MIC3291 1.2MHz PWM White LED Driver with Internal Schottky Diode and Single-Wire Linear Brightness Control General Description Features The MIC3291 is a PWM switching boost regulator that is • Single wire combines 16 level linear brightness and optimized for constant current white LED (WLED) driver shutdown control applications. The MIC3291 features an internal Schottky • 18V / 25V OVP options supports up to four and six diode, allowing an efficient DC/DC solution that requires WLEDs only four external components. • Startup in any one of 16 brightness levels The MIC3291 allows for a single-wire simple digital • Internal Schottky diode interface to control the dimming over 16 steps with a linear • 2.5V to 6.5V input voltage scale. The preprogramming feature allows the user to • 1.2MHz PWM operation select any one of the 16 WLED current levels as the start up brightness level. • Over 500mA switch current The feedback voltage of the MIC3291 is only 250mV, • 250mV reference voltage allowing high efficiency while retaining excellent accuracy • ±5% LED current accuracy for the WLED current. • <1µA shutdown current The MIC3291 implements a constant frequency 1.2MHz • UVLO and over-temperature protection PWM control scheme. The high frequency PWM operation • Thin SOT23-6L package option saves board space by reducing external component sizes. The 1.2MHz PWM scheme also reduces switching noise • 2mm × 2mm leadless MLF® package option and ripple to the input power source. • –40oC to +125oC junction temperature range The 2.5V to 6.5V input voltage range of the MIC3291 allows direct operation from single cell Li-Ion as well as 3 Applications to 4 cell NiCad/NiMH/Alkaline batteries. Battery life is preserved with a low 1µA shutdown current. • Mobile handsets The MIC3291 is available in a low profile Thin SOT23 6• LCD handset backlighting ® pin and 2mm × 2mm MLF 8-pin packages with a junction • Digital cameras temperature range of –40°C to +125°C. • Portable media players/MP3 players Data sheets and support documentation can be found on • Portable applications Micrel’s web site at: www.micrel.com. ___________________________________________________________________________________________________________ Typical Application White LED Driver with OVP and Digital Control MLF and MicroLead Frame are registered trademarks of Amkor Technologies, 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 September 2010 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Ordering Information Marking Code4 Output Voltage Over-Voltage Protection Junction Temperature Range Package2,3 MIC3291-18YD6 W18F Adjustable 18V −40°C to +125°C TSOT23-6 MIC3291-25YD6 W25F Adjustable 25V −40°C to +125°C TSOT23-6 MIC3291-18YML WAF Adjustable 18V −40°C to +125°C 2mm × 2mm MLF® MIC3291-25YML WBF Adjustable 25V −40°C to +125°C 2mm × 2mm MLF® Part Number1 Notes: 1. Other options available. Contact Micrel Marketing for details. 2. MLF is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free. 3. MLF 4. Overbar ( ¯ )and Underbar symbols ( _ ) may not be to scale. ® ® ● = Pin 1 identifier. Pin Configuration 2mm × 2mm 8-Pin MLF® (ML) (Top View) TSOT23-6 (D6) (Top View) Pin Description Pin Number 8-pin MLF ® Pin Number SOT23-6 Pin Name Pin Name 1 6 OUT Output and over-voltage protection (output) 2 5 VIN Supply (Input): 2.5V to 6.5V for internal circuitry. 3 4 DC Single pin digital control. See diagrams. 4 − GND 5 − NC No connect (no internal connection to die) 6 3 FB Feedback (Input): Output voltage sense node. Connect the cathode of the LED to this pin. 7 1 SW Switch Node (Input): Internal power BIPOLAR collector. 8 2 GND Ground (Return): Ground. Pad − GND Ground (Return): Backside pad. September 2010 Ground (Return): Ground. 2 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Absolute Maximum Ratings(1) Operating Ratings(3) Supply Voltage (VIN) .................................................... 7.5V Switch Voltage (VSW) ..................................... –0.3V to 27V Digital Control Voltage (VDC) ..............................–0.3 to VIN FB Voltage (VFB)............................................................. 6V Switch Current (ISW)........................................................ 2A Ambient Storage Temperature (TS)......... –65°C to +150°C ESD Rating(2) ................................................................2KV Supply Voltage (VIN) …………………..…… ......2.5V to 6.5V Output Voltage (VOUT) …………….… ............... (VIN to VOVP) Junction Temperature Range (TJ) …… .... −40°C to +125°C Package Thermal Impedance θJA 2mm × 2mm MLF®-8L ................................. 93°C/W θJA TSOT23-6 .................................................. 235°C/W Electrical Characteristics(4) TA = +25oC, VIN = 3.6V, VOUT = 10V, IOUT = 20mA, unless otherwise noted. Bold values indicate −40°C ≤ TJ ≤ +125°C. Symbol Parameter VIN VUVLO IVIN Supply Voltage Range Under-Voltage Lockout Quiescent Current ISD VFB IFB Typ. Max. Units VFB >500mV 2.1 2 6.5 2.4 4 V V mA Shutdown Current (DC Pin Low ) VDC = 0V for > 2ms. 0.01 1 μA Feedback Voltage 250 263 mV Feedback Input Current (±5%) VFB = 250mV Line Regulation 2.5V ≤ VIN ≤ 4.5V 0.5 Load Regulation 5mA ≤ IOUT ≤ 20mA 0.5 DMAX ISW Maximum Duty Cycle Switch Current Limit VDC DC Pin Thresholds IDC DC Pin Current tshutdown Shutdown Pulse Width tMODE_UP Count UP Mode Pulse Width tMODE_DOWN Count Down Mode Pulse Width tstart_up tprog_low tprog_high Turn-On Delay Time Programming Pulse Width Low Programming Pulse Width High tdelay Minimum Delay for Mode Change Tprog_setup fSW First Pulse Window for Preprogramming Oscillator Frequency September 2010 Condition Min. 2.5 1.8 237 450 86 500 1.1 VIN = 3.6V High Low 90 750 nA % 1200 0.4 VDC = 3.6V 5 10 % mA V μA VIN = 2.8V to 5.5V VDC = Low VIN = 2.8V to 5.5V VDC = Low VIN = 2.8V to 5.5V VDC = Low VIN = 2.8V to 5.5V VIN = 2.8V to 5.5V VIN = 2.8V to 5.5V VIN = 2.8V to 5.5V VDC = High 1260 140 1 1 140 32 32 VIN = 2.8V to 5.5V 35 50 µs 1.35 MHz 100 160 420 500 1 3 µs µs µs µs µs µs µs 1.2 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Electrical Characteristics(4) (Continued) TA = +25oC, VIN = 3.6V, VOUT = 10V, IOUT = 20mA, unless otherwise noted. Bold values indicate −40°C ≤ TJ ≤ +125°C. Symbol Parameter Condition VD Schottky Forward Drop ID = 150mA Min. IRD Schottky Leakage Current VR = 30V VOVP Over-Voltage Protection 3291- 18 only (nominal voltage) 3291- 25 only (nominal voltage) Tj Over-Temperature Threshold Shutdown 15 22.1 Typ. Max. Units 0.8 1 V 4 μA 18 25 V 16.5 23.5 150 °C Notes: 1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(Max), the junction-to-ambient thermal resistance, θ JA, and the ambient temperature, TA. The maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. 2. IC devices are inherently ESD sensitive. Handling precautions required. Human body model, 1.5kΩ in series with 100pF. 3. This device is not guaranteed to operate beyond its specified operating rating. 4. Specification for packaged product only. September 2010 4 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Typical Characteristics 100 250 225 200 175 150 125 100 75 80 70 70 60 VIN = 3.6V 30 20 25 10 0 VIN = 4.2V 50 50 L = 10µH COUT = 0.27µF 70 VIN = 3.6V VIN = 2.8V 40 30 20 60 20 0 5 10 15 20 30 25 L = 22µH COUT = 0.27µF 5 10 15 20 600 500 400 250 0 4.5 INPUT VOLTAGE (V) September 2010 5 5.5 6 LEDs 100 200 4 250 248 246 244 3 3.5 4 4.5 5 5.5 6 Current Limit vs. Input Voltage 0.95 150 300 3.5 252 1 200 50 3 254 INPUT VOLTAGE (V) CURRENT LIMIT (A) INPUT CURRENT (mA) 700 2.5 256 2.5 25 L=10µH 300 800 25 242 Input Current vs. Input Voltage 350 900 20 258 WHITE LED CURRENT (mA) Peak Switch Current vs. Input Voltage 15 240 0 WHITE LED CURRENT (mA) 1000 10 Feedback Voltage vs. Input Voltage 260 VIN = 2.8V VIN = 4.2V 40 5 WHITE LED CURRENT (mA) 0 0 L = 10µH COUT = 0.27µF 25 50 10 0 FEEDBACK VOLTAGE (mV) 15 VIN = 3.6V 20 L = 22µH COUT = 0.27µF 10 10 FEEDBACK VOLTAGE (mV) 70 EFFICIENCY (%) EFFICIENCY (%) 80 50 5 90 80 VIN = 4.2V 30 10 3 Series White LED Efficiency 100 VIN = 4.2V 60 VIN = 3.6V 40 WHITE LED CURRENT (mA) 6 Series White LED Efficiency 90 50 0 0 BRIGHTNESS LEVEL (0-15) 100 60 20 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 VIN = 2.8V 90 80 40 3 Series White LED Efficiency 100 VIN = 2.8V 90 EFFICIENCY (%) FEEDBACK VOLTAGE (mV) 275 6 Series White LED Efficiency EFFICIENCY (%) Feedback Voltage vs. Brightness Level 0.9 0.85 0.8 0.75 0.7 0.65 3 LEDs 0.6 2.5 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5 5.5 6 2.6 3.1 3.6 4.1 4.6 5.1 5.6 6.1 6.6 INPUT VOLTAGE (V) M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Functional Characteristics September 2010 6 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Functional Characteristics (Continued) September 2010 7 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Functional Diagram MIC3291 Block Diagram September 2010 8 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Functional Description The MIC3291 is a constant frequency, PWM current mode boost LED driver. It is composed of an oscillator, slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, bipolar output transistor, digital interface with D/A converter and Schottky rectifier diode. It features true single-wire linear digital control that may be used to vary the brightness of the output LEDs. The oscillator generates a 1.2MHz clock which triggers the PWM generator that turns on the output transistor and resets the slope compensation ramp generator. The current amplifier is used to measure the switch current by amplifying the voltage signal from the internal sense resistor. The output of the current amplifier is summed with the output of the slope compensation ramp generator. This summed current loop signal is fed to one of the inputs of the PWM generator. MIC3291 Block Diagram The gm error amplifier measures the LED current through the external sense resistor and amplifies the error between the detected signal and the reference voltage indicated by the digital interface. The output of the gm error amplifier provides the voltage loop signal that is fed to the other input of the PWM generator. When the current loop signal exceeds the voltage loop signal, the PWM generator turns off the bipolar output transistor. The next clock period initiates the next switching cycle, maintaining the constant frequency current mode PWM control. The LED current level at maximum brightness is set by the feedback resistor: ILED = Brightness Level FB Voltage (mV) 15 250 14 235 13 220 12 205 11 190 10 175 9 160 8 145 7 130 6 115 5 100 4 85 3 70 2 55 1 40 0 25 Table 1. Brightness Level vs. Ideal FB Voltage Startup Presuming no presetting brightness command is issued (discussed in a later section), the MIC3291 will startup in its default state approximately 140µs (tSTART_UP) after a logic level high has been applied and maintained at the DC pin. In the default state the LED drive current is at the maximum brightness level of 15 and brightness counter is set to count down mode. Any falling edges during the tPROG_SETUP period will cause the initial brightness level of the LEDs to be below the maximum brightness level. This is discussed in more detail in the Presetting Brightness section. 250mV RLED MIC3291 Digital Interface The MIC3291 incorporates an easy to use single-wire, serial programming interface allowing users to set LED brightness to one of sixteen levels spaced in a linear manner. In contrast to other solutions requiring a PWM drive signal to maintain LED brightness, the MIC3291 is “set and forget”, relieving the controlling processor of the constant burden of supplying a drive signal. Additionally, brightness levels can be preset so that LEDs can be turned on at a particular brightness level. Figure 2. Typical Startup Timing September 2010 9 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Shutdown Whenever a logic level LOW is applied to the DC input pin for a period greater than or equal to tSHUTDOWN(1260µs), the MIC3291 will be in power saving shutdown mode. Figure 5. Mode Change to Count Down Programming the Brightness Level MIC3291 is designed to start driving the output LEDs (tSTART_UP) in 140µs at the maximum brightness level of 15. After startup, the internal control logic is ready to decrease the LED brightness upon receiving programming pulses (negative edges applied to DC pin). Since MIC3291 starts in count down mode, the brightness level is decreased one level by applying two programming pulses, as shown in Figure 6. Each programming pulse has a high (tPROG_HIGH) and a low (tPROG_LOW) pulse width that must be between 1µs to 32µs. Note that n+1 number of pulses are needed to decrease brightness by n level(s) since the first clock pulse is ignored. Ignoring the first clock pulse is necessary so mode change (tMODE_UP, tMODE_DOWN) pulses do not result in adjustments to the brightness level. The MIC3291 internal circuit can be changed from count down mode to count up mode and vice versa. The user may elect to send a mode change as shown in Figure 4 to set the MIC3291 to step up the brightness level with subsequent programming pulses. For proper operation, ensure the DC pin has remained HIGH for at least tDELAY(140µs) before issuing a mode change command. Figure 3. Shutdown Timing Once the device is shutdown, the boost supply is disabled and the LEDs are turned off. Brightness level information stored in the MIC3291 prior to shutdown will be lost. Programming Pulse Counter Modes At power up the MIC3291 defaults to count down mode. In count down mode, the brightness level is decreased one level by applying two programming pulses, as shown in Figure 6. The counting mode can be changed to count up mode by pulling the DC pin LOW for a period equal to tMODE_UP (100µs to 160µs). The device will remain in count up mode until its state is changed to count down mode or by disabling the MIC3291. Figure 4. Mode Change to Count up To change the state back to count down mode, pull the DC pin LOW for a period equal to tMODE_DOWN (420µs to 500µs). Now the internal circuitry will remain in count down mode until changed to count up mode as described previously. September 2010 Figure 6. Brightness Programming Pulses Multiple brightness levels can be changed together with multiple programming pulses, as shown in Figure 7. When issuing multiple brightness level adjustment commands to the DC pin, ensure both tPROG_LOW and tPROG_HIGH are within 1µs and 32µs. 10 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 To maintain operation at the current brightness level simply maintain a logic level high signal at the DC pin. Figure 9. Up Counter Rollover Figure 7. Decreasing Brightness Several Levels One Step Brightness Changes For applications where a keypad button press is to be translated into a brightness level change, the following method of decreasing the brightness level may be useful. This “one step” brightness change procedure relieves the user from keeping track of the MIC3291’s up/down counter mode. It combines a counter mode change with a programming pulse, therefore a one step decrease in brightness is assured no matter what the previous up/down counter mode was. As mentioned, MIC3291 can be programmed to set LED drive current to produce one of 16 distinct brightness levels. The internal logic keeps track of the brightness level with an up/down counter circuit. The Counter Rollover section explains how the brightness counter functions with continued programming edges. Counter Rollover The MIC3291 internal up/down counter contains registers from 0 to 15. When the brightness level is at 0 and a programming pulse forces the brightness to step down, then the counter will rollover to Level 15. This is illustrated in Figure 8. Figure 10. One step Brightness Decrease This method is quite simple and the only requirement is that the first DC LOW period be equal to the tMODE_DOWN (420µs to 500µs) and immediately followed by a falling edge within tPROG_HIGH (1µs to 32µs) as shown in Figure 10 for one step brightness decrease. Similarly a one step increase can be assured by first generating a DC down pulse whose period is equal to the tMODE_UP (100µs to 160µs) and immediately followed by a falling edge within tPROG_HIGH (1µs to 32µs). Figure 11 illustrates the proper timing for execution of a one step brightness increase. Figure 8. Down Counter Rollover Similarly, when the counter mode is set to count up and a programming pulse forces the brightness level to step up from level 15, then the counter will rollover to level 0 as illustrated in Figure 9. September 2010 11 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Figure 12 shows the correct presetting sequence to set the MIC3291 brightness to Level 6 prior to startup. The sequence is initiated by driving the DC pin LOW for a period exceeding tSHUTDOWN (1260µs) to insure that the part has entered the power saving shutdown state erasing all brightness level state and mode setting. Then the DC pin is driven HIGH and the first presetting pulse edge is entered within the tPROG_SETUP window. Notice that when using the presetting feature the first programming pulse is not ignored. This is because the counter’s default mode is count down and a mode change cannot be performed in the presetting mode. (Note that the same timing requirements of standard brightness programming also apply during presetting brightness.) Figure 11. One step Brightness Increase Presetting Brightness The brightness level can be preset before the MIC3291 begins to drive the LEDs by sending a series of programming edges via the DC pin during the tSTART_UP (140µs) period and between 35µs to 50µs after the DC pin is first pulled HIGH. The 15µs timeframe between 35µs and 50µs is the tPROG_SETUP period. The MIC3291 does not drive current into the load until DC pin is kept HIGH for tSTART_UP (140µs) after presetting has concluded in order to grant the user sufficient time to preset LED brightness. The first presetting pulse edge must occur somewhere between the timeframe of 35µs to 50µs after DC pin is first pulled HIGH otherwise the MIC3291 may continue to start at the full (default) brightness level. Figure 12. Preset Timing September 2010 12 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Typical Application Circuit (MIC3291-xxYML) Bill of Materials Item Part Number C1 GRM185R61A105KE36D C2 GRM21BR71E474KCO1L R1 CRCW060312R40FRT1 L1 VLS252010T-100M U1 MIC3291-xxYML Manufacturer Murata(1) (1) Murata (2) Vishay TDK(3) Micrel, Inc.(4) Description Qty. Capacitor, 1µF Ceramic, 10V, X5R, Size 0603 1 Capacitor, 0.47µF Ceramic, 25V, X7R, Size 0805 1 12.4Ω, 1%, 0603 1 10µH, 650mA, 712mΩ, L2.5mm x W2.0mm x H1.0mm 1 1.2MHz PWM Boost LED Driver with Single-Wire Linear Digital Control 1 Notes: 1. Murata: www.murata.com. 2. Vishay: www.vishay.com. 3. TDK: www.tdk.com. 4. Micrel, Inc.: www.micrel.com. September 2010 13 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Typical Application Circuit (MIC3291-xxYD6) Bill of Materials Item Part Number C1 GRM185R61A105KE36D C2 GRM21BR71E474KCO1L R1 CRCW060312R40FRT1 L1 VLS252010T-100M U1 MIC3291-xxYD6 Manufacturer Murata(1) (1) Murata (2) Vishay TDK(3) Micrel, Inc.(4) Description Qty. Capacitor, 1µF Ceramic, 10V, X5R, Size 0603 1 Capacitor, 0.47µF Ceramic, 25V, X7R, Size 0805 1 12.4Ω, 1%, 0603 1 10µH, 650mA, 712mΩ, L2.5mm x W2.0mm x H1.0mm 1 1.2MHz PWM Boost LED Driver with Single-Wire Linear Digital Control 1 Notes: 1. Murata: www.murata.com. 2. Vishay: www.vishay.com. 3. TDK: www.tdk.com. 4. Micrel, Inc.: www.micrel.com. September 2010 14 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 PCB Layout Recommendations Top Layer Bottom Layer September 2010 15 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Package Information 6-Pin TSOT23 (D6) September 2010 16 M9999-092810 (408) 944-0800 Micrel, Inc. MIC3291 Package Information (Continued) 8-Pin MLF® (ML) 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. © 2010 Micrel, Incorporated. September 2010 17 M9999-092810 (408) 944-0800