ROHM provides more than 220 motor driver ICs, which have extensive track records. The motor types covered by these driver ICs run the gamut, including brushed DC motors, stepping motors, single-phase brushless DC motors, and 3-phase brushless DC motors (including high-voltage models). The ROHM lineups of motor driver ICs feature high efficiency and reliability supporting broad ranges of voltages, currents and packages, and pin-compatible products are also available.
Over 40 stepping motor driver models are offered, with main emphasis on efficiency and reliability. CLK-IN, PARA-IN, and CLK-IN/PARA-IN control methods can be selected, and lineups span broad ranges of voltages and currents for each interface type. Features include MIX DECAY functions, support for a single power supply, simple CLK-IN control, replete protection functions, PWM constant-current control (separate-excitation type), integrated spike noise blanking functions (no external noise filter needed), malfunction prevention when power is not applied, power-saving functions, and extremely compact and thin packages.
MIX DECAY Function
When the motor current diminishes, depending on the current regeneration mode (SLOW DECAY, FAST DECAY), current tracking worsens, possibly causing vibrations and noise in the motor. A means to deal with this is a MIX DECAY function that enables external adjustment of the ratio of SLOW DECAY to FAST DECAY during current decay.
In SLOW DECAY mode, the voltage across the motor coils is low and the regeneration current declines gradually, so that current ripple is small, and advantages with respect to motor torque result. SLOW DECAY mode is well-suited to FULL STEP mode and low pulse-rate driven HALF STEP, Quarter STEP, and 1/16 STEP modes. However, due to the increased output current caused by worsened current controllability at small currents and a tendency for motor operation to be affected by the motor back emf during high-pulse rate driving, changes in current limiting values cannot be followed, and consequently the current waveform is distorted and motor vibrations increase.
In FAST DECAY mode, the regeneration current decreases sharply, so that current waveform distortion is diminished during high-pulse rate driving, making this mode suitable for high-pulse rate driving in HALF STEP, Quarter STEP, and 1/16 STEP modes. However, because output current ripple is increased, the average current is reduced, and so the reduced motor torque and increased heat generation due to higher motor losses are matters requiring consideration.
The MIX DECAY method resolves the problems with each of the SLOW DECAY and the FAST DECAY modes, by switching between the SLOW DECAY and FAST DECAY modes during current attenuation to improve current controllability without increasing current ripple. The time ratio of SLOW DECAY to FAST DECAY can be adjusted, enabling optimization for various motor control states.
Replete Protection Functions
Various protection circuits are provided as described below, for enhanced safety and reliability.
Malfunction prevention on low voltage (UVLO): When the voltage applied to the VCC pin is at or below a specified value, the motor output is set to OPEN. When UVLO is activated, the electrical angle is reset.
Malfunction prevention when power is not applied (Ghost Supply Prevention function): If a control signal (logic signal, MTH, VREF) is input in a state in which a power supply is not being applied, malfunctions due to indirect voltage transmission to VCC are prevented.
Overtemperature protection circuit (TSD): For overtemperature protection, a thermal shutdown circuit is incorporated. If the IC chip temperature exceeds 175°C (typ.), the motor output is set to OPEN. When the temperature falls to 150°C (typ.) or lower, operation is automatically restored.