Application Note 1861 Author: Paul Orfanu ISL85415DEMO1Z Wide VIN 500mA Synchronous Buck Regulator - Short Form Description Quick Setup Guide The ISL85415DEMO1Z kit is intended for use for Point-ofLoad applications sourcing from 3V to 36V. The kit is used to demonstrate the performance of the ISL85415 Wide VIN Low Quiescent Current High Efficiency Sync Buck Regulator with 500mA output current. 1. Ensure that the circuit is correctly connected to the supply and loads prior to applying any power. The ISL85415 is offered in a 4mmx3mm 12 Ld DFN package with 1mm maximum height. The converter occupies 1.516 cm2 area. 3. Turn on the power supply. Key Features • Wide input voltage range 3V to 36V • Synchronous operation for high efficiency • No compensation required • Integrated high-side and low-side NMOS devices 2. Connect the bias supply to VIN, the plus terminal to VIN (P4) and the negative return to GND (P5). 4. Verify the output voltage is 3.3V for VOUT. Evaluating the Other Output Voltage The ISL85415DEMO1Z kit output is preset to 3.3V; however, output voltages can be adjusted from 0.6V to 15V. Please refer to the application note (AN1860 and to the ISL85415 datasheet (FN8373 for further information. Frequency Control • Internal or external soft-start The ISL85415 has an FS pin that controls the frequency of operation. Default switching frequency is 500kHz when FS is tied to VCC (R10 = 0). By removing R10 the switching frequency could be changed from 300kHz (R12 = 340k) to 2MHz (R12 = 32.4k). Please refer to datasheet ISL85415 (FN8373) for calculating the value of R10. Do not leave this pin floating. • Minimal external components required Disabling/Enabling Function • Selectable PFM or forced PWM mode at light loads • Internal fixed (500kHz) or adjustable switching frequency 300kHz to 2MHz • Continuous output current up to 500mA • Power-good and enable functions available Recommended Equipment The following materials are recommended to perform testing: • 0V to 50V Power Supply with at least 2A source current capability • Electronic Loads capable of sinking current up to 1.5A • Digital Multimeters (DMMs) • 100MHz quad-trace oscilloscope • Signal generator ISL85415DEMO1Z board has EN pin tied to VCC via R7. This keeps the part enabled all the time. To disable the part, remove R7 and populate R8 with a 0Ω resistor. SYNC Control The ISL85415 evaluation board has a SYNC pin that allows external synchronization frequency to be applied. Default board configuration has R6 = 200k to VCC, which defaults to PWM operation mode and also to the pre-selected switching frequency set by R12 (see datasheet and previous section” Frequency Control” for details). If this pin is tied to GND the IC will operate in PFM mode. For PFM operation, remove R6 and populate R9 with 0Ω resistor Soft-Start /COMP Control R15 selects between internal (R15 = 0) and external soft-start. R11 selects between internal (R11 = 0) and external compensation. Please refer to Pin Description Table (Page 3) of the ISL85415 (FN8373) datasheet. July 22, 2013 AN1861.0 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. Copyright Intersil Americas LLC 2013. All Rights Reserved. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries. All other trademarks mentioned are the property of their respective owners. Application Note 1861 100 VIN = 12V VIN = 15V 95 VIN = 5V EFFICIENCY (%) 90 85 80 75 70 VIN = 33V VIN = 24V 65 60 55 50 FIGURE 1. FRONT OF EVALUATION BOARD ISL85415DEMO1Z 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 OUTPUT LOAD (A) FIGURE 2. EFFICIENCY vs LOAD, PFM, VOUT = 3.3V ISL85415DEMO1Z Schematic R10 OPEN VCC CSS 0.033UF R15 OPEN ? A SS 1 SS SYNC P4 C3 P7 C1 10UF C10 150UF C2 10UF 2 SYNC VO C6 22UF C5 22UF FS 12 COMP11 3 BOOT 0.1UF VIN R12 120K 4 VIN 5 PHASE L1 22UH 6 PGND EN 7 EP DFN12 P5 C7 470PF C8 OPEN ISL85415 R11 OPEN R3 100K VO R1 FB 10 VCC 9 PG 8 VCC VCC PG EN 90.9K P8 C9 1UF C4 100PF R2 20K A A VIN P9 A VCC R7 200K R6 200K SYNC EN P2 P1 R9 OPEN A PG R8 OPEN A NOTE: If the IC is used in an application where the input test leads have large parasitic inductance, the input electrolytic capacitor C10 may be added to prevent transient voltages on the input pin. ISL85415DEMO1Z Board Layout FIGURE 3. SILK SCREEN TOP FIGURE 4. SILKSCREEN BOTTOM 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 AN1861.0 July 22, 2013