FAN5068

www.fairchildsemi.com

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www.fairchildsemi.com

FAN5068
DDR-1/DDR-2 plus ACPI Regulator Combo
Features
PWM regulator for VDDQ (2.5V or 1.8V) Linear LDO regulator generates VTT VDDQ/2, 1.5A Peak sink/source capability 1 independent programable ULDO controllers driving external N-Channel MOSFET ACPI drive and control for 5V DUAL generation 3.3V Internal LDO for 3V-ALW generation 300kHz fixed frequency switching RDS(ON) current sensing or optional current sense resistor for precision over-current detect Internal Synchronous Boot diode Power Good signal for all voltages Input Under-Voltage Lock-Out (UVLO) Thermal Shutdown Latched Multi-Fault Protection 24-pin 5x5mm MLP package

General Description
The FAN5068 DDR memory regulator combines a highefficiency PWM controller to generate the supply voltage, VDDQ, and a linear regulator to generate VTT, the termination voltage. Synchronous rectification provides highefficiency over a wide range of load currents. Efficiency is further enhanced by using the low-side MOSFET s RDS(ON) to sense current instead of a series sense resistor. In S3 mode, only the VDDQ switcher and the 3.3V regulators remain on while the VTT and ULDO regulators are shut off. To avoid "glitching" the VDDQ output during the transition from S3 to S0, the three linear regulators use the SS capacitor to limit their slew rates, thereby limiting the surge current from the VDDQ output. PGOOD becomes true in S0 only when all 3 regulators have achieved stable outputs. In S5 (EN 0), the 3.3V internal LDO stays on, while the other regulators are powered down. The VDDQ PWM regulator is a sampled current mode control with external compensation to achieve fast load transient response and provide sy
stem design optimization. The VTT regulator derives its reference and takes its power from the VDDQ PWM regulator output using a precision internal voltage divider to set its output at 1/2 of VDDQ. The VTT termination regulator is capable of sourcing or sinking at least 1.5A peak current.

Applications
DDR-1/DDR-2 VDDQ and VTT voltage generation with ACPI support Desktop PC s Servers

REV. 1.0.1 9/9/04