Powering SOCs with integrated approaches
By Chitra Giridhar, EDN Asia -- EDN, January 4, 2007
A typical portable electronic device, such as a mobile phone or an MP3 player, comprises a variety of chips—many of which need different power-supply voltages. For instance, USB OTG (on the go) needs a 5V source, analog sections and interfaces require 3.3V, and RF chips need 2.5 and 1.8V sources. To compound the issue, current requirements for the chips vary, as does the quality of the power. Design engineers usually resort to a plethora of power-supply regulators with varying voltage, current, and noise specifications to meet the power demand, which results in a proliferation of power-regulator chips, consumption of precious board space, and increased bill-of-material costs. Spotting an opportunity, Cosmic Circuits has created a set of IP (intellectual-property) cores that can integrate power regulators on an SOC (system on chip) to reduce component count and costs. The company has created about 10 types of power circuits in its Power-On SoC family on 130- and 90-nm TSMC (Taiwan Semiconductor Manufacturing Co) process technology for various portable applications, including wireless LANs, MP3 players, UWB (ultrawideband) systems, and connectivity devices.
According to Krishnan Ramabadran, vice president of Cosmic Circuits, the principal challenge in designing the IP cores was to achieve high power efficiency in dc/dc-switching converters for battery-powered applications, even at low load currents. The space-constrained environment of portable electronic systems also means that Cosmic had to design the cores in a way that would minimize the size of the inductors and capacitors on the board. The team also had to tackle 5V in a deep-submicron process to avoid the need for a step-down converter.
The company is now claiming a few industry firsts with its IP cores: a buck-boost converter that operates as low as 2.7V to extract the last bit of juice out of a battery; low-dropout regulators with a PSRR (power-supply-rejection-ratio) as high as 50 dB at 1 MHz; greater-than-90%-efficient capacitive switching regulators or charge pumps for supplying power to LEDs; a lithium-ion-battery charger that integrates a charging transistor in 130-nm digital-CMOS technology; and a super-low-power, low-dropout regulator that supplies trickle power to real-time-clock circuitry.
With many of the power blocks offering features and performance levels previously unavailable as IP to fabless companies, Cosmic is hopeful that it can become a supplier of choice to semiconductor-design houses in the consumer-electronics market. Ramabadran concedes that some applications may not benefit from this kind of power-management integration. For example, systems that require load currents exceeding 2A or those operating at input voltages of 9 to 12V could work equally well with designs based on discrete components rather than an SOC-integrated approach.
