Texas Instruments UCC2891 Benutzerhandbuch
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Introduction
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Description
User's Guide
SLUU178A – November 2003 – Revised December 2006
Using the UCC2891 Active Clamp Current Mode PWM
Controller
The UCC2891EVM evaluation module (EVM) is a forward converter providing a 3.3-V regulated output at
30 A of load current, operating from a 48-V input. The EVM operates over the full 36 V to 72 V telecom
input range, and is able to fully regulate down to zero load current. The module uses the UCC2891 current
mode active clamp PWM controller for effectively demonstrating the active clamp transformer reset
technique.
30 A of load current, operating from a 48-V input. The EVM operates over the full 36 V to 72 V telecom
input range, and is able to fully regulate down to zero load current. The module uses the UCC2891 current
mode active clamp PWM controller for effectively demonstrating the active clamp transformer reset
technique.
Benefits of the active clamp include a control driven transformer reset scheme allowing zero voltage
switching (ZVS) to increase overall efficiency, lower drain-to-source voltage stress, extended duty cycle
beyond 50% and reduced electromagnetic radiated emissions. Combined with synchronous rectification,
this EVM is configured to operate at 300 kHz and exhibits a peak efficiency of just over 92%, with a full
load efficiency of 89%. The EVM displays many features that might be typical of a more complex design,
yet its compact board layout and low component count make it elegantly simple.
switching (ZVS) to increase overall efficiency, lower drain-to-source voltage stress, extended duty cycle
beyond 50% and reduced electromagnetic radiated emissions. Combined with synchronous rectification,
this EVM is configured to operate at 300 kHz and exhibits a peak efficiency of just over 92%, with a full
load efficiency of 89%. The EVM displays many features that might be typical of a more complex design,
yet its compact board layout and low component count make it elegantly simple.
The UCC2891 controller family provides advanced active clamp control features such as programmable
maximum duty cycle clamp, programmable dead time between the two primary switches and the ability to
drive either a P-channel, or N-channel MOSFET in either a high-side or low-side active clamp
configuration. The UCC2891 also allows the ability to start-up directly from the 48-V telecom bus voltage,
eliminating the need for external start-up circuitry. It includes programmable soft start, internal slope
compensation for peak current mode control, internal low-line voltage sensing, internal syncronizable clock
input, cycle-by-cycle current limiting, and a robust 2-A sink/source TrueDrive™ internal gate drive circuit.
The result is a highly efficient design loaded with features, requiring very few external components.
maximum duty cycle clamp, programmable dead time between the two primary switches and the ability to
drive either a P-channel, or N-channel MOSFET in either a high-side or low-side active clamp
configuration. The UCC2891 also allows the ability to start-up directly from the 48-V telecom bus voltage,
eliminating the need for external start-up circuitry. It includes programmable soft start, internal slope
compensation for peak current mode control, internal low-line voltage sensing, internal syncronizable clock
input, cycle-by-cycle current limiting, and a robust 2-A sink/source TrueDrive™ internal gate drive circuit.
The result is a highly efficient design loaded with features, requiring very few external components.
The TrueDrive™ hybrid output architecture used in the UCC2891 uses TI's unique TrueDrive™
Bipolar/CMOS output. To the user, this simply means ultra-fast rise and fall times by providing the highest
possible drive current where it is needed most, at the MOSFET Miller plateau region.
Bipolar/CMOS output. To the user, this simply means ultra-fast rise and fall times by providing the highest
possible drive current where it is needed most, at the MOSFET Miller plateau region.
The UCC2891/2/3/4 is available in either a 16-pin SOIC or 16-pin TSSOP package for applications where
absolute minimal board space is required.
absolute minimal board space is required.
The UCC2891EVM highlights the many benefits of using the UCC2891 active clamp current mode PWM
controller. This user's guide provides the schematic, component list, assembly drawing, artwork and test
set up necessary to evaluate the UCC2891 in a typical telecom application. More detailed design
information can be found listed in the References section.
controller. This user's guide provides the schematic, component list, assembly drawing, artwork and test
set up necessary to evaluate the UCC2891 in a typical telecom application. More detailed design
information can be found listed in the References section.
SLUU178A – November 2003 – Revised December 2006
Using the UCC2891 Active Clamp Current Mode PWM Controller
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