LM3423_11

LM3423 Buck-Boost 2 Layer Evaluation Board LM3423 Buck-Boost 2 Layer Evaluation Board National Semiconductor Application Note 2010 James Patterson March 7, 2011 Introduction This wide range evaluation board showcases the LM3423 NFET controller used with a buck-boost current regulator. It is designed to drive 4 to 8 LEDs at a maximum average LED current of 700mA from a DC input voltage of 10 to 70V. The evaluation board showcases most features of the LM3423 including PWM dimming, fault and LED status flags, output overvoltage protection and input under-voltage lockout. Note that there are two revisions of this PCB. The documentation for the latest revision (551600305-002 RevA) is shown first. The schematic, layout and bill of materials for the first revision (551600305-001 Rev1) can be found at the end of this document. The buck-boost circuit can be easily redesigned for different specifications by changing only a few components (see the Alternate Designs section found at the end of this application note). Note that design modifications can change the system efficiency. See the LM3423 datasheet for a comprehensive explanation of the device and application information. EFFICIENCY WITH 6 SERIES LEDS AT 700mA 30107701 Schematic for 551600305-002 REVA AN-2010 30107763 © 2011 National Semiconductor Corporation 301077 www.national.com AN-2010 Pin Descriptions LM3423 1 2 3 LM3421 1 2 3 Name VIN EN COMP Description Input Voltage Enable Compensation Function Bypass with 100 nF capacitor to AGND as close to the device as possible in the circuit board layout. Connect to AGND for zero current shutdown or apply > 2.4V to enable device. Connect a capacitor to AGND to set the compensation. Connect a resistor to AGND to set the signal current. For analog dimming, connect a controlled current source or a potentiometer to AGND as detailed in the Analog Dimming section. External RC network sets the predictive “off-time” and thus the switching frequency. Connect to PGND through the DAP copper pad to provide ground return for CSH, COMP, RCT, and TIMR. Connect to a resistor divider from VO to program output over-voltage lockout (OVLO). Turn-off threshold is 1.24V and hysteresis for turn-on is provided by 23 µA current source. Connect a PWM signal for dimming as detailed in the PWM Dimming section and/or a resistor divider from VIN to program input under-voltage lockout (UVLO). Turn-on threshold is 1.24V and hysteresis for turn-off is provided by 23 µA current source. Connect to pull-up resistor from VIN and N-channel MosFET open drain output is high when a fault condition is latched by the timer. Connect a capacitor to AGND to set the time delay before a sensed fault condition is latched. Connect to pull-up resistor from VIN and N-channel MosFET open drain output pulls down when the LED current is not in regulation. Connect to AGND if dimming with a series P-channel MosFET or leave open when dimming with series Nchannel MosFET. Connect to the gate of the dimming MosFET. Connect to AGND through the DAP copper pad to provide ground return for GATE and DDRV. Connect to the gate of the main switching MosFET. Bypass with 2.2 µF–3.3 µF ceramic capacitor to PGND. Connect to the drain of the main N-channel MosFET switch for RDS-ON sensing or to a sense resistor installed in the source of the same device. Connect the low side of all external resistor dividers (VIN UVLO, OVP) to implement “zero-current” shutdown. Connect through a series resistor to the positive side of the LED current sense resistor. Connect through a series resistor to the negative side of the LED current sense resistor. Star ground, connecting AGND and PGND. 4 4 CSH Current Sense High 5 6 5 6 RCT AGND Resistor Capacitor Timing Analog Ground 7 7 OVP Over-Voltage Protection 8 8 nDIM Dimming Input / Under-Voltage Protection 9 - FLT Fault Flag 10 - TIMR Fault Timer 11 - LRDY LED Ready Flag 12 13 14 15 16 17 9 10 11 12 13 DPOL DDRV PGND GATE VCC IS Dim Polarity Dim Gate Drive Output Power Ground Main Gate Drive Output Internal Regulator Output Main Switch Current Sense 18 14 RPD Resistor Pull Down 19 20 DAP (21) 15 16 DAP (17) HSP HSN DAP LED Current Sense Positive LED Current Sense Negative Thermal PAD on bottom of IC www.national.com 2 AN-2010 Bill of Materials for 551600305-002 REVA Qty 2 2 1 1 4 1 1 1 1 1 1 4 1 1 2 2 1 1 1 2 1 2 1 3 1 1 1 3 3 1 5 1 Part ID C1, C12 C2, C8 C3 C4 C6(a-d) C7 C9 C10 C11 D1 D2 J1, J2, J4, J5 J3 L1 Q1, Q2 Q3, Q7 Q4 Q5 Q6 R1, R11 R2 R3, R20 R4 R5, R7, R8 R6 R9 R10 R12, R13, R19 R14, R15, R17 R18 TP1, TP5, TP6, TP10 U1 Part Value 0.1 µF X7R 10% 50V 1.0 µF X7R 10% 50V 68 µF 20% 100V 0.1 µF X7R 10% 100V Manufacturer TDK MURATA UCC TDK Part Number C1608X5R1H104K GRM21BR71H105KA12L KA01L EMVY101ARA680MKE C2012X7R2A104M C5750X7R1H106 C2012X5R2E102K GRM21BR71C225KA01L ECJ2VB1H103 KA12L ECJ2VG1H470 KA01L 12CWQ10FNPBF (or 6CWQ10FNPBF) BZX84C10-V 575-8 TSW-102-07-T-S MSS1260-473MLB IPD200N15N3 (or FDD3682) 2N7002ET1G MMBT3906 MMBT5401 MMBTA42 CRCW080512k4FKEA CRCW08050000Z0EA CRCW080510R0FKEA CRCW080516k9FKEA CRCW08051k40FKEA WSL2512R0600FEA ERJ12RSFR20U CRCW080535k7FKEA CRCW080510k0FKEA CRCW0805100kFKEA CRCW0805432kFKEA 1502-2 LM3423MH 10 µF X7R 10% 50V (4 installed TDK for a total of 40 µF) 1000 pF X5R 5% 100V 2.2 µF X7R 10% 16V 10 nF X7R 10% 50V 47 pF COG/NPO 5% 50V Schottky 100V 12A (or 6A) Zener 10V banana jack 1x2 male header (with shunt tab) 47 µH 20% 6.3A MURATA MURATA PANASONIC PANASONIC VISHAY ON-SEMI KEYSTONE SAMTEC COILCRAFT NMOS 150V 50A (or 100V 32A) INFINEON (or FAIRCHILD) NMOS 60V 260 mA PNP 40V 200 mA PNP 150V 600 mA NPN 300V 500 mA 12.4 kΩ 1% 0Ω 1% 10Ω 1% 16.9 kΩ 1% 1.40 kΩ 1% 0.06Ω 1% 1W 0.2Ω 1% 1W 35.7 kΩ 1% 10.0 kΩ 1% 100 kΩ 1% 432 kΩ 1% turret Buck-boost controller ON-SEMI FAIRCHILD FAIRCHILD FAIRCHILD VISHAY VISHAY VISHAY VISHAY VISHAY VISHAY PANASONIC VISHAY VISHAY VISHAY VISHAY KEYSTONE NSC 3 www.national.com AN-2010 PCB Layout for 551600305-002 REVA 30107765 Top Layer 30107764 Bottom Layer www.national.com 4 AN-2010 Design Procedure Refer to LM3423 datasheet for design considerations. SPECIFICATIONS N=6 VLED = 3.5V rLED = 325 mΩ VIN = 24V VIN-MIN = 10V; VIN-MAX = 70V fSW = 700 kHz VSNS = 150 mV ILED = 700 mA ΔiL-PP = 350 mA ΔiLED-PP = 50 mA ΔvIN-PP = 100 mV ILIM = 4A VTURN-ON = 10V; VHYS = 3.4V VTURN-OFF =44V; VHYSO = 10V 1. OPERATING POINT Solve for VO and rD: 3. AVERAGE LED CURRENT Solve for R9: Assume R1 = 12.4 kΩ and solve for R8: The closest standard resistor for R9 is 0.2Ω and the closest for R8 (and R7) is actually 1.4 kΩ therefore ILED is: The chosen components from step 3 are: 4. INDUCTOR RIPPLE CURRENT Solve for L1: Solve for D, D', DMAX, and DMIN: The closest standard inductor is 47 µH therefore the actual ΔiL-PP is: Determine minimum allowable RMS current rating: 2. SWITCHING FREQUENCY Assume C7 = 1 nF and solve for R10: The closest standard resistor is actually 35.7 kΩ therefore the fSW is: The chosen component from step 4 is: The chosen components from step 2 are: 5 www.national.com AN-2010 5. OUTPUT CAPACITANCE Solve for CO: TU0 is approximated: To ensure stability, calculate ωP2: A total value of 40 µF (using 4 10 µF X7R ceramic capacitors) is chosen therefore the actual ΔiLED-PP is: Solve for C8: To attenuate switching noise, calculate ωP3: Determine minimum allowable RMS current rating: The chosen components from step 5 are: Assume R20 = 10Ω and solve for C12: 6. PEAK CURRENT LIMIT Solve for R6: Since PWM dimming can be evaluated with this board, a much larger compensation capacitor C8 = 1.0 µF is chosen and a smaller high frequency capacitor C12 = 0.1 µF is chosen. The chosen components from step 7 are: The closest standard resistor is 0.06 Ω therefore ILIM is: The chosen component from step 6 is: 8. INPUT CAPACITANCE Solve for the minimum CIN: 7. LOOP COMPENSATION ωP1 is approximated: To minimize power supply interaction a much larger capacitance of 68 µF is used, therefore the actual ΔvIN-PP is much lower. Determine minimum allowable RMS current rating: ωZ1 is approximated: The chosen components from step 8 are: www.national.com 6 AN-2010 9. NFET Determine minimum Q1 voltage rating and current rating: Solve for R4: A 100V NFET is chosen with a current rating of 40A due to the low RDS-ON = 50 mΩ. Determine IT-RMS and PT: The closest standard resistor is 16.9 kΩ making VHYS: The chosen component from step 9 is: The chosen components from step 11 are: 10. DIODE Determine minimum D1 voltage rating and current rating: 12. OUTPUT OVLO Solve for R18: A 100V diode is chosen with a current rating of 12A and VD = 600 mV. Determine PD: The closest standard resistor is 432 kΩ therefore VHYSO is: The chosen component from step 10 is: Solve for R11: 11. INPUT UVLO Since PWM dimming will be evaluated, a three resistor network will be used. Assume R13 = 10 kΩ and solve for R5: The closest standard resistor is 12.4 kΩ making VTURN-OFF: The closest standard resistor is 1.4 kΩ therefore VTURN-ON is: The chosen components from step 12 are: 7 www.national.com AN-2010 13. PWM DIMMING The LM3423 Buck-boost Evaluation board is configured to demonstrate PWM dimming of the LEDs. For best operation, use a PWM signal that has greater than 3V amplitude at a frequency between 120Hz and 5kHz. Apply the PWM signal to the BNC connector (J6) and the inverted signal (seen by the nDIM pin) can be monitored at TP5. The output PWM drive signal (DDRV) is level shifted to the floating LED stack using several components (R19, R17, Q4, Q6, Q7, and D2) and ultimately controls the series dimming FET (Q2). This level shift adds a several microsecond delay from input to output as seen in the Typical Waveforms section. This delay, along with the time it takes to slew the LED current from zero to its nominal value, limits the contrast ratio for a given dimming frequency. Using the evaluation board (24V input, 21V output), at 5kHz dimming frequency the best case contrast ratio is approximately 40:1, but at 200Hz the same system is more like 1000:1 ratio. In general, contrast ratios much above 2000:1 are not possible for any operating point using the LM3423 buck-boost evaluation board. 13. FAULT AND LED CURRENT MONITORING The LM3423 has a fault detection flag in the form of an opendrain NFET at the FLT pin. Using the external pull-up resistor (R14) to VIN, the fault status can be monitored at the FLT pin (high = fault). The fault timer interval is set with the capacitor (C10) from TIMR to GND (10nF yields roughly 1ms). If a fault is detected that exceeds the programmed timer interval, such as an output over-voltage condition, the FLT pin transitions from high to low and internally GATE and DDRV are latched off. To reset the device once the fault is removed, either the input power must be cycled or the EN pin must be toggled. This can be tested directly with the evaluation board by opening the LED load. An OVP fault will occur which disables GATE and DDRV. Then if the LEDs are reconnected, the EN pin jumper (J3) can be removed and reinserted to restart normal operation of the LM3423. The LED status flag (LRDY) can be seen by monitoring TP4. LRDY is also an open-drain NFET connection which has an external pull-up resistor (R15) to VIN. If the LED current is in regulation the voltage at TP4 will be high, but when it falls out of regulation the NFET turns on and pulls TP4 low. The LM3423 datasheet lists all of the conditions that affect LRDY, FLT, and TIMR. Typical Waveforms TA = +25°C, VIN = 24V and VO = 21V. 30107761 30107762 1kHz 50% PWM DIMMING TP5 dim voltage (VDIM) LED current (ILED) 1kHz 50% PWM DIMMING (Rising Edge) TP5 dim voltage (VDIM) LED current (ILED) www.national.com 8 AN-2010 Schematic for 551600305-001 REV1 30107702 9 www.national.com AN-2010 PCB Layout for 551600305-001 REV1 30107703 Top Layer 30107704 Bottom Layer www.national.com 10 AN-2010 Bill of Materials for 551600305-001 REV1 Qty 2 2 1 1 1 4 1 1 1 1 1 1 4 1 1 1 1 2 2 1 1 1 2 1 2 1 3 1 1 1 3 3 1 1 5 1 Part ID C1, C12 C2, C8 C3 C4 C5 C6 C7 C9 C10 C11 D1 D2 J1, J2, J4, J5 J3 J6 J7 L1 Q1, Q2 Q3, Q7 Q4 Q5 Q6 R1, R11 R2 R3, R20 R4 R5, R7, R8 R6 R9 R10 R12, R13, R19 R14, R15, R17 R16 R18 TP1, TP4, TP5, TP7, TP10 U1 Part Value 0.1 µF X7R 10% 50V 1.0 µF X7R 10% 50V 68 µF 20% 100V 0.1 µF X7R 10% 100V DNP 10 µF X7R 10% 50V (4 installed TDK for a total of 40 µF) 1000 pF X5R 5% 100V 2.2 µF X7R 10% 16V 10 nF X7R 10% 50V 47 pF COG/NPO 5% 50V Schottky 100V 7A Zener 10V banana jack BNC connector DNP 47 µH 20% 6.3A NMOS 100V 40A NMOS 60V 260 mA PNP 40V 200 mA PNP 150V 600 mA NPN 300V 500 mA 12.4 kΩ 1% 0Ω 1% 10Ω 1% 16.9 kΩ 1% 1.40 kΩ 1% 0.06Ω 1% 1W 0.2Ω 1% 1W 35.7 kΩ 1% 10.0 kΩ 1% 100 kΩ 1% DNP 432 kΩ 1% turret Buck-boost controller VISHAY KEYSTONE NSC CRCW0805432kFKEA 1502-2 LM3423MH COILCRAFT VISHAY ON-SEMI FAIRCHILD FAIRCHILD FAIRCHILD VISHAY VISHAY VISHAY VISHAY VISHAY VISHAY PANASONIC VISHAY VISHAY VISHAY MSS1260-473MLB SUD40N10-25 2N7002ET1G MMBT3906 MMBT5401 MMBTA42 CRCW080512k4FKEA CRCW08050000Z0EA CRCW080510R0FKEA CRCW080516k9FKEA CRCW08051k40FKEA WSL2512R0600FEA ERJ12RSFR20U CRCW080535k7FKEA CRCW080510k0FKEA CRCW0805100kFKEA MURATA MURATA PANASONIC PANASONIC VISHAY ON-SEMI KEYSTONE AMPHENOL C5750X7R1H106 C2012X5R2E102K GRM21BR71C225KA01L ECJ2VB1H103 KA12L ECJ2VG1H470 KA01L 6CWQ10FNPBF BZX84C10-V 575-8 TSW-102-07-T-S 112536 Manufacturer TDK MURATA UCC TDK Part Number C1608X5R1H104K GRM21BR71H105KA12L KA01L EMVY101ARA680MKE C2012X7R2A104M 1x2 male header (with shunt tab) SAMTEC 11 www.national.com AN-2010 Alternate Designs Alternate designs with the LM3423 evaluation board are possible with very few changes to the existing hardware. The evaluation board FETs and diodes are already rated higher than necessary for design flexibility. The input UVLO, output OVP, input and output capacitance can remain the same for Specification / Component VIN VO fSW ILED R9 R10 L1 Design 1 10V - 45V 14V 600kHz 2A 0.05Ω 41.2 kΩ 22µH Design 2 15V - 50V 21V 700kHz 500mA 0.2Ω 35.7 kΩ 68µH the designs shown below. These alternate designs can be evaluated by changing only R9, R10, and L1. The table below gives the main specifications for four different designs and the corresponding values for R9, R10, and L1. PWM dimming can be evaluated with any of these designs. Design 3 20V - 55V 28V 500kHz 2.5A 0.04Ω 49.9 kΩ 15µH Design 4 25V - 60V 35V 700kHz 1.25A 0.08Ω 35.7 kΩ 33µH www.national.com 12 AN-2010 13 www.national.com LM3423 Buck-Boost 2 Layer Evaluation Board Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Amplifiers Audio Clock and Timing Data Converters Interface LVDS Power Management Switching Regulators LDOs LED Lighting Voltage References PowerWise® Solutions Temperature Sensors PLL/VCO www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/vref www.national.com/powerwise WEBENCH® Tools App Notes Reference Designs Samples Eval Boards Packaging Green Compliance Distributors Quality and Reliability Feedback/Support Design Made Easy Design Support www.national.com/webench www.national.com/appnotes www.national.com/refdesigns www.national.com/samples www.national.com/evalboards www.national.com/packaging www.national.com/quality/green www.national.com/contacts www.national.com/quality www.national.com/feedback www.national.com/easy www.national.com/solutions www.national.com/milaero www.national.com/solarmagic www.national.com/training Applications & Markets Mil/Aero PowerWise® Design University Serial Digital Interface (SDI) www.national.com/sdi www.national.com/wireless www.national.com/tempsensors SolarMagic™ THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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