Electronic Design

True Digital

Power-One paved the way for digital control in the IBA marketplace in 2004 with its Zsystem. It comprised point-of-load (POL) converters, a digital power-management module (DPM), a single-wire bus to interconnect them, and friendly GUI-based software to make the system simple to use. Along with digital feedback-loop compensation, the Zsystem offered multi-POL control over output voltage, output tracking and sequencing, switching frequency, interleaving, and active digital current sharing (Fig. A).

The Z-system preceded PMBus (see ED Online 11714). While its controller communicated via an I2C interface, communication between the controller and POLs occurred over a single synchronization/data line called the Zbus. The Zbus synchronized multiple Z-POLs to a master clock in the manager chip and carried bidirectional data between POLs and the DPM.

Originally, the DPM was a module. Last year, Power-One replaced it with a monolithic version. The line of hardware-configurable"No-Bus" Z-POLs started with the 20-A ZY7120 POL, which is directly programmable via I2C. It could provide a digitally controlled 0.5- to 5.5-V dc output to 61% accuracy, with from 3 to 13.2 V on its inputs.

Other programmable parameters included output tracking and sequencing, switching frequency, interleaving, feedback-loop compensation, and active digital current sharing with multiple Z-POL converters. Programmable protection features included output overcurrent and overvoltage, input undervoltage, power-good signal limits, and fault management. Real-time reporting included output voltage and current and POL temperature. Last month, the company introduced a 15-A version.

Late in 2005, Primarion unveiled its PX7510, the first of what is to be a family of Di-POL digital controller/management ICs. The chip offers programmable switching from 150 kHz to 2 MHz. On startup, an internal calibration feature measures and corrects current-sense error sources.

On the Primarion chips, PMBus provides the usual control and monitoring functions. It also lets designers program current-sense temperature compensation. In turn, designers can tailor response for the best accuracy over temperature. The company also offers a series of four-, five-, and six-phase digital VR11-specific controllers for the voltage-regulator modules used on Intel and AMD motherboards. The PX3539 is Primarion's latest VR11 digital multiphase power controller for core power regulation and intelligent POL power regulation in server and desktop PC applications. These are second-sourced by Intersil, which is a major investor in Primarion.

The Si8250 developed by Silicon Laboratories starts with a voltage-mode digital controller (Fig. B). It then adds a system management processor based on a 50-MIPS 8051 CPU and a dedicated analog-to-digital converter (ADC).

The digital control section goes beyond the basic proportional-integrating/ differentiating (PID) control-loops controller to add a selectable digital filter. This filter can be programmed as either a two-pole low-pass filter (LPF) or a sinc (sin(x)/x) decimation filter.

In the first case, the LPF and the PID form a three-pole, two-zero composite filter. In the latter, the sinc filter and PID create a single-pole, multiple-zero composite filter. Here, the zeros can be programmed to fall exactly on the pulse-width-modulation (PWM) frequency and its harmonics.

Within Silicon Labs' system management controller, the dedicated ADC digitizes analog parameters that the MCU uses to provide protection, control, and power management. On-board digital peripherals include timers, an SMBus interface port (for PMBus or other protocols), and a UART for serial communications. Silicon Labs also supplies a development kit, which includes a reference design board and software.

The digital FMS7401L from Fairchild Semiconductor features an unusual eight-input multiplexer ahead of its ADC. Five inputs are multifunction input channels, and three are used for system calibration.

The multifunction input channels may be configured to perform standard conversions on any of the analog input pins (G4/AIN0, G3/AIN1, G2/AIN2, G3/AIN3, or G7/AIN4). Three of the multifunction input channels may be programmed to perform analog-to-digital conversions through the internal auto-zero amplifier, uncommitted amplifier, and current source generator for special control system and battery-management applications.

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