LM5115DCEVAL

User's Guide SNVA106B – September 2005 – Revised April 2013 AN–1367 LM5115 HV DC Evaluation Board 1 Introduction The LM5115 HV DC evaluation board provides a synchronous buck dc-dc converter using the LM5115 secondary side post regulator control IC. The evaluation board specifications are: • DC Input voltage range: 7V to 70V • Regulated Output voltage: 5V • Output current range: 0 to 6A • Measured efficiency: 94% at 1.5A, VIN = 24V • Load regulation: 0.1% (1A-6A) • Switching Frequency: 215kHz, typical • Onset of current limiting: ≊ 8A • Board Size: 3.0 x 1.7 x 0.43in The printed circuit board (PCB) consists of 4 layers of 2 oz copper on FR4 material, with a thickness of 0.050 in. It is designed for continuous operation at rated load with a minimum airflow of 200 LFPM. 2 Theory of Operation The LM5115 is a secondary side post regulator (SSPR) controller that can be configured as a high voltage DC buck controller. In the buck application, the power input of the LM5115 is a dc voltage instead of a pulsed signal from the transformer secondary winding of an isolated converter (SSPR configuration). The free running oscillator within the LM5115 sets the clock frequency for the high and low side drivers of external synchronous buck power MOSFETs. The LM5115 controls the buck power stage with leading edge pulse width modulation (PWM) to hold off the high side driver until the necessary volt*seconds is established for regulation. A resistor from the VCC bias voltage to the SYNC pin sets the current that charges a RAMP pin capacitor for voltage mode PWM control. The internal oscillator terminates the buck switch pulse and discharges the RAMP capacitor before initiating another cycle. Adaptive deadtime control delays the top and bottom drivers to avoid shoot through currents. See typical and adaptive delay waveforms in Figure 10 and Figure 11. All trademarks are the property of their respective owners. SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback AN–1367 LM5115 HV DC Evaluation Board Copyright © 2005–2013, Texas Instruments Incorporated 1 Board Layout and Probing www.ti.com Figure 1. DC Evaluation Board Top Side Figure 2. Evaluation Board Bottom Side 3 Board Layout and Probing Figure 1 and Figure 2 shows the board layout, main components, and critical probe points for testing the LM5115 DC mode evaluation board. The following notes should be considered prior to applying power to the board: • Main input power (7V to 70V) is applied to points J5 and J6, connected to VIN and GND, respectively. • The main current carrying components (L1, Q1, and Q2) will be hot to the touch at maximum load current. USE CAUTION. When operating at load currents in excess of 3A the use of a fan to provide forced air flow IS NECESSARY. • The diameter and length of the wire used to connect the load is important. To ensure that there is not a significant voltage drop in the wires, a minimum of 14 gauge wire is recommended. 4 Board Connections/Start-Up The input connections are made to terminals J5 (+) and J6 (-). The input source must be capable of supplying the load dependent input current shown in Figure 3. The load is connected to terminals J3 (+) and J4 (-). Before start-up, a voltmeter should be connected to the input terminals and to the output terminals. The input current should be monitored with an ammeter or a current probe. Soft-start provided by the LM5115 will insure that the output rises with a smooth turn on without overshoot (Figure 8). The LM5115 evaluation board operates in the continuous conduction mode even with a light or no load. 2 AN–1367 LM5115 HV DC Evaluation Board SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated Performance LM5115 DC - DC Regulator www.ti.com 5 Performance LM5115 DC - DC Regulator Performance of the LM5115 evaluation board can be seen in the following figures: • Power Conversion Efficiency (Figure 4) • Load Regulation (Figure 5) • Step Load Response (Figure 6) • Ripple Voltage (Figure 7) • Gate Delays (Figure 7 and Figure 8) • Startup and Shutdown Response (Figure 8 and Figure 9) • Operational Waveforms (Figure 10 to Figure 13 ) • Output Short Circuit Response (Figure 14) 6 VBIAS VBIAS is initially powered up by the input supply through a 6.2V clamp and an NPN. Once VOUT is regulating the voltage doubler will supply a doubled output voltage (10V) to Vbias. 7 VCC The LM5115 produces a LDO 7V regulated output (VCC) that can supply up to 40mA of DC current. In the DC evaluation board, the VCC supplies the control current that sets the frequency of the oscillator. The VCC regulator also supplies power for the high current gate drive for the low side MOSFET and the bootstrap capacitor of the high side MOSFET driver. 8 Current Limit Operation Inductor current is sensed through the parallel resistances of R7, R8, and R9. The resistor values are designed for a current limit of ≊8A. Current limiting occurs when the sense resistor voltage exceeds 45mV threshold causing the current sense amplifier to pull down the CO and COMP pins. Pulling CO and COMP low reduces the width of pulses to the high side driver, limiting the output current of the converter. After reaching the current limit, the voltage feedback causes the COMP pin to rise and turn on the high side driver until the inductor current again reaches the ≊8A current limit threshold. (Figure 14). 9 Foldback Current Limit Current limit foldback can be implemented with the following components: R17, R18, D5, and R16 (see Figure 16). At nominal output voltage (VOUT > 3V) D5 is reversed biased and the current limit threshold is still ≊45mV. At lower output voltage the resistor divider network along with the forward biased diode (D5) will increase the voltage across R16. In order to reach the 45mV current limit threshold, the voltage across the sense resistor (R7-R9) is reduced due to the increase in voltage across R16. Thus, the current limit is reduced providing current limit foldback. The resistor divider sets the voltage when current limit foldback kicks in and R16 sets the amount of current limit foldback. 10 Internal Oscillator The frequency of the dc-dc converter system is set by the VCC voltage, the SYNC pin resistor (R4), and the RAMP pin capacitor (C4) according to Equation 1: FCLK = 1 (C4 x 2.25V) (VCC/R4 x 3) | 215 kHz + 300 ns (1) SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback AN–1367 LM5115 HV DC Evaluation Board Copyright © 2005–2013, Texas Instruments Incorporated 3 Internal Oscillator www.ti.com 100 5.0 VIN = 7V 4.5 95 4.0 VIN = 7V EFFICIENCY (%) INPUT (A) 3.5 3.0 2.5 2.0 VIN = 24V 1.5 VIN = 48V 90 85 VIN = 48V VIN = 24V 80 VIN = 70V VIN = 70V 1.0 75 0.5 0.0 1.0 70 2.0 3.0 4.0 5.0 6.0 1 2 LOAD (A) 3 4 5 6 LOAD (A) Figure 3. Input Current vs Load Current Figure 4. System Efficiency vs. Load Current and VIN 4 VOUT (V) 3.38 3.36 3.34 3.32 3.3 1 2 3 4 5 6 LOAD (A) Figure 5. Output Voltage vs. Load Current Conditions: VIN = 24V, 6A load CH1= 5V output, 20mV/div (AC mode) Horizontal Resolution = 2µs/div Figure 7. Ripple Voltage 4 AN–1367 LM5115 HV DC Evaluation Board Conditions: VIN = 24V CH1= 5V output, 200mV/div (AC mode) CH4 = Output current load (1A to 5A), 2A/div Horizontal Resolution = 1ms/div Figure 6. Step Load Response Conditions: VIN=24V; Load=6.0A CH1 = 5V Output, 2V/div CH4 = Output Current load, 2A/div Horizontal Resolution = 10ms/div Figure 8. Startup Response SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated Internal Oscillator www.ti.com Conditions: VIN=24V; Load=6.0A CH1 = 5V Output, 2V/div CH4 = Output Current load, 2A/div Horizontal Resolution = 10ms/div Conditions: VIN = 24V, 1A CH1= High Side Gate Driver (HO), 10V/div CH2= Low Side Gate Driver (LO), 5V/div CH3= RAMP, 1V/div Horizontal Resolution = 1µs/div Figure 9. Shutdown Response Figure 10. Typical Waveforms Conditions: VIN = 24V, 1A CH1= High Side Gate Driver (HO), 10V/div CH2= Low Side Gate Driver (LO), 5V/div CH3= RAMP, 1V/div Horizontal Resolution = 200ns/div Conditions: VIN = 24V, 1A CH1= High Side Gate Driver (HO), 10V/div CH2= Low Side Gate Driver (LO), 5V/div CH3= RAMP, 1V/div Horizontal Resolution = 100ns/div Figure 11. Adaptive Delays Figure 12. Gate Turn-on Delay Conditions: VIN = 24V, 1A CH1= High Side Gate Driver (HO), 10V/div CH2= Low Side Gate Driver (LO), 5V/div CH3= RAMP, 1V/div Horizontal Resolution = 100ns/div Figure 13. Gate Turn-off Delay SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback Conditions: VIN = 24V, Short Circuit Load CH1= High Side Gate Driver (HO), (20V/div) CH2= COMP/CO, (1V/div) CH4= Inductor current (2A/div) Horizontal Resolution = 50µs/div Figure 14. Output Short Circuit Response AN–1367 LM5115 HV DC Evaluation Board Copyright © 2005–2013, Texas Instruments Incorporated 5 Application Circuit Schematic 11 www.ti.com Application Circuit Schematic Figure 15. LM5115 HV DC Evaluation Board 6 AN–1367 LM5115 HV DC Evaluation Board SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated Application Circuit Schematic www.ti.com Figure 16. Foldback Current Limit SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback AN–1367 LM5115 HV DC Evaluation Board Copyright © 2005–2013, Texas Instruments Incorporated 7 Bill of Materials (BOM) 12 www.ti.com Bill of Materials (BOM) Table 1. Bill of Materials Item 8 Part Number Description Value C 1 C3216X7R1C105K CAPACITOR, CER, TDK 1.0 µF, 16V C 2 C2012X7R1H104K CAPACITOR, CER, TDK 0.1 µF, 50V C 3 C3216X7R1C105K CAPACITOR, CER, TDK 1.0 µF, 16V C 4 C2012C0G1H331K CAPACITOR, CER, TDK 330 pF, 50V C 5 C2012X7R1H104K CAPACITOR, CER, TDK 0.1 µF, 50V C 6 C4532X7R2A225M CAPACITOR, CER, TDK 2.2µF, 100V C 7 C2012X7R1H104K CAPACITOR, CER, TDK 0.1µF, 50V C 8 C2012C0G1H471K CAPACITOR, CER, TDK 470 pF, 50V C 10 C 11 EEFUE0J221R CAPACITOR, SP, PANASONIC 220µF, 6.3V C 12 C4532X7R0J107M CAPACITOR, CER, TDK 100 µF, 6.3V C 13 C4532X7R0J107M CAPACITOR, CER, TDK 100µF, 6.3V C 14 C4532X7R0J476M CAPACITOR, CER, TDK 47µF, 6.3V C 15 C4532X7R2A225M CAPACITOR, CER, TDK 2.2µF, 100V C 16 C4532X7R2A225M CAPACITOR, CER, TDK 2.2µF, 100V C 17 C4532X7R2A225M CAPACITOR, CER, TDK 2.2µF, 100V C 19 C3216X7R1C475M CAPACITOR, CER, TDK 4.7µF, 16V C 20 C3216X7R1C475M CAPACITOR, CER, TDK 4.7µF, 16V C 21 C3216X7R1C475M CAPACITOR, CER, TDK 4.7µF, 16V Not Used C 23 EEVFK2A330P CAPACITOR, CER, 33µF, 100V CR 1 CCLM0500 CURRENT REGULATOR, CENTRAL, SEMI 0.5mA, 100V D 1 CMPD2838E-NSA DIODE, SIGNAL, CENTRAL, SEMI 200mA, 120V D 2 BAT54S DIODE SHOTTKY, CENTRAL, SEMI 200mA, 30V D 4 CMSH3-100M DIODE SHOTTKY, CENTRAL, SEMI D 5 J 3 2515-1-01-01-00-00-07-0 SOLDER TERMINAL SLOTTED, MILL-MAX VOUT J 4 2515-1-01-01-00-00-07-0 SOLDER TERMINAL SLOTTED, MILL-MAX VOUT RTN J 5 3104-2-00-01-00-00-08-0 TERMINAL, SOLDER, .040" MILL-MAX VIN J 6 3104-2-00-01-00-00-08-0 TERMINAL, SOLDER, .040" MILL-MAX GND TP 1 5002 TERMINAL, SMALL TEST POINT, KEYSTONE VBIAS TP 2 5002 TERMINAL, SMALL TEST POINT, KEYSTONE GND TP 3 5002 TERMINAL, SMALL TEST POINT, KEYSTONE SYNC TP 4 5002 TERMINAL, SMALL TEST POINT, KEYSTONE GND R 1 CRCW080510R0J RESISTOR, VISHAY R 2 R 3 CRCW08051002F RESISTOR, VISHAY 10.0kΩ R 4 CRCW08051153F RESISTOR, VISHAY 115kΩ R 5 CRCW080510R0J RESISTOR, VISHAY R 6 R 7 CRCW1206R02F RESISTOR, VISHAY , R 8 CRCW1206R02F RESISTOR, VISHAY , 0.02Ω R 9 CRCW1206R015F RESISTOR, VISHAY , 0.015Ω R 10 CRCW08050000Z RESISTOR, VISHAY R 11 R 12 3A, 100v Not Used 10 Not Used 10Ω Not Used 0.02Ω 0Ω Not Used CRCW08052801F AN–1367 LM5115 HV DC Evaluation Board RESISTOR, VISHAY 2.80kΩ SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated PCB Layout(s) www.ti.com Table 1. Bill of Materials (continued) Item 13 Part Number Description Value R 13 CRCW08054990F RESISTOR, VISHAY 499Ω R 14 CRCW080510R0J RESISTOR, VISHAY 10Ω R 15 CRCW08050000Z RESISTOR, VISHAY 0Ω R 16 CRCW08050000Z RESISTOR, VISHAY R 17 R 18 R 19 CRCW08050000Z RESISTOR, VISHAY 0Ω Q 1 SI7852DP MOSFET, N-CH, POWER S0-8 PKG, VISHAY 80V, 11A Q 2 SI7852DP MOSFET, N-CH, POWER S0-8 PKG, VISHAY 80V, 11A Q 4 CZT3019 NPN, CENTRAL SEMI 120V, 2W L 1 D1787-AL CUSTOM INDUCTOR, COILCRAFT 33 µH - 6A U 1 LM5115 IC, SECONDARY SIDE CONTROLLER LM5115 U 2 LM2665M6 IC, CHARGE PUMP CONVERTER LM2665 VR 1 CMHZ4691 DIODE, ZENER, 6.2V 0Ω Not Used Not Used PCB Layout(s) Figure 17. Top Layer Figure 18. Layer 2 SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback AN–1367 LM5115 HV DC Evaluation Board Copyright © 2005–2013, Texas Instruments Incorporated 9 PCB Layout(s) www.ti.com Figure 19. Layer 3 Figure 20. Bottom Layer LM5115, as Viewed from Top 10 AN–1367 LM5115 HV DC Evaluation Board SNVA106B – September 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated 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. 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