PG5 20 T GND 18 49 0 1 100 6 3 D6 gt GND PG6 VDD uw raa VDD 1L PF2 VDD GREEN J1 pri PG7 42 x voo 4H Pro PC7 T20UT 48 NON 20 45 VDD PC6 T2IN 4 21L PD1 T3OUT DBG 44 gt gt GND p43 0s EXTAL 224 PDO T3IN PC1 T1OUT gt Pci Saar EXTAL PCO T1IN 22 XAL 24 XTAL GND 4 u19 R17 B vcc 2 ceoocxoonomasz EXTAL XTAL 999999999999 GND ET 52 100K RESET ph QOzxxaxxzxx muo RESET hd SOST REARS ERATLHS YA CGazannnuauonununuauunur la DS1233A 15 VDD M S8 S aay 18 432MHz ala aS C45 C46 C49 C50 zie s aee C30 ogs Oeo sw4 0 1uF O 1uF 0 1uF 0 1uF R3 im ajajaja x GND SEIS MN RESET 4 L r r m m t ca ex e 0 01 ajajaja amp a aja Gi c2 PS 5 A 18pF 18pF E PB3 itle PBI Battery Charger using Z8 Encore gt ERR ize Document Number Rev x PHO A lt Doc gt Date Tuesday January 07 2003 Sheet 1 of 1 5 4 3 2 1 Figure 7 Schematic for Z8 Encore Interface ANO013703 0708 Page 10 of 17 Z8 Encore Based Battery Charger 5 4 3 2 1 vp DC DC Step Down Converter i R3 D 1K R37 p M 9 ot IRF9540 gt gt V_out 18E Q1 D2 R1 L1 Q2 C PC1 T1OUT NDA fe 3 3K 120uH MBR360 R4 C1 c2 470E 4 R2 D3 pr R5 gt bat 2 2K MBR360 100uF 100uF 79E B
7. PORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF ZILOG CORPORATION As used herein Life support devices or systems are devices which a are intended for surgical implant into the body or b support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness Document Disclaimer 2008 by Zilog Inc All rights reserved Information in this publication concerning the devices applications or technology described is intended to suggest possible uses and may be superseded ZILOG INC DOES NOT ASSUME LIABILITY FOR OR PROVIDE A REPRESENTATION OF ACCURACY OF THE INFORMATION DEVICES OR TECHNOLOGY DESCRIBED IN THIS DOCUMENT ZILOG ALSO DOES NOT ASSUME LIABILITY FOR INTELLECTUAL PROPERTY INFRINGEMENT RELATED IN ANY MANNER TO USE OF INFORMATION DEVICES OR TECHNOLOGY DESCRIBED HEREIN OR OTHERWISE The information contained within this document has been verified according to the general principles of electrical and mechanical engineering eZ8 Z8 Z8 Encore and Z8 Encore XP are trademarks or registered trademarks of Zilog Inc All o
8. Ti BATTERY D1 TOBE CHARGED LED 25V batt c x C r REA A ALOE m R6 10E Rsense 7 c3 0 1uF 5 out P 3 3 Volts LED Indicator Port 551 out R7 R8 R9 R10 R11 R12 R13 560E 560E 560E 560E 560E 560E 560E D4 D5 D6 D7 D8 D9 D10 LED VW D VW D VW D VW eD W eD VW D ES X x x x X X PE1 PE2 PES PE4 PES PEG PE7 A Title Using Z8 Encore as a Battery Charger Size Document Number Rev A lt Doc gt 0 0 Date Tuesday January 07 2003 Bheet 1 of 2 5 4 3 2 1 Figure 8 DC DC Step Down Converter and LED Indicator Port ANO013703 0708 Page 11 of 17 Z8 Encore Based Battery Charger I 4 3 2 1 0 1uF 0 1uF C7 C7 I I ne 1K Feedback Circuits E 12V LM324 gt U1C 1K 10K T R22 9 10K R14 2 Lout gt g amp Hos gt PB2 ANA2 V_batt gt PB1 ANA1 R23 10 R15 3 Lout gt T Battery Current V_batt gt gt T Battery Voltage 1K 10K R16 R24 c8 1K 1K 1OuF 0 1uF C7 IT vec 4 R21 2 E 10K s cii c9 C10 R18 6 V_out gt gt 100uF 0 1uF 0 1uF Voute 3p 8 5 PB3 ANA3 OUVE Converter Output Voltage 10K R20 1K 3 3 Volts Jumpers for Battery Selection L d R30 R31 R32 R33 10K 10K 10K 10K Note 1 R14 R30 all 1 MFR 2 Signal Digital and Power Grounds are connected on the evaluation board PH
9. arger Z8 amp Encore Flash Microcontrollers Features The features of Z8 Encore are as follows e New high performance 20 MHz eZ8 CPU e Up to 64 KB Flash memory with in circuit pro gramming capability e Upto4 KB register SRAM e 12 channel 10 bit analog to digital converter ADC e Two full duplex UARTs e Two Infrared Data Association IrDA compliant endecs e SPI and PC ports e Four 16 bit timers with capture compare and PWM capability e Watchdog Timer WDT with internal RC oscillator e 3 channel DMA e Upto 60 I O pins e 24 interrupts with configurable priority e On Chip Debugger e Voltage Brownout protection VBO e Power On Reset POR The Z8 Encore CPU is capable of a nominal 10 MIPs throughput at 20 MHz The 4 KB SRAM extends the Z8 Encore s reach to a wider range of applications The 10 bit sigma delta ADC provides high measurement resolution and the SPI UART and IC interfaces can be used concurrently The versatile DMA controllers can be configured in many useful combinations to free the CPU from performing unnecessary data transfer overhead Copyright 2008 by Zilog Inc All rights reserved www zilog com Discussion A discussion on designing a battery charger is pre sented in this section For further details see Refer ence on page 8 Theory of Operation When designing a battery charger the following aspects are considered e Power control techniques to suit
10. control signal according to the magnitude and direction of the error It minimizes the steady state error and also responds quickly to transient fluctua tions during input or output Controllers usually work at lower power levels and therefore require an external actuator to generate the appropriate output ANO013703 0708 In a battery charger the actuator is a step down DC DC converter also known as a buck converter The buck converter converts a higher DC voltage to a lower one depending on the Pulse Width Modulated PWM control signal generated by the controller The frequency of the PWM signal is maintained at a constant while the width of the pulse or the duty cycle of the signal varies This variation is reflected as a change in voltage and or current at the output Controllers are differentiated according to the way they handle errors generated during regulation of Page 2 of 17 the system output in the case of a charger these errors are either voltage or current errors In a pro portional controller the actual value and the set value are compared and the resulting error value is used In such a system there exists the possibility of a steady state error which is a drawback for the proportional controller Adding an integral compo nent to the proportional controller eliminates this steady state error The equation for a proportional plus integral PI controller is v t kl x e t k2 x fear To be useful f
11. different battery types and capacities e Charging and charge termination techniques to avoid overcharging thus facilitating fast charg ing e Safety techniques to ensure safe operation throughout the charging process Setpoint Veer N ser Controller Feedback Signal V s lzs Control Signal Feedback Circuits Z8 Encore Based Battery Charger rlan ZIlLOQ These aspects are discussed in the following section Power Control Techniques At the core of a battery charger is the DC DC converter that acts as a regulated power source The charger hardware is capable of regulating its output in various modes such as constant voltage constant current or constant voltage with a current limit The charger can be viewed as a control sys tem in itself In Figure 1 an initial setpoint is a charger output value chosen by you In a battery charger the type and capacity of the battery is the determinant of the mode of operation namely a constant current source or a constant voltage source It also deter mines the required current and voltage setpoints These setpoints can be expressed as Isgr or Vopr Output Vou N our PWM Actuator Buck Converter Figure 1 Feedback Control System The feedback circuits displayed in Figure 1 measures actual output The difference between the initial setpoint and the actual value feedback signal is called an error The controller generates a
12. icated in the HyperTerminal window The LED status indicators as displayed in Figure 2 reflect the charging status during the charging operation Figures 4 5 and 6 display the test results obtained while charging various types of batteries For SLA batteries initially the current is effec tively limited to 200 mA it continually falls while battery voltage increases The charging profiles also demonstrate the constant voltage output Vout of the DC DC converter at 4900 mV See Figure 4 4700 s 88 lout mAmps Voatt Vout in mVolts 8 3700 X A A Er Time in minutes 181 271 301 331 361 Figure 4 SLA Charging Profile The NiCd charging profile displayed in Figure 5 indicates a marked hump towards the full charge before dropping down The software effectively detects this drop and the charging is terminated ANO013703 0708 Z8 Encore Based Battery Charger g I a Mt IITA AN Z l i U U d 6500 310 300 6000 290 5500 280 270 5000 lout in mAmps 260 Vbatt Vout in mVolts 250 4500 240 4000 JA rt 230 o NO On OD DO 2 Time in Minutes Figure 5 NiCd Charging Profile The NiMH charging profile displayed in Figure 6 lacks a significant drop and is thus terminated using the zero AV termination scheme 200 190 180 170 160 150 140 130 4400 4 eee eee EE EH 120 4200 Leere erecti 110 A OOO i technic einai
13. or a microcontroller based discrete system the integral is approximated by a running sum of the error signal Thus an equation can be expressed as follows called Equation 1 v k C1 x e k C2 x Seti j 0 where C1 and C2 are constants Equation is the position algorithm A better rep resentation for Equation is described in Equation 2 as follows ofk 1 C1 x e k 1 C2 x S epj j 0 Subtracting Equation 2 from Equation 1 and rear ranging the terms yields Equation 3 as follows o k v k 1 Kp x e k Ki x e k 1 ANO013703 0708 Z8 Encore Based Battery Charger m p ILTA AN Z ItOU where Kp and Ki are the proportional and integral constants respectively Equation 3 is the velocity algorithm It is a conve nient expression as only the incremental change in the manipulated variable is calculated For a detailed discussion on controllers see Refer ence on page 8 Charging and Charge Termination Techniques Different battery types require different charging methods The basic charging methods are the con stant current and constant voltage charging The NiCd and NiMH batteries are charged using the constant current method whereas the SLA and Li Ion batteries are charged via the constant voltage method An on off current limiter is required when performing constant voltage charging These charging methods are based on the type of battery and the present state of charge for
14. r The charge termination mechanism is simple and is achieved as battery voltage reaches the charging voltage At the same time there is a corresponding drop in charging current Nickel Cadmium NiCd NiCd batteries are used in camcorders Walkmans and other similar consumer portable equipment The single cell voltage for NiCd batteries is 1 2 V These batteries are charged using the constant cur rent charging method While charging as the volt age crosses the full charge point it starts dropping This drop is approximately 15 mV per cell in the battery This drop is recognized as a full charge condition and charging is terminated This termi nation mechanism is named as AV termination During charging battery voltage rises to 1 65 V per cell The disadvantage of the NiCd battery is that the battery must be periodically discharged to protect performance In battery parlance this phenomenon is known as memory effect Nickel Metal Hydride NiMH NiMH batteries exhibit higher power density com pared to NiCd batteries The per cell voltage of the NiMH battery type is 1 2 V similar to NiCd batter ies NiMH batteries are charged via the constant cur rent charging method While charging as the volt age crosses the full charge point the voltage drop is not as low as for the NiCd batteries As a conse quence AV charge termination is usually not rec ommended for these batteries Instead of the fall in cell vol
15. rce supplies necessary voltage and current for the various circuits involved The external DC power supply provides two differ ent voltages to the charger circuits the DC DC step down converter and the feedback attenuators The operational amplifier based feedback attenua tor circuits are fed with a 12 V supply The DC DC converter works on a 8 12 V DC input for the batteries tested The control algorithm provides the necessary line regulation to sustain the voltage variation at the input During testing HyperTerminal is set at 57600 baud 8 bit data no parity 1 stop bit and no flow control Table 2 lists the equipment used to test the Z8 Encore based battery charger Table 2 Z8 Encore Battery Charger Test Equipment Z8 Encore Evaluation Board Z8BENCOREO00ZCO External power supply Oscilloscope Tektronix TDS 724D 500 MHz 1 GSps Multimeter PC The HyperTerminal utility is used via the COM2 port of the PC Batteries Used Make Type Ratings BP T40 Sony Sealed Lead Acid 4 V 500 mAh BP T16 Sony Nickel Cadmium 3 6 V 270 mAh CP2010H T 014 Panasonic Nickel Metal Hydride 3 6 V 150 mAh ANO013703 0708 Page 6 of 17 The circuits are connected as per the schematics in Appendix B Schematics on page 10 When the external power supply and the Evalua tion Board power supply are switched on the PWM waveforms are observed on the oscilloscope The battery converter s actual values are ind
16. re used to indicate various states such as successful completion of charging safety error no battery selection and the specific battery type undergoing the charging process Table 1 lists the status indicators along with a brief description Table 1 LED Status Indicators LED Status Description D4 ON SLA battery is selected and charging is ON D5 ON NiCad battery is selected and charging is ON D6 ON NiMH battery is selected and charging is ON D7 ON Li lon battery is selected and charging is ON D8 ON No battery is selected D9 ON Safety error charging is aborted D10 ON Charging is successfully completed Page 4 of 17 For the battery charger schematics see Appendix B Schematics on page 10 Software Implementation All Z8 Encore peripherals are initialized to the required mode of operation The jumper settings are read and the battery type is validated When the battery type is fixed the battery parameters are loaded into the variables At present these battery parameters are defined in the header file Initially based on battery ratings each module sets the safety and termination thresholds Then type dependent settings such as converter voltage cur rent outputs and current limit are calculated When these one time calculations are completed the charger software enters an infinite loop which is broken only by a successful charge completion or a safety error Inside the loop
17. ry types Reference The documents associated with Z8 Encore avail able on www zilog com and electronics references are provided below Z8 Encore Flash Microcontroller Develop ment Kit User Manual UM0146 e Power Electronics Design Handbook Low Power Components and Applications author Nihal Kularatna ISBN 0 7506 7073 8 Pub lisher Oxford Newnes 1998 ANO013703 0708 Z8 Encore Based Battery Charger j I A FS Z ILOU High Frequency Switching Power Supplies The ory and Design author George Chryssis ISBN 0 07 010949 4 Publisher McGraw Hill Book Company Digital Control Systems Volume 1 Fundamen tals Deterministic Control author Rolf Iser mann ISBN 0 387 50266 1 Publisher Springer Verlag Yuasa Technical Manual http www yuasab atteries com literature asp Duracell http www duracell com batteries Eveready Energizer http data energizer com Panasonic Li Ion battery documents http www panasonic com industrial battery oem chem lithion index html Sanyo http www sanyo com industrial bat teries index html Page 8 of 17 Z8 Encore Based Battery Charger Zilog Appendix A Glossary Definitions for terms and expansions for abbreviations used in this application note that are not commonly used are listed in Table 3 Table 3 Glossary Term Abbreviation Definition Expansion ADC Analog to Digital Converter ISR In
18. tage the battery tends to plateau after a small drop This flat region is the preferred indica tion for full battery charging rather than the drop Consequently this termination mechanism is named zero AV termination Page 15 of 17 NiMH batteries do not suffer from memory effect as do NiCd batteries As a result they replace NiCd battery types in applications such as cell phones because the increase in price is justified by the reduction in weight and absence of memory effect Lithium lon Li lon Li Ion batteries are lighter in weight than NiCd and NiMH batteries Available with a high voltage rat ing of 3 7 V one Li Ion battery can replace three NiCd NiMH battery types These two features make Li Ion high energy density batteries They exhibit flat discharge characteristics and are free from memory effect If the starting voltage of these batteries is initially too low a small constant current is applied until the battery reaches a certain threshold specified by the manufacturer The battery is charged with constant voltage when this threshold is crossed Charging is terminated when battery voltage reaches the rated voltage ANO013703 0708 Z8 Encore Based Battery Charger zilog Page 16 of 17 Z8 Encore Based Battery Charger Bc 0E y fy Zz i U U J N Warning DO NOT USE IN LIFE SUPPORT LIFE SUPPORT POLICY ZILOG S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUP
19. terrupt Service Routine Li lon Lithium lon mAh milli Ampere hour a unit of battery capacity NiCd Nickel Cadmium NiMH Nickel Metal Hydride Pl Proportional plus Integral PWM Pulse Width Modulation SLA Sealed Lead Acid ANO013703 0708 Page 9 of 17 Z8 Encore Based Battery Charger Appendix B Schematics This section provides the schematics for the Z8 Encore battery charger implementation 5 4 3 2 1 7 U14 LM7805C TO220 0 5A Z8 Encore Interface B un 1 3 5y gt gt vec ala al D5 RXE160 za are lt PA4 S2G eom lo gt gt PAS 2 PWR JACK Ui y C17 _ c15 ENyonnrOR pan22H Cp 2zozarggoo oozagodo C21 C22 100 10 O 6G Z EES SEES P3 E 47uF E S D FOF oz 0 1 T lt e QOO LLA lt a2 amp gaan aa a 1 PAO TOIN PA7 SDA 94 2 pp2 _ PD6 CTS1 G8 7 H PC2 88 PC3 SCK 82 U16 RESET 4 PFS PD7 RCOUT 1 eS Sd RESET PGo S2 DD 6 vpp GND 39 SND YEG 3 vw yout H2 33 DD vpp prs PGI p GND pra PG2 prs PES 39 gt gt pes Hid o 55 lt T PE4 PE4 oE PEG PE6 LT1086 3 3 TO220 Y i ad l D4 PES GND PES PE7 VDD PE7 EG DE 12 GND vop 38 727 43 PE2 PE2 PGs 82 eod ETE PE1 l4 PE P
20. th a mechanism specific to their requirement It is also important to know when to terminate charging because overcharging of a battery invari ably results in poor performance and can damage the battery in extreme cases Different battery types behave differently near full charge condition and thus require specific charge termination tech niques During charging all batteries exhibit a marked rise in voltage above the rated battery volt age The four major rechargeable battery types SLA NiCd NiMH and Li Ion are briefly discussed below For further details see Reference on page 8 Sealed Lead Acid SLA Sealed Lead Acid batteries are most commonly seen in automobiles The single cell voltage for SLA is 2 V According to their use several such cells are connected in series to get higher voltages such as 12 V 24 V SLA batteries are usually charged with a constant voltage supply of 2 45 V per cell For this Applica tion Note 4 90 V is used as the charging voltage for the 4 V SLA battery At the start of charging depending on their state of charge SLA batteries require huge amounts of cur rent If this current uptake is not controlled the bat tery electrolyte may boil producing gasses inside the battery It is therefore necessary to limit the charging current When the battery achieves some charge the current is limited and constant voltage charging is enforced ANO013703 0708 Z8 Encore Based Battery Charge
21. that battery In a constant current method of charging fast charging occurs when the charging current equals the rated battery capacity C Fast charging requires constant monitoring of battery parameters and precise termination techniques It is therefore important to know when to terminate charging The behavior of different batteries near full charge varies and demands different termination tech niques The most common termination techniques are the negative AV zero AV and the absolute battery voltage all of which are based on battery types For more information see Appendix D Battery Technology on page 15 Safety Techniques A battery charger must ensure the safety of batter les Battery safety is implemented by monitoring the battery terminal voltage and current against the battery ratings provided by the manufacturer When battery ratings are exceeded the charging voltage or current is switched off Page 3 of 17 Z8 Encore Based Battery Charger This section offers an overview of the functional architecture of the battery charger implementation using Z8 Encore Hardware Architecture The Z8 Encore based charger features the follow ing hardware blocks Figure 2 displays the follow ing hardware blocks Z8 Encore MCU e Step down DC DC buck converter e Feedback section e Battery selector jumper settings e LED status indicators l I External i i Power Source Sus co Step Down Buck
22. ther product or service names are the property of their respective owners ANO013703 0708 Page 17 of 17
23. trol to derive the PWM output based on the equations mentioned in the Theory of Oper ation on page 2 The timer ISR is invoked every 5 ms The PWM value computed by the controller is loaded into the PWM generators to be sent out via the output pin The 16 bit timer PWM mode offers a programma ble switching frequency based on the reload value This flexibility allows you to trade off between accuracy and frequency of the PWM switching signal The higher the frequency the lesser the reload value and the lower the resolution in the pulse width variation and vice versa The timer ISR also updates the charge termination variables every 10 seconds Testing This section contains a detailed test procedure to demonstrate the working of the Z8 Encore battery charger as described in this Application Note The test setup to demonstrate the battery charger using Z8 Encore is displayed in Figure 3 Page 5 of 17 Z8 Encore Based Battery Charger eg j A F5 Z I C O on wj a External DC Power Supply Z8 Encore Evaluation Board DC DC Step Down Converter Oscilloscope Battery Feedback Attenuators PC HyperTerminal Charger Hardware External Circuits Figure 3 Battery Charger Test Setup The test setup consists of an oscilloscope and a PC running the HyperTerminal application For test ing the Z8 Encore Evaluation Board is used with the DC DC converter and the feedback circuits An external DC sou
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