Single chip control solution for dual industrial motor drives

The device is one of the first of Renesas’ embedded flash controllers to make use of the powerful SH-2A core. This core, an enhanced version of Renesas’ SH-2 core and having a superscalar architecture, has two execution units in the pipeline. Allowing two instructions to be processed concurrently, code can be executed up to twice as fast as the CPU clock. In addition, its Harvard-based architecture ensures that no bus conflicts occur between instruction fetch and data access. The SH-2A also features the addition of an optional Floating Point Unit (FPU) and although not featured on the SH7285, provides an upgrade path for codes needing faster DSP functionality.

The core’s CPU registers are now arranged in “banks”, with the 19 registers being mirrored 15 times. Using this technique, an interrupt subroutine can use a second set of registers leaving the current ones ready for use upon return from the interrupt subroutine. This means that the registers don’t need to be popped onto and back from the stack, providing a quicker return from the interrupt subroutine. As a result, the response time to an interrupt request (IRQ) is as quick as a simple branch instruction.

The SH7285 device offers a comprehensive MTU2 timer unit with six channels of 16-bit timers, support for up to 16 input capture/output compare functions, and a three-phase PWM capability for electrical motors. Additional motor control features are enabled by a quadrature encoder feedback capability and a special channel that can measure dead times at the power stage, thus enabling both the shortest possible dead times for highest efficiency and safe, non-destructive operation of the power stage. The MTU2 also incorporates additional safety features with its Port Output Enable (POE) pins that provide a faster and more deterministic response time to ensure safe quick shutdown of the motor. Also included is an MTU2S peripheral, this is simply a subset of the MTU2. This means that the SH7285 can drive two vector controlled industrial inverters simultaneously.

The IC hosts two ADCs with four channels each, 12-bit resolution and 1.0us conversion time. Each ADC can be triggered by the MTU2 with an additional defined delay time to support algorithms such as single-shunt motor drive. Single shunt motor drive is a technology that has replaced expensive shunt resistors in motors using CPU calculation power. For a very small additional increase in microcontroller cost (cents), designers can replace several Euros worth of shunts and so achieve significantly lower system cost in applications such as pumps, fans and vacuum cleaners.

The SH7285 also includes a USB2.0 module, five SCI channels, one SSU(Synchronous Serial communication Unit) channel and one IIC channel. The peripheral set is complimented by, a watchdog timer, two channels of compare-match timers, 32k or 24kbytes of RAM and comes in a 144pin package that operates at 5V +/- 10% or 3.3V +/- 10%.