Evaluates: MAX20078 MAX20078 Evaluation Kit Procedure General Description The EV kit is fully assembled and tested. Follow the steps The MAX20078 evaluation kit (EV kit) provides a proven below to verify board operation. Caution: Do not turn on design to evaluate the MAX20078 synchronous buck the power supply until all connections are complete. controller for high-power, high-brightness (HB) LED drivers. The EV kit is set up as a buck LED driver and 1) Verify that all jumpers (J1, JU1JU4) are in their operates from a 4.5V to 65V DC supply voltage. The default positions, as shown in Table 1. EV kit is configured to deliver up to 2A to one string of 2) Connect the HB LED string anode to the LED+ PCB LEDs. The total voltage of the string can vary from 3V to pad and the cathode to the PGND PCB pad. 55V. The anode of the LED string should be connected 3) Connect DVM1 across the LED+ and PGND PCB to the LED+ terminal and the cathode of the LED string pads. connected to PGND. 4) Connect DVM2 across the REFI and AGND test Features points. 4.5V to 65V Input Voltage 5) Connect the power supply to the VIN PCB pad and the power supplys ground to the PGND PCB pad. Drives 1 to 16 LEDs 6) Clip the current probe across the wire connecting the 0A to 2A LED Current HB LED string to the EV kit. Demonstrates UVLO, Output Short Protection, and Overload 7) Turn on the power supply and set to a voltage greater than the maximum HB LED string voltage, but less Demonstrates Current-Limit and than the 65V maximum input voltage. Thermal-Shutdown Features 8) Use the screwdriver to turn the potentiometer until Proven PCB Layout and Thermal Design DVM2 reads 1.2V. Fully Assembled and Tested 9) Measure the HB LED current using the current probe and verify that current is 2A. Quick Start 10) Verify DVM1 shows the expected LED string voltage. Required Equipment 11) Use the screwdriver to turn the potentiometer until MAX20078 EV kit DVM2 reads 0.7V. 5V to 65V, 4A DC power supply 12) Measure the HB LED current using the current probe Two digital voltmeters (DVM1, DVM2) and verify that current is 1A. Series-connected HB LED string rated to no less than 2.5A Current probe to measure the HB LED current Potentiometer Small flat-blade screwdriver to turn the potentiometer Ordering Information appears at end of data sheet. wiper-adjustment pin 19-8972 Rev 0 3/17MAX20078 Evaluation Kit Evaluates: MAX20078 Table 1. MAX20078 EV Kit Jumper Descriptions (J1, JU1JU4) SHUNT JUMPER DESCRIPTION POSITION Allows the connection of an external 5V (4.5V to 5.5V) supply to V . The internal LDO is CC 1-2 not used. J1 2-3* The internal V LDO is powered from the input voltage applied on IN pin of the device. CC Open V unconnected. Do not leave J1 open. CC REFI pin is now connected to a voltage-divider from V to ground. Adjusting R8 allows CC 1-2* programming the LED current from 0 to 2.2A. JU1 Disconnects the REFI pin of the device from the external voltage-divider on the V pin. CC Open Allows the user to apply an external voltage to set the LED current level. Open* No HUD application. Turning on Q3 does not short the output. JU2 Allows testing of the device in HUD applications. 1-2 Allows shorting the output by turning on Q3. 1-2* DIM pin pulled up to V through a 10k resistor. CC JU3 2-3 DIM pin pulled up to V through a 10k resistor. IN Open DIM pin of the device not connected. Open* DIM pin of the device not synchronized to HUD PWM signal. JU4 1-2 DIM pin of the device synchronized to HUD PWM signal. *Default position. Analog Dimming Control (ICTRL) Detailed Description The EV kit demonstrates the analog dimming feature The MAX20078 EV kit demonstrates the MAX20078 of the buck controller. R7 and R8 form a resistor-divider synchronous buck controller for high-power HB LED between V and AGND. R7 is a 10k resistor and R8 is drivers. The buck controller consists of a fully synchronous CC a 10k potentiometer, with the wiper shorted to the high step-down converter with external MOSFETs, and can drive side of the potentiometer. Install the shunt on JU1 (see a series string of LEDs at currents as high as 30A. The Table 1 for jumper descriptions). Using a flat-blade screw- buck controller uses a proprietary average current-mode- driver, turn the wiper-adjustment pin clockwise to increase control scheme to regulate the inductor current. This control the voltage on the REFI input. Turn the wiper-adjustment method does not need any control-loop compensation, pin counterclockwise to decrease the voltage on the REFI while maintaining nearly constant switching frequency. input. The REFI input allows for analog dimming of the Inductor current sense is achieved by sensing the current HB LED string. A REFI input voltage of 0.2V turns off in the bottom synchronous n-channel MOSFET. It does not the LED driver, an input voltage between 0.2V and 1.2V require any current sense at high voltages. The buck con- provides linear dimming of the HB LED string, and an troller offers both analog and PWM dimming. The EV kit is input voltage > 1.2V sets the HB LED string current to configured to deliver up to 2A to a series LED string. The maximum current (based on the current-sense resistor). string forward voltage can vary from 3V to 55V. Alternatively, the analog dimming input can be set with a power supply. Remove the shunt on JU1 and connect an external power supply directly to the REFI PCB pad to perform analog dimming with a power supply. Do not violate the absolute maximum voltage rating of V + CC 0.3V (refer to the Absolute Maximum Ratings section in the MAX20078 IC data sheet). Maxim Integrated 2 www.maximintegrated.com