UCC2891EVM-520

Using the UCC2891 Active-Clamp Current-Mode PWM Controller User's Guide Literature Number: SLUU407A June 2010 – Revised May 2013 User's Guide SLUU407A – June 2010 – Revised May 2013 48-V to 3.3-V Forward Converter With Active-Clamp Reset Using the UCC2891 ActiveClamp Current-Mode PWM Controller 1 Introduction The UCC2891EVM-520 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 75-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 90%. The EVM displays many features that might be typical of a more complex design, yet the compact board layout and low component count make it elegantly simple. This EVM features active-current limiting on the output. Because the unit continues to operate into a short circuit or overload condition the operator must shut the unit off before the thermal limitations of the components are exceeded. 2 Description 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. The EVM 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 BipolarCMOS output. To the user, TrueDrive 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. The UCC2891EVM-520 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 setup necessary to evaluate the UCC2891 in a typical telecom application. More detailed design information is listed in the Section 10 section. 2 48-V to 3.3-V Forward Converter With Active-Clamp Reset Using the UCC2891 Active-Clamp Current-Mode PWM Controller Copyright © 2010–2013, Texas Instruments Incorporated SLUU407A – June 2010 – Revised May 2013 Submit Documentation Feedback Description www.ti.com 2.1 Applications The UCC2891 is suited for use in isolated telecom 48-V input systems requiring high-efficiency and highpower density for very low-output voltage, high-current converter applications, including: • Server Systems • Datacom • Telecom • DSP's, ASIC's, FPGA's 2.2 Features The UCC2891EVM-520 features include: • ZVS transformer reset using active-clamp technique in forward converter • All surface mount components, double-sided half-brick (2.2 × 2.28 × 0.5) inches • Complementary auxiliary drive for active clamp with programmable dead time for ZVS • Current-mode control with synchronization function • Internal PWM-slope compensation • Start up directly from telecom input voltage • Synchronous rectifier-output stage allows high-efficiency operation • Programmable soft-start • Up to 30-A dc-output current • Regulation to zero-load current • Non-latching output-current limiting • Non-latching input-undervoltage protection • 1500-V isolation primary to secondary SLUU407A – June 2010 – Revised May 2013 Submit Documentation Feedback 48-V to 3.3-V Forward Converter With Active-Clamp Reset Using the UCC2891 Active-Clamp Current-Mode PWM Controller Copyright © 2010–2013, Texas Instruments Incorporated 3 UCC2891EVM-520 Electrical Performance Specifications 3 www.ti.com UCC2891EVM-520 Electrical Performance Specifications The UCC2891EVM-520 electrical performance specifications are listed in Table 1. Table 1. UCC2891EVM-520 Performance Summary PARAMETER TEST CONDITIONS MIN TYP MAX UNITS Input Characteristics Input voltage range 36 48 75 V mA No load input current VIN = 36 V, IOUT = 0 A 75 100 Maximum input current VIN = 36 V, IOUT = 30 A 3.00 3.25 A Input voltage ripple VIN = 75 V, IOUT = 30 A 1.50 1.75 VP-P 3.30 3.35 V Input voltage ripple Output voltage 36 V ≤ VIN ≤ 75 V, 0 A ≤ IOUT ≤ 30 A Output voltage regulation Line regulation (36 V ≤ VIN ≤ 75 V, IOUT = 0 A) ±0.30% Load regulation (0 A ≤ IOUT ≤ 30 A, VIN = 48 V) 0.050% Output voltage ripple VIN = 48 V, IOUT = 30 A Output load current VIN = 48 V, IOUT = 30 A Output current limit 36 V ≤ VIN ≤ 72 V 3.25 30 40 0 30 32