NuMicro™ Mini51 Technical Reference ManualFeb 9, 2012 Page 203 of 342 Revision V1.03NUMICRO™ MINI51 TECHNICAL REFERENCE MANUAL5.10.5 PWM Operation ModesThis powerful PWM unit supports independent mode which may be applied to DC or BLDC motorsystem, Complementary mode with dead-zone insertion which may be used in the application ofAC induction motor and synchronous motor, and Synchronous mode that makes both pins of eachpair are in phase. Besides, the Group mode, which forces the PWM0, PWM2 and PWM4synchronous with PWM0 generator, may simplify updating duty control in DC and BLDC motorapplications.5.10.5.1 Independent modeIndependent mode is enabled when PWMMOD[1:0] = 00.By default, the PWM is operated in independent mode with six PWM channels outputs. Eachchannel is running off its own duty-cycle generator module.Note: Only even channels (PWM0, PWM2 and PWM4) can be set as inverter bit (CHnINV,n = 0, 2, 4) in independent mode.5.10.5.2 Complementary modeComplementary mode is enabled when PWMMOD[1:0] = 01.In this module there are three duty-cycle generators utilized for complementary mode, with total ofthree PWM output pair pins in this module. The total six PWM outputs are grouped into outputpairs of even and odd numbered outputs. In complimentary modes, the internal odd PWM signalPGn, must always be the complement of the corresponding even PWM signal. For example, PG1will be the complement of PG0. PG3 will be the complement of PG2 and PG5 will be thecomplement of PG4. The time base for the PWM module is provided by its own 16-bit timer, whichalso incorporates selectable pre-scalar options.5.10.5.3 Dead-zone insertionThe dead-zone generator inserts an “off” period called “dead-zone” between the turnings off of onepin to the turning on of the complementary pin of the paired pins. This is to prevent damage to thepower switching devices that will be connected to the PWM output pins. The complementaryoutput pair mode has an 8-bit down counter used to produce the dead-zone insertion. Thecomplementary outputs are delayed until the timer counts down to zero.The dead-zone can be calculated from the following formula:dead-zone = PWM_CLK * (DZIxy[7:0]+1). where xy, could be 01, 23, 45The timing diagram below indicates the dead-zone insertion for one pair of PWM signals.PG0 withoutdead-zonePG1 withoutdead-zonePWM0 withdead-zonePWM1 withdead-zoneDead-zone IntervalEffect of dead-zone for complementary pairsFigure 5.10-16 Dead-zone Insertion
