FAN5236

The FAN5236 PWM controller provides high efficiency and regulation for two output voltages adjustable in the range from 0.9V to 5.5V that are required to power I/O, chip-sets, and memory banks in high-performance notebook computers, PDAs and Internet appliances. Synchronous rectification and hysteretic operation at light loads contribute to a high efficiency over a wide range of loads. The hysteretic mode of operation can be disabled separately on each PWM converter if PWM mode is desired for all load levels. Efficiency is even further enhanced by using MOSFET's R_DS(ON) as a current sense component.

Feed-forward ramp modulation, average current mode control scheme, and internal feedback compensation provide fast response to load transients. Out-of-phase operation with 180 degree phase shift reduces input current ripple. The controller
can be transformed into a complete DDR memory power supply solution by activating a designated pin. In DDR mode of operation one of the channels tracks the output voltage of another channel and provides output current sink and source capability - features essential for proper powering of DDR chips. The buffered reference voltage required by this type of memory is also provided. The FAN5236 monitors these outputs and generates separate PGx (power good) signals when the soft-start is completed and the output is within ±10% of its set point. A built-in over-voltage protection prevents the output voltage from going above 120% of the set point. Normal operation is automatically restored when the over-voltage conditions go away. Under-voltage protection latches the chip off when either output drops below 75% of its set value after the softstart sequence for this output is completed. An adjustable over-current function monitors the output current by sensing the voltage drop across the lower MOSFET. If precision current- sensing is required, an external current-sense resistor may optionally be used.