ISL6444
PWM Controller with DDR Memory Option for Gateway Applications

Key Features

• Provides regulated output voltage in the range 0.9V to 5.5V
• High efficiency over wide load range
• Synchronous buck converter with hysteretic operation at light load
• Complete DDR memory power solution
• VTT tracks VDDQ/2
• VDDQ/2 buffered reference output
• No current-sense resistor required
• Uses MOSFET's rDS(ON)
• Optional current-sense resistor for precision overcurrent
• Undervoltage lock-out on VCC pin
• Dual mode operation
• Operates directly from battery 5.0V to 24V input
• Operates from 3.3V or 5V system rail
• Excellent dynamic response
• Combined voltage feed-forward and current mode control
• Power-good signal for each channel
• 300kHz switching frequency
• Out-of-phase operation for reduced input ripple
• In-phase operation in DDR mode for reduced channel interference
• Out-of-phase operation with 90° phase shift for two-stage conversion in DDR mode
• Pb-free plus anneal available (RoHS compliant)

Description

The ISL6444 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 continuous conduction operation is desired for all load levels. Efficiency is even further enhanced by using MOSFET's rDS(ON) as a current sense component.

Feed-forward ramp modulation, current mode control scheme, and internal feed-back compensation provide fast response to load transients. Out-of-phase operation with a 180o phase shift reduces the input current ripple.

The controller can be transformed in a complete DDR memory power supply solution by activating a DDR 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 ISL6444 monitors the output voltages. Each PWM controller generates a PGOOD (power good) signal when the soft-start is completed and the output is within ±10% of the set point.

A built-in overvoltage protection prevents output voltage from going above 115% of the set point. Normal operation automatically restores when the overvoltage conditions go away. Undervoltage protection latches the chip off when either output drops below 75% of its set value after the soft-start sequence for this output is completed. An adjustable overcurrent function monitors the output current by sensing the voltage drop across the lower MOSFET. If precision current-sensing is required, an external currentsense resistor may optionally be used.

The IC comes in a 28 Ld SSOP package.

Applications

• Residential and Enterprise Gateways
• DSL Modems