Using the ISL8105AEVAL1Z PWM Controller Evaluation Board ® Application Note November 1, 2007 AN1258.1 Introduction The ISL8105AEVAL1Z evaluation board highlights the operations of the ISL8105A controller in a DC/DC application. The evaluation board is configured for an output voltage of 1.8V and 15A maximum load. VIN = 12V, VOUT = 1.8V, IOUT = 10A VOUT COMP-EN FIGURE 2. SOFT-START FIGURE 1. ISL8105AEVAL1Z EVALUATION BOARD Figure 1 shows the start-up profile of the ISL8105AEVAL1Z in relation to the start-up of the 12V input supply and the bias supply. Power and Load Connections Soft-Start with Pre-Biased Output INPUT VOLTAGE If the output is pre-biased to a voltage less than the expected value, the ISL8105A will detect that condition. Neither MOSFET will turn on until the soft-start ramp voltage exceeds the output; VOUT starts seamlessly ramping from there. The evaluation board is optimized for an input supply of 12V, however, the input supply based on the connection can range from 4.5V to 5.5V or 6.5V to 14.4V. The IC bias supply and the converter input voltage are connected together through R10 to provide single rail power supply application. VIN = 12V, VOUT = 1.8V, IOUT = 1A OUTPUT VOLTAGE LOADING AND MONITORING VOUT Connect the positive lead of the electronic load and the positive lead of a digital multimeter to the VOUT terminal (J4) and the ground lead to the GND terminal (J5). The scope probe terminal (TPV01) can be used to monitor VOUT with an oscilloscope. COMP-EN Start-up The ISL8105A starts up when VBIAS rises above POR threshold and the COMP/EN rises above VDISABLE level. The entire start-up time sequence from POR typically takes up to 17ms. There is fixed 6.8ms delay for the POR to initiate the Overcurrent Protection (OCP) sample and hold operation. The OCP sample and hold operation takes an additional 0ms to 3.4ms (the longer time occurs with the higher overcurrent setting). When the OCP sampling and hold operations are done, the soft-start function internally ramps the reference on the non-inverting terminal of the error amp from 0V to 0.6V in 6.8ms (typ). 1 FIGURE 3. SOFT-START WITH PRE-BIASED OUTPUT CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2007. All Rights Reserved All other trademarks mentioned are the property of their respective owners. Application Note 1258 Output Performance VOUT Switching Frequency The evaluation board comes with a ISL8105A that has a fixed switching frequency of 600kHz. IOUT Output Ripple Figure 4 shows the ripple voltage on the output of the regulator. VOUT FIGURE 6. TRANSIENT RESPONSE VOUT IOUT FIGURE 4. OUTPUT VOLTAGE RIPPLE (20MHz BW) VOUT FIGURE 7. TRANSIENT RESPONSE VOUT FIGURE 5. OUTPUT VOLTAGE RIPPLE AND NOISE (500MHz BW) IOUT Transient Performance Figures 6, 7 and 8 show the response of the output when subjected to transient loading from 7.5A to 15A. Overcurrent Protection The overcurrent function limits the output current by using the bottom-side MOSFET’s rDS(ON) to monitor the current. A resistor, RBSOC, (R8) programs the overcurrent trip level. This method enhances the converter's efficiency and reduces cost by eliminating a current sensing resistor. If overcurrent is detected, the output immediately shuts off, it cycles the soft-start function in a hiccup mode (2 dummy soft-start time-outs, then up to one real one) to provide fault protection. If the shorted condition is not removed, this cycle will continue indefinitely. Figure 9 shows the overcurrent response and hiccup mode operation. 2 FIGURE 8. TRANSIENT RESPONSE AN1258.1 November 1, 2007 Application Note 1258 Efficiency ISL8105A based regulators enable the design of highly efficient systems. The efficiency of the evaluation board using a 5V and a 12V input supply is shown in Figure 11. VOUT 100 IOUT VIN = 5V 90 EFFICIENCY (%) 80 FIGURE 9. OVERCURRENT HICCUP MODE VIN = 12V 70 60 50 40 30 The overcurrent function will trip at a peak inductor current (IPEAK) determined by Equation 1: 20 10 0 2 • I OCSET • R OCSET I PEAK = -----------------------------------------------------------r DS ( ON ) (EQ. 1) where IOCSET is the internal 21.5µA OCSET current source. The OC trip point varies mainly due to the MOSFET’s rDS(ON) variations. To avoid overcurrent tripping in the normal operating load range, calculate the ROCSET resistor from Equation 1 using: 1. The maximum rDS(ON) at the highest junction temperature. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 IOUT (A) FIGURE 11. EVALUATION BOARD EFFICIENCY (VOUT = 1.8V) References For Intersil documents available on the web, see http://www.intersil.com/ [1] ISL8105, ISL8105A Data Sheet, Intersil Corporation, FN6306 2. The minimum IOCSET from the specification table. Determine I PEAK for I PEAK > I OUT ( MAX ) + ( ΔI ) ⁄ 2 where ΔI is the output inductor ripple current. The overcurrent trip point on the evaluation board has been set to 19A for 5VBIAS (24A for 12VBIAS). Figure 10 shows the output voltage recovers from overcurrent condition. VOUT IOUT FIGURE 10. OVERCURRENT HICCUP MODE 3 AN1258.1 November 1, 2007 ISL8105AEVAL1Z Schematic 4 J1 VIN TP2 R10 zero VCC LGATE/OCSET 4 GND 3 UGATE 2 BOOT 1 Q1 DNP FB Q5 RJK0305 G2 S2 G1 S1 SO-8 DUAL R8 1.33k 5 6 7 8 J4 VOUT TP8 L1 DNP 2 COMP/SD 8 PHASE 1.0uH 1 + C6 0.1uF 3 C30 + C34 TP1 ISL8105A SOIC SW1 GND J6 2 7 4 DPAK FET J3 GND 1 Q2 DNP DNP DNP DNP D2_5 D2_6 D1_7 D1_8 C26 1uF C25 1uF 2200uF 220uF DNP DNP + Q6 RJK0301 C33 220uF C35 100uF C32 1.0uF C38 1.0uF DNP C31 100uF C36 100uF C37 1.0uF DNP TP3 GND J5 R1 10.5k 1 C1 47pF R4 5.23k C3 1500pF 2 R3 187 Probe Socket 4 TPVO1 DNP 3 R2 9.53k U2 VCC ISL8105A DFN VCC LGATE/OCSET 7 NC2 GND 4 NC1 3 FB 8 FB COMP 9 COMP/SD 10 PHASE 11 PH DNP 6 EP C2 0.01uF 5 LG UGATE 2 UG BOOT 1 BT Application Note 1258 6 DPAK FET 5 TP7 4 3 2 1 C24 10uF C22 10uF 470uF DNP Q7 TP4 U1 TP6 C21 10uF C23 + 470uF J2 VCC C20 + C4 1.0uF AN1258.1 November 1, 2007 Application Note 1258 ISL8105AEVAL1Z Bill of Materials ID REFERENCE 1 U1 2 QTY 1 PART NUMBER PART TYPE DESCRIPTION PACKAGE VENDOR ISL8105AIBZ IC, Linear IC, Single PWM Controller 8LD SOIC Intersil U2 DNP ISL8105AIRZ IC, Linear IC, Single PWM Controller 10LD DFN Intersil 3 Q1, Q2 DNP MOSFET N-Channel DPAK 4 Q5 1 RJK0305 MOSFET N-Channel, 30V LFPAK Renasas 5 Q6 1 RJK0301 MOSFET N-Channel, 30V LFPAK Renasas 6 Q7 DNP MOSFET N-Channel, Dual 8LD SOIC 7 L1 1 IHLP5050FDER1R0M01 Inductor 1.0µH, high current inductor SMD Vishay 8 SW1 1 EVQ-PAD04M Push Switch SWITCH-PUSH, TH, 6mm, 1P, PUSHB MOM-SPST PANASONIC CAPACITORS 9 C1 1 Capacitor, Ceramic, X7R 47pF, 50V, 5%, NPO, ROHS SM_0603 TDK/Generic 10 C2 1 Capacitor, Ceramic, X7R 0.01µF, 50V, 10%, ROHS SM_0603 TDK/Generic 11 C3 1 Capacitor, Ceramic, X7R 1500pF, 50V, 10%, ROHS SM_0603 TDK/Generic 12 C4 1 Capacitor, Ceramic, X7R 1µF, 16V, 10%, X7R, ROHS SM_0603 TDK/Generic 13 C6 1 Capacitor, Ceramic, X7R 0.1µF, 16V, 10%, ROHS SM_0603 TDK/Generic Capacitor, Alum. Elec RADIAL 8x11 RUBYCON 14 C20, C23 15 C21, C22, C24 DNP 16MCZ470M8X11.5 470µF, 16V, 20%, 21mΩ, Pb-free 3 Capacitor, Ceramic, X5R 10µF, 16V, 10%, ROHS SM_1210 TDK/Generic 16 C25, C26 DNP Capacitor, Ceramic, X5R 1µF, 6.3V, 20%, ROHS SM_1812 TDK/Generic 17 C30, C33, C34 DNP 6.3MCZ1200M8X16 Capacitor, Alum. Elec 18 C31, C35, C36 Capacitor, Ceramic, X5R 100µF, 6.3V, 20%, ROHS SM_1812 TDK/Generic DNP Capacitor, Ceramic, X5R 1µF, 6.3V, 10%, ROHS SM_0603 TDK/Generic 2 Capacitor, Ceramic, X5R 1µF, 6.3V, 10%, ROHS SM_0603 TDK/Generic 21 R1 1 Resistor, Film 10.5kΩ, 1%, 1/16W SM_0603 Panasonic/Generic 22 R2 1 Resistor, Film 9.53kΩ, 1%, 1/16W SM_0603 Panasonic/Generic 23 R3 1 Resistor, Film 187Ω, 1%, 1/16W SM_0603 Panasonic/Generic 24 R4 1 Resistor, Film 5.23kΩ, 1%, 1/16W SM_0603 Panasonic/Generic 25 R8 1 Resistor, Film 1.33kΩ, 1%, 1/16W SM_0603 Panasonic/Generic 26 R10 1 Resistor, Film 1/8W, TF, ROHS SM_0805 YAGEO 19 C32 20 C37, C38 3 1200µF, 6.3V, 20%, 18mΩ, RADIAL 8x16 RUBYCON Pb-free RESISTORS RC0805JR-070RL OTHERS 27 TPVO1 DNP 0293-0-15-15-16-27-10-0 Terminal, Scope Probe CONN-PIN RECEPTACLE, 0.086 DIA, 0.200 L, ROHS MILL-MAX 28 J1, J3, J4, J5 4 111-0702-001 Banana Connector CONN-GEN, BIND. POST, THMBNUT-GND JOHNSON COMPONENTS 29 J2, J6 2 1514-2 Turrett Post CONN-TURRET, TERMINAL POST, TH, ROHS Keystone Test Point CONN-MINI TEST POINT, VERTICAL, WHITE, ROHS Keystone 30 TP1-TP4, TP6-TP8 DNP 5002 5 AN1258.1 November 1, 2007 Application Note 1258 ISL8105AEVAL1Z Printed Circuit Board Layers ISL8105AEVAL1Z FIGURE 12. ISL8105AEVAL1Z - TOP LAYER (SILKSCREEN) FIGURE 13. ISL8105AEVAL1Z - TOP LAYER (COMPONENT SIDE) FIGURE 14. ISL8105AEVAL1Z - LAYER 2 6 AN1258.1 November 1, 2007 Application Note 1258 ISL8105AEVAL1Z Printed Circuit Board Layers (Continued) FIGURE 15. ISL8105AEVAL1Z - LAYER 3 FIGURE 16. ISL8105AEVAL1Z - LAYER 4 FIGURE 17. ISL8105AEVAL1Z - BOTTOM LAYER (SOLDER SIDE) Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that the Application Note or Technical Brief is current before proceeding. For information regarding Intersil Corporation and its products, see www.intersil.com 7 AN1258.1 November 1, 2007