MIC2845A High Efficiency 6 Channel Linear WLED Driver with DAM™, Ultra Fast PWM™ Control and Dual Low IQ LDOs General Description Features The MIC2845A is a high efficiency White LED (WLED) driver designed to drive up to six LEDs, greatly extending battery life for portable display backlighting, keypad backlighting, and camera flash in mobile devices. The MIC2845A provides the highest possible efficiency as this architecture has no switching losses present in traditional charge pumps or inductive boost circuits. The MIC2845A provides six linear drivers channels which maintain constant current for up to six LEDs. It features a typical dropout of 40mV at 20mA. This allows the LEDs to be driven directly from the battery eliminating switching noise/losses present with the use of boost circuitry. The MIC2845A features Dynamic Average Matching™ (DAM™) which is specifically designed to provide optimum matching across all WLEDs. The six channels are matched better than ±1.5% typical, ensuring uniform display illumination under all conditions. The brightness is controlled through an Ultra Fast PWM™ Control interface operating down to less than 1% duty cycle. The MIC2845A also features two independently enabled low quiescent current LDOs. Each LDO offers ±3% accuracy from the nominal voltage over temperature, low dropout voltage (150mV @ 150mA), and low ground current under all load conditions (typically 35µA). Both LDOs can be disabled to draw virtually no current. The MIC2845A is available in the 14-pin 2.5mm x 2.5mm Thin MLF® leadless package 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. WLED Driver • • • • • • • • High Efficiency (no Voltage Boost losses) Dynamic Average Matching™ (DAM™) Ultra Fast PWM™ control (200Hz to 500kHz) Input voltage range: 3.0V to 5.5V Dropout of 40mV at 20mA Matching better than ±1.5% (typical) Current accuracy better than ±1.5% (typical) Maintains proper regulation regardless of how many channels are utilized LDOs • • • • • Very low ground current – Typical 35µA Stable with 1µF ceramic output capacitor Dropout of 150mV at 150mA Thermal shutdown and current limit protection Available in a 14-pin 2.5mm x 2.5mm Thin MLF® package Applications • Mobile handsets • LCD Handset backlighting • Handset keypad backlighting • Digital cameras • Portable media/MP3 players • Portable navigation devices (GPS) • Portable applications DAM, Dynamic Average Matching and Ultra Fast PWM are trademarks of Micrel, Inc. MLF and MicroLeadFrame are registered trademark Amkor Technology Inc. Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com April 2010 M9999-041210-C Micrel Inc. MIC2845A Typical Application LCD Display Backlight with 6 WLEDs and Camera Module High Current Flash Driver April 2010 2 M9999-041210-C Micrel Inc. MIC2845A Ordering Information Mark Code(1) LDO1 VOUT LDO2 VOUT Temperature Range Package(2) MIC2845A-MFYMT YNMF 2.8V 1.5V –40°C to +125°C 14-Pin 2.5mm x 2.5mm Thin MLF® MIC2845A-MGYMT YNMG 2.8V 1.8V –40°C to +125°C 14-Pin 2.5mm x 2.5mm Thin MLF® MIC2845A-PGYMT YNPG 3.0V 1.8V –40°C to +125°C 14-Pin 2.5mm x 2.5mm Thin MLF® MIC2845A-PPYMT YNPP 3.0V 3.0V –40°C to +125°C 14-Pin 2.5mm x 2.5mm Thin MLF® MIC2845A-SCYMT YNSC 3.3V 1.0V –40°C to +125°C 14-Pin 2.5mm x 2.5mm Thin MLF® Part Number Notes: ® 1. Thin MLF ▲ = Pin 1 identifier. ® 2. Thin MLF is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is halogen free. 3. Contact Micrel for other voltage options. D5 D6 EN1 LDO1 Pin Configuration VIN D4 LDO2 GND EPAD EN2 D2 D1 RSET END D3 14-Pin 2.5mm x 2.5mm Thin MLF® (MT) (Top View) Pin Description Pin Number Pin Name 1 VIN 2 LDO2 3 EN2 4 END Enable for LED driver. Can be used as a PWM input for dimming of LEDs. Do not leave floating. 5 RSET An internal 1.27V reference sets the nominal maximum LED current. Example, apply a 20.5kΩ resistor between RSET and GND to set LED current to 20mA at 100% duty cycle. 6 D1 LED1 driver. Connect LED anode to VIN and cathode to this pin. 7 D2 LED2 driver. Connect LED anode to VIN and cathode to this pin. 8 D3 LED3 driver. Connect LED anode to VIN and cathode to this pin. 9 GND 10 D4 LED4 driver. Connect LED anode to VIN and cathode to this pin. 11 D5 LED5 driver. Connect LED anode to VIN and cathode to this pin. 12 D6 LED6 driver. Connect LED anode to VIN and cathode to this pin. 13 EN1 14 LDO1 EPAD HS PAD April 2010 Pin Function Voltage Input. Connect at least 1µF ceramic capacitor between VIN and GND. Output of LDO2. Connect at least 1µF ceramic output capacitor. Enable Input for LDO2. Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. Ground. Enable Input for LDO1. Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. Output of LDO1. Connect at least 1µF ceramic output capacitor. Heat sink pad. Not internally connected. Connect to ground. 3 M9999-041210-C Micrel Inc. MIC2845A Absolute Maximum Ratings(1) Operating Ratings(2) Main Input Voltage (VIN) .................................. –0.3V to +6V Enable Input Voltage (VEND, VEN1, VEN2) .......... –0.3V to +6V LED Driver Voltage (VD1-D6) ............................ –0.3V to +6V Power Dissipation .................................. Internally Limited(3) Lead Temperature (soldering, 10sec.)....................... 260°C Storage Temperature (Ts) .........................–65°C to +150°C ESD Rating(4) ................................................. ESD Sensitive Supply Voltage (VIN)..................................... +3.0V to +5.5V Enable Input Voltage (VEND, VEN1, VEN2) ................ 0V to VIN LED Driver Voltage (VD1-D6) ................................... 0V to VIN Junction Temperature (TJ) ........................ –40°C to +125°C Junction Thermal Resistance 2.5mm x 2.5mm Thin MLF-14L (θJA) .................89°C/W Electrical Characteristics WLED Linear Drivers VIN = VEND = 3.8V, VEN1 = VEN2 = 0V, RSET = 20.5kΩ; VD1-D6 = 0.6V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted. Parameter Conditions Min Typ Max Units Current Accuracy(5) 1.5 (6) 1.5 3.6 % Matching % Drop-out Where ILED = 90% of LED current seen at VDROPNOM = 0.6V, 100% brightness level 40 80 mV Supply Bias Current ILED = 20mA 1.4 1.8 mA Shutdown Current (current source leakage) VEND = 0V 0.01 1 µA 0.2 V 0.01 1 µA 80 µs PWM Dimming Enable Input Voltage (VEND) Logic Low Logic High V 1.2 Enable Input Current VIH = 1.2V Current Source Delay (50% levels) Shutdown to On 40 Standby to On 2 µs On to Standby 0.3 µs TRISE 1.3 µs TFALL 0.3 µs Current Source Transient Time (10%-90%) Stand-by to Shutdown Time April 2010 VEND = 0V 10 4 24 40 ms M9999-041210-C Micrel Inc. MIC2845A LDOs VIN = VEN1 = VEN2 = 3.8V, VEND = 0V, COUT1 = COUT2 = 1µF, IOUT1 = IOUT2 = 100µA; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted. Parameter Conditions Output Voltage Accuracy Variation from nominal VOUT Min Max Units –2 +2 % –3 +3 % 0.3 %/V 150 330 mV 35 70 µA 0.05 1 µA 500 mA VIN Line Regulation 0.02 Load Regulation IOUT = 100µA to 150mA Dropout Voltage(7) VOUT ≥ 3.0V, IOUT = 150mA 7 Ground Pin Current Ground Pin Current in Shutdown Typ VEN = 0V Ripple Rejection f = 1kHz; COUT = 2.2µF Current Limit VOUT =0V Output Voltage Noise Frequency 10Hz to 100kHz mV 65 175 300 dB 200 µVRMS Enable Inputs (EN1, EN2) Enable Input Voltage Logic Low 0.2 Logic High Enable Input Current VEN1 = VEN2 = 1.2V Turn-on Time COUT = 1µF; 90% of VOUT V V 1.2 0.01 1 µA 50 100 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. The maximum allowable power dissipation of any TA (ambient temperature) is PD(max) = (TJ(max) – TA) / θJA. Exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown (150°C). 4. Devices are ESD sensitive. Handling precautions recommended. Human Body Model (HBM), 1.5kΩ in series with 100pF. 5. As determined by average current of all channels in use and all channels loaded. 6. The current through each channel meets the stated limits from the average current of all channels. 7. Dropout voltage is defined as the input-output differential at which the output voltage drops 2% below its nominal value measured at VIN = VOUT+ 1V. April 2010 5 M9999-041210-C Micrel Inc. MIC2845A Typical Characteristics April 2010 6 M9999-041210-C Micrel Inc. MIC2845A Typical Characteristics (LDO) April 2010 7 M9999-041210-C Micrel Inc. MIC2845A Functional Characteristics (WLED Driver) April 2010 8 M9999-041210-C Micrel Inc. MIC2845A Functional Characteristics (LDO) April 2010 9 M9999-041210-C Micrel Inc. MIC2845A Functional Diagram EN2 EN1 VIN VIN EN V-to-I OUT TSD LDO1 D1...D6 BG 1.27V VREF GND 6 VIN EN TSD PWM CONTROL END OUT LDO2 POR VREF TSD GND OSC RSET GND Figure 1. MIC2845A Functional Block Diagram which reduces the operating current to less than 1µA in shutdown. Both linear regulators are stable with just 1µF of output capacitance. Functional Description The MIC2845A is a six channel linear LED driver with dual 150mA LDOs. The LED driver is designed to maintain proper current regulation with LED current accuracy of 1.5% while the typical matching between the six channels is 1.5% at room temperature. The LED currents are independently driven from the input supply and will maintain regulation with a dropout of 40mV at 20mA. The low dropout of the linear drivers allows the LEDs to be driven directly from the battery voltage and eliminates the need for boost or large and inefficient charge pumps. The maximum LED current for each channel is set via an external resistor. Dimming is controlled by applying a PWM signal to the END pin. The MIC2845A accommodates a wide PWM frequency range as outlined in the application information section. The MIC2845A has two LDOs with a dropout voltage of 150mV at 150mA and consume 35µA of current in operation. Each LDO has an independent enable pin, April 2010 Block Diagram As shown in Figure 1, the MIC2845A consists of two LDOs with six current mirrors set to copy a master current determined by RSET. The linear LED drivers have a designated control block for enabling and dimming of the LEDs. The MIC2845A dimming is controlled by the Ultra Fast PWMTM control block that receives PWM signals for dimming. The LDOs each have their own control and are independent of the linear LED drivers. Each LDO consists of internal feedback resistors, an error amplifier, a PFET transistor and a control circuit for enabling. 10 M9999-041210-C Micrel Inc. MIC2845A VIN The input supply (VIN) provides power to the linear LED drivers and the control circuitry. The VIN operating range is 3V to 5.5V. 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). LDO1/LDO2 The output pins for LDO one and LDO two are labeled LDO1 and LDO2, respectively. A minimum of 1µF bypass capacitor should be placed as close as possible to the output pin of each LDO. Refer to the layout recommendations section for details on placing the output capacitor (C2, C3) of the LDOs. Figure 2. Peak LED Current vs. RSET EN1/EN2 A logic high signal on the enable pin activates the LDO output voltage of the device. A logic low signal on the enable pin deactivates the output and reduces supply current to less than 1µA. EN1 controls LDO1 and EN2 controls LDO2. Do not leave these control pins floating. D1-D6 The D1 through D6 pins are the linear driver for LED 1 through 6, respectively. Connect the anodes of the LEDs to VIN and each cathode of the LEDs to D1 through D6. When operating with less than six LEDs, leave the unused D pins unconnected. The six LED channels are independent of one another and may be combined or used separately. END The END pin is equivalent to the enable pin for the linear drivers on the MIC2845A. It can also be used for dimming applying a PWM signal. See the PWM Dimming Interface in the Application Information section for details. Pulling the END low for more than 24ms puts the MIC2845A into a low Iq sleep mode. The END pin cannot be left floating; a floating enable pin may cause an indeterminate state on the outputs. A 200kΩ pull down resistor is recommended. GND The ground pin is the ground path for the linear drivers and LDOs. 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. RSET The RSET pin is used to set the peak current of the linear driver by connecting a RSET resistor to ground. The average LED current can be calculated by equation (1): (1) ILED (mA) = 410 * D / RSET (kΩ) D is the duty cycle of the LED current during PWM dimming. When the device is fully on the duty cycle equals 100% (D = 1). A plot of ILED versus RSET is shown in Figure 2. April 2010 11 M9999-041210-C Micrel Inc. MIC2845A Application Information Dynamic Average Matching (DAM™) The Dynamic Average Matching architecture multiplexes four current references to provide highly accurate LED current and channel matching. The MIC2845A achieves industry leading LED channel matching of 1.5% across the entire dimming range. Ultra Fast PWM™ Dimming Interface The MIC2845A supports a wide range of PWM control signal frequencies from 200Hz to 500kHz. This extremely wide range of control provides ultimate flexibility for handheld applications using high frequency PWM control signals. Figure 4. Channel Current Response to PWM Control Signal Frequencies from 50kHz to 500kHz WLED dimming is achieved by applying a pulse width modulated (PWM) signal to the END pin. For PWM frequencies between 200Hz – 20kHz the MIC2845A supports a duty cycle range from 1% to 100%, as shown in Figure 3. The MIC2845A incorporates an internal shutdown delay to ensure that the internal control circuitry remains active during PWM dimming. This feature prevents the possibility of backlight flickering when using low frequency PWM control signals. The MIC2845A also supports Ultra Fast PWM™ frequencies from 20kHz to 500kHz. Due to input signal propagation delay, PWM frequencies above 20kHz have a non-linear relationship between the duty cycle and the average LED current, as shown in Figure 4 and Figure 5. Figures 6 through 10 show the WLED current response when a PWM signal is applied to the END pin (1). Figure 5. Minimum Duty Cycle for Varying PWM Frequency (1) From the low Iq sleep mode PWM frequencies above 15kHz require a logic high enable signal for 80μs to first enable the MIC2845A prior to PWM dimming. Figure 6. PWM Signal at 1% Duty Cycle (Iavg = 0.2mA) Figure 3. Average Current per LED Dimming by Changing PWM Duty Cycle for PWM Frequencies up to 20kHz April 2010 12 M9999-041210-C Micrel Inc. MIC2845A Figure 10. PWM Signal at 100% Duty Cycle (Iavg = 20mA) Figure 7. PWM Signal at 20% Duty Cycle (Iavg = 4mA) High Current Parallel Operation Figure 8. PWM Signal at 50% Duty Cycle (Iavg = 10mA) Figure 11. Six Channel (Parallel) Application Circuit The linear drivers are independent of each other and can be used individually or paralleled to provide larger current. A single LED can be driven with all 6 linear drivers by connecting D1 through D6 together with the cathode of the LED as shown in Figure 11. This will generate a current 6 times the LED current setting and can be used for higher current LEDs such as those used in flash or torch applications. The current is set by the RSET resistor, and can be calculated by the following equation. ILED (mA) = 6 * 410 * D / RSET (kΩ). D is the duty cycle of the LED current during PWM dimming. When the device is fully on the duty cycle equals 100% (D = 1). Figure 12 shows the response time of the six paralleled linear drivers to the enable signal, while Figure 13 shows the turn off response. With a RSET resistor of 1.65k, each linear driver is set to 250mA, with all 6 linear drivers connected in parallel, the MIC2843 is capable of driving a total current of 1.5A. Figure 9. PWM Signal at 80% Duty Cycle (Iavg = 16mA) April 2010 13 M9999-041210-C Micrel Inc. MIC2845A Output Capacitor The MIC2845A LDOs require an output capacitor of at least 1µF or greater to maintain stability, however, the output capacitor can be increased to 2.2µF to reduce output noise without increasing package size. The design is optimized for use with low-ESR ceramic chip capacitors. High ESR capacitors are not recommended because they may cause high frequency oscillation. X7R/X5R dielectric-type ceramic capacitors are recommended due to their improved temperature performance compared to Z5U and Y5V capacitors. X7R-type capacitors change capacitance by 15% over their operating temperature range and are the most stable type of ceramic capacitors. Z5U and Y5V dielectric capacitors change value by as much as 50% and 60%, respectively, over their operating temperature ranges. While using Z5U and Y5V ceramic capacitors, ensure that the loss in capacitance does not drop below the minimum requirement of the device. Figure 12. Current Response Time to Enable Signal Turning On (Six Paralleled Channels) No-Load Stability Unlike many other voltage regulators, the MIC2845A LDOs will remain stable and in regulation with no load. Thermal Considerations The MIC2845A LDOs are each designed to provide 150mA of continuous current. Maximum ambient operating temperature can be calculated based on the output current and the voltage drop across the part. For example if the input voltage is 3.6V, the output voltage is 2.8V, and the output current = 150mA. The actual power dissipation of the regulator circuit can be determined using the equation: Figure 13. Current Response Time to Enable Signal Turning Off (Six Paralleled Channels) PLDO1 = (VIN – VOUT1) I OUT + VIN IGND Because this device is CMOS and the ground current (IGND) is typically <100µA over the load range, the power dissipation contributed by the ground current is < 1% and can be ignored for this calculation. PLDO1 = (3.6V – 2.8V) x 150mA LDO MIC2845A LDOs are low noise 150mA LDOs. The MIC2845A LDO regulators are fully protected from damage due to fault conditions, offering linear current limiting and thermal shutdown. PLDO1 = 0.120W Since there are two LDOs in the same package, the power dissipation must be calculated individually and then summed together to arrive at the total power dissipation. PTOTAL = PLDO1 + PLDO2 Input Capacitor The MIC2845A LDOs are high-performance, high bandwidth devices. 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. April 2010 To determine the maximum ambient operating temperature of the package, use the junction-to-ambient thermal resistance (θJA = 60°C/W) of the device and the following basic equation: ⎛ TJ(max) − TA PTOTAL(max) = ⎜⎜ θ JA ⎝ 14 ⎞ ⎟ ⎟ ⎠ M9999-041210-C Micrel Inc. MIC2845A PLDO2 = (3.6V – 1.5V) x 150mA = 0.315W PTOTAL=0.120W+ 0.315W = 0.435W = (125°C – TA)/(60°C/W) TA = 125°C – 0.435W x 60°C/W TA = 98.9°C Therefore, under the above conditions, the maximum ambient operating temperature of 98.9°C is allowed. TJ(max) = 125°C, is the maximum junction temperature of the die and θJA, is the thermal resistance = 60°C/W. Substituting PTOTAL for PTOTAL(max) and solving for the ambient operating temperature will give the maximum operating conditions for the regulator circuit. For example, when operating the MIC2845A LDOs (LDO1 = 2.8V and LDO2 = 1.5V) at an input voltage of 3.6V with 150mA load on each, the maximum ambient operating temperature TA can be determined as follows: PLDO1 = (3.6V – 2.8V) x 150mA = 0.120W April 2010 15 M9999-041210-C Micrel Inc. MIC2845A MIC2845A Typical Application Circuit Bill of Materials Item C1, C2, C3 Part Number Manufacturer C1608X5R0J105K TDK 06036D105KAT2A AVX(2) GRM188R60J105KE19D Murata(3) VJ0603G225KXYAT Vishay(4) SWTS1007 Seoul Semiconductor(5) D1 – D6 99-116UNC EverLight (6) CRCW060320K5F5EA Vishay(4) R2 CRCW06032003FKEA (4) U1 MIC2845A-xxYMT R1 Description Qty. (1) Vishay Micrel, Inc.(7) Ceramic Capacitor, 1µF, 6.3V, X5R, Size 0603 1 WLED 6 Resistor, 20.5k, 1%, 1/16W, Size 0603 1 Resistor, 200k, 1%, 1/16W, Size 0603 1 6 Channel Ultra Fast PWM™ Linear WLED Driver with DAM™ and Dual Low IQ LDOs 1 Notes: 1. TDK: www.tdk.com 2. AVX: www.avx.com 3. Murata: www.murata.com 4. Vishay: www.vishay.com 5. Seoul Semiconductor: www.seoulsemicon.com 6. EverLight: www.everlight.com 7. Micrel, Inc.: www.micrel.com April 2010 16 M9999-041210-C Micrel Inc. MIC2845A PCB Layout Recommendations Top Layer Bottom Layer April 2010 17 M9999-041210-C Micrel Inc. MIC2845A Package Information 14-Pin (2.5mm x 2.5mm) Thin MLF® (MT) 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 a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2009 Micrel, Incorporated. April 2010 18 M9999-041210-C