19-0965; Rev 0; 8/07 MAX16812 Evaluation Kit The MAX16812 evaluation kit (EV kit) demonstrates the MAX16812 peak-current-mode PWM high-brightness LED (HBLED) driver IC. The MAX16812 EV kit is configured in a step-up/step-down topology with peak-current-mode and average LED current control for the external LEDs. The EV kit is capable of supplying stable LED output currents up to 360mA and operates at supply voltages between 7V and 28V. The maximum output voltage of the LED string can be up to 15V. The MAX16812 EV kit features two different types of dimming controls, using either an analog linear input voltage or a digital PWM input signal to control the LEDs' brightness. This EV kit also has an undervoltage lockout (UVLO) feature that disables the EV kit and overvoltage protection to protect the EV kit under no-load conditions. The MAX16812 EV kit is a fully assembled and tested surface-mount printed-circuit board (PCB). Features 7V to 28V Wide Supply Voltage Range Peak-Current-Mode Control Up to 360mA Output Current Analog Linear Dimming Control PWM Dimming Control Programmable Switching Frequency Shutdown Control Output Overvoltage Protection Fully Assembled and Tested Ordering Information PART TYPE MAX16812EVKIT+ EV Kit +Denotes lead-free and RoHS-compliant. Component List DESIGNATION QTY DESCRIPTION C1, C9, C10, C11 4 4.7F 10%, 50V X7R ceramic capacitors (1210) Murata GRM32R71H475K C2, C18 2 0.1F 10%, 50V X7R ceramic capacitors (0603) Murata GRM188R71H104K C3, C8 2 3.3F 10%, 16V X7R ceramic capacitors (0805) Murata GRM21BR71C335KA73 C4, C6 C5, C15, C16, C17 C7 C12 DESIGNATION QTY DESCRIPTION C13 1 0.47F 10%, 25V X7R ceramic capacitor (0805) Murata GRM219R71E474K C14 1 0.047F 10%, 25V X7R ceramic capacitor (0603) Murata GRM188R71E473K C19, C20 0 Not installed, capacitors D1 1 3A, 60V Schottky diode (SMB) Diodes Inc. B360B 1 150mA, 100V diode (SOD-323) Diodes Inc. 1N4148WS-7-4 2 0.22F 10%, 25V X7R ceramic capacitors (0603) Murata GRM188R71E224K D2 JU1 1 3-pin header 4 1000pF 10%, 50V X7R ceramic capacitors (0603) Murata GRM188R71H102K JU2, JU3 2 2-pin headers L1 1 68H, 3A inductor Coilcraft DO3340P-683ML 1 220pF 10%, 50V X7R ceramic capacitor (0603) Murata GRM188R71H221K N1 1 60V, 4.3A n-channel MOSFET (6-pin SuperSOT) Fairchild Semiconductor FDC5612 R1 1 100k 1% resistor (0603) R2, R9 2 100k potentiometers (single turn) 1 1F 10%, 16V X7R ceramic capacitor (0603) Murata GRM188R71C105K R3 1 1k 1% resistor (0603) R4, R15 2 10k 1% resistors (0603) ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 Evaluates: MAX16812 General Description Evaluates: MAX16812 MAX16812 Evaluation Kit Component List (continued) DESIGNATION QTY DESCRIPTION R5 1 2.49k 1% resistor (0603) R6 1 113k 1% resistor (0603) R7 1 100 5% resistor (0603) R8 1 200k 1% resistor (0603) 2 0.6 1%, 500mW sense resistors (1206) IRC/TT Electronics LRC-LRF-1206LF-01-R600-F R10, R11 R12 R13 1 10 1% resistor (0603) 1 1.8 1%, 250mW sense resistor (1206) Panasonic ERJ-8RQF1R8V DESIGNATION QTY DESCRIPTION R14 1 1.5 1%, 250mW sense resistor (1206) Panasonic ERJ-8RQF1R5V R16 1 2.32k 1% resistor (0603) TP1, TP2, TP3 3 PC mini red test points U1 1 Maxim integrated high-voltage LED driver with analog and PWM dimming control MAX16812ATI+ (28-pin TQFN, 5mm x 5mm x 0.8mm) -- 3 Shunts -- 1 PCB: MAX16812 Evaluation Kit+ Component Suppliers SUPPLIER PHONE WEBSITE Coilcraft, Inc. 847-639-6400 www.coilcraft.com Diodes Inc. 805-446-4800 www.diodes.com Fairchild Semiconductor 888-522-5372 www.fairchildsemi.com IRC/TT Electronics 361-992-7900 www.irctt.com Murata Mfg. Co., Ltd. 770-436-1300 www.murata.com Panasonic Corp. 714-373-7366 www.panasonic.com Note: Indicate that you are using the MAX16812 when contacting these component suppliers. 2 _______________________________________________________________________________________ MAX16812 Evaluation Kit Recommended Equipment Before beginning, the following equipment is needed: * 5V to 28V, 2A power supply * Two digital voltmeters * A series-connected LED string rated at 350mA (15V, max) * One current probe to measure LED current Procedures The MAX16812 EV kit is fully assembled and tested. Follow the steps below to verify operation. Caution: Do not turn on the power supply until all connections are completed. Avoid powering up the EV kit without connecting a load to the LED+ and LED- pads. 1) Connect the power supply's positive terminal to the VIN PCB pad on the EV kit. Connect the power supply's ground terminal to PGND PCB pad. 2) Connect digital voltmeters across the IN and PGND PCB pads and the LED+ and LED- PCB pads. 3) Install a shunt across jumper JU1 (MAX16812 EV kit enabled). 4) Install a shunt across jumper JU2 and verify that a shunt is not installed across jumper JU3 (analog dimming control). 5) Connect the anode-end of the LED string to the LED+ pad. 6) Connect the cathode-end of the LED string to the LED- pad. 7) Adjust potentiometer R9 clockwise. 8) Clip the current probe across the LED wire to measure the LED current. 9) Turn on the power supply and increase the input voltage to 7V. 10) Adjust potentiometer R2 counterclockwise until the LED current amplitude is 350mA. 11) Measure the voltage between the LED+ to LEDPCB pads. Detailed Description The MAX16812 evaluation kit (EV kit) demonstrates the MAX16812 IC peak-current-mode PWM HBLED driver. The MAX16812 EV kit is configured in a step-up/stepdown topology with peak-current-mode and average LED current control for a string of user-supplied external HBLEDs. The EV kit is capable of supplying stable LED output currents up to 350mA and operates at supply voltages between 7V and 28V. The MAX16812 EV kit sets the inductor peak current to 2A using parallel resistors R10 and R11. The average LED current is set to a maximum of 360mA using parallel resistors R13 and R14, and by adjusting potentiometer R2. The MAX16812 EV kit is set to a 300kHz switching frequency using resistor R8. Refer to the Internal Oscillator Switching Frequency section in the MAX16812 IC data sheet for information on setting other switching frequencies. A PCB pad is available to monitor the MAX16812 reference voltage output (REF). A PCB pad is also provided for the external LED intensity voltage-control input DIM. Input Supply UVLO Jumper JU1 controls the MAX16812 EV kit enable mode. Place a shunt across pins 1-2 to enable the MAX16812 EV kit when VIN voltage rises above the IC's 5V UVLO default threshold. Place a shunt across pins 2-3 to disable the EV kit. See Table 1 for JU1 jumper selection. Table 1. JU1 Jumper Selection (EN) SHUNT POSITION EN PIN EV KIT FUNCTION 1-2 Connected to IN Enabled 2-3 Connected to GND Disabled Peak Inductor Current-Limit Setting The parallel combination of current-sense resistors R10 and R11 sets the EV kit's peak inductor current limit to 2A. Use the following equation to calculate the peak current limit: IILIM = 600mV RTOTAL where IILIM is the inductor peak current and RTOTAL is the total parallel resistance placed at the R10 and R11 PCB pads. Refer to the Internal Switching MOSFET Current Limit section in MAX16812 IC data sheet for additional information on setting the peak current-limit threshold. Setting External LEDs Current Resistors R13 and R14 set the MAX16812 EV kit average LED current up to a maximum 360mA. The potentiometer R2 allows the external LED current to be adjusted from 175mA (min) to 360mA (max). The LED string current can be programmed using the following equation: ILED(A) = VREFI 4 x 0.82 where ILED is the LED current, VREFI is the voltage at TP1, and 0.82 is the parallel resistance of R13 and R14. _______________________________________________________________________________________ 3 Evaluates: MAX16812 Quick Start Evaluates: MAX16812 MAX16812 Evaluation Kit PWM Dimming Control (Jumpers JU2 and JU3) PWM dimming is achieved by turning on and off the MOSFET (N1) in series with the LED string. LED dimming is achieved on the MAX16812 EV kit by applying a digital PWM signal or an analog DC voltage at the DIM PCB input pad, or by adjusting potentiometer R9. The voltage at the MAX16812 DIM pin can be adjusted using potentiometer R9 to control the external LEDs' brightness. When adjusting the DC voltage using R9, install a shunt across jumper JU2 and remove the shunt at jumper JU3. The MAX16812 IC DIM pin voltage can be monitored by placing a voltmeter across the DIM and AGND PCB pads. LED dimming can also be accomplished by removing the shunt at jumper JU2 and connecting an external power source at the DIM PCB pad. The DC voltage at the DIM PCB pad sets the MAX16812 duty cycle of the driver controlling the gate of the dimming MOSFET (N1), which controls the external LED brightness. Use the following equation to calculate the voltage at the DIM PCB pad, necessary for the N1 dimming FET output duty cycle (D): DIM D x 1.24V where DIM is the DC voltage at the MAX16812 EV kit DIM PCB pad in volts and D is the output duty cycle of the LED current. For additional information on operating the MAX16812 EV kit in linear dimming or PWM dimming operation, refer to the PWM Dimming section in the MAX16812 IC data sheet. During PWM dimming, there may be audible noise due to the piezo effect of the output capacitors connected at LED+. To alleviate the audible noise, remove ceramic capacitors C9, C10, and C11, and add electrolytic capacitors at the C19 and C20 pads. For proper PWM dimming operation, when using electrolytic capacitors, it may be required to change some of the compensation components. Output Overvoltage Protection The maximum voltage on the LED+ pin is limited to 54.4V with respect to GND, by a feedback network formed by resistors R5 and R6. When the voltage at LED+ exceeds the programmed 54.4V threshold, PWM switching is terminated and no further energy is transferred to the load connected between LED+ and LED-. If the MAX16812 EV kit is turned on with no load, the voltage at LED+ may rise to unsafe levels. Even though the EV kit has overvoltage protection, it is recommended to connect the specified load before powering up the EV kit. Refer to the Setting the Overvoltage Threshold section in the MAX16811/MAX16812 IC data sheet for setting the overvoltage threshold. To control LED dimming using a PWM signal at the DIM PCB pad, remove the shunt from jumper JU2 and place a shunt across jumper JU3. Connect a digital PWM signal with a 5V TTL or 3.3V CMOS logic level and switching frequencies up to 2kHz. See Table 2 for jumpers JU2 and JU3 settings for PWM dimming operation. Table 2. PWM Dimming Operation (Jumpers JU2 and JU3) SHUNT POSITION 4 EV KIT DIMMING OPERATION JU2 JU3 Not installed Not installed Analog DC voltage applied at DIM PCB pad Not installed Installed PWM signal applied at DIM PCB pad Installed Not installed Analog DC voltage at DIM pin adjusted using potentiometer R9 Installed Installed Not applicable _______________________________________________________________________________________ MAX16812 Evaluation Kit PGND R1 100k 1% TP1 VREF 1 2 3 JU1 8 L_REG C2 0.1F R16 2.32k 1% 25 3 REF 2 REFI COMP R4 10k 1% 1 R6 113k R5 1% 2.49k 1% 5 FB CS_OUT IN OV 28 C17 R8 1000pF 200k 1% L_REG 27 3 12 4 13 R13 1.8 1% C18 0.1F 3 TGRM DIM JU2 2 26 C15 1000pF U1 N1 TP3 AGND JU3 6 5 2 1 R14 1.5 1% C14 0.047F 6 4 RT 11 TP2 EN C5 1000pF L_REG 9 R15 C6 10k 0.22F 1% LED+ C8 3.3F 7 C3 3.3F R3 1k 1% 2 1 C1 4.7F 50V PGND C4 0.22F 3 R2 100k VIN VIN Evaluates: MAX16812 AGND C16 1000pF AGND VREF SLP MAX16812 DD DGT SRC SRC CS+ R9 100k 1 24 DIM C7 220pF 23 R10 0.6 1% AGND 22 R11 0.6 1% VIN 14 CS- SGND H_REG LV 15 16 C12 1F HV DRV 17 18 R12 10 1% L1 68H C13 0.47F 1 2 D2 10 GT LX LX 19 20 21 R7 100 VIN LED+ D1 C9 4.7F C10 4.7F C11 4.7F 50V 50V 50V C19 OPEN C20 OPEN LED+ LED- Figure 1. MAX16812 EV Kit Schematic _______________________________________________________________________________________ 5 Evaluates: MAX16812 MAX16812 Evaluation Kit Figure 2. MAX16812 EV Kit Component Placement Guide-- Component Side 6 Figure 3. MAX16812 EV Kit PCB Layout--Component Side _______________________________________________________________________________________ MAX16812 Evaluation Kit Evaluates: MAX16812 Figure 4. MAX16812 EV Kit PCB Layout--GND Layer 2 Figure 5. MAX16812 EV Kit PCB Layout--VCC Layer 3 _______________________________________________________________________________________ 7 Evaluates: MAX16812 MAX16812 Evaluation Kit Figure 6. MAX16812 EV Kit PCB Layout--Solder Side Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.