Power Electronics

Single-chip Power Management Solution for Mobile Computing

STMicroelectronics has introduced the first device in a new family of products designed to provide cost-effective and compact solutions for mobile PC power management. The PM6685 is a dual step-down controller specifically designed to provide the four output voltages necessary for a notebook system power during normal working conditions and in stand-by mode, with extremely high efficiency conversion (up to 96%) using a lossless current-sensing technique.

The PM6685 integrates two PWM voltage regulators and two LDO linear regulators in one package. The PWM regulators provide fixed 5-V and 3.3-V outputs that power the system during normal operation, while the LDO regulators provide constant 5-V and 3.3-V outputs for use during system standby. The integrated LDOs are designed to power the complete notebook during suspend states, sinking the current directly from the battery, while during normal working conditions an internal MOSFET switches the output PWM sections to the 5-V and 3.3-V LDOs, thereby increasing efficiency and extending the battery life.

The device also features a constant on-time architecture that ensures fast-load transient response and an embedded voltage feed-forward circuit that provides nearly constant switching frequency operation. An embedded integrator control loop compensates the dc voltage error due to the output ripple, thereby allowing the designer to specify cheaper output capacitors without sacrificing performance. A “Soft Off” discharge feature discharges the output capacitor on turn-off, ensuring that no voltages remain present in the system that could affect the next start up. Dedicated output pins that verify correct operation of the two switching regulators and the 3.3-V linear regulator are also provided.

Built with mature Bipolar-CMOS-DMOS (BCD) smart power technology, the PM6685 is housed in a compact VFQFPN 32-pin, lead-free package measuring just 5 mm × 5 mm. The PM6685 is priced at $2 in quantities of 2000 pieces.

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