FAN5236: Wide Input Voltage Dual-Output/DDR PWM/PFM Controller

The FAN5236 PWM controller provides high efficiency and regulation for two output voltages adjustable in the range of 0.9V to 5.5V 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 high efficiency over a wide range of loads. The Hysteretic Mode can be disabled separately on each PWM converter if PWM Mode is desired for all load levels. Efficiency is enhanced by using MOSFET RDS(ON) as a current-sense component.

Feedforward 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, one of the channels tracks the output voltage of another channel and provides output current sink and source capability — 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 the set point. 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 cease. Under-voltage protection latches the chip off when output drops below 75% of the set value after the soft-start 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 be used.

Features

• Highly Flexible, Dual Synchronous Switching PWM Controller that Includes Modes for:
  • DDR Mode with In-phase Operation for Reduced Channel Interference
  • 90° Phase-shifted, Two-stage DDR Mode for Reduced Input Ripple
  • Dual Independent Regulators, 180° Phase Shifted
• DDR Mode with In-phase Operation for Reduced Channel Interference
• 90° Phase-shifted, Two-stage DDR Mode for Reduced Input Ripple
• Dual Independent Regulators, 180° Phase Shifted
• Complete DDR Memory Power Solution
  • VTT Tracks VDDQ/2
  • VDDQ/2 Buffered Reference Output and HSTL
• V_TT Tracks V_DDQ/2
• V_DDQ/2 Buffered Reference Output and HSTL
• Light-load Hysteretic Mode Maximizes Efficiency
• TSSOP28 Package
• Lossless Current Sensing on Low-side MOSFET or Precision Over-Current Using Sense Resistor
• V_CC Under-Voltage Lockout
• Converters can Operate from +5V or 3.3V or Battery Power Input (5V to 24V)
• Excellent Dynamic Response with Voltage Feedforward and Average-Current-Mode Control
• Power-Good Signal
• Supports DDR-II and HSTL
• Light-load Hysteretic Mode Maximizes Efficiency
• TSSOP28 Package

Application Notes