EVAL6229PD

AN1625 APPLICATION NOTE L6235 THREE PHASE BRUSHLESS DC MOTOR DRIVER by Vincenzo Marano Modern motion control applications need more flexibility that can be addressed only with specialized ICs products. The L6235 is a fully integrated motor driver IC specifically developed to drive a wide range of BLDC motors with Hall effect sensors. This IC is a one-chip cost effective solution that includes several unique circuit design features. These features, including a universal decoding logic that allows the device to be used with most common Hall effect spacing, will be described. The principal aim of this development project was to produce an easy to use, fully protected power IC. In addition several key functions as protection circuit and high speed PWM current control allow to drastically reduce the external components count to meet requirements for many different applications. 1 INTRODUCTION For small-motor applications many appliance designers favor modern three phase brushless DC motors be- cause of the high efficiency (as great as 95%) and small size for a given delivered power. Designers have to handle control logic, torque and speed control, power-delivery issues and ensure safe operation in every load condition. The L6235 is a highly integrated, mixed-signal power IC that allows to easily design a complete motor control system for BLDC motor. Figure 1 shows the L6235 block diagram. The IC integrates six Power DMOS, a centralized logic circuit to decode hall effect sensors and a constant t PWM current control technique (Syn- OFF chronous mode) plus other added features for safe operation and flexibility. Figure 1. L6235 Block Diagram. V BOOT VS A VBOOT V BOOT THERMAL CHARGE VCP PROTECTION PUMP OCD1 OUT 1 DIAG OCD1 10V OCD OCD2 OCD3 OCD V EN BOOT BRAKE FWD/REV OCD2 OUT 2 H GATE 10V 3 LOGIC HALL-EFFECT SENSORS H 2 DECODING SENSE LOGIC A H V VS BOOT 1 B TACHO RCPULSE OCD3 MONOSTABLE OUT 3 10V TACHO 10V 5V SENSE B PWM VOLTAGE + ONE SHOT MASKING REGULATOR MONOSTABLE TIME SENSE - VREF COMPARATOR RCOFF D99IN1095B October 2003 1/39AN1625 APPLICATION NOTE Table of Contents 1 INTRODUCTION................................................................................................................................1 2 DESIGNING AN APPLICATION WITH L6235 ...................................................................................3 2.1 Current Ratings........................................................................................................................3 2.2 Voltage Ratings and Operating Range ....................................................................................3 2.3 Choosing the Bulk Capacitor....................................................................................................5 2.4 Layout Considerations .............................................................................................................5 2.5 Sensing Resistor......................................................................................................................7 2.6 Charge pump external components.........................................................................................8 2.7 Sharing the Charge Pump Circuitry .........................................................................................9 2.8 Reference Voltage for PWM Current Control.........................................................................10 2.9 Input Logic pins......................................................................................................................11 2.10 DIAG pin.................................................................................................................................11 2.11 Programmable off-time Monostable.......................................................................................12 2.11.1 Off-time Selection and minimum on-time ........................................................................14 2.11.2 Slow Decay Mode ...........................................................................................................14 2.12 Over Current Detection .........................................................................................................16 2.13 Power Management...............................................................................................................20 2.13.1 Maximum output current vs. selectable devices..............................................................20 2.13.2 Power Dissipation Formulae ...........................................................................................21 2.14 The decoding logic................................................................................................................24 2.15 Tacho Output and Speed Loop.............................................................................................25 2.15.1 Static performance - Speed Regulation vs. Resistant Torque: .......................................28 2.15.2 Dynamic performance: ....................................................................................................29 2.15.3 Loop Stability:..................................................................................................................30 2.15.4 Reference voltage ripple: ................................................................................................30 2.16 Brake.....................................................................................................................................31 3 APPLICATION EXAMPLE................................................................................................................32 4 APPENDIX - EVALUATION BOARDS .............................................................................................34 4.1 PractiSPIN..............................................................................................................................34 4.2 EVAL6235N ...........................................................................................................................35 4.2.1 Important Notes................................................................................................................36 5 REFERENCES.................................................................................................................................39 2/39