1
www.semtech.com
POWER MANAGEMENT
SC2643VX
Multi-Platform
Multi-Phase PWM Controller
September 16, 2003
Description
Applications
The SC2643VX provides microprocessor core voltage
regulation solution up to 4 paralleled PWM channels. The
solution can also be configured as 2, 3, or 4-phase form.
Multi-phase buck regulator utilizes the phase-shift tim-
ing control to allow interleaved switching of the power
switches. This architecture minimizes the core voltage
ripple and the input current ripple, which leads to opti-
mized voltage regulator design for power density, tran-
sient responses, and the thermal performances.
To satisfy the highly dynamic nature of the modern
microprocessors, the SC2643VX adopts peak current
mode control topology which ensures wide control loop
bandwidth and fast transient responses. The current
mode control provides intrinsic phase current matching.
The maximum ripple frequency is greater than 2.8MHz.
One of the outstanding features of the SC2643VX is its
voltage regulation accuracy. Not only it provides better
than 0.5% set point accuracy, but also the accuracy to
fully complaint with the stringent load line slope
specifications mandated by the modern microprocessors.
Lossless output current sensing ensures the regulator
output voltage is accurately positioned according to the
load current condition, and an internal temperature
compensation technology further enhances the perfor-
mance of voltage accuracy.
The patented Combi-Sense
TM
topology is employed by
SC2643VX. The MOSFET R
ds(on)
and the output inductor
winding resistance are used to generate the phase cur-
rent information. The Combi-Sense
TM
MOSFET driver plus
the SC2643VX enables the complete solution.
The SC2643VX is a multi-platform controller. It conforms
to Intel VRM/VRD10.X, VRM9.X, and AMD K-8 (Opteron
TM
)
VID specifications. With very minor changes of the sche-
matic and the layout, the SC2643VX based solution can
be ported form one platform to another. This greatly
benefits the system manufactures for reductions of de-
sign cycle and minimize the inventory management.
VRD/VRM10.X, VRM9.X, and K-8 compliant
Core Voltage Set Point Accuracy 0.5%
Combi-Sense
TM
Current Mode Control
Intrinsic Phase Current Matching
Fast Transient Responses
Active Droop with Temperature Compensation to
Meet Load Line Slope
Support VID-on-Fly with 5 or 6 bit VID
Enable Function for Power Sequencing
Cycle-by-Cycle Peak Current Limit
Intelligent Over Current Shut Down
Over Voltage Protection When Using Semtech
Combi-Sense
TM
Driver
Under Voltage Protection Built in
External programmable Soft-Start
Externally programmable switching frequency (up to
2.8MHz output voltage ripple frequency)
2, 3, or 4-Phase Configurations
24-Pin SOIC or TSSOP Packages
Voltage Regulator VRD/VRM10.X
Voltage Regulator VRM9.X
Voltage Regulator K-8
High Current, Low Voltage Step Down DC/DC
Converters
Features
The SC2643VX supports VID-on-Fly applications for any
platform. The cycle-by-cycle current limit plus the intelli-
gent over current shut down provide the maximum ver-
satility of the system without false tripping under all pos-
sible changes of VID and load conditions. The differen-
tial voltage feedback sense eliminates the error caused
by high load current on the ground plane. External offset
is easy to achieve for any platforms and the VID settings.
The enable function is also provided to interface with
the corresponding system signal for correct start up tim-
ing and shut down timing.
(Multiple Patents Pending)
(Multiple Patents Pending)
(Multiple Patents Pending)
(Multiple Patents Pending)
(Multiple Patents Pending)
3
2003 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC2643VX
Absolute Maximum Ratings
Electrical Characteristics
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied. Unless otherwise specified, all other voltages are referenced to AGND.
Unless specified: V
CC
= 12V, VID=1.30V (110110,VRD10) or 1.50V (101110,VRD10), F
OSC
= 600kHz, T
A
= 27
o
C. See Typical Application Circuit.
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NOTES: 1)Guaranteed by design, not tested in production.
Specifications subject to change without notice.
4
2003 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC2643VX
Electrical Characteristics (Cont.)
Unless specified: V
CC
= 12V, VID=1.30V (110110,VRD10) or 1.50V (101110,VRD10), F
OSC
= 600kHz, T
A
= 27
o
C. See Typical Application Circuit.
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NOTES: 1)Guaranteed by design, not tested in production.
Specifications subject to change without notice.
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