Dual 5V Synchronous Buck Pulse-Width
Modulator (PWM) Controller for DDRAM
Memory VDDQ and VTT Termination
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 VDDQ for powering
DDRAM memory, VREF for DDRAM differential signalling,
and VTT for signal termination. The ISL6531 integrates all of
the control, output adjustment, monitoring and protection
functions into a single package.
The VDDQ 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. VTT accurately tracks VREF.
During V2_SD sleep mode, the VTT output is maintained by
a low power window regulator.
The ISL6531 provides simple, single feedback loop, voltage-
mode control with fast transient response for the VDDQ
regulator. The VTT 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 gain-
bandwidth 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 VDDQ regulator by using the rDS(ON) of the upper
MOSFET which eliminates the need for a current sensing
PART NUMBER RANGE(oC) PACKAGE PKG. DWG. #
0 to 70 24 Lead SOIC M24.3
0 to 70 32 Lead 5x5 QFN L32.5x5
ISL6530/31EVAL1 Evaluation Board
• Provides VDDQ, VREF, and VTT voltages for one- and
two- channel DDRAM memory systems
• Excellent voltage regulation
- VDDQ = 2.5V ±2% over full operating range
- VTT = VREF ± 30mV
• Supports ‘S3’ sleep mode
VTT is held
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• Fast transient response
- Full 0% to 100% duty ratio
• Operates from +5V Input
• VTT regulator internally compensated
• Overcurrent fault monitor on VDD
- 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
• VDDQ, VTT, and VREF regulation for DDRAM memory
- 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
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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