ISL6700EVAL1Z General Purpose Design Tool ® Application Note August 12, 2008 Description VDD The ISL6700 General Purpose Design Tool (ISL6700EVAL1Z) is a very simple evaluation board which can help the user rapidly construct an isolated DC/DC converter in several configurations. The board consists of the Intersil ISL6700 Half-Bridge Driver IC, two Intersil IRFR120 MOSFETs, a bootstrap diode, a bootstrap capacitor and two input voltage decoupling capacitors. The ISL6700 can operate at frequencies in excess of 500kHz and has typical propagation delay times of 30ns. It has 1.25A output drive capability and can switch an IRFR120 load with rise and fall times of less than 20ns. VIN VDD VDD HB 1 HI HI C3 0.022µ 8 7 2 U1 6 ISL6700 LI LI Q2 HO HS Q2-S Q1 3 5 VIN HI Q2-S ISL6700EVAL1Z BOARD SECONDARY CIRCUIT Q1-D LI GND PWM PWM ISOLATION FIGURE 2. TWO-SWITCH FORWARD CONVERTER Application #2: Half-Bridge Converter D1 C2 0.1µ AN1006.2 To use the ISL6700EVAL1Z as part of a half-bridge converter, the user needs the configuration depicted in Figure 3. In this topology, the MOSFETs are driven alternately, with some dead time between turn-off of one and turn-on of the other. Therefore, HI and LI are driven with alternating signals PWMA and PWMB from the PWM controller. Q1-D LO VDD 4 VIN C1 0.47µ VSS HI GND FIGURE 1. ISL6700EVAL1Z SCHEMATIC Q2-S LI Application Information The ISL6700 General Purpose Design Tool (ISL6700EVAL1Z) is intended for users who have some experience in power converter design. The 80V rating of the ISL6700 makes it an ideal choice for many isolated DC/DC converters, which are point-of-load converters in a distributed power architecture. To insure adequate design margin, the maximum voltage that should be applied to this input should be less than 80VDC. Three possible application converters are described briefly as follows: Application #1: Two-Switch Forward Converter To use the ISL6700EVAL1Z as part of a two-switch forward converter, the user needs the configuration depicted in Figure 2. In this topology, both MOSFETs are turned on and off together, therefore, HI and LI are tied together. The input signal comes from a pulse-width modulator (PWM) controller, which is sensing the output voltage (and input switch current if current-mode control is used). The Schottky rectifiers clamp the reverse swing of the power transformer and must be rated to handle the input voltage. 1 SECONDARY CIRCUIT ISL6700EVAL1Z BOARD Q1-D PWMA GND PWM ISOLATION PWMB FIGURE 3. HALF-BRIDGE CONVERTER Application #2: Active-Clamp Forward Converter To use the ISL6700EVAL1Z as part of an active-clamp forward converter, the user needs the configuration depicted in Figure 4. In this topology, the MOSFETs are again driven alternately, and HI and LI need to be driven alternately as well. The high-side MOSFET (Q2 in the ISL6700EVAL1Z board), along with capacitor CRESET, is used in this topology as a means to reset the power transformer in a lossless manner. This topology lends itself well to running at duty cycles exceeding 50%, unlike Applications 1 and 2. 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. 2002, 2005, 2008. All Rights Reserved All other trademarks mentioned are the property of their respective owners. Application Note 1006 VDD Additional Information VIN HI The applications previously highlighted, are three possible DC/DC converter topologies where the ISL6700 half-bridge driver can help simplify the design procedure and provide value to the designer and the end user. There are many other possible applications. More detailed information regarding the ISL6700 can be found in the Intersil data sheet. Q2-S CRESET ISL6700EVAL1Z BOARD LI PWMA SECONDARY CIRCUIT Q1-D GND ISOLATION PWM PWMB FIGURE 4. ACTIVE-CLAMP FORWARD CONVERTER ISL6700EVAL1Z Parts List QUANTITY REFERENCE DESIGNATOR 1 1 U1 IC, Half-Bridge Driver, 80V, 1.25A Intersil 2 2 Q1, Q2 MOSFET, N-channel, 100V, 8.4A Fairchild IRFR120 3 1 D1 Diode, Schottky, 100V, 1A On Semi MBRS1100T3 4 1 C1 Capacitor, Ceramic, 0.47µF, 20%, 100V AVX 22251C474MAT2A 4a (Note) 1 C1 Capacitor, Ceramic, 0.47µF, 20%, 200V NIC NMCH2225X7R474K200TR 5 1 C2 Capacitor, Ceramic, 0.1µF, 10%, 50V AVX 12065C104KAT2A 6 1 C3 Capacitor, Ceramic, 0.022µF, 10%, 50V AVX 12065C223KAT2A 7 8 TP1 thru TP8 Cambion 160-2044-02-01-00 8 1 N/A ITEM DESCRIPTION Terminal, Solder, Turreted, Feed-thru ISL6700EVAL1Z PCB VENDOR Intersil PART NUMBER ISL6700IB ISL6700EVAL1ZREVAPCB NOTE: Can be substituted for item #4. 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 2 AN1006.2 August 12, 2008