Digital power controllers offer digital and analog architecture
By Margery Conner, Technical Editor -- 6/26/2006
Since EDN last covered digital-power controllers, three more digital-power-controller ICs have appeared: Microchip’s new part is a close-the-loop digitally device; Maxim’s is a hybrid approach in that the control loop is still analog, but the power management and communication are digital; and Primarion’s, new addition to its Di-POL family, uses a PID-control loop (see “Digital power lures system architects, power-supply vendors,” EDN, May 25, 2006, pg 47). When you add this influx of parts to the digital-control and -management parts from Texas Instruments, Zilker Labs, and Silicon Labs, you get the indication that power-supply-chip vendors view digital power as worth their serious attention (see “A bit-o’-power: digitally controlled power conversion,” EDN, July 21, 2005, pg 59).
Microchip’s dsPIC30F1010/202X family (click for picture) relies on the company’s DSC (digital-signal-control) engine to deliver a complete digital-power-control loop with 1-nsec PWM (pulse-width-modulation) resolution and 2M-sample/sec performance from its built-in 10-bit ADC.
Unlike digital-power controllers that rely on a dedicated hardware PID controller, the chips do not adhere to any one control algorithm or topology. “Any algorithm you can conceive, you can code up,” says Brian Kris, staff architect for Microchip. In addition, direct communication between the ADC, the PWM, and the analog comparators in the form of a configurable control fabric allows you to configure their intercommunication upon start-up. For example, says Kris, “You can automate the precise taking of voltage and current measurements during each cycle and trigger an asynchronous conversion process.” The parts also have multiple analog comparators that allow you to select from a variety of input references to modify the behavior of the PWM generators—for example, to assert the output of the PWM generator for feed-forward compensation. Prices for the two-chip set start at $2.99.
Like the previous member of Primarion’s Di-POL (point-of-load) family of digital-power controllers, the PX7510, the PX7520 is PID-control-loop based. The new part offers dual-phase control capability at a switching frequency of 150 kHz to 2 MHz in addition to the Di-POL family features, such as a PMBus/I2C serial interface, a library of 60 common PMBus commands, internal voltage and temperature referencing, and an internal oscillator. Linear Technology will act as a second source for the part.
-management ability to legacy analog power supplies. The chip interfaces with the system controller through the PMBus, sending and receiving system-level control queries and commands, such as peak-temperature, output-current, and output-voltage data for all of the power-subsystem modules, allowing the system controller to poll each module at fixed intervals and log the information for future analysis of field failures. The chip taps into the enable node, the feedback node, or the reference input of the power supply’s analog-control circuitry to provide voltage tracking and sequencing, as well as setting the output voltage at within ±0.2% accuracy over the –40 to +85°C industrial-temperature range. The MAX8688 requires a 3.3V±10% supply voltage and can control output voltages of 0 to 5.5V. Prices start at $1.95.
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