LM5642EVAL-KIT

User's Guide SNVA070B – May 2004 – Revised April 2013 AN-1292 LM5642 Evaluation Board 1 Introduction The LM5642 IC is a dual channel, current-mode, synchronous buck converter controller. It can handle input voltages of up to 36V and delivers two independent output voltages from 1.23V up to 90% of the input voltage. Current sensing can be done using a dedicated resistor or using the RDS(ON) of the high-side FET. This application note describes the dedicated evaluation PCBs that are available for both methods. 2 Resistor Sense PCB The first, more common method of sensing current in current-mode controllers is with an external sense resistor, placed in series with the high-side FET of each channel. Sense resistors provide an accurate voltage as the load current passes through them, and have stable, linear resistance change with temperature. As shipped the Resistor Sense PCB is designed to deliver 1.8V on Channel 1 at a maximum current of 7A, and 3.3V on Channel 2 at a maximum current of 4A. The input voltage can vary anywhere from 5.5 to 36V. The board has been designed to be flexible and allow many other circuit configurations by replacing the original components with user selected ones. Figure 1 shows the circuit diagram representing the standard BOM that comes with the PCB. Table 1 lists all the components that are used for this standard configuration BOM. Figure 2 shows the complete circuit diagram with all extra footprints. Two SPST switches, S1 and S2, are provided to turn the two channels of the converter on and off. The standard BOM that comes with the LM5642 Resistor Sense evaluation board uses 10mΩ current sense resistors (R7 for Channel 1 and R15 for Channel 2) to provide independent feedback signals to the IC. The board provides additional resistor and capacitor footprints for noise filtering, ringing control, and to enable operation at low input voltages. 3 Current Sense Filters R-C filters have been added to the current sense amplifier inputs of the Resistor Sense evaluation board, comprised of components C3, C4, C14, C15, R2, R6, and R16. These resistors and capacitors reduce the sensitivity to switching noise, especially during high currents, load-transients, and circuits with short ontimes. 4 Parallel Operation The two channels of the LM5642 Resistor Sense evaluation board can be paralleled to provide one high current rail. At the nominal switching frequency of 200kHz the converter will run 180° out-of-phase. Care must be taken when using this feature combined with the frequency synchronization, as the two channels of the converter are no longer 180° out-of-phase when the frequency is above or below 200kHz. The two feedback inputs FB1 and FB2 should be tied together by soldering a 0Ω resistor in the position marked J1 on the bottom side of the PCB. The two COMP pins should be tied together by soldering a 0Ω resistor in the position J3. The ON/SS1 and ON/SS2 pins must also be connected using a 0Ω resistor in the position J2. One of the two SPDT switches S1 and S2 should be left ‘ON’ and the other used to turn the converter off and on. Finally, the two outputs VO1 and VO2 must be tied together by the user, external to the PCB. Only one of the two resistor divider networks (R10/R11 or R19/R20) and only one of the compensation networks should be used (C18/C19/R22/R23 or C20/C21R24/R25). All trademarks are the property of their respective owners. SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1292 LM5642 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 1 VDS Sense PCB 5 www.ti.com VDS Sense PCB The LM5642 IC offers a second current sensing mechanism that uses the RDS(ON) of the high-side FET to sense the load current. This method reduces the parts count on the BOM, however the RDS(ON) of a FET is not as tightly controlled as a sense resistor, and suffers from non-linear changes in resistance with temperature. As a result, the IC is more sensitive to noise in this mode, especially at input voltages above 30V. The maximum recommended current using VDS sensing is 5A per channel. The VDS Sense board has been designed to deliver 1.8V on Channel 1 with a maximum current of 5A, and 3.3V on Channel 2 with a maximum current of 4A. Figure 3 shows the circuit diagram representing the standard BOM that comes with the PCB. Table 2 lists all the components that are used for this standard configuration BOM. Figure 4 shows the complete circuit diagram with all extra footprints. 6 Frequency Synchronization A connection point labeled ‘SYNC’ is available on both versions of the LM5642 evaluation boards in order to adjust the switching frequency of the IC between 150 and 250kHz. Both CMOS and TTL level square wave signals can be used. The SYNC input has a minimum low-to-high transition threshold of 2.0V and a maximum high-to-low threshold of 0.8V. The SYNC pin is grounded by a 220kΩ pull-down resistor. 7 Low Input Voltage Operation When the input voltage is between 4.5V and 5.5 on either evaluation board, a 4.7Ω resistor should be installed in position R26. This will ensure than VLIN5 does not fall below the UVLO threshold of the IC. When R26 is in place the input voltage must not exceed 5.5V. 8 Gate Drive Current Limiting The LM25642 IC includes powerful gate drivers which can drive small FETs at high speed, often inducing noise or ringing into the board. Slowing the gate drivers can help reduce this noise by increasing the drain current transition time. While slowing the gate drives can help suppress noise, it also increases switching losses and gate-charge losses in the top FET. Slowing of the gate drives can be accomplished with resistors in series with the CBOOT1 and CBOOT2 pins. (R9,R18) Placing resistors in series with the CBOOT pins will slow the top FET rise time only. Generally the values for gate drive limiting resistors are between 1 and 5Ω. R9 and R18 are 0Ω by default. 9 Parallel Low-Side Schottky Diode The LM5642 evaluation boards include footprints for Schottky diodes D4 and D5 (SMB footprint or smaller) in parallel to the low side FETs. Placing these diodes on the PCB can improve efficiency because Schottky diodes have a lower forward voltage drop and lower reverse recovery charge than the parasitic diode of the bottom FET. 10 Parallel Low-Side FET Footprints Q3 and Q6 have been placed on both boards so that two SO-8 N-FETs can be placed in parallel for the low-side of each channel. Paralleling FETs reduces the RDS(ON) of the system and spreads the heat dissipated by the load current over two packages. This is especially important for converters with high input voltage and low output voltage, where the low duty cycle forces the low side FET or FETs to carry the load current for a much greater percentage than the high-side FET. 11 Additional Footprints Additional footprints are provided to add more surface mount or through-hole capacitors (with 3.5 or 5mm lead spacing) in parallel to the input and output capacitors. 2 AN-1292 LM5642 Evaluation Board SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Additional Footprints www.ti.com C2 10 nF VIN 22 C1 VIN ILIM1 KS1 1 PF RSNS1 6 C34 UV_DELAY 100 nF HDRV1 CBOOT1 SYNC 5 SYNC SW1 R28 220 k: 9 S1 C11 ON/SS1 LDRV1 PGND 10 nF FB1 10 S2 C12 24 VDD 19 R27 7 4.7 : C27 C26 1 PF 4.7 PF 3 C19 8.2 nF C20 R23 8.45 k: R24 12 VDD1 ILIM2 KS2 VDD2 RSNS2 C4 100 pF R6 26 25 27 C7 COMP1 COMP2 HDRV2 CBOOT2 SW2 LDRV2 SGND FB2 VIN R2 100 : 12 k: Q1 100 : D3A BAT54A VDD R7 C29 10 m: 1 PF 50V L1 100 nF 23 R10 R11 2.26 k: C13 10 nF C14 100 pF R13 C16 100 pF 17 18 16 C25 20 11 C9 330 PF 6.3V 10 m: VIN R14 100 : 6.8 k: 14 15 + 4.99 k: 4 13 10 PF 50V 2.8Arms Vo1 = 1.8V, 7A 4.2 P+ 7 m: Si4840DY 21 C6 Si4850EY Q2 VLIN5 15 nF 13.7 k: 8 28 ON/SS2 10 nF R1 2 1 C3 100 pF R16 Q4 100 : D3B BAT54A VDD 100 nF Q5 Si4840DY R15 C31 10 m: 1 PF 50V C6 10 PF 50V 2.8Arms Si4850EY L2 Vo2 = 3.3V, 4A 10 PH 12 m: R19 R20 2.26 k: + C23 330 PF 6.3V 10 m: 4.99 k: Figure 1. Standard Resistor Sense Circuit SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1292 LM5642 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 3 Additional Footprints www.ti.com Table 1. Standard Resistor Sense Bill of Materials 4 ID Part Number Type Size U1 LM5642 Dual Synchronous Controller TSSOP-28 Q1, Q4 Si4850EY N-MOSFET SO-8 Q2, Q5 Si4840DY N-MOSFET D3 BAT54A Schottky Diode L1 RLF12560T4R2N100 L2 Parameters Qty Vendor 1 Texas Instruments 60V 2 Vishay SO-8 40V 2 Vishay SOT-23 30V 1 ON Inductor 12.5 x 12.5 x 6mm 4.2µH, 7mΩ, 10A 1 TDK RLF12545T100M5R1 Inductor 12.5 x 12.5 x 4.5mm 10µH, 12mΩ, 5.1A 1 TDK C1, C29, C31 C3216X7R1H105K Capacitor 1206 1µF, 50V 3 TDK C3, C4, C14, C15 VJ1206Y101KXXAT Capacitor 1206 100pF, 25V 3 Vishay C27 C2012X5R1C105K Capacitor 0805 1µF, 16V 1 TDK C6, C16 C5750X5R1H106M Capacitor 2220 10µF, 50V, 2.8A 2 TDK C9, C23 6TPD330M Capacitor 7.3 x 4.3 x 3.8mm 330µF, 6.3V, 10mΩ 2 Sanyo C2, C11, C12, C13 VJ1206Y103KXXAT Capacitor 1206 10nF, 25V 4 Vishay C7, C25, C34 VJ1206Y104KXXAT Capacitor 1206 100nF, 25V 3 Vishay C19 VJ1206Y822KXXAT Capacitor 1206 8.2nF, 10% 1 Vishay C20 VJ1206Y153KXXAT Capacitor 1206 15nF, 10% 1 Vishay C26 C3216X7R1C475K Capacitor 1206 4.7µF, 25V 1 TDK R1 CRCW1206123J Resistor 1206 12kΩ, 5% 1 Vishay R2, R6, R14, R16 CRCW1206100J Resistor 1206 100Ω, 5% 1 Vishay R13 CRCW1206682J Resistor 1206 6.8kΩ, 12% 1 Vishay R7, R15 WSL-2512 .010 1% Resistor 2512 10mΩ, 1W 2 Vishay R18, R9 CRCW1206000Z Resistor 1206 0Ω 2 Vishay R10 CRCW12062261F Resistor 1206 2.26kΩ, 1% 1 Vishay R23 CRCW12068451F Resistor 1206 8.45kΩ, 1% 1 Vishay R24 CRCW12061372F Resistor 1206 13.7kΩ, 1% 1 Vishay R11, R20 CRCW12064991F Resistor 1206 4.99kΩ, 1% 2 Vishay R19 CRCW12068251F Resistor 1206 8.25kΩ, 1% 1 Vishay R27 CRCW12064R7J Resistor 1206 4.7Ω, 5% 1 Vishay R28 CRCW1206224J Resistor 1206 220kΩ, 5% 1 Vishay AN-1292 LM5642 Evaluation Board SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Additional Footprints www.ti.com VIN + C6 + C16 + C28 + C30 C1 C2 C3 VIN 22 6 VLIN5 UV-DLY C34 VIN ILIM1 KS1 RSNS1 R1 2 R2 1 R7 C29 R6 28 C4 5 SYNC R28 SYNC/PGOOD HDRV1 9 ON/SS1 SW1 CBOOT1 10 ON/SS2 C12 S2 LDRV1 FB1 3 25 C8 + C10 Q2 and Q3 21 4 C14 VIN ILIM2 KS2 RSNS2 R13 13 R14 14 R15 C31 R16 15 C15 VIN J1 17 R26 12 HDRV2 COMP2 SW2 7 VDD L2 16 C25 VLIN5 CBOOT2 24 19 18 LDRV2 R19 VDD C22 + C23 + C24 D5 20 R20 Q5 and Q6 C27 8 R18 VDD1 VDD2 Vo2 Q4 C21 C26 C9 R11 C13 R23 R27 + D4 23 C19 R25 R10 VDD R9 COMP1 J3 R24 L1 27 D3A PGND C20 Vo1 C7 J2 R22 Q1 C11 S1 C18 26 SGND FB2 11 Figure 2. Complete Resistor Sense Evaluation Board Schematic SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1292 LM5642 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 5 Additional Footprints www.ti.com C2 10 nF VIN 22 C1 VIN ILIM1 KS1 1 PF HDRV1 6 C34 UV_DELAY 100 nF SYNC 5 RSNS1 CBOOT1 SW1 9 S1 C11 ON/SS1 LDRV1 PGND 10 nF FB1 10 S2 C12 10 nF 24 VDD 19 R27 7 4.7 : C27 C26 1 PF 4.7 PF 3 C19 8.2 nF C20 R23 8.45 k: R24 12 D3A 25 BAT54A VDD C7 100 nF VDD1 Q2 23 Si4840DY 21 KS2 L1 4.2 PH 7 m: R10 R11 2.26 k: HDRV2 COMP1 RSNS2 COMP2 CBOOT2 14 22 k: SGND FB2 11 10 PF 50V 2.8Arms Si4850EY D3B BAT54A VDD 100 nF SW2 LDRV2 1 PF 50V Q4 15 18 C16 C31 17 20 330 PF 6.3V 10 m: R13 16 C25 13.7 k: C9 + VIN VDD2 VLIN5 Vo1 = 1.8V, 5A 4.99 k: 4 13 10 PF 50V 2.8Arms Si4850EY C13 10 nF ILIM2 1 PF 50V Q1 28 27 C6 C29 26 ON/SS2 15 nF 8 33 k: SYNC R28 220 k: R1 2 1 VIN Q5 Si4840DY L2 Vo2 = 3.3V, 4A 10 PH 12 m: R19 R20 2.26 k: + C23 330 PF 6.3V 10 m: 4.99 k: Figure 3. Standard VDS Sense Circuit 6 AN-1292 LM5642 Evaluation Board SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Additional Footprints www.ti.com Table 2. Standard VDS Sense Bill of Materials ID Part Number Type Size U1 LM5642 Dual Synchronous Controller TSSOP-28 Q1, Q4 Si4850EY N-MOSFET SO-8 Q2, Q5 Si4840DY N-MOSFET D3 BAT54A Schottky Diode L1 RLF12560T4R2N100 L2 Parameters Qty Vendor 1 Texas Instruments 60V 2 Vishay SO-8 40V 2 Vishay SOT-23 30V 1 ON Inductor 12.5 x 12.5 x 6mm 4.2µH, 7mΩ, 10A 1 TDK RLF12545T100M5R1 Inductor 12.5 x 12.5 x 4.5mm 10µH, 12mΩ, 5.1A 1 TDK C1, C29, C31 C3216X7R1H105K Capacitor 1206 1µF, 50V 1 TDK C27 C2012X5R1C105K Capacitor 0805 1µF, 16V 1 TDK C6, C16 C5750X5R1H106M Capacitor 2220 10µF, 50V, 2.8A 2 TDK C9, C23 6TPD330M Capacitor 7.3 x 4.3 x 3.8mm 330µF, 6.3V, 10mΩ 2 Sanyo C2, C11, C12, C13 VJ1206Y103KXXAT Capacitor 1206 10nF, 25V 4 Vishay C7, C25, C34 VJ1206Y104KXXAT Capacitor 1206 100nF, 25V 3 Vishay C19 VJ1206Y822KXXAT Capacitor 1206 8.2nF, 10% 1 Vishay C20 VJ1206Y153KXXAT Capacitor 1206 15nF, 10% 1 Vishay C26 C3216X7R1C475K Capacitor 1206 4.7µF, 25V 1 TDK R1 CRCW1206333J Resistor 1206 33kΩ, 5% 1 Vishay R13 CRCW1206223J Resistor 1206 22kΩ, 5% 1 Vishay R10 CRCW12062261F Resistor 1206 2.26kΩ, 1% 1 Vishay R23 CRCW12068451F Resistor 1206 8.45kΩ, 1% 1 Vishay R24 CRCW12061372F Resistor 1206 13.7kΩ, 1% 1 Vishay R11, R20 CRCW12064991F Resistor 1206 4.99kΩ, 1% 2 Vishay R19 CRCW12068251F Resistor 1206 8.25kΩ, 1% 1 Vishay R27 CRCW12064R7J Resistor 1206 4.7Ω, 5% 1 Vishay R28 CRCW1206224J Resistor 1206 220kΩ, 5% 1 Vishay SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1292 LM5642 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 7 Additional Footprints www.ti.com VIN + C6 + C16 + C28 + C30 C1 C2 VIN 22 6 VLIN5 UV-DLY VIN ILIM1 C34 R1 2 1 C29 KS1 5 SYNC R28 SYNC/PGOOD 26 Q1 RSNS1 28 9 S1 HDRV1 ON/SS1 Vo1 L1 SW1 27 C11 C7 CBOOT1 10 S2 ON/SS2 25 R9 VDD C8 + C9 + C10 D3A LDRV1 R10 D4 23 R11 C12 Q2 and Q3 PGND FB1 3 C18 4 C13 COMP1 VIN C19 ILIM2 R22 21 R23 KS2 R13 13 C31 14 VIN HDRV2 R26 12 RSNS2 COMP2 SW2 C20 R24 C21 7 VLIN5 VDD 17 Q4 15 Vo2 L2 27 C25 CBOOT2 18 R18 VDD 24 V DD1 R25 R27 C26 19 V DD2 C27 LDRV2 8 SGND FB2 R19 C22 + C23 + C24 D5 20 Q5 and Q6 R20 11 Figure 4. Complete VDS Sense Eval Board Schematic 8 AN-1292 LM5642 Evaluation Board SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Additional Footprints www.ti.com Figure 5. Resistor Sense PCB Top Layer Figure 6. Resistor Sense PCB Bottom Layer SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1292 LM5642 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 9 Additional Footprints www.ti.com Figure 7. Resistor Sense PCB Internal Planes Figure 8. VDS Sense PCB Top Layer 10 AN-1292 LM5642 Evaluation Board SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Additional Footprints www.ti.com Figure 9. VDS Sense PCB Bottom Layer Figure 10. VDS Sense PCB Internal Planes SNVA070B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1292 LM5642 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 11 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. 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