ISL6531
Dual 5V Synchronous Buck Pulse-Width Modulator (PWM) Controller for DDRAM Memory V_DDQ and V_TT Termination

Key Features

• Provides V_DDQ, V_REF, and V_TT voltages for one- and twochannel DDRAM memory systems
• Excellent voltage regulation
• V_DDQ = 2.5V ±2% over full operating range
• V_REF = 1/2 · V_DDQ ±1% over full operating range
• V_TT = V_REF ±30mV
• Supports 'S3' sleep mode
• V_TT is held at 1/2 · V_DDQ via a low power window regulator to minimize wake-up time
• Fast transient response
• Full 0% to 100% duty ratio
• Operates from +5V Input
• V_TT regulator internally compensated
• Overcurrent fault monitor on V_DD
• Does not require extra current sensing element
• Uses MOSFET's rDS(ON)
• Drives inexpensive N-Channel MOSFETs
• Small converter size
• 300kHz fixed frequency oscillator
• 24 Lead, SOIC or 32 Lead, 5mm×5mm QFN
• Pb-Free Plus Anneal Available (RoHS Compliant)

Description

The ISL6531 provides complete control and protection for dual DC-DC converters optimized for high-performance DDRAM memory applications. It is designed to drive low cost N-channel MOSFETs in synchronous-rectified buck topology to efficiently generate 2.5V V_DDQ for powering DDRAM memory, V_REF for DDRAM differential signalling, and V_TT for signal termination. The ISL6531 integrates all of the control, output adjustment, monitoring and protection functions into a single package.

The V_DDQ output of the converter is maintained at 2.5V through an integrated precision voltage reference. The VREF output is precisely regulated to 1/2 the memory power supply, with a maximum tolerance of ±1% over temperature and line voltage variations. V_TT accurately tracks V_REF. During V2_SD sleep mode, the V_TT output is maintained by a low power window regulator.

The ISL6531 provides simple, single feedback loop, voltagemode control with fast transient response for the V_DDQ regulator. The V_TT regulator features internal compensation that eases the design. It includes two phase-locked 300kHz triangle-wave oscillators which are displaced 90o to minimize interference between the two PWM regulators. The regulators feature error amplifiers with a 15MHz gainbandwidth product and 6V/µs slew rate which enables high converter bandwidth for fast transient performance. The resulting PWM duty ratio ranges from 0% to 100%.

The ISL6531 protects against overcurrent conditions by inhibiting PWM operation. The ISL6531 monitors the current in the V_DDQ regulator by using the r_DS(ON) of the upper MOSFET which eliminates the need for a current sensing resistor.

Applications

• V_DDQ, V_TT, and V_REF regulation for DDRAM memory systems
• Main memory in AMD® Athlon™ and K8™, Pentium® III, Pentium IV, Transmeta, PowerPC™, AlphaPC™, and UltraSparc® based computer systems
• High-power tracking DC-DC regulators