LM5008EVAL

User's Guide SNVA090B – May 2004 – Revised April 2013 AN-1330 LM5008 Evaluation Board 1 Introduction The LM5008 evaluation board is designed to provide the design engineer with a fully functional step down switching regulator to evaluate LM5008 regulator IC, in a typical environment. The performance of evaluation board is as follows: • Input range: 12V to 95V, transients upto 100V (absolute maximum) • Output voltage: 10V • Output current: 300mA • Measured efficiency: 89% at 200mA and VIN = 30V • Board size: 31.9mm x 44.4mm 2 Theory of Operation The LM5008 step-down switching regulator features all of the functions needed to implement low cost, efficient, Buck bias regulators. This high voltage regulator contains an 100V, 0.5A N-channel Buck switch. The regulator is based on hysteretic control scheme using an on-time inversely proportional to input voltage (VIN). This feature allows the operating frequency to remain relatively constant with load and input voltage variations. The hysteretic control requires no control loop compensation, while providing fast load transient response. Additional protection features include : Thermal Shutdown, VCC undervoltage lockout and maximum duty–cycle limiter. LM5008 can be used in numerous applications to efficiently regulate step down higher voltage inputs. This regulator is well suited for 48V telecom and the new 42V automotive power bus ranges. The LM5008 operates in discontinuous conduction mode at light load currents or continuous conduction mode at heavier load currents. In discontinuous conduction mode, current through the output inductor starts at zero and ramps up to the peak value during the buck switch on time, and then back to zero during buck switch off time. In discontinuous conduction mode, the operating frequency can be relatively low and will vary with load. Therefore at light loads the conversion efficiency is maintained , since switching losses decrease with reduction in switching frequency. The evaluation board just needs one high voltage power-supply (upto 100V and current rating of 0.5A). The maximum output power is 3 watts. Either an electronic load or resistor bank can be used for testing evaluation board. 3 Start-up Feature There is no soft-start feature in LM5008, and it normally comes up with full load current to supply the power demanded by the load within a short time. The LM5008 contains an intelligent current limit OFF timer intended to reduce the foldback characteristic inherent with fixed off-time over-current protection. If the current in the Buck FET exceeds 550mA the present cycle is immediately terminated (cycle by cycle current limit). Following the termination of the cycle a non-resetable current limit off timer is initiated. The duration of off time is a function of the external setting resistor (Rcl) and the FB pin voltage. When FB pin voltage = 0V the current limit off time is internally preset to 35µs. This condition occurs in short circuit operation when a maximum amount of off time is required. In cases of overload (not complete short circuit) the current limit off time can be reduced as a function of the output voltage (measured at the FB pin). Reducing the off time during smaller overloads reduces the amount of foldback and also reduces the initial start-up time. All trademarks are the property of their respective owners. SNVA090B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1330 LM5008 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 1 Low Ripple Configuration 4 www.ti.com Low Ripple Configuration For applications where lower output voltage ripple is required the output load can be connected directly to the low ESR output capacitor, as shown below. The evaluation board is laid out in such a way that, user can use either (high ripple or low ripple) options by simply shifting the output connector. The series resistor (R) will degrade the load regulation however. VIN L SW R1 R FB + + R2 REF 2.5V VOUT COUT LM5008 Figure 1. Low Ripple Configuration Output 7V SERIES REGULATOR 12 -95V C1 1 PF LM5008 VCC 7 8 VIN C5 0.1 PF, 100V SD C3 0.01 PF THERMAL SHUTDOWN UVLO ON TIMER START R1 357k COMPLETE 6 SD / RON BST Ron START OVER-VOLTAGE COMPARATOR SHUTDOWN + - 2.875V UVLO 300ns MIN OFF TIMER 2 VIN SD DRIVER COMPLETE LEVEL SHIFT 2.5V SW 220 PF L1 1 10V SET + - 5 S FB R REGULATION COMPARATOR FB 3 RCL CLR 4 Q R3 3.01k COMPLETE RCL START CURRENT LIMIT OFF TIMER R2 280k Q + 0.550A BUCK SWITCH CURRENT SENSE R6 1 D1 RTN R4 1k C2 22 PF Figure 2. Evaluation Board Schematic Diagram 2 AN-1330 LM5008 Evaluation Board SNVA090B – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Low Ripple Configuration www.ti.com Table 1. Bill of Materials ITEM PART NUMBER DESCRIPTION VALUE C 1 C4532X7R2A105M CAPACITOR, CER, TDK 1µ, 100V C 2 C3225X7R1C226M CAPACITOR, CER, TDK 22µ, 16V C 3 C1206C104K5RAC CAPACITOR, CER, KEMET 0.1µ, 50V C 4 C1206C103K5RAC CAPACITOR, CER, KEMET 0.01µ, 50V C 5 C3216X7R2A104KT CAPACITOR, CER, TDK 0.1µ, 100V D 1 MURA110T3 DIODE, 100V, ON SEMI L 1 SLF10145T-221MR65-1 BUCK INDUCTOR, TDK 220µH R 1 CRCW12063573F RESISTOR 357K R 2 CRCW12062803F RESISTOR 280K R 3 CRCW12063011F RESISTOR 3.01K R 4 CRCW12061001F RESISTOR 1K R 5 CRCW12061R00F RESISTOR 1 U 1 LM5008 REGULATOR, NATIONAL SNVA090B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1330 LM5008 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 3 Efficiency Measurements 5 www.ti.com Efficiency Measurements Start-up Behavior VIN = 50V, VOUT = 10V, Load Resistance = 30Ω 1 50 Ps 20.0V 95 VIN = 15V 90 3 50 Ps 200 mA EFFICIENCY (%) 85 1 80 2 50 Ps 5.0V VIN = 30V VIN = 50V 75 2 VIN = 70V 70 65 VIN = 90V 60 0.0 0.1 3 VIN = 100V 0.2 0.3 0.4 0.5 LOAD CURRENT (A) CH1: Switch Node Voltage CH2: Output Voltage CH3: Inductor Current Figure 3. LM5008 Efficiency Figure . Normal Operation VIN = 50V, VOUT = 10V, Load Resistance = 30Ω Load Transient VIN = 50V, VOUT = 10V, Load change from 1kΩ to 20kΩ 1 2 Ps 20.0V 1 10 Ps 20.0V 3 2 Ps 200 mA 1 3 10 Ps 200 mA 1 2 2 Ps 5.0V 2 2 10 Ps 5.0V 2 3 CH1: Switch Node Voltage CH2: Output Voltage CH3: Inductor Current Load Current vs Switching Frequency 300 Input Voltage vs Switching Frequency 270 SWITCHING FREQUENCY (kHz) SWITCHING FREQUENCY (kHz) 3 CH1: Switch Node Voltage CH2: Output Voltage CH3: Inductor Current 250 200 150 100 50 260 250 240 230 220 210 200 0 0 100 200 300 400 500 0 LOAD CURRENT (mA) 4 AN-1330 LM5008 Evaluation Board 20 40 60 80 100 120 INPUT VOLTAGE (V) SNVA090B – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated PCB Layouts www.ti.com 6 PCB Layouts Figure 4. Top Layer Figure 5. Silk Screen Figure 6. Bottom Layer Figure 7. Top Soldermask SNVA090B – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1330 LM5008 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 5 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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