October 2004
LM27262
Intel CPU Core Voltage Regulator Controller for VRD10
Compatible PCs
n User programmable, low loss, load line slope
n User programmable Standard VID offset
n User programmable VCORE slew rate
n 5V power rail Under Voltage Lock Out (UVLO)
General Description
The LM27262 is a versatile synchronous buck voltage regu-
lator controller designed according to the Intel VRD10 Speci-
fication. It’s a fixed-frequency voltage-mode control PWM
n Over Voltage Protection (OVP), Under Voltage
Protection (UVP), and Over Current Protection (OCP) to
defend against potentially catastrophic events
n User programmable fault latch that can be used to
disable the regulator in the event a power system fault
n Very fast transient response
n VID-transition masked PWRGOOD output
n True-differential current sensing for each phase ensures
accurate load current sharing
with average current modulation of the reference voltage to
achieve the desired output impedance. This approach im-
parts a pseudo current mode behavior to the control loop.
The part provides the control for a voltage regulator consist-
ing of either 2-, 3- or 4-phases to provide power to a desktop
CPU. Pulse-by-pulse phase current balancing ensures ac-
curate current sharing. CPU core currents of over 90A can
be supported without requiring significant over design of the
power path. The LM27262 contains a precision 6-bit digital-
to-analog converter (DAC) that uses a VID-code provided by
the CPU to program the desired CPU core voltage. The
regulator output voltage can be dynamically adjusted by
changing the VID-code “on the fly”.
n User programmable cycle-by-cycle current limit
Key Specifications
n Fast transient response to minimize output capacitor
requirements
The part is intended to provide all the specified functions laid
out in the VRD-10 specification, making it as simple as
possible for the user to realize a fully compliant CPU core
n Shorter design cycles through the use of external gate
drivers for reduced power dissipation, ease of PCB
layout and reduced noise sensitivity
n Fully integrated solution. All VRD-10 control functions
provided by a single device
™
™
supply for Intel’s Pentium 4 and Prescott processors.
The LM27262 is available in a 48-lead TSSOP package and
in a 48-lead LLP package.
n Accurate current balancing eliminates need to over
design the power path
n Fixed frequency PWM minimizes EMI issues
n Low input capacitor requirements due to multi-phase
interleaving
n Fault latching allows use of smaller power path
components and minimizes the chance of damage to
the load in the event of a fault
n Only need to buy as many drivers as the design needs
while keeping only one controller in inventory
Features
n Compatible with “VRD10 Voltage Regulation
Specification” for Intel Pentium 4 and Prescott
Processors
™
n Supports Intel SpeedStep technology
(Geyserville-III ), which enables real-time dynamic
switching of the CPU core voltage and the CPU clock
frequency
n Uses external gate drivers (LM2724) for maximum
layout flexibility and noise immunity
™
n Fixed frequency PWM architecture
Applications
n Pin selectable internal or external voltage reference
n 0.5% core voltage set-point accuracy when using
external voltage reference
n 0.9% accurate internal bandgap reference
n 2-, 3- or 4-phase operation
n Out-of-phase switching reduces input ripple current,
thereby minimizing input capacitor requirements
n VID-code programmable output voltage range of
0.8375V through 1.6000V
n Server and desktop computer CPU core power supplies
requiring a 2, 3- or 4-phase voltage regulator delivering
up to 100A
n Transportable notebook computers using desktop CPUs
n Low cost transportable notebook computers using 2- or
3-phase designs
™
Pentium is a trademark of Intel Corporation.
© 2005 National Semiconductor Corporation
DS200834
www.national.com
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