Micrel, Inc MIC3287 MIC3287 1.2MHz PWM White LED Driver with OVP in Thin SOT-23 and 2mm x 2mm MFL® General Description Features The MIC3287 is a 1.2MHz pulse width modulated (PWM) step-up switching regulator that is optimized for constant current white LED driving applications. With a switch current of over 350mA, the MIC3287-24 drives a string of up to 4 white LEDs in series, ensuring uniform brightness and eliminating several ballast resistors. The MIC3287 implements a constant frequency 1.2MHz PWM current-mode control scheme. The high frequency PWM operation saves board space by reducing external component sizes. The added benefit of the constant frequency PWM control scheme as opposed to variable frequency control schemes is much lower noise and input ripple injected back to the battery source. To optimize efficiency, the feedback voltage is set to only 250mV. The MIC3287 is also available with a maximum 24V over-voltage protection. The MIC3287 is available in low profile Thin SOT-23 5-pin and Thin SOT-23 6-pin packages. The MIC3287 has a junction temperature range of –40°C to +125°C. All support documentation can be found on Micrel’s web site at: www.micrel.com. • • • • • • • • • • • • • • 2.8V to 6.5V Input Voltage 350mA Switch Current 1.2 MHz PWM Operation 250mV Feedback Voltage Optional 24V Output Over-Voltage Protection (OVP) Up to 36V Output Voltage without OVP <1% Line and Load Regulation <1µA Shutdown Current Over-Temperature Protection Under-Voltage Lock Out (UVLO) Low Profile Thin SOT-23-5 Package Option Low Profile Thin SOT-23-6 Package Option 8-pin 2mm x 2mm MLF® Package Option –40°C to +125°C Junction Temperature Range Applications • White LED Driver for Backlighting: - Cell phones - PDAs - GPS systems - Digital cameras - MP3 players - IP phones • LED Flashlights • Constant Current Power Supplies Typical Application 10µH 10µH 5 1-Cell Li Ion 1µF 4 MIC3287YD5 VIN SW FB EN MIC3287-24YD6 1 6 1-Cell Li Ion 0.22µF 3 250mV 1µF 4 SW 1 OVP 5 FB 3 VIN EN GND GND 0.22µF 250mV 2 2 4-Series White LED Driver with Output OVP in Thin SOT-23-6 3-Series White LED Driver in Thin SOT-23-5 MLF and MicroLeadFrame are registered trademarks of 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 1 M9999-042910 Micrel, Inc. MIC3287 Ordering Information Marking Code Part Number Overvoltage Protection Junction Temp. Range Package Lead Finish MIC3287YD5 WGAA N/A -40°C to +125°C Thin SOT-23-5 Lead Free MIC3287-24YD6 WHAA 24V -40°C to +125°C Thin SOT-23-6 Lead Free MIC3287-24YML WLA 24V -40°C to +125°C 8-Pin 2mm x 2mm MLF Lead Free Pin Configuration FB GND SW 3 2 1 FB GND SW 1 2 3 4 EN 4 5 6 EN OVP VIN 5 VIN TSOT-23-5 (YD5) VIN 1 8 PGND OVP 2 7 SW EN 3 6 FB 5 NC AGND 4 TSOT-23-6 (YD6) EP 8-Pin 2mm x 2mm MLF™ (YML) Pin Description Pin Number Pin Number TSOT-23-5 TSOT-23-6 Pin Number 8-Pin MLF Pin Name 1 1 7 SW 2 2 4 AGND Pin Function Switch Node (Input): Internal power bipolar collector. Analog Ground (Return): Ground. 2 2 8 PGND 3 3 6 FB Feedback (Input): Output voltage sense node. Connect the cathode of the LED to this pin. A resistor from this pin to ground sets the LED current. 4 4 3 EN Enable (Input): Logic high enables regulator. Logic low shuts down regulator. 5 6 1 VIN Supply (Input): 2.8V to 6.5V for internal circuitry. — 5 2 OVP Overvoltage Protection (Input): Connect to the output. — — 5 NC Not Connected — — EP EP Exposed Backside Pad: Connect to ground. April 2010 Power Ground (Return): Ground. 2 M9999-042910 Micrel, Inc MIC3287 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VIN)......................................................... 7V Switch Voltage (VSW).......................................–0.3V to 40V Enable Pin Voltage (VEN).................................... –0.3 to VIN FB Voltage (VFB).............................................................. 6V Switch Current (ISW)...................................................... 1.2A Ambient Storage Temperature (TS)........... –65°C to +150°C ESD Rating(3)................................................................. 2kV Supply Voltage (VIN)..........................................2.8V to 6.5V Output Voltage (VOUT)..........................................VIN to 36V Output Voltage (VOUT)(4)....................................VIN to VOVP Junction Temperature Range (TJ)............. –40°C to +125°C Package Thermal Impedance Thin SOT-23-5 (θJA)(5). ...................................... 207°C/W Thin SOT-23-6 (θJA)(5). ...................................... 134°C/W 8-Pin MLF (θJA).................................................... 90°C/W Electrical Characteristics(6) TA = 25°C, VIN = VEN = 3.6V, VOUT = 10V, IOUT = 10mA, unless otherwise noted. Bold values indicate –40°C ≤ TJ ≤125°C. Symbol Parameter Condition Min Typ Max Units Supply Voltage Range 2.8 6.5 V VUVLO Under Voltage Lockout 1.8 2.1 2.4 V ISD Shutdown Current IFB Feedback Input Current Line Regulation Load Regulation VIN IVIN VFB Quiescent Current Feedback Voltage 2.1 5 mA VEN = 0V(7) VFB > 500mV, (not switching) 0.04 1 µA 250 269 mV VFB = 250mV –450 1 % 5mA ≤ IOUT ≤ 20mA(8) 0.5 % (±7.5%) 3V ≤ VIN ≤ 231 5V(8) 0.4 Maximum Duty Cycle 85 ISW Switch Current Limit 350 ISW Switch Leakage Current DMAX VSW Switch Saturation Voltage Enable Threshold VEN IEN Enable Pin Current VIN = 3.6V VIN = 3.6V, ISW = 300mA VEN = 0V, VSW = 10V VEN = 10V Oscillator Frequency 1 TJ Overtemperature Threshold Shutdown Hysteresis % mA 250 mV 1 µA 0.01 TURN ON 1.5 TURN OFF 0.4 fSW Overvoltage Protection VOVP 90 nA V V 21 40 µA 1.2 1.4 MHz MIC3287-24YD6 17 19 24 MIC3287-24YML 150 10 V °C °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, θJA, 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. This device is not guaranteed to operate beyond its specified operating ratings. 3. Devices are inherently ESD sensitive. Handling precautions required. Human body model. 4. For options with OVP. 5. Using 4 layer PCB. 6. Specification for packaged product only. 7. ISD = IVIN. 8. Guaranteed by design. April 2010 3 M9999-042910 Micrel, Inc. MIC3287 Typical Characteristics 60 L = 10µH COUT = 0.22µF Frequency vs. Temperature FREQUENCY (MHz) VIN=4.2V VIN=3.6V 45 2 260 Feedback Voltage vs. Temperature VIN=3.2V VIN=3.6V 248 Quiescent Current vs. Input Voltage SHUTDOWN CURRENT (uA) 254 VEN=1.8V Feedback Voltage vs. Input Voltage 251 248 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 INPUT VOLTAGE (V) 900 CURRENT LIMIT (mA) 800 Curremt Limit vs. Temperature VIN=3.6V 750 2.2 700 2.1 840 2 VEN=3.3V 850 2.3 0.001 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 INPUT VOLTAGE (V) 4 VEN=2.5V 249 2.4 0.002 6 250 240 -40 -25 -10 5 20 35 50 65 80 TEMPERATURE (°C) 2.5 8 252 QUIESCENT CURRENT (mA) Shutdown Current vs. Input Voltage VEN=5V 253 256 244 1.0 -40 -25 -10 5 20 35 50 65 80 TEMPERATURE (°C) Enable Pin Current vs. Temperature 0 -40 -25 -10 5 20 35 50 65 80 TEMPERATURE (°C) 4 6 8 10 12 14 16 18 20 WHITE LED CURRENT (mA) 252 1.1 0.003 L = 10µH COUT = 0.22µF 50 4 6 8 10 12 14 16 18 20 WHITE LED CURRENT (mA) 1.4 1.2 VIN=4.2V 55 50 1.3 65 60 55 1.5 VIN=3.2V 70 VIN=4.2V 12 10 75 70 45 2 VIN=3.6V 80 EFFICIENCY (%) EFFICIENCY (%) 75 VIN=3.2V 4 Series White LED Efficiency ENABLE PIN CURRENT (µA) VIN=3.6V 80 65 85 FEEDBACK VOLTAGE (mV) 3 Series White LED Efficiency FEEDBACK VOLTAGE (mV) 85 650 2.0 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 INPUT VOLTAGE (V) 600 -40 -25 -10 5 20 35 50 65 80 TEMPERATURE (°C) Current Limit vs. Input Voltage CURRENT LIMIT (mA) 820 800 780 760 740 720 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 INPUT VOLTAGE (V) April 2010 4 M9999-042910 Micrel, Inc MIC3287 Functional Diagram VIN FB EN OVP* OVP VREF SW Error Amplifier VREF PWM Generator gm 250mV ∑ Current Amplifier 1.2MHz Oscillator Ramp Generator GND * OVP available on TSOP-23-6 and MLF™ package options only. MIC3287 Block Diagram Functional Description The gm error amplifier measures the LED current through the external sense resistor and amplifies the error between the detected signal and the internal 250mV reference voltage. 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, thus maintaining the constant frequency current-mode PWM control. The LED current is set by the feedback resistor: 250mV ILED = R FB The enable pin shuts down the internal power bipolar transistor and disables the control circuitry to reduce input current-to-leakage levels. Enable pin input current is zero at zero volts. The MIC3287 is a constant frequency pulse width modulated (PWM) current-mode step-up regulator. The block diagram is shown above. The MIC3287 is composed of an oscillator, slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, and a 350mA minimum bipolar output transistor. The oscillator generates a 1.2MHz clock. The clock’s two functions are to trigger the PWM generator that turns on the output transistor and to reset 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. April 2010 5 M9999-042910 Micrel, Inc. MIC3287 External Component Selection The table below shows recommended inductor and output capacitor combinations for optimal performance. Series LEDs L Min COUT 2 22µH 2.2µF 3 4 April 2010 15µH 1µF 10µH 0.22µF 6.8µH 0.22µF 4.7µH 0.22µF 22µH 2.2µF 15µH 1µF 10µH 0.22µF 6.8µH 0.22µF 4.7µH 0.27µF 22µH 1µF 15µH 1µF 10µH 0.22µF 6.8µH 0.27µF 4.7µH 0.27µF 6 M9999-042910 Micrel, Inc MIC3287 Dimming Control There are two techniques for dimming control. One is PWM dimming, and the other is continuous dimming. 1.PWM dimming control is implemented by applying a PWM signal to the EN pin, as shown in Figure 1. The MIC3287 is turned on and off by the PWM signal. With this method, the LEDs operate with either zero or full current. The average LED current is increased proportionally to the duty-cycle of the PWM signal. This technique has high-efficiency because the IC and the LEDs consume no current during the off time of the PWM signal. Typical PWM frequency should be between 100Hz and 10kHz. 2.Continuous dimming control is implemented by applying a DC control voltage to the FB pin of the MIC3287 through a series resistor, as shown in Figure 2. The LED intensity (current) can be dynamically varied with the applied DC control voltage. The DC voltage can come from a DAC signal, or a filtered PWM signal. The advantage of the filtered PWM signal approach is a high frequency PWM signal (>10kHz) can be used to control LED intensity (current). Open-Circuit Protection If the LEDs are disconnected from the circuit, or in the case that an LED fails, the sense resistor will then pull the FB pin to ground. This will cause the MIC3287 to switch with a high dutycycle, resulting in output over-voltage. This may cause the SW pin voltage to exceed its maximum voltage rating, damaging the IC and the external components. To ensure the highest level of protection, the MIC3287 has buit-in 24V over-voltage protection functionality in the TSOT-23-6 pin and 8-pin MLF™ package options. The OVP will clamp the output voltage to within the specified limits. Start-Up and Inrush Current If the inrush current needs to be limited, a soft-start circuit, similar to Figure 3, could be implemented. The soft-start capacitor, CSS, provides overdrive to the FB pin at start-up, resulting in gradual increase of switch duty cycle and limited in rush current. VIN CSS 2200pF VIN SW EN FB GND VIN PWM VIN SW EN FB R 10k Figure 3. Soft-Start Circuit GND Figure 1. PWM Dimming Method VIN VIN SW EN FB GND 5.11k 49.9k DC� Equivalent Figure 2. Continuous Dimming April 2010 7 M9999-042910 Micrel, Inc. MIC3287 Package Information 5-Pin TSOT (YD5) 6-Pin TSOT (YD6) April 2010 8 M9999-042910 Micrel, Inc MIC3287 8-Pin 2mm x 2mm 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 This 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. © 2006 Micrel, Inc. April 2010 9 M9999-042910