MIC2860-D High Efficiency 2 Channel WLED Driver with Single Wire Digital Control General Description Features The MIC2860-2D is a high efficiency White LED (WLED) driver designed to drive two WLEDs and greatly extend battery life for portable display backlighting, and keypad backlighting in low cost mobile devices. The MIC2860-2D architecture provides the highest possible efficiency by eliminating switching losses present in traditional charge pumps or inductive boost circuits. It features a typical dropout of 52mV at 30.2mA per channel. This allows the WLEDs to be driven directly from the battery eliminating switching noise and losses present with the use of boost circuitry. The two channels have better than ±0.5% matching, which ensures uniform display illumination under all conditions. The WLEDs brightness is externally preset by a resistor and dimmed using a single wire digital control signal. The MIC2860-2D single wire digital interface accepts digital programming pulses providing 32 dimming steps. The MIC2860-2D is available in Thin SOT-23 and SC-70 six pin packages with a junction temperature range of -40°C to +125°C. Datasheets and support documentation can be found on Micrel’s web site at: www.micrel.com. • • • • • • • • • High Efficiency (no switching losses) No charge pumps 2 WLED driver channels Single wire digital control Input voltage range: 3.0V to 5.5V WLED driver dropout of 52mV at 30.2mA Matching better than ±0.5% (typical) Current Accuracy better than ±1.0% (typical) Available in Thin SOT-23 and SC-70 6 pin packages Applications • Mobile handsets • Digital cameras • Portable media/MP3 players • Portable navigation devices (GPS) • Portable applications ____________________________________________________________________________________________________________ Typical Application LCD Display Backlight with 2 WLEDs Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com July 2010 M9999-072010-A Micrel Inc. MIC2860-2D Ordering Information Mark Code(1) Part Number Temperature Range Package(2) MIC2860-2DYC6 62D –40°C to +85°C 6-Pin SC-70 MIC2860-2DYD6 602D –40°C to +85°C 6-Pin Thin SOT-23 Note: 1. Under bar symbol ( _ ) may not be to scale. 2. Package is GREEN RoHS compliant. Lead finish is NiPdAu. Mold compound is halogen free. Pin Configuration 6-Pin SC-70 (C6) (Top View) 6-Pin Thin SOT-23 (D6) (Top View) Pin Description Pin Number MIC2860-2D Pin Name Pin Function 1 SC 2 GND Ground. 3 VIN Voltage Input. Connect at least 1µF ceramic capacitor between VIN and GND. 4 D2 LED2 driver. Connect LED anode to VIN and cathode to this pin. Do not leave floating.(1) 5 RSET 6 D1 Serial Control Digital input. Do not leave floating. Connect an external resistor from this pin to GND to set the maximum LED current. Example, apply a 9.53kΩ resistor between RSET and GND to set LED current to 30mA at 100% duty cycle. LED1 driver. Connect LED anode to VIN and cathode to this pin. Do not leave floating. (1) Note 1. When driving only 1 LED, connect D1 and D2 in parallel to the LED cathode and adjust the RSET resistor for half the desired output. July 2010 2 M9999-072010-A Micrel Inc. MIC2860-2D Absolute Maximum Ratings(1) Operating Ratings(2) Main Input Voltage (VIN) ................................... -0.3V to +6V Enable Input Voltage (VSC).................................-0.3V to VIN LED Driver Voltage (VD1, D2) ..............................-0.3V to VIN Power Dissipation .....................................Internally Limited Lead Temperature (soldering, 10sec.)....................... 260°C Storage Temperature (Ts) ..........................-65°C to +150°C ESD Rating(3) ................................................. ESD Sensitive Supply Voltage (VIN)..................................... +3.0V to +5.5V Enable Input Voltage (VSC) .................................... 0V to VIN LED Driver Voltage (VD1, D2) .................................. 0V to VIN Junction Temperature (TJ) ........................ –40°C to +125°C Junction Thermal Resistance SC-70 (θJA).....................................................256 °C /W SOT-23 (θJA) ..................................................177 °C /W Electrical Characteristics VIN = VSC = 3.6V, CIN = 1µF, RSET = 9.53kΩ; VD1, D2 = 0.6V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 85°C; unless noted. Parameter Conditions (4) Current Accuracy Min Typ Max Units 27.18 30.2 33.22 mA ±0.5 ±3 % (5) Matching Drop-out (VD1, D2) Where ILED = 90% of LED current seen at VDROPNOM = 0.6V, 100% brightness level 52 125 mV Ground/Supply Bias Current IOUT = 30.2mA 0.7 1.5 mA Shutdown Current (current source leakage) VSC = 0V > 500µs 0.01 1 µA 0.4 V Digital Dimming VSC Input Voltage Logic Low 1.4 Logic High VSC Enable Input Current VSC = 1.2V tSHUTDOWN Time SC pin is low to put into shutdown tPROG_HIGH, tPROG_LOW Time for valid SC edge; Ignored if outside limit range tSTART_UP Delay from SC is high to start up V 0.01 1 100 500 µs 75 µs 0.3 33 µA µs Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF. 4. As determined by average current of all channels in use and all channels loaded. 5. The current through each LED meets the stated limits from the average current of all LEDs. July 2010 3 M9999-072010-A Micrel Inc. MIC2860-2D Typical Characteristics Dropout Voltage vs. RSET 35 60 40 LED1 30 LED2 20 DROPOUT VOLTAGE (mV) 50 25 20 15 10 5 10 0 0 5 10 15 20 25 30 8 35 12 16 Dropout Voltage vs. Temperature LED2 50 LED1 25 RSET = 9.53kΩ 0 32 0 5 10 15 20 25 30 35 BRIGHTNESS LEVEL RSET = 9.53kΩ 0.45 0.40 60 BL-31 40 BL-21 20 BL-0 MATCHING (%) 32.0 20 40 60 0.25 0.20 BL-31 0.15 BL-11 0.05 RSET = 9.53kΩ 0 BL-21 0.30 0.10 BL-11 -40 -20 0.35 0.00 -40 -20 80 100 120 0 20 40 60 80 100 120 TEMPERATURE (°C) TEMPERATURE (°C) LED Current vs.Temperature LED Current vs. Temperature 22.0 LED CURRENT (mA) 31.0 LED1-BL31 30.5 30.0 LED2-BL31 29.5 29.0 28.5 10.9 28.0 -40 -20 0 20 40 60 TEMPERATURE (°C) 80 21.0 LED1-BL21 20.5 20.0 LED2-BL21 19.5 19.0 18.5 RSET = 9.53kΩ RSET = 9.53kΩ 10.8 10.7 LED2-BL11 10.6 10.5 LED1-BL11 10.4 10.3 10.2 10.1 RSET = 9.53kΩ 10.0 18.0 100 LED Current vs. Temperature 11.0 21.5 31.5 LED CURRENT (mA) DROPOUT VOLTAGE (mV) 28 75 Matching vs. Temperature 0.50 80 0 LED CURRENT (mA) 24 100 RSET (kΩ) RSET (kΩ) 100 20 Dropout Voltage vs. Brightness Level 125 30 LED CURRENT (mA) DROPOUT VOLTAGE (mV) 70 Peak LED Current vs. RSET -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) Note: BL = Brightness Level July 2010 4 M9999-072010-A Micrel Inc. MIC2860-2D Functional Characteristics July 2010 5 M9999-072010-A Micrel Inc. MIC2860-2D Functional Diagram Figure 1. MIC2860-2D Functional Block Diagram RSET The RSET pin is used by connecting an RSET resistor to ground to set the peak current of the linear drivers. The maximum LED current set by the RSET resistor is shown in the table below: Functional Description The MIC2860-2D is a 2 channel WLED driver. The WLED driver is designed to maintain proper current regulation with LED current accuracy of 1.0% while the typical matching between the 2 channels is 0.5% at room temperature. The WLEDs are driven independently from the input supply and will maintain regulation with a dropout of 52mV at 30.2mA. The low dropout of the linear drivers allows the WLEDs to be driven directly from the battery voltage and eliminates the need for large and inefficient charge pumps. The maximum WLED current for each channel is set via an external resistor. Block Diagram As shown in Figure 1, the MIC2860-2D consists of 2 current mirrors set to copy a master current determined by RSET. The linear drivers have a designated control block for enabling and dimming of the WLEDs. The MIC2860-2D dimming is controlled by an internal Digital Control Interface. VIN The input supply (VIN) provides power to the linear drivers and the control circuitry. The VIN operating range is 3V to 5.5V. Due to wire inductance a minimum bypass capacitor of 1µF should be placed close to the input (VIN) pin and the ground (GND) pin. Refer to the layout recommendations section for details on placing the input capacitor (C1). ILED (mA) 9.53 30.2 11.5 25.0 14.3 20.1 15.8 18.2 19.1 15.1 28.7 10.0 Table 1. Maximum LED Current vs. RSET Resistor Values A plot of maximum ILED versus RSET is shown in Figure 2. Peak LED Current vs. RSET 35 LED CURRENT (mA) 30 25 20 15 10 5 SC The SC pin is equivalent to the enable pin for the linear drivers on the MIC2860-2D. It can also be used for dimming using a single wire digital interface. See the MIC2860-2D Digital Dimming Interface in the Application Information section for details. Do not leave control pins floating. July 2010 RSET (kΩ) 0 8 12 16 20 24 28 32 RSET (kΩ) Figure 2. Peak LED current vs. RSET 6 M9999-072010-A Micrel Inc. MIC2860-2D D1, D2 The D1 and D2 pins are the linear driver inputs for WLED 1 and 2 respectively. Connect the anodes of the WLEDs to VIN and each cathode of the WLEDs to D1 and D2. When operating with a single WLED, D1 and D2 should be connected to the WLED cathode to parallel the outputs for improved dropout performance. Paralleling these pins can also be done to drive a higher current through a single WLED. Do not leave these pins floating July 2010 GND The ground pin is the ground path for the linear drivers. The current loop for the ground should be as small as possible. The ground of the input capacitor should be routed with low impedance traces to the GND pin and made as short as possible. Refer to the layout recommendations for more details. 7 M9999-072010-A Micrel Inc. MIC2860-2D Application Information Brightness levels are linearly spaced with a maximum current equal to 100% of the current set by RSET. The MIC2860-2D is designed to receive programming pulses to decrease brightness from the initial start up default (level 1 maximum current). Once the brightness change signal is received, the SC pin is simply pulled high to maintain the brightness. This “set and forget” feature relieves processor computing power by eliminating the need to constantly send a PWM signal to the dimming pin. Start Up Assuming the MIC2860-2D has been off for a long time, the MIC2860-2D will start-up in its default mode approximately 33µs (tSTART_UP) after a logic level high is applied to the SC pin. In the default mode the WLEDs are turned on at the maximum brightness (level 31). Each falling edge will cause the default brightness level to decrease by one. Digital Dimming Interface Brightness Level (0 - 31) ILED (mA) RSET=14.3kΩ ILED (mA) RSET=19.1kΩ % of Max. Current 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 20.1 19.4 18.8 18.2 17.5 16.8 16.2 15.6 14.9 14.2 13.6 13.0 12.3 11.6 11.0 10.4 9.7 9.1 8.5 7.8 7.1 6.5 5.9 5.2 4.5 3.9 3.3 2.6 1.9 1.3 0.7 0.3 15.1 14.6 14.1 13.6 13.1 12.6 12.2 11.7 11.2 10.7 10.2 9.7 9.2 8.7 8.3 7.8 7.3 6.8 6.4 5.8 5.3 4.8 4.4 3.9 3.4 2.9 2.4 1.9 1.4 0.9 0.5 0.2 100 96.7 93.7 90.4 87.1 83.8 80.8 77.5 74.2 70.9 67.9 64.6 61.3 57.9 55.0 51.7 48.3 45.0 42.1 38.7 35.4 32.1 29.1 25.8 22.5 19.2 16.2 12.9 9.6 6.3 3.3 1.7 Figure 3. Typical Start-Up Timing Shutdown When the SC input pin is pulled low for a period greater than or equal to tSHUTDOWN (500µs), the MIC2860-2D will turn off the current sinks as shown in Figure 4. Table 2. Digital Interface Brightness Level Table The MIC2860-2D incorporates an easy to use single wire, serial programming interface that allows users to set WLED brightness up to 32 different levels as shown in Table 2. To calculate the brightness level for other RSET values, multiply the percentage of max current values by the maximum LED current set by the RSET resistor value from table 1. For example with RSET = 19.1kΩ, the max current (brightness level = 31) is 15.1mA and brightness level 20 would equate to 15.1mA x 0.646 = 9.7mA. Figure 4. Shutdown Timing Once the device is shutdown, the control circuit supply is disabled and the WLEDs are turned off drawing only 0.01µA. Brightness level information stored in the MIC2860-2D prior to shutdown will be erased and upon a following startup signal the WLEDs will be turned on at maximum brightness (level 31). Programming the Brightness Level MIC2860-2D is designed to start driving the WLEDs July 2010 8 M9999-072010-A Micrel Inc. MIC2860-2D 33µs (tSTART_UP) after the SC pin is first pulled high at the maximum brightness level 1. After start up, the internal control logic is ready to decrease the WLED brightness upon receiving programming pulses (positive edges applied to SC pin). The brightness level can be decreased one level by applying a single programming pulse as shown in Figure 5. Brightness settings can be quickly changed by sending programming pulses one after each other. Each programming pulse has a high (tPROG_HIGH) and a low (tPROG_LOW) pulse width that must be between 0.3µs to 75µs. Counter Roll-Over The MIC2860-2D internal counter contains registers from 0 to 31 (32 levels). When the brightness level is at 32 (minimum brightness) and a programming pulse forces the brightness to step down, the counter will rollover to level 31 (maximum brightness). This is illustrated in Figure 7. Figure 7. Down Counter Roll-Over Input Capacitor The MIC2860-2D is a high performance, high bandwidth device. Stability can be maintained using a ceramic input capacitor of 1µF. Low ESR ceramic capacitors provide optimal performance at a minimum amount of space. Additional high-frequency capacitors, such as small valued NPO dielectric type capacitors, help filter out high frequency noise and are good practice in any noise sensitive circuit. X5R or X7R dielectrics are recommended for the input capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore not recommended. Figure 5. Brightness Programming Pulses Multiple brightness levels can be changed as shown in Figure 6. When issuing multiple brightness level adjustments to the SC pin, ensure both tPROG_LOW and tPROG_HIGH are within 0.3µs and 75µs. To maintain operation at the current brightness level simply maintain a logic level high at the SC pin. Figure 6. Consecutive Brightness Level Commands The MIC2860-2D can be programmed to set WLED drive current to produce one of 32 distinct brightness levels. The following section explains how the brightness counter functions with continued programming edges. July 2010 9 M9999-072010-A Micrel Inc. MIC2860-2D MIC2860-2D Typical Application Circuit Bill of Materials Item C1 Part Number C1608X5R0J105K R1 CRCW06032052FT1 U1 MIC2860-2DYC6 Manufacturer TDK (1) (2) Vishay Micrel, Inc.(3) Description Qty. 1µF Ceramic Capacitor, 6.3V, X5R, Size 0603 1 9.53kΩ, 1%, Size 0603 1 2 Channel Digital Control Linear WLED Driver 1 Notes: 1. TDK: www.tdk.com 2. Vishay: www.vishay.com 3. Micrel, Inc.: www.micrel.com July 2010 10 M9999-072010-A Micrel Inc. MIC2860-2D Package Information 6-Pin SC-70 (C6) 6-Pin Thin SOT-23 (D6) July 2010 11 M9999-072010-A Micrel Inc. MIC2860-2D MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is at Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2010 Micrel, Incorporated. July 2010 12 M9999-072010-A