MA828

The MA828 PWM generator has been designed to provide waveforms for the control of variable speed AC machines, uninterruptible power supplies and other forms of power electronic devices which require pulse width modulation as a means of efficient power control.

The six TTL level PWM outputs (Fig. 2) control the six switches in a three-phase inverter bridge. This is usually via an external isolation and amplification stage.

The MA828 is fabricated in CMOS for low power consumption. Information contained within the pulse width modulated sequences controls the shape, power frequency, amplitude, and rotational direction (as defined by the red-yellow-blue phase sequence) of the output waveform. Parameters such as the carrier frequency, minimum pulse width, and pulse delay time may be defined during the initialisation of the device. The pulse delay time (underlap) controls the delay between turning on and off the two power switches in each output phase of the inverter bridge, in order to accommodate variations in the turn-on and turn-off times of families of power devices.

The MA828 is easily controlled by a microprocessor and its fully-digital generation of PWM waveforms gives unprecedented accuracy and temperature stability. Precision pulse shaping capability allows optimum efficiency with any power circuitry. The device operates as a stand-alone microprocessor peripheral, reading the power waveform directly from an internal ROM and requiring microprocessor intervention only when operating parameters need to be changed.

An 8-bit multiplexed data bus is used to receive addresses and data from the microprocessor/controller. This is a standard MOTELTM bus, compatible with most microprocessors/controllers. Rotational frequency is defined to 12 bits for high accuracy and a zero setting is included in order to implement DC injection braking with no software overhead.

This family is functionally identical to the MA818 PWM generator IC except that the waveform ROM is integrated onchip; in addition, the MA828 features three Zero Phase Pulse (ZPP) outputs and a Waveform Sampling Synchronisation output (WSS) for use as feedback in, for example, slip compensaton systems. Two standard wave shapes are available to cover most applications; in addition, any symmetrical wave shape can be integrated on-chip to order.