MAX16802BEVKIT

19-0560; Rev 0; 5/06 MAX16802B Evaluation Kit The MAX16802B evaluation kit (EV kit) demonstrates a current-controlled, high-output-current LED driver based on the MAX16802B. This EV kit is capable of supplying stable output currents of up to 750mA, can run at supply voltages between 10.8V and 30V, and can operate at temperatures ranging from -40°C to +85°C. The MAX16802B EV kit features two different types of dimming controls using either a linear input voltage or a PWM input signal to control the LED brightness. This EV kit also has a UVLO feature to turn off the EV kit operation during low input supply voltage and an overvoltage protection to protect the EV kit under an open-LED condition. The MAX16802B EV kit is a fully assembled and tested board. Warning: Under severe fault or failure conditions, this EV kit may dissipate large amounts of power, which could result in the mechanical ejection of a component or of component debris at high velocity. Operate this EV kit with care to avoid possible personal injury. Features ♦ 10.8V to 30V Wide Supply Voltage Range ♦ Current-Controlled Output ♦ Up to 750mA LED Current at 12V Output ♦ Linear and PWM Dimming Control ♦ Over 80% Efficiency at Full Load ♦ Supply Undervoltage Lockout ♦ Output Overvoltage Protection Ordering Information PART TEMP RANGE IC PACKAGE MAX16802BEVKIT -40°C to +85°C 8 µMAX® µMAX is a registered trademark of Maxim Integrated Products, Inc. Component List DESIGNATION C1, C2, C5, C6 C3, C4, C7 C8 QTY DESCRIPTION DESIGNATION QTY R1 1 R2 1 11kΩ ±1%, 1/8W resistor (0603) R3 1 499kΩ ±1%, 1/8W resistor (0603) 73.2kΩ ±1%, 1/8W resistor (0603) 4 4.7µF, 50V X7R ceramic capacitors Murata GRM32ER71H475KA88L L1 1 Q1 1 3 0.1µF, 50V X7R SMD ceramic capacitors Murata GRM188R71H104KA93D or TDK C1608X7R1H104K 470pF, 50V X7R ceramic capacitor Murata GRM188R71H471KA01D or TDK C1608X7R1H471K 1nF, 50V X7R ceramic capacitor Murata GRM188R71H102KA01D or TDK C1608X7R1H102K 22V, 1.5W zener diode Vishay SMZG3797B 60V, 1A Schottky diode Central Semiconductor CMSH1-60M or Diodes Inc. B160 20V, small-signal Schottky diode Vishay SD103CWS or Diodes Inc. SD103CWS 0.1in, 2-pin hole headers (through hole) 1 C9 1 D1 1 D2 1 D3 1 J1, J2 2 DESCRIPTION 4.7µH, 4.2A peak SMD inductor Coilcraft DO3308P-472ML 60V, 3.2A n-channel MOSFET Vishay Si3458DV 392kΩ ±1%, 1/8W resistor (0603) R4 1 R5, R7 2 1kΩ ±1%, 1/8W resistors (0603) R6 1 330Ω ±1%, 1/4W resistor (1206) R8 1 220Ω ±1%, 1/8W resistor (0603) R9 1 R10 1 0.10Ω ±1%, 1/2W resistor (1206) Susumu RL1632R-R100-F 1Ω ±5%, 1/8W resistor (0603) U1 1 MAX16802B (8-pin µMAX) 4 0.1in, 2-pin male connectors (through hole) 1 MAX16802B PC board VIN, VLED, PWM_IN, LIN_IN — ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 Evaluates: MAX16802B General Description Evaluates: MAX16802B MAX16802B Evaluation Kit Quick Start The MAX16802B EV kit is fully assembled and tested. Follow these steps to verify operation. Do not turn on the power supply until all connections are completed. 1) Connect a DC power supply (0 to 30V or above, 1A) to +VIN and GND. 2) Connect a voltmeter or oscilloscope and the LED array (connected in series to drop about 12V at 750mA forward current) to +VLED and -VLED with anode connected to +VLED and cathode to -VLED. 3) Close the jumpers J1 and J2 to disable dimming. 4) Turn on the power supply and increase the input voltage to above 10.8V. The output voltage increases to forward bias the LED array and delivers approximately 750mA regulated average LED current. Increase the supply further up to 30V and the output average current will be regulated throughout the range. 5) Open shunt J1 and apply a PWM signal to PWM_IN with a frequency of 200Hz and 0 to 2V amplitude. Vary the duty cycle from 0 to 100% and the LED brightness varies from 100% to 0%. When the PWM duty cycle is 0%, the LED brightness is 100%. 6) Close J1, and then open J2. Connect a variable voltage source to LIN_IN and vary the voltage between 0 and 1.6V. The LED brightness varies from 100% to 0%. When the voltage input at LIN_IN is 0V, the LED brightness is 100%. Caution: Avoid powering up the EV kit without connecting load. Detailed Description The MAX16802B evaluation kit is a current-controlled, high-output-current LED driver capable of supplying constant currents up to 750mA, irrespective of supply voltage variations. This EV kit is based on a discontinuous current mode (DCM) buck-boost converter operating at 262kHz to deliver a finite amount of energy to the output every cycle. The amount of this energy depends primarily on the value of the inductor and the user-programmable peak inductor current and does not depend on the supply voltage. Due to this configuration, the power output of the EV kit, and thus the output current supplied to the LED at a given LED operating voltage, becomes independent of the supply voltage. This EV kit is designed to drive LED loads capable of taking up to 750mA of maximum current at a 12V operating voltage. If an LED load with lower operating voltage is used, then the maximum output current will increase by the same ratio to maintain the output power constant. To drive an LED array with a different operating voltage, the value of the current-sense resistor needs to be adjusted. Calculation of the current-sense resistor for a different output operating voltage is explained in later sections. Input Supply UVLO Input supply UVLO is implemented by using a resistor network that combines R3 and R4, which senses the input supply voltage and uses the EN pin to turn on the circuit when the input supply voltage goes above 10.8V. The wake-up threshold of EN is 1.23V when the voltage at EN is rising, and it has a hysteresis of 50mV. Once the device is turned on, due to the hysteresis, the device turns off only if the input supply voltage goes below 10.4V. The UVLO threshold can be adjusted by varying R1 or R2 using the equation below: ⎛V ⎞ R3 = ⎜ UVLO − 1⎟ × R4 ⎝ 1.23 ⎠ where VUVLO is the desired UVLO threshold. To maintain threshold accuracy, keep the value of R4 less than 100kΩ. Component Suppliers PHONE FAX Central Semiconductor SUPPLIER 631-435-1110 631-435-3388 www.centralsemi.com WEBSITE Coilcraft 847-639-6400 847-639-1469 www.coilcraft.com Diodes Inc. 805-446-4800 805-446-4850 www.diodes.com Murata 770-436-1300 770-436-3030 www.murata.com Susumu Co Ltd. 208-328-0307 208-328-0308 www.susumu-usa.com TDK 847-390-4373 847-390-4428 www.component.tdk.com Vishay 402-563-6866 402-563-6296 www.vishay.com Note: Indicate you are using the MAX16802B when contacting these manufacturers. 2 _______________________________________________________________________________________ MAX16802B Evaluation Kit PWM Dimming The PWM dimming is for controlling the LED brightness by adjusting the duty cycle of the PWM input signal connected to the PWM_IN input. A HIGH at PWM_IN input turns off the LED current and LOW turns on the LED current. Connect a signal with peak amplitude between 1.5V to 5.0V and with frequency between 100Hz to 1000Hz and vary the duty cycle to adjust the LED brightness. Frequencies lower than 100Hz can introduce flickering in the light output. LED brightness reduces when duty cycle is increased and vice-versa. When the PWM duty cycle is 0%, the LED brightness will be 100%. Linear Dimming The linear dimming is for controlling the LED brightness by varying the amplitude of the voltage connected to the LIN_IN input. The voltage at the LIN_IN input modulates the current-sense signal and makes the MOSFET trip at a different current level. This process, in turn, changes the output current and thus controls the LED brightness. Since the LED is continuously on at all brightness levels, flickering effect is not present with linear dimming. Vary the LIN_IN voltage between 0 and 1.6V to adjust LED brightness from 100% to 0%. LED brightness reduces when the voltage at LIN_IN is increased and vice-versa. When the voltage at LIN_IN is 0V the LED brightness is 100%. Adjusting the Output Power To change the maximum output power of the EV kit from 12V at 750mA to a different level, adjust the value of the current-sense resistor, R9, using the following equations. Note that the maximum output current of the EV kit is limited to 750mA, the maximum output voltage is limited to 15V, and the maximum output power is limited to 8.25W. Initially calculate the approximate optimum ON duty cycle required at the minimum input voltage: VLED + VD VINMIN + VLED + VD DON = where V INMIN is the minimum input supply voltage, VLED is the LED operating voltage, ILED is the desired LED current and VD is the forward voltage of D2. Calculate the approximate required peak inductor current: k × 2 × ILED IP = f 1 − DON where kf is a noncritical “fudge factor” set equal to 1.1 for this circuit. Calculate the approximate required inductor value and choose the closest standard value smaller than the calculated value: L= DON × VINMIN fSW × IP where L is the inductance value of inductor L1, and fSW is the switching frequency equal to 262kHz. Power transferred to the output circuit by the flyback process is: PIN = 1 × L × IP2 × fSW 2 Power consumed by the output circuit is: POUT = VLED × ILED + VD × ILED Conservation of power requires that the above two equations can be equated and solved for a more precise value of the required peak inductor current. ⎛ 2 × (VLED + VD ) × ILED ⎞ IP = ⎜ ⎟ ⎝ ⎠ fSW × L Set the value of the current-sense resistor, R9, based on the IPEAK value using the following equation: R9 = 0.292 × (R8 + R7) IPEAK × R7 where 0.292V is the current-sense trip threshold voltage. R7 and R8 form a voltage-divider, which scales down the voltage across the current-sense resistor before reaching the current-sense pin of the device. Jumper Selection Keep jumper J1 closed when PWM dimming is not used. Keep jumper J2 closed when linear dimming is not used. _______________________________________________________________________________________ 3 Evaluates: MAX16802B Output Overvoltage Protection The maximum voltage at the positive pin of VLED with respect to GND is limited to 45V by a feedback network formed by R1 and R2, which is connected to the FB pin of the MAX16802B. If the EV kit is turned on with no load or if the LED connection opens, the voltage at the positive pin of VLED may rise to unsafe levels. This condition is sensed by the internal error amplifier, which reduces the peak inductor current to limit the voltage at the positive pin of VLED to 45V. Even if this protection is present, it is recommended to connect the specified load before powering up the EV kit. Evaluates: MAX16802B MAX16802B Evaluation Kit -VLED +VIN R1 392kΩ 1% GND R3 499kΩ 1% R5 1kΩ 1% PWM_IN C2 4.7µF 50V C1 4.7µF 50V 1 R6 330Ω 1% D1 22V L1 4.7µH C3 0.1µF 50V IN UVLO/EN 8 D2 CMSH1-60M MAX16802B 2 R4 73.2kΩ 1% J1 PWM_GND C9 1nF 50V LIN_IN LIN_GND R2 11kΩ 1% J2 3 COMP 4 C8 470pF 50V R7 1kΩ 1% DIM/FB CS VCC NDRV GND 7 6 5 R8 220Ω 1% R10 1Ω 12 56 3 C7 0.1µF 50V Q1 Si3458DV 4 R9 0.10Ω 1% Figure 1. MAX16802B EV Kit Schematic 4 C5 4.7µF 50V C6 4.7µF 50V +VLED U1 D3 SD103CWS C4 0.1µF 50V _______________________________________________________________________________________ MAX16802B Evaluation Kit Figure 3. MAX16802B EV Kit PC Board Layout—Component Side Figure 4. MAX16802B EV Kit PC Board 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 5 © 2006 Maxim Integrated Products Boblet Printed USA is a registered trademark of Maxim Integrated Products, Inc. Evaluates: MAX16802B Figure 2. MAX16802B EV Kit Component Placement Guide— Component Side