Digital Power IC Exceeds Analog Efficiency

Oct 1, 2005 12:00 PM
By David Morrison, Editor, Power Electronics Technology

The first product offering from Zilker Labs of Austin, Texas, is a power management and conversion IC that provides the configurability, control and monitoring capabilities of digital control technology while exceeding the efficiency of analog designs. The ZL2005 combines a synchronous buck controller and adaptive gate drivers with power and thermal management functions. Based on Zilker Labs' Digital-DC technology, the ZL2005 eliminates the need for programming, simplifying and speeding power supply design. The chip is fully configurable using simple pin-strap connections, resistor selection or industry-standard PMBus commands over the chip's serial interface.

“Zilker Labs' Digital-DC technology enables world-class efficiency, and unlike competing digital solutions, does not require software development. The ZL2005 is the first digital power conversion IC that overcomes these two main impediments to widespread adoption of digital power,” says Jim Templeton, founder and vice president of marketing at Zilker Labs.

With its many power management features, the chip eliminates the need for dedicated power management ICs and the numerous discretes associated with them. The ZL2005 performs soft-start and soft-stop; power good and enable; output voltage and current monitoring; input voltage monitoring; output voltage tracking, sequencing and margining; and thermal monitoring and shutdown. In addition, the ZL2005 integrates the PMBus code into the IC.

The chip is versatile with respect to power conversion, operating at switching frequencies up to 2 MHz, generating output voltages ranging from 0.6 V to 5 V, and operating from inputs ranging from 3.3 V to 12 V. Suited to single or multiphase operation — simply by connecting two or more ZL2005s via the SMBus — the controller supports operation at up to 25 A per phase. This functionality is achieved in a 36-pin 6-mm × 6-mm MLF package.

As evidence of the ZL2005's high efficiency, the company cites the case where V_IN = 12 V, V_OUT = 2.5 V, I_OUT = 10 A, and constant output ripple is 30%. Under these conditions, the chip's efficiency ranges from about 93% at a 250-kHz switching frequency to greater than 85% at 2 MHz. While this performance is said to be slightly better than existing analog power controllers, it is claimed to be three or more percentage points better than competing digital power controllers.

There are two keys to the ZL2005's high efficiency. One is a mixed-signal implementation of a digital control architecture that minimizes quiescent power. Rather than using a high-speed A-D converter (ADC) to sample the output voltage and generate the error signal, the ZL2005 employs comparators that accurately sense the value of the feedback signal around the value that corresponds to zero error. And whereas the output of the ADC might otherwise be fed to an MCU or DSP that controls the digital pulse-width modulator, the ZL2005 employs state machines, which provide programmability but not the power penalty associated with running a high-speed processor or DSP. The comparators and state machines are buried within the mixed-signal block shown in the figure. The control portion of the chip including the gate drivers consumes just 75 mW with a 5-V input.

The ZL2005 also maximizes power-conversion efficiency through a technique that minimizes the PWM duty cycle at the desired output voltage. This has the effect of accurately adjusting dead time on the MOSFETs, but in a manner that is said to be more efficient than the conventional approach of sensing voltages across the FETs.

Available for general sampling, the ZL2005 is priced starting at $4.25 in quantities of 1000. For more information, see www.zilkerlabs.com.

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