2, 3 or 4 Phase
Combi-Sense
TM
PWM Controller
POWER MANAGEMENT
Description
The SC2646B controller provides a microprocessor core
voltage regulation solution for up to 4 paralleled PWM
channels. The solution can be configured in 2, 3, or 4-
phase form. This multi-phase buck regulator utilizes
phase-shift timing control to allow interleaved switching of
the power switches. The product鈥檚 architecture minimizes
the core voltage ripple and the input current ripple, which
leads to optimized voltage regulator design for power den-
sity, transient responses, and thermal performances.
To satisfy the highly dynamic nature of the modern micro-
processors, the SC2646B adopts peak current mode con-
trol 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 2MHz.
One of the outstanding features of the SC2646B device is
its voltage regulation accuracy. Not only does it provide
0.5% set point accuracy, but also the accuracy to be fully
compliant with stringent load line slope specifications man-
dated by the modern microprocessors. Lossless output
current sensing ensures the regulator output voltage is
accurately positioned according to the load current condi-
tion.
Semtech鈥檚 patented Combi-Sense
TM
topology is employed
by SC2646B controller. The MOSFET R
ds(on)
and the output
inductor winding resistance is used to generate the phase
current information. Semtech鈥檚 SC1211 Combi-Sense
TM
MOSFET driver works with the SC2646B to enable a com-
plete solution.
The cycle-by-cycle current limit plus the intelligent over cur-
rent shut down provide the maximum versatility of the sys-
tem without false tripping under all possible changes of
VID and load conditions. The differential voltage feed-
back sense eliminates the error caused by high load cur-
rent on the ground plane. External offset is easy to achieve
for the VID settings. The enable function is also provided
to interface with the corresponding system signal for cor-
rect start up timing and shut down timing.
SC2646B
Features
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VRD/VRM10.X compliant
Core Voltage Set Point Accuracy 0.5%
Combi-Sense
TM
Current Mode Control
Intrinsic Phase Current Matching
Fast Transient Responses
Active Droop to Meet Load Line Slope
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 SC1211
Under Voltage Protection Built in
Externally Programmable Soft-Start
Externally Programmable Switching Frequency
2, 3, or 4-Phase Configurations
24-Pin TSSOP Package
Combi-Sense
TM
is a Trademark of Semtech Corporation
Applications
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Voltage Regulator VRD/VRM10.X
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Voltage Regulation Modules
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High Current, Low Voltage Step Down DC/DC
Converters
Revision: Sept. 12, 2005
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