Sunday, October 29, 2006

Digital Signal Controllers Expand Options for Power Conversion and Motor Control

Texas Instruments has expanded its TMS320C2000 family of digital signal controllers by adding new options for on-chip memory and more PWM peripherals. The new controllers include the TMS320F2809 and TMS320F2802 flash-based controllers and custom ROM-based TMS320C2801 and TMS320C2802, which are fully hardware- and software- compatible with the three existing TMS320F280x controllers. With the wider mix of memory options, the new controllers make it easier for system designers to tradeoff memory and cost (see the table). That flexibility will aid designers as they apply these ICs in applications such as motor control, digital power conversion, intelligent sensor control and other applications in industrial, appliance, automotive, medical and consumer products.

The TMS320F2809 offers 256 kbytes of on-chip flash, double the size of the previously introduced ‘F2808. It also increases the number of PWM channels with 150-ps resolution from four to six. In addition, this flagship member of the TMS320C2000 family doubles the sampling speed on the 12-bit pipelined A-D converter to 12.5 Msamples/s. In contrast, most embedded A-D converters are typically limited to sampling rates in the single megahertz range. Furthermore, the F2809’s A-D converter boasts an effective number of bits (ENOB) of 10.9 and is valid across the full -40 to +125° C temperature range. As with other members of the TMS320C2000 family, the ‘F2809 features a 100-MIPS CPU.

The controllers’ high resolution PWMs provide 16 bits of accuracy in a 100-kHz control loop and 12 bits at 1.5 MHz. According to Texas Instruments, competing processors limit accuracy to less than 10 bits at 100 kHz and less than 6 bits at 1.5 MHz. In digital power applications, the higher resolution PWM results in a faster transient response with a smaller ripple amplitude. The high resolution PWM also eliminates ‘limit cycle’ issues, which means power supply designers are able to use digital control in high-switching frequency supplies.

Furthermore, the new combinations of performance, memory, and peripherals offered by the C28x and F28x benefit advanced motor control applications. For example, one TI customer—Self-Guided Systems—recently integrated F280x controllers into the brushless dc motors used to guide the company’s Hybrid Z self-stabilizing, autonomous lawnmower. The mower’s cutting blades triangulate their position based upon mower position and reflector location. The Hybrid Z then navigates itself and cuts grass to a pre-set length without any human intervention.

All C280x and F280x devices feature a 32-bit wide data path for superior performance and mixed 16-/32-bit instruction set for improved code density. These chips provide complete control system capabilities from signal input through the on-chip A-D converter, quadrature encoder pulse (QEP), and timer captures and compares through signal output with up to 16 independent PWM channels. Besides the 150-ps PWMs, there are as many as 10 PWM outputs with 10-ns resolution. For communications, the TMS320C2000 family offers a range of interface options including multiple CAN, I2C, UART and SPI ports.

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