LM5034EVAL/NOPB

User's Guide SNVA108A – February 2005 – Revised May 2013 AN-1370 LM5034 Evaluation Board 1 Introduction The LM5034EVAL evaluation board provides the power supply design engineer with a fully functional 200W dual interleaved DC-DC power switching regulator using forward/active clamp topology. A single LM5034 dual current mode PWM controller is employed to control the two converter channels. Jumpers on the board permit configuring the board as two independent regulators (3.3V and 2.5V outputs), or as a single high current regulator providing 3.3V. The two controller channels operate 180° out of phase thereby reducing input ripple current. Power dissipation in the primary side switches is minimized through the use of high speed, high current compound gate drivers in the LM5034 capable of sourcing 1.5A and sinking 2.5A. Power dissipation associated with the transformer reset is minimized through the use of active clamps. Synchronous rectifiers reduce rectification losses in the secondaries. Features of the LM5034 which can be investigated on this board include: • Switching frequency can be changed with a single resistor (R8) • Switching frequency can be synchronized to an external source • Dead time between main switches and active clamp switches can be adjusted (R7) • Maximum allowed duty cycle limit can be changed with a single resistor (R3) • Hiccup mode timing during extended overload conditions can be adjusted (C8) • Under-voltage lockout threshold can be adjusted (R4, R5) • Soft-start timing can be changed separately on each channel (C10, C11) Other features of the LM5034 include an integrated high voltage start-up regulator, cycle-by-cycle current limit, maximum duty cycle fold back at high input voltage, integrated slope compensation, direct interface with opto-coupler transistor, and thermal shutdown. The evaluation board’s specifications are as follows: • Input voltage: 36V to 78V • Output voltages: 3.3V, ±2.5% and 2.5V, ±1.5%, or a single 3.3V, ±2.5% high current output • Output current: 30A from each separate output, or 60A when configured for a single output • Measured efficiency: 94% (Vin = 48V, Iout = 20A, single 3.3V output) • Switching frequency: 200 kHz • Current limit: ≊31.5A at each output • Input voltage UVLO: ≊34.3V increasing, and ≊32.3V decreasing • On/Off (shutdown) input • Synchronizing input • Size: 3.4 x 2.4 x 0.48 in. All trademarks are the property of their respective owners. SNVA108A – February 2005 – Revised May 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated AN-1370 LM5034 Evaluation Board 1 Schematic 2 www.ti.com Schematic Referring to the schematic in Figure 14 , the circuit is comprised of the LM5034 dual controller, and two almost identical forward converter channels. Channel 2 is along the top half of the schematic providing the 3.3V output. Current sensing transformer T1 provides primary side current information to the LM5034’s CS2 pin for current mode PWM control, and for over-current detection. Q1 is the main switch for the power transformer (T3), and Q2 is the active clamp switch. Q5-Q8 are the self-driven synchronous rectifiers for the secondary. The output filter is made up of L2 and C28-C32. In addition, L2 has an auxiliary winding to power the LM5034’s VCC pin when this channel is enabled. Error amplifier U3, along with reference U5, provide the voltage feedback signal to the LM5034’s COMP2 pin via the opto-coupler. T2 J 8 OUT1 T4 E L3 36V to 78V INPUT B D U2 G A C F L2 OUT2 J 2 ON/OFF J 1 3.3V OUTPUT J 5 IN OR SINGLE 3.3V OUTPUT J 6 L1 2.5V OUTPUT LM503 4 EVALUATION J BOARD 7 J 3 SYNC IN J 4 T1 T3 P/N 551012359-001 REV B C2004 Figure 1. Evaluation Board - Top Side Q5 G G Q7 U3 J6 G J5 R22 J2 ON/OFF Q2 G Q1 OUT2 IN J1 Q6 G C17 R20 C50 Q8 U1 F G C G G R49 OUT1 C19 E A B U4 J4 IN Q4 R51 Q3 G Q12 G Q9 J8 C5 J7 J3 SYNC Q11 D G Q10 Figure 2. Evaluation Board - Bottom Side 3 Layout and Probing The pictorials in Figure 1 and Figure 2 show the placement of the significant components which may be probed in evaluating the circuit’s operation. The following should be kept in mind when the board is powered: 1. The board has two circuit grounds - one associated with the input power, and one associated with the output power. The ground plane on the primary side is shared by the two channels, as is the ground plane on the secondary side. The primary and secondary grounds are DC isolated, but are AC coupled by high voltage capacitors C5 and C50. 2. The power train components (L1, T3, T4, L2, L3, and Q1 - Q12) may get hot to the touch at high load currents. USE CAUTION. When operating either channel at a load current in excess of 15A, the use of 2 AN-1370 LM5034 Evaluation Board SNVA108A – February 2005 – Revised May 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated Output Configuration www.ti.com J8 a fan to provide forced air flow IS NECESSARY. 3. Use care when probing the primary side at maximum input voltage. 78V is enough to produce a shock or sparks, and cause component damage through accidental contact. 4. At maximum load current the size and length of the wires used to connect the load become important. Ensure there is not a significant drop in the wires. A minimum of 12 gauge wire is recommended for 30A. When configured for a single high current output, it is recommended that equal length 12 gauge wires be used from each output pin to the load. See Figure 3. 5. The input wires will carry up to 6A (average) at maximum load current. Ensure these wires are adequately sized. 36V to 78V INPUT J2 ON/OFF + J7 - + J1 - J5 IN 2.5V LOAD min. 12 gauge J6 LM5034 EVALUATION BOARD J3 SYNC IN J4 3.3V LOAD 36V to 78V INPUT J2 ON/OFF + - J6 LM5034 EVALUATION BOARD J3 SYNC IN J4 J7 J8 Independent Outputs 3.3V LOAD J5 IN J1 min. 12 gauge each Single, high current output Figure 3. Connecting the Load(s) 4 Output Configuration Prior to applying power, the jumpers must be set for the desired output configuration. The board is initially shipped with jumper A-B in place, which configures the board for independent outputs - i.e., 2.5V at OUT1 and 3.3V at OUT2. To configure the board for a single 3.3V high current output, it is necessary to remove jumper A-B, and install jumpers in locations B-C, D-E, and F-G. Output pins J6 and J8 must be connected together at the load, as well as output pins J5 and J7, as shown in Figure 3. See Figure 1 for the jumper locations. 5 Connections/Start-Up When operating at load currents in excess of 15A from either channel, forced air flow is NECESSARY. The input connections are made to terminals J1 (+) and J4 (-). The power source must be capable of supplying the input current as shown in Figure 8 or Figure 9. Upon turn-on, the input current increases with little or no overshoot, due to the LM5034’s soft-start function. When configured for separate outputs, the 3.3V load is connected to J6 (+) and J5 (-) and the 2.5V load is connected to J8 (+) and J7 (-). When configured for a single 3.3V high current output, output pins J6 and J8 (+) are connected together at the load, as are J5 and J7 (-). See Figure 3. A minimum of 12 gauge wire should be used for the 30A load currents. SNVA108A – February 2005 – Revised May 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated AN-1370 LM5034 Evaluation Board 3 Performance www.ti.com Before start-up a voltmeter should be connected to the input terminals, and to each output. The input current should be monitored with an ammeter or a current probe. It is recommended that the input voltage be increased gradually until the under-voltage lockout threshold (≊34.3V) is reached, at which time the outputs become active. At this point the meters should be checked immediately to ensure they indicate nominal values. 6 Performance When configured for separate outputs, the output impedance is