Application Note 1490 ISL97801BOOSTEVALZ HPLED Driver Boost Configured Evaluation Board Introduction The schematic of the ISL97801BOOST EVALZ Demo Board is shown in Figure 1. This board is suitable for evaluation of the ISL97801 in a boost mode LED driving scheme. On the demo board, there are two resistors (R2 and R4). They are used to bypass the optional MOSFETs Q1 and Q2, which can be omitted in low cost applications. MOSFET Q1 is used as a fault protection switch to disconnect the input supply if a fault occurs for more than 50ms. It is also used to provide load-dump protection in automotive applications. For applications not requiring load dump or fault protection, it can bypass Q1 with R2 (0Ω). Q2 is used as an optional PWM dimming and load isolation switch. When using PWM dimming control, the LED bias current will vary with the PWM duty-cycle due to the discharge of the output capacitor by the LED’s during the PWM off time. Without Q2, (due to the discharge of the output capacitor), the linear accuracy of the average output current in the LED’s can not be controlled. With Q2, the discharge of the capacitor is eliminated, leading to better linearity of the LED current. For applications not requiring high linear accuracy, MOSFET Q2 can be bypassed with Resistor (0Ω). Using the Board Connect the load to the output marked “2 Power Post”. The load of series LEDs must be connected between the LED+ and LED- pins. The ISL97801 is a current mode output converter, and the output voltage is the product of the programmed output current and the load impedance. September 15, 2009 AN1490.1 1 If the output circuit is opened, the output voltage can rise, and the part will enter overvoltage protection and the device will be shutdown. Set-up the required output current. The output load current is determined with the voltage on the Level pin in this demo board, and the current sense resistor R9. (Vlevel pin biased can be omitted with internal fixed voltage 0.4V if the mode pin is grounded in the actual application). Apply a DC power voltage source on VBAT and PGND pins. For ISL97801, the allowed input voltage range is from 5V to 18V. Due to the boost function, the input DC voltage must be lower than the output voltage. The ISL97801 includes a circuit to generate a 5V voltage which is used to drive the chip, and offer a reference voltage for the system control (VDC). If the applied DC power voltage is lower than 5V, the VDC voltage will track with the applied DC power voltage. It is recommended to apply DC power voltage of over 5V for optimum demo board performance. Apply VLEVEL voltage. The LED bias current is determined by the LEVEL pin voltage (0V to 3V range) and the sense resistor R9. The board is set-up with a 0.5Ω R9 resistor with 1V VLEVEL. The output current will be ~350mA to 400mA depending on the tolerance of the resistor. Apply EN/PWM signal. Apply EN/PWM pin a DC signal for enable signal. If PMW dimming is needed, apply a PWM signal at EN/PWM pin. 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. 2009. All Rights Reserved All other trademarks mentioned are the property of their respective owners. Application Note 1490 ISL97801BOOSTEVALZ Boost Configured Evaluation Board Schematic R2 0Ω Q1 SI4482 J1 VBAT L1 10µH C1 47nF/25V PGND R1 100 C2 22µF/25V J5 SS25 D1 C8 C9 C10 C11 C5 4.7µF/50V 4.7µF/50V 4.7µF/50V 4.7µF/50V 0.1µF/50V J2 J8 C4 ISL97801 12 SWSI R5 10 OVP 3 C14 SWDI 4 SWD2 5 R10 0 J3 LEVEL J9 0.1µF/16V 6 7 TEMP 8 LEVEL FB 9 TMAX 10 11 SWSI R3 OPEN VDD 1 LED+ LED- VHI 2 BOOST/BUCK 13 EN/PWM 20 VIN 14 MODE EN/PWM J4 19 FAULT 18 GND 17 NC 16 VBAT 15 ENL U1 0.1µF/6.3V SGND PGND R7 0 6 5 2 1 4 3 R4 OPEN FDC3512 R8 OPEN R9 0.5 R6 OPEN FIGURE 1. ISL97801BOOSTEVALZ BOOST CONFIGURED EVALUATION BOARD SCHEMATIC ISL97801BOOSTEVALZ Board Layout FIGURE 2. TOP VIEW 2 FIGURE 3. BOTTOM VIEW AN1490.1 September 15, 2009 Application Note 1490 TABLE 1. BILL OF MATERIALS PART DESIGNATOR FOOTPRINT 0.1µF/16V C14 603 0.1µF/50V C5 603 0.5 R9 603 0 R10 603 0 R7 603 0 R4 (Open) 1206 0 R2 1206 Open R6 603 4.7µF/50V C8, C9, C10, C11 1812 10 R5 603 10µF/6.3V C4 603 10µH L1 DS3316 22µF/25V C2 1210 47nF/25V C1 603 100 R1 603 FDC3512 Q2 SOT23-6 ISL97801 U1 LPP-20 SI4482 Q1 (open) SO-8 SS25 D1 DO-214 VBAT J1 POWERPOST open R3 603 open R8 603 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 3 AN1490.1 September 15, 2009