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Controller with two PWM regulators, two LDO linear regulators

Posted: 26 Oct 2005 ?? ?Print Version ?Bookmark and Share

Keywords:stmicroelectronics? st? pm6685? step-down controller?

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

The PM6685 integrates two PWM (Pulse Width Modulation) voltage regulators and two LDO (low drop out) linear regulators in one compact package. The PWM regulators provide fixed 5V and 3.3V outputs that power the system during normal operation, while the LDO regulators provide constant 5V and 3.3V 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 5V and 3.3V 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 almost constant switching frequency operation. In addition, the PM6685 promises to reduce PCB area, design cycle time and BoM, thereby enabling the customers to minimize the complete system cost.

For maximum system reliability and ease-of-use, the PM6685 provides power management status information via dedicated output pins that verify correct operation of the two switching regulators and the 3.3V linear regulator. It also supports disabling of the 3.3V LDO with a consequent increase in the current capability of the 5V LDO. Typically, each of the two LDOs can deliver 100mA output current.

Other key benefits of the PM6685 include overcurrent protection without power dissipation to maximize system efficiency while reducing system cost, and a selectable switching frequency, allowing either 200/300kHz, 300/400kHz or 400/500kHz operation of the 5V/3.3V switching sections. Additionally, the device incorporates a pulse skipping technique that increases efficiency at light load, with a selectable minimum switching frequency of 25kHz to avoid audio noise issues. 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.

Built with mature BCD (Bipolar-CMOS-DMOS) smart power technology, the PM6685 is housed in a VFQFPN 32-pin, Pb-free package measuring 5-by-5mm, and is priced at $2 in quantities of 2,000 pieces.

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