Many consumer electronic appliances, such as television set top boxes and remote control devices, are implemented as electronic systems incorporating integrated circuits. These electronic systems typically include integrated circuits forming the core digital logic circuitry and integrated circuits forming the input/output (I/O) interface circuitry. Conventional electronic systems employ multiple DC-to-DC converters to convert a main bus voltage from a power source supplying the system to one or more voltages necessary for driving these integrated circuits.
Switch mode power supplies or switching regulators, also referred to as DC to DC converters, are used to convert an input supply voltage to a desired output voltage at a voltage level appropriate for integrated circuits in an electronic system. For example, a 12 volts supply voltage provided to an electronic system may need to be reduced to 5 volts for supplying the I/O interface circuits and reduced to 1V for supplying the core digital logic circuits, especially if the core digital logic circuits are built using deep sub-micron integrated circuits. A switching regulator provides power supply function through low loss components such as capacitors, inductors, and transformers, and power switches that are turned on and off to transfer energy from the input to the output in discrete packets. A feedback control circuit is used to regulate the energy transfer to maintain a constant output voltage within the desired load limits of the circuit.
Government agencies have started to implement standby power regulations, requiring that appliances with standby power function use no more than 1 watt of power in their standby power consuming mode. These “green” regulations require electronic appliances to have high power efficiency with low standby power consumption. Power efficiency is a measure of the fraction of power consumed which achieves functionality, rather than waste heat.
When switching regulators are incorporated in electronic systems, standby power regulations demand high efficiency from the switching regulators when in standby mode, such as greater than 80% when drawing 10 mA at 5V during standby. Switching regulators are designed to deliver peak efficiency when driving some specific “normal” load. Switching regulators lose efficiency when operated in a wide range of load conditions, and the most drastic degradation occurs at light load conditions. Thus, it is often difficult for switching regulators to meet the standby power requirements in light load conditions.
In an electronic system including a digital core circuit and an I/O interface circuit, the digital core circuit typically demands high current but operates at a low power supply voltage (e.g. 1V) while the I/O interface circuit typically requires lower current but operates at a higher power supply voltage (e.g. 5V or 3.3V).
The digital core circuit requires a power supply capable of fast load transient response to handle varying load current transitions quickly. Since the digital core is typically turned off during standby mode, the efficiency of the digital core power supply is not critical for the standby regulations. Therefore, a DC-to-DC converter capable of fast load transient is typically selected, regardless of the converter's power efficiency at light load. In most cases, a pulse width modulation (PWM) switching regulator is used to supply the digital core circuit.
On the other hand, the I/O interface circuit remains turned on during the standby mode of operation. Thus, the I/O interface circuit requires a power supply capable of delivering high efficiency to a normal load as well as to a light load. In order to meet the requirements of the “green” regulations, a power supply for the I/O interface circuit needs to have high efficiency at the light load condition when the system is in standby mode. In most cases, a pulse frequency modulation (PFM) switch regulator is desired for high efficiency light load operation.
Accordingly, to optimize both the performance requirement and the power efficiency demand of an electronic system, an electronic system may end up being designed to use different types of switching regulators for the digital core circuit and the I/O interface circuit. A manufacturer of an electronic system thus have to procure multiple DC-to-DC converter solutions, rendering the design and manufacturing process more complex and less cost effective.