Introduction The bq2031 incorporates the necessary PWM control cir cuitry to support switch mode voltage and current regu lation as required by its charge control function block This application note describes how to configure the bq2031 in buck mode switching power supply topology A methodology for phase compensation of the voltage and current feedback loops is recommended A brief de scription of the PWM control circuitry and phase com pensation criteria appears below followed by a discussion dealing with topology specific issues

Texas Instruments, Incorporated

Description

Niveau: Secondaire, Lycée, Terminale
Introduction The bq2031 incorporates the necessary PWM control cir- cuitry to support switch-mode voltage and current regu- lation, as required by its charge control function block. This application note describes how to configure the bq2031 in buck mode switching power supply topology. A methodology for phase compensation of the voltage and current feedback loops is recommended. A brief de- scription of the PWM control circuitry and phase com- pensation criteria appears below, followed by a discussion dealing with topology-specific issues. The Pulse-Width Modulator The bq2031 incorporates two voltage mode direct duty cycle Pulse-Width Modulators, one for each control loop (voltage and current). A block diagram is shown in Fig- ure 1. Each PWM runs off a common saw-tooth wave- form whose time-base is controlled by a capacitor, CPWM on the TPWM pin. The relationship of CPWM to the switching frequency, FS is given by: Equation 1 F C kHzS PWM = 0 1. where: CPWM is in µF. The PWM for either loop consists of a comparator whose positive terminal is driven by the output of the sawtooth ramp signal, VS, while the negative terminal is driven by the output of an Operational Transcon- ductance Amplifier (OTA). The output is the control signal, VC. The output of each PWM is logically ORed to generate a constant frequency pulse width modu- lated rectangular waveform at the MOD output.

• pwm transfer


• only func- tion


• characteristics can


• loop


• pwm control


• db gain


• during voltage


• output power


• voltage control


• function

Sujets

• Première
• Target
• Function

Informations

• Publié par: profil-zyan-2012
• Nombre de lectures: 32
• Langue: English

Extrait

U-511 Switch-Mode Power Conversion Using the bq2031

Introduction i T s h g e iv r e e n la b ti y o : nshipofC PWM to the switching frequency, FS The bq2031 incorporates the necessary PWM control cir -  Equation 1 cuitry to support switch-mode voltage and current regu - lation, as required by its charge control function block.  F S = C 0.1 kHz This application note describes how to configure the PWM bq2031 in buck mode switching power supply topology. A methodology for phase compensation of the voltage  where: and current feedback loops is recommended. A brief de - ■ C P i in µ F. scription of the PWM control circuitry and phase com - WM s p e n s a t i o n c r i t e r i a a p p e a r s b e l o w, f o l l o w e d b y a discussiondealingwithtopology-specificissues. T w h h e ose P p W os M iti f v o e r t e e i r th m e i r na l l o i o s p d c ri o v n e si n st b s yt of he a o c u o tp m u p t a o r f a t t h or e ne tive terminal The Pulse-Width Modulator i s s aw d t r o iv ot e h n r b a y m t p h s e ig o n u a t l p , u V t S , of w a hi n le O t p h e e rati g o a nalTranscon- nce Am fier (OTA Thebq2031incorporatestwovoltagemodedirectduty ductapli).Theoutputisthecontr e o d l cyclePulse-WidthModulators,oneforeachcontrolloop t s o ig g n e a n l, er V a C t . e T a h c e o o n u s t t p a u n t t o f f re e q a u c e h n P cy W p M ul i s s e lo w gi i c d a t l h ly m O o R du- (voltage and current). A block diagram is shown in Fig-  lat ular wav ure1.EachPWMrunsoffacommonsaw-toothwave- rel e a d tio r n ec s tang o eformattheMODoutput.Th e e form whose time-base is controlled by a capacitor, C PWM OTAcont hipftheMODoutputwithrespecttoth on the TPWM pin.  V S ,issho r w o n l i s n ig F n i a g l u , r V e C 2 , . andthesawtoothrampsignal,

6/96

Figure 1. Block Diagram of the bq2031 PWM Control Circuitry

1