UM1661 EVB User’s Guide UM1661 Evaluation Board User’s Guide V1.0 Version Date 1.0 2011-08-16 http://www.union-ic.com Prvoider Approve Note Initial version. 1/10 UM1661 EVB User’s Guide Table of Contents 1.Board Information 1.1 Schematic 1.2 PCB Layout 1.3 Interface Define 2. Board Operation 2.1 Power Supply 2.2 Enable 2.3 LED Load 3. Board Component 3.1 Capacitor 3.2 Inductor 3.3 Schottky Diode 3.4 Sampling Resistor 4. Circuit Protect 4.1 Over Voltage Protect 4.2 Over Current Protect 5. Other Application 5.1 Muti-string LED Application 5.2 Dimming Control Application http://www.union-ic.com 2/10 UM1661 EVB User’s Guide 1 . Board Information UM1661 is a high efficient LED driver chip, It can be used for LED constant current driver in battery-powered systems.UM1661 EVB board is a evaluation test platform. The board can be used for the chip performance test validation, to modify some components of the parameters, the user can verify the circuit characteristics and parameters, to ensure the practical application of user interests.UM1661 EVB board also can demonstrate the main function of the chip, allowing users to fully experience the advantages of using the chip. 1.1 Schematic Fig 1.1 is UM1661 EVB board design schematic (without LED load). Fig 1.1 UM1661 EVB board schematic http://www.union-ic.com 3/10 UM1661 EVB User’s Guide 1.2 PCB Layout Fig 1.2, Fig 1.3 is PCB layout and components location diagram of UM1661 EVB board. Fig 1.2 UM1661 EVB board PCB top layer Fig 1.3 http://www.union-ic.com UM1661 EVB board PCB bottom layer 4/10 UM1661 EVB User’s Guide 1.3 Interface Define Tab 1.1 is the directions of UM1661 EVB board interface signals Tab 1.1 UM1661 EVB board interface Interface Function VIN Power supply input . GND Ground. EN VOUT FB Chip enable/disable option. The board output. The output feedback. Note 2.0V -- 6.0V power supply. EN=ON (1): enable. EN=OFF (0): disable. LED drive output. 2 . Board Operation Use UM1661 EVB board, you need to properly connect an external power supply and external LED load, set EN signal. When these condition is good ,the output and LX pin have Fig 2.1 waveform diagram (VIN=3.6V, 3 pcs LED load).Fig 2.2 is current waveform diagram in inductor (voltage on 1Ohm). http://www.union-ic.com 5/10 UM1661 EVB User’s Guide Fig 2.1 Output waveform diagram (Vin=3.6V, 3 pcs LED load) Fig 2.2 Inductor current waveform diagram 2.1 Power Supply http://www.union-ic.com 6/10 UM1661 EVB User’s Guide UM1661 EVB board's input supply voltage VIN range: 2.0V - 6.0V, can use the power supply or Li battery and so on. Power supply when using, you need to confirm there is sufficient margin with the current limit set. Input power cable should be thicker to reduce the loss of input voltage when the load current is larger. 2.2 Enable EN signal should be set to ON, UM1661 EVB board is in normal working condition. 2.3 LED Load LED load can use white LED. If using the other type LED, some circuit parameters need to re-calculate. UM1661 EVB board to set the drive current of 20mA, can drive a string or two strings LED load. Driving more LED strings, need to adjust the resistance value of R2, improving LED brightness. The EVB board can drive following LED load if no change R2. z 1 string white LED: (1 x 3) pcs to (1 x 7) pcs z 2 strings white LED: (2 x 3) pcs to (2 x 7) pcs 3. Board Component http://www.union-ic.com 7/10 UM1661 EVB User’s Guide Tab 3.1 is the BOM list of UM1661 EVB board. Tab 3.1 UM1661 EVB board BOM list Reference Description U1 LED Driver Chip. C1 Capacitor,4.7uF,10V,Ceramic,0805. C4 Capacitor,4.7uF,50V,Ceramic,0805. L1 Inductor,10uH,500mA,SMT. D1 Schottky diode,SS14,SMT. R2 Resistor,10Ohm,0603. R1,CFF EN Part No. UM1661 SS14 (No used.) Option jumper 3.1 Capacitor The input current is discontinuous during UM1661 switching on-off, and therefore an input capacitor is necessary to ensure the VIN does not drop excessively. The recommended input capacitance is 2.2uF to 22uF depending on the application. The EVB board use a 4.7uF capacitor. A low ESR capacitor is required to reduce the noise and increase stability. The surface mount multilayer ceramic capacitors (MLCC) have very low ESR and are strongly recommended to use .The X5R, X7R type MLCC are good choices for input capacitors, the tantalum and low-ESR electrolytic capacitors may also suffice. The output capacitor is required to maintain output voltage low ripple. The recommended output capacitor is 4.7uF minimum. The ESR characteristics of the output capacitor also affect the stability of system, and a low ESR capacitor is necessary. Like input capacitor, recommended to use the X5R, X7R type MLCC for output capacitor. For the tantalum and electrolytic type, the ESR need less than 50mOhm. When a string load have a lot of LED light, the output voltage is higher, and the output capacitor operating voltage require to double check for MLCC type. 3.2 Inductor The inductor maintain a continuous current to the output load. The inductor value determines the input ripple. The value increase will decrease the input ripple current. http://www.union-ic.com 8/10 UM1661 EVB User’s Guide The recommended inductor vale is 10uH, suit to the load current less than 200mA.If the load current is increase, the value should be decreased. When selecting an inductor, make sure that it is capable of supporting the peak input current without saturating. Inductor staturation will result in a sudden reduction in inductance and prevent the regulator from operating correctly. The inductor saturation current is recommended 1.3 to 1.5 time of the peak input current. 3.3 Schottky Diode During the switch off, the schottky diode conducts current. The schottky diode reverse voltage require greater than maximum VOUT. The recommended reverse voltage is 1.2 to 1.5 time of the maximum VOUT. The schottky diode peak forward current require greater than maximum output current. The recommended value is 1.5 time of the peak output current. In the demo board, SS14, RB551, MBR0530 can be use. 3.4 Sampling Resistor When UM1661 is running normally, the feed back voltage FB is feeded back to inside for LED constant current control. The feed back voltage is 200mV. The LED load current Iout is determined by the sampling resistor R2’s value. When LED current is given, the resistor R2’s value is: R2 (Ohm) = 200 (mV) / Iout (mA). In the EVB board,R2’s value is 10 Ohm, the LED load current is 20mA. 4. Circuit Protect 4.1 Over Voltage Protect When the output voltage exceeds 24V,OVP feedback signal make the chip into the protected status with the output off. If you do not use the OPV protection, output voltage can exceed 24V. In general, the maximum should be used to about 30V, driving a string LED load with 9 to 10 pcs LED. In this application, It will lead to the risk of damage of the chip when there is no OVP protection http://www.union-ic.com 9/10 UM1661 EVB User’s Guide 4.2 Over Current Protect OCP can effectively protect the on-chip MOS unit, output will be closed when LED load current is too large. For the high current caused by output short, OCP have no the function of protecting. 5. Other Application 5.1 Muti-string LED Application Fig 5.1 is the application circuit of UM1661 EVB board diving multi-string LED load. Fig 5.1 UM1661 EVB board driver multi-string LED In this application, the relationship between single-string LED current lout1 and the resistance value of R2: R2 (Ohm) = 200 (mV) / (n * Iout1 (mA)). Where, n is the number of LED load string. http://www.union-ic.com 10/10 UM1661 EVB User’s Guide 5.21 Dimming Control Application Please find the LED dimming control information in UM1661 datasheet R01. http://www.union-ic.com 11/10