19-1967; Rev 0; 11/07 MAX16821B Evaluation Kit The MAX16821B evaluation kit (EV kit) is a fully assembled and tested surface-mount printed-circuit board (PCB) designed to evaluate the MAX16821B pulsewidth-modulation (PWM) LED driver controller in a boost configuration. The MAX16821B EV kit operates from a DC supply voltage of 7V to 24V. The EV kit's output is configured to deliver 660mA of current into series LED string with a maximum forward voltage of 28V. The LED brightness can be dimmed using a digital PWM signal. The EV kit provides an option to configure the MAX16821B IC's overvoltage protection, switching frequency, and frequency compensation. The MAX16821B EV kit also features a clock output PCB pad to drive a second LED current regulator out-of-phase. Features 7V to 24V Input-Voltage Range 660mA Output Current Pulse-Width-Modulated LED Current Dimming Resistor-Adjustable Overvoltage Protection and Switching Frequency Clock Output Fully Assembled and Tested Ordering Information PART TYPE MAX16821BEVKIT+ EV Kit +Denotes lead-free and RoHS-compliant. Component List DESIGNATION QTY C1, C5, C6 3 DESIGNATION QTY 10F10%, 50V X7S ceramic capacitors (1210) Taiyo Yuden UMK325BJHI06K L1 1 8.8H, 4A inductor Sumida CDEP105-8R8 N1-N4 4 60V, 115mA n-channel MOSFETs (SOT23) Central Semiconductor 2N7002 LEAD-FREE DESCRIPTION DESCRIPTION C2 1 0.1F10%, 50V X7R ceramic capacitor (1206) Murata GRM319R71H104K C3, C4 2 1000pF10%, 25V X7R ceramic capacitors (0603) Murata GRM188R71E102K N5 1 40V, 4.9A n-channel MOSFET (8-pin SO) Vishay Si4446DY C7 1 0.022F10%, 50V X7R ceramic capacitor (0603) Murata GRM188R71H223K N6 1 60V, 3.2A n-channel MOSFET (6-pin TSOP) Vishay Si3458DV-E3 R1 1 249k 1% resistor (0603) 1 4.7F10%, 6.3V X7R ceramic capacitor (0603) Murata GRM188R70J475K R2, R5, R10 3 10k 1% resistors (0603) R3 0 0.1F10%, 50V X7R ceramic capacitors (0603) Murata GRM188R71H104K Not installed, resistor--shorted (0603) R4 1 124k 1% resistor (0603) R6 1 0.007 2%, 0.5W sense resistor (1206) IRC LRC-LRF1206LF-01-R007-G C8 C9, C10 D1 2 1 3A, 60V Schottky diode (SMA) Diodes Inc. B360A-13-F ________________________________________________________________ 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: MAX16821B General Description Evaluates: MAX16821B MAX16821B Evaluation Kit Component List (continued) DESIGNATION R7 QTY 1 DESCRIPTION DESIGNATION QTY R13 1 1k 1% resistor (0603) U1 1 Maxim PWM LED driver controller MAX16821BATI+ (28-pin thin QFN-EP*, 5mm x 5mm x 0.8mm) -- 1 PCB: MAX16821B Evaluation Kit+ 0.15 1%, 0.5W sense resistor (1206) IRC LRC-LRC1206LF-01-R150-F R8 1 1 5% resistor (0603) R9 1 2k 1% resistor (0603) R11 1 2.49k 1% resistor (0603) R12 1 1.24k 1% resistor (0603) DESCRIPTION *EP = Exposed pad. Component Suppliers SUPPLIER PHONE WEBSITE Central Semiconductor Corp. 631-435-1110 www.centralsemi.com Diodes Inc. 805-446-4800 www.diodes.com IRC Inc. 361-992-7900 www.irctt.com Murata Mfg. Co., Ltd. 770-436-1300 www.murata.com Sumida Corp. 847-545-6700 www.sumida.com Taiyo Yuden 800-348-2496 www.t-yuden.com Vishay 203-268-6261 www.vishay.com Note: Indicate that you are using the MAX16821B when contacting these component suppliers. Quick Start Recommended Equipment Before beginning, the following equipment is needed: * 7V to 24V, 4A DC power supply * One series-connected LED string rated at 660mA (28V maximum LED voltage) * One current probe to measure LED current * One voltmeter Procedure The MAX16821B EV kit is fully assembled and tested. Follow the steps below to verify board operation. Caution: Do not turn on the power supply until all connections are completed. 1) Connect the positive terminal of the power supply to the VIN pad on the EV kit. Connect the negative terminal of the power supply to the PGND pad next to the VIN pad. 2) Connect the anode end of the LED string to the LED+ pad. 3) Connect the cathode end of the LED string to the LED- pad. 2 4) Clip the current probe across the string wires to measure the LED current. 5) Turn on the power supply and increase the voltage to 7V or above. 6) Verify that the LED string DC current is approximately 660mA. 7) Measure the voltage between the LED+ to LEDPCB pads. Detailed Description The MAX16821B EV kit circuit is designed to evaluate the MAX16821B PWM LED driver controller. The EV kit is configured in a boost topology and provides 660mA LED current for a string of user-supplied external highbrightness LEDs (HBLEDs) rated up to 28V. The MAX16821B EV kit operates from a DC supply voltage of 7V to 28V. The EV kit average input current is set to 3.75A using resistor R6. The LED current is set to 660mA using resistor R7. A PWMDIM PCB pad is provided for PWM dimming operation of the external LEDs. A CLKOUT PCB pad is also available to drive a second LED current regulator 180 out-of-phase with the first EV kit. _______________________________________________________________________________________ MAX16821B Evaluation Kit LED+ exceeds the programmed 33V threshold, the low-side driver turns off to prevent current through the LED string connected between LED+ and LED-. Use the following equation to calculate R1 and R2 resistor values for a new overvoltage threshold: R1 = R2 x 100mV R7 = ILED where 100mV is the MAX16821B regulated SENSE+ to SENSE- differential current-sense voltage and ILED is the desired LED current. Input Current-Limit Setting Current-sense resistor R6 sets the EV kit's circuit average input current limit to 3.75A. During an overload condition at low line, the MAX16821B regulates the average input current to 3.75A. Use the following equation to calculate a new R6 value when reconfiguring the input current limit: R6 = 26.4mV IIN where IIN is the input current limit. For additional information, refer to the Average Current Limit section in the MAX16821A/MAX16821B/MAX16821C IC data sheet for setting the input current limit when configuring the MAX16821B in a boost configuration. (VOV _ LIM - VOV ) VOV where VOV_LIM is the desired overvoltage threshold, R2 is typically 10k, and VOV is 1.276V. Switching Frequency The MAX16821B EV kit switching frequency (fSW) is configured to 500kHz by resistor R4. To reconfigure the MAX16821B switching frequency from 125kHz to 1.5MHz, use the equations below to calculate the new value for R4: R4 = R4 = 6.4 x 1010 , for 40k R4 120k fSW 6.25 x 1010 , for 120k R4 500k fSW where fSW is the desired switching frequency. When reconfiguring the MAX16821B EV kit switching frequency, other components may need to be changed for proper stable operation. LED Brightness Dimming Clock Output The LED brightness can be dimmed using a PWM signal with a 5V logic-high level and frequency range of 100Hz to 5kHz. Connect the PWM signal to the PWMDIM and SGND PCB pads to control the LEDs' brightness. The MAX16821B EV kit also features a clock output signal that is 180 out-of-phase with respect to MOSFET N5. The clock output is available at the CLKOUT PCB pad. Use the SGND PCB pad as a reference ground for the CLKOUT signal. Output Overvoltage Protection Output Enable (EN) The maximum voltage on the LED+ pin is limited to 33V, with respect to GND, by a resistor feedback network formed by resistors R1 and R2. When the voltage at The MAX16821B is enabled through pullup resistor R5. To disable the MAX16821B EV kit, connect the EN PCB pad to the SGND pad. _______________________________________________________________________________________ 3 Evaluates: MAX16821B LED Output Current The MAX16821B delivers 660mA into an LED string rated up to a maximum of 28V. Resistor R7 sets the MAX16821B EV kit LED output current. Use the following equation to calculate R7 when reconfiguring the LED current: Evaluates: MAX16821B MAX16821B Evaluation Kit R5 10k 1% EN VIN VIN VCC SGND 15 R13 1k 1% 16 3 3 EN N.C. OVI U1 DH N3 R12 1.24k 1% 3 1 LX MAX16821B 17 N4 R11 2.49k 1% SGND 7 VIN BST 6 LED+ L1 8.8H 5 4 2 D1 5, 6, 7, 8 18 2 2 CLP 2 C10 0.1F CLKOUT 9 EP N2 2 PWMDIM CLKOUT N.C. 1 1 PWMDIM I.C. 19 20 PGND 8 C3 1000pF R2 10k 1% VCC 14 10 MODE R1 249k 1% 11 12 RT/SYNC R3 SHORTED OUTV 13 LED+ SGND R4 124k 1% OUTV C1 10F 50V C2 0.1F 50V C4 1000pF DL 3 EAOUT 4 EAN LED+ 1 C5 10F 50V N5 C6 PWMDIM 10F 50V 3 PGND CSP R6 0.007 2% 1 CSN VCC PWMDIM 1 SGND R9 2k 1% C7 0.022F 22 25 23 24 26 28 VCC VDD IN SENSE+ CSP SGND N1 2 CLP 21 CSP SGND R10 10k 1% 3 SENSE- PGND SGND PWMDIM VIN R8 1 27 VCC C9 0.1F C8 4.7F Figure 1. MAX16821B EV Kit Schematic 4 1, 2, 5, 6 N6 4 231 DIFF LED- _______________________________________________________________________________________ R7 0.15 1% MAX16821B Evaluation Kit Figure 3. MAX16821B EV Kit PCB Layout--Component Side Figure 4. MAX16821B 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 5 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. Evaluates: MAX16821B Figure 2. MAX16821B EV Kit Component Placement Guide-- Component Side