Electronic Design

Smart Dual-Input Regulator Includes Auxiliary Switch

PC systems today are being designed with several modes of operation for conserving power. That means that the semiconductor devices and PC cards in these systems must switch efficiently from one state to another without degrading performance. To address such requirements, California Micro Devices has expanded its SmartOR line with a complete dual-input smart regulator with a built-in low-impedance auxiliary switch.

The latest line member, the CMPWR300, can provide a 3.3-V output at 500 mA from three independent input voltage sources on a prioritized basis. These include the primary power source (VCC), a standby (VSBY), and an auxiliary voltage (VAUX) (see the figure). This chip also implements all of the necessary switch and control circuitry to provide a smooth transition from all three inputs to the 3.3-V output. A 5-V VCC is given the top priority. But when the primary source falls below the 4.2-V threshold, the 5-V standby input becomes effective.

The threshold has a built-in hysteresis of 300 mV, which ensures that only VCC is selected when the threshold exceeds 4.5 V. When neither VCC nor VSBY is available, the internal switch is enabled to provide a very low impedance (0.12 Ω typical) direct connection from VAUX to VOUT. To provide stability and minimal disturbance during transition, the supplier recommends a 10-µF capacitor at the output. The glitch is around 100 mV during transition. For instance, during transition from VAUX to VCC under full-load condition, the disturbance on the output is only about 120 mV. Likewise, a bypass capacitor in the range of 1 to 10 µF safeguards adequate filtering at the input.

The device also exhibits steady response over the operating temperature range. Tests show that the output variation at maximum load is below 10 mV from 0°C to 70°C. Aimed at instantly available PC, battery back-up, and other advanced modes of power-management solutions, the CMPWR300 is fabricated in 1.5-µm CMOS. It comes in an 8-pin SOIC package and costs $1.23 each in quantities of 10,000.

California Micro Devices, 215 Topaz St., Milpitas, CA 95035-5430; (408) 263-3214; www.calmicro.com.

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