Electronic Design

dsPIC Controllers Take On Heavy-Duty SMPS Control Roles

Digital power continues to move deeper into the mainstream. Last month, Microchip Technology introduced seven PIC microcontrollers customized for switch-mode power supply (SMPS) applications. Microchip has offered SMPS controller chips before, but the new, in-circuit programmable, 16-bit dsPIC digital signal controllers (DSCs) are smaller and offer twice the performance (40 MIPS) at a lower price than the old SMPS family.

The dsPIC33F “GS” series DSCs for digital power applications enable control loops with four to eight 1-ns resolution pulse-width-modulators (PWMs). Each chip has one or two 10-bit, 2-Msample/s analog-to-digital converters (ADCs) with up to 12 input channels, along with other typical PIC peripherals. One version has 6 kbytes of flash and two PWM generators. Another has 16 kbytes of flash and three PWM generators. Yet another has 16 kbytes of flash and four PWM generators.

The computational engine is Microchip’s dsPIC DSC. This 16-bit (data) modified-Harvard RISC machine combines the control of a high-performance 16-bit microcontroller with the computation speed of a fully implemented DSP. Most instructions require only one clock cycle to execute. The dsPIC DSC has a fixed, deterministic interrupt latency, allowing very predictive, real-time performance. For design support, Microchip offers its standard development tools for its DSCs, plus a buck/boost converter PICtail Plus daughter board that works with the standard Explorer 16 development board.

What really makes this a story about digital control of SMPS for the masses is a complete ac-dc reference design (see the figure) for a 300-W (continuous power rating) unit that accepts a wide range of input voltages (85 to 265 V ac at 45 to 65 Hz, which is essentially universal ac input) and produces three dc output voltages (12 V at 30 A, 3.3 V at 69 A, and 5 V at 23 A). Fitting its purpose as a reference design intended to introduce designers to best practices in digital power (each stage operates at better than 90% efficiency), the supply is practically a front end for a data center rack. Thus, its range of topologies offers a lot of diversity.

A front-end power factor correction (PFC) boost circuit converts the input voltage to 420 V dc. A full-bridge transformer-isolated buck converter, which incorporates a phase-shift zero-voltage transition (ZVT) circuit, then produces an isolated 12-V dc bus voltage rated at 30 A from the 420 V bus. That 12-V rail is used to produce 3.3 V dc via a multiphase synchronous buck converter and 5 V dc via a single-phase buck converter. The design also implements programmable soft-start, automatic fault handling, and remote power management.

Internally, one of the dsPIC33F GS series DSCs controls the PFC boost circuit and the primary-side ZVT full-bridge circuit. A second dsPIC33F monitors the 12-V dc bus voltage and controls the four buck converters. The two controller DSCs communicate across the isolation boundary via UART ports. Complete documentation, including software and Gerber files, can be downloaded for free at www.microchip.com/SMPS.

Packaging ranges from 18- and 28-pin small-outline ICs (SOICs) and shrink-package dual-inline packages (SPDIPs) to 44-pin quad flat packs (QFPs) and 6- by 6-mm quad flat no-lead (QFN) packages. Pricing starts at $1.96 each in 5000-unit quantities.



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