QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER LT1952-1 DESCRIPTION Demonstration circuit 1317A-G is isolated input to high current output 1/8th Brick footprint converter featuring the LT®1952 switching controller with Active Reset circuit. The Active Reset circuit can improve the efficiency in wide input voltage applications. Also, the Active Reset allows the implementation of self-driven synchronous secondary rectifiers in some applications. The DC1317A-G (Figure 7) converts isolated 9V to 36V input to 12V output and provides over 8A of output current depending on cooling. When determining the cooling requirements the actual input voltage range and continuous maximum output current must be taken into account. The converter operates at 200kHz with the peak efficiency greater than 94%. The DC1317 can be easily modified to generate output voltages in the range from 0.6V to 48V. The output currents are limited by total output power of up to 150W. The available versions of DC1317A are: DC1317A-F, 9-36Vin to 3.3V, 22A * DC1317A-F5, 9-36Vin to 5V, 20A DC1317A-G, 9-36Vin to 12V, 8A * DC1317A-G18, 9-36Vin to 18V, 5A DC1317A-H, 9-36Vin to 48V, 1.5A * The DC1317A-G18 is a slightly modified design featuring 18V @6A output. Please contact the LTC factory for details. The DC1317 circuit features soft-start which prevents output voltage overshoot on startup or when recovering from overload condition. The DC1317 has precise over-current protection circuit that allows for continuous operation under short circuit conditions. The low power dissipation under short circuit conditions insures high reliability even during short circuits. The LT1952 can be synchronized to an external clock of up to 400kHz. Please refer to LT1952 data sheet for design details and applications information. DC1317A-A, 34-75Vin to 3.3V, 35A DC1317A-B, 18-72Vin to 5V, 25A DC1317A-C, 18-72Vin to 12V, 8A-12A Design files for this circuit board are available. Call the LTC factory. DC1317A-D, 18-72Vin to 24V, 5A LT is a trademark of Linear Technology Corporation DC1317A-E, 36-72Vin to 5V, 12A Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage IOUT = 0A to 8A 9V Maximum Input Voltage IOUT = 0A to 8A 36V VOUT VIN = 9V to 36V, IOUT = 0A to 8A (27Amax) 12V ±3% Typical Output Ripple VOUT VIN = 9V to 36V, IOUT = 0A to 8A Nominal Switching Frequency 50mVP–P 200kHz 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER QUICK START PROCEDURE Demonstration circuit 1317 is easy to set up to evaluate the performance of LT1952-1 circuit. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE: When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2. for proper scope probe technique. 1. With power off, connect the input power supply to Vin and GND. Make sure that the input power supply has sufficient current rating at minimum input voltage for the required output load. 2. Turn on the power at the input. NOTE: Make sure that the input voltage does not exceed 36V. 3. Check for the proper output voltage. Vout = 12V. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 4. Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 5. The DC1317 is equipped with an output capacitor CSYS (220uF) that approximates typical system rail capacitance. If system board already has capacitance of similar value CSYS can be removed. Figure 1. Proper Measurement Equipment Setup 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER Figure 2. Scope Probe Placement for Measuring Input or Output Ripple ACTIVE RESET CIRCUIT Also the active reset circuit shapes the reset voltage into a square waveform that results in lower drain voltages for Q1 and Q2 MOSFETs. The lower MOSFET drain voltages allow lower voltage and lower Rdson MOSFETs to be used. The MOSFETs must be avalanche rated for the peak reset voltage. If non-avalanche rated MOSFETs are used a proper drain voltage derating should be used. The main benefit of active reset circuit in the case of DC1317A-G demo board is high efficiency (shown in Figure 3), wide input range, high power density and small size. To achieve such high efficiency all of the power components were carefully selected. Please consult LT factory for assistance if any changes to the circuit are required. If PCB space is limited, a smaller 1825R2-3366.006 transformer from Champs engineering can be used. However, the efficiency will be about 1% lower. For more information please consult LT factory. DC1317A-G 12V Output Efficiency 95% 94% Efficiency The Active Reset circuit on DC1317A-F demo board consists of a small P-Channel MOSFET Q13 and reset capacitor C25. The MOSFET Q13 is used to connect the reset capacitor across the transformer T1 primary winding during the reset period when Q1 MOSFET is off. The voltage across capacitor C25 automatically adjusts with the duty cycle to provide complete transformer reset under all operating conditions. 93% 92% 12V input 91% 24V input 90% 89% 0 1 2 3 4 5 6 7 8 9 Iout [A] Figure 3. High efficiency of DC1317A-G allows the board to be used in thermally critical applications 18V OUTPUT CIRCUIT The DC1317A-G demo board can easily be modified for 18V output. Only few minor component changes are required and are shown in the schematic in Figure 8. The efficiency of 18V Output version of DC1317A-G is shown in the Figure 4. The efficiency is slightly lower than the efficiency of 12V version due to higher DC resistance of transformer and output MOSFETs. Also, the 18V output can be further increased to 19.5V just by changing the voltage divider on the FB pin of LT4430 circuit. The 19.5V version is suitable for supplying laptop computer power from 12V automotive power source. 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER DC1317A-G-18V 18V Output Efficiency, 95% Efficiency 94% 93% 92% 12V input 91% 24V input 90% 89% 0 1 2 3 4 5 6 7 8 Iout [A] Figure 4. The efficiency of modified DC1317A-G demo board for 18V output. OUTPUT LOAD STEP RESPONSE The load step response of DC1317A-G is very fast even though relatively small amount of output capacitance is present (200uF ceramic and 220uF electrolytic). This is thanks to fast error amplifier of LT4430, optimal amount of current slope compensation of LT1952, fast opto coupler and fast error amplifier of LT1952. If higher load steps need to be handled more output capacitance can be added in order to keep the voltage transients at the desired level. The load step transients are shown in Figure 5. Figure 5. Fast transient response of DC1317A-F is superior to many competing power modules without the additional output capacitors. SOFT START FUNCTION The DC1317 features LT4430 opto coupler driver that has soft start function which produces monotonic startup ramp shown if Figure 6. The rise time of output voltage is controlled by capacitor C19 that is connected to OC (Overshoot Control) pin of LT4430. Also, the soft-start function will prevent input current surges even with full load at the output. Figure 6. The LT4430 opto coupler driver produces monotonic output voltage rise at startup without output voltage overshoot. DEBUGGING AND TESTING The DC1317 can easily be tested and debugged by powering the bias circuit separately from the main power circuit. To place DC1317 into debug mode 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER remove the resistor R1 and connect 12V, 100mA power source to +Vb node (right side of R1). By doing this, the primary PWM controller LT1952 can be activated without the main primary power being applied to +Vin. To activate the secondary side control circuit LT4430 diode OR a 5V, 100mA power source into pin 1 of LT4430 controller. If possible use solid ground planes on layers 2 and n-1. The ground planes will prevent the switching noise from coupling into sensitive lines. Place sensitive lines on the inner layers that will be shielded by grounds on layers 2 and n-1. Keep the loop formed by Q1, RCS1, Cin and T1 tight. Keep the loop formed by Q2, Q3 and T1 tight. Once the primary and secondary controllers are running the main power (+Vin) can be applied slowly while observing the switching waveforms and output voltage. Keep noise sensitive nodes like SD/VSEC, ROSC, FB, COMP, ISENSE, BLANK and DELAY as small as posible by placing the associated components close to the LT1952 and LT4430 chips. The input current supplying the power transformer T1 should not exceeded 200mA without the output load. If one of the MOSFETs is damaged, the input current will exceed 200mA. Use local vias for all components that connect to ground planes. PCB LAYOUT The PCB layout should be carefully planned to avoid potential noise problems. The PCB layout for DC1317A can be used as a guide. Since demo board DC1317A has 8 versions the PCB layout has optional components that can be removed. The schematic in figure 7 is showing the circuit without any optional components. Also, the circuit in figure 7 does not show any zero-ohm resistors. Please consult the schematic on page 7 to determine if any of the options should be included in your PCB layout. Do not place any traces on the layers 2 and n-1 to avoid ground planes from being compromised. If the PCB layout has to be done on 2 or 4-layer PCB try to stay close to the guidelines outlined above. Also, maximize the ground connections between components by placing the components tight together. Please contact LT factory for additional assistance. Also, the PCB layout has a common schematic that is used just for the layout. The PCB layout schematic is not included in this quick start guide but it is included with PCB design files. Please note that the actual circuit schematic on page 7 shows the component values. The PCB layout schematic included with design files does not show the component values. In some cases, a different component like a diode is used in a place holder for a capacitor such as in the case of C6. Please modify the reference designators in your schematic to reflect the actual component used. The following simple PCB layout rules should be helpful. 5 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER 1 2.2R 9-36V Input Q10 PBSS8110 Cin 3x6.8uF R11 10k -Vin D3 +Vr2 6 3 R3 665R R14 33K 1 2 R15 178k 3 4 C13 .47u 5 C10 0.1u 6 R22 7 13.3k 8 Comp R28 115k R32 196k +Vr2 TG Inp TS FB=1.23V Vin Rosc Out Sync MaxDC PGND Delay Vr=2.5V OC SD Isense GND Blank R2 560k 6 Q1 HAT2266 5 4 D17 BAS516 16 C33 0.1u Vu1 15 D10* 100p 14 C8 100p R10 1k D14 BAS516 11 10 R23 910R R24 100k 1 CS+ 2 R21 10k 4 D9 PDZ10B Sync CS- Timer 3 CG U5 LTC3900 CG GND Vcc FG 60.4k U4 LT4430 U6 PS2801-1 R26 220R 1 Vu1 2 Vfb R30 1.2k C15 2.2nF, 2kV C19 1uF 3 6 5 T2A PE-68386 470p R27 470R Opto GND Comp FB C17 15n 6 5 4 R34 12.1k R35 348k +Vo1 R38 18.2K NOTE: This schematic shows only the components required for operation of -G version of DC1317A demo board. All optional components of DC1317A demo board have been removed. Also, all zero-ohm resistors have been replaced with wires. Please consult the full DC1317A-G schematic to decide if any of the optional components should be included in your design. 7 C12 Vcc SS 8 L4 10uH R17 560R FG R19 D11 BAS516 C23 1uF 9 R18 10k C7 220p C14 1u Cu1 4.7u R20 100k R16 33k Q9 BCX55 13 12 D7 BAS521 C5 0.22u R45 10k GND Out C6* BAS521 C34 0.33u + CG L3 680uH Q13 Si7309 R53* 10uH Q3 HAT2173 FG R54 2.2R Rcs1 0.005R D1 BAS516 Sout R29* PMEG3002 +Vb GND U1 LT1952-1 Vfb Q12 BC856T Boost Q2 HAT2266 2, 3 4, 5 33n 2 C21 220p R13 22K Vcc 10, 11 G45R2-0306.006 C25 1 C3 1u L1 T1 U2 LTC4440-5 Vu1 +Vout D2 BAS516 L2 D5 PDZ10B 1.5mH +Vin Figure 7. DC1317A-G schematic. HR-PQA2050-16 +Vo1 7, 8 220uF, APXE Vu1 Csys +Vb R1 Co1 33uF, X7R +Vin +Vin Demo Board DC1317A-G schematic * Please change the ref designator to reflect the symbol. 6 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER +Vb R1 Vu1 1 2.2R 9-36V Input Q10 PBSS8110 Cin 3x6.8uF R11 10k -Vin 3 R3 511R 1 Vfb 2 R15 178k 3 4 C13 .47u 5 6 C10 0.1u R22 7 13.3k 8 Comp R28 115k R32 196k +Vr2 GND TG Inp TS 6 FB=1.23V Vin Rosc Out Sync PGND MaxDC Delay Vr=2.5V OC SD Isense GND Blank 6 Q1 RJK0652 2, 3 5 4 BAS516 16 Vu1 15 C8 100p D14 BAS516 Cu1 4.7u R20 100k 11 10 R23 910R NOTE: R24 100k 1 4 D9 PDZ10B Sync CS- Timer 3 CG CG GND Vcc FG 60.4k U4 LT4430 U6 PS2801-1 R26 220R 1 Vu1 2 Vfb R30 1.2k C15 2.2nF, 2kV C19 1uF 3 7 6 5 T2A PE-68386 C12 470p R27 470R Vcc Opto GND Comp SS 8 L4 10uH R17 560R FG R19 FB C17 15n 6 5 4 R34 12.1k R35 348k +Vo1 R38 11K This schematic shows the required modifications of DC1317A-G for 18V @6A output. The component values and part numbers shown in RED are the only changes required for 18V output. Please contact LT factory for assistance. R2 560k CS+ 2 R21 10k U5 LTC3900 D11 BAS516 C23 1uF 9 R18 10k C7 220p C14 1u 13 12 R16 33k Q9 BCX55 R10 1k GND Out C5 0.22u R45 10k Csys 150uF, 20V, APXE + D7 BAS521 C6* BAS521 C34 0.33u 18V Output CG L3 1.5mH Q13 Si7309 C33 0.1u Q3 RJK2055 FG R54 2.2R R53* 10uH D10* 100p Q2 HAT2266 4, 5 D17 14 10, 11 G45R2-0207.005 Rcs1 0.005R D1 BAS516 Sout R29* PMEG3002 +Vb Boost U1 LT1952-1 R14 33K +Vr2 C25 2 C21 220p Q12 BC856T Vcc L1 T1 33n 1 C3 1u R13 22K D3 U2 LTC4440-5 Vu1 +Vout D2 BAS516 L2 D5 PDZ10B 1.5mH +Vin Figure 8. The 18V @6A version of DC1317A-G. HR-PQA2050-27 +Vo1 7, 8 Co1 33uF, X7R +Vin +Vin Demo Board DC1317A-G18V schematic * Please change the ref designator to reflect the symbol. 7 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER 8 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER 9