MIC2289C White LED Driver Internal Schottky Diode and OVP General Description Features The MIC2289C is a PWM (pulse width modulated), boostswitching regulator that is optimized for constant-current white LED driver applications. The MIC2289C features an internal Schottky diode and three levels of output overvoltage protection providing a small size and efficient DC/DC solution that requires only four external components. To optimize efficiency, the feedback voltage is set to only 95mV. This reduces power dissipation in the current set resistor and allows the lowest total output voltage, hence minimal current draw from the battery. The MIC2289C implements a constant frequency 1.2MHz PWM control scheme. The high frequency, PWM operation saves board space by reducing external component sizes. The added benefit of the constant frequency PWM scheme in caparison to variable frequency is much lower noise and input ripple injected to the input power source. The MIC2289C clamps the output voltage in case of open LED conditions, protecting itself and the output capacitor. The MIC2289C is available with an output OVP option of 34V. The MIC2289C is available in low profile 6-pin Thin SOT23 package. The MIC2289C has a junction temperature range of –40°C to +125°C. Data sheets and support documentation can be found on Micrel’s web site at: www.micrel.com. • • • • • • • • • • • • • 2.5V to 10V input voltage Output voltage up to 34V with OVP Internal Schottky diode 1.2 MHz PWM operation Over 500mA switch current 95mV feedback voltage <1% line and load regulation <1µA shutdown current Overtemperature protection UVLO Thin SOT-23 6-pin package –40°C to +125°C junction temperature range For higher performance specifications see the MIC2289 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 82 3-Series LED Efficiency 1-Cell Li Ion VIN 1µF SW 0.22µF/50V OUT FB EN 95mV GND EFFICIENCY (%) 80 MIC2289C-34YD6 78 76 74 72 70 0 VIN =3.6V 5 10 15 IOUT (mA) 20 25 7-Series White LED Driver 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 August 2007 M9999-081507-B Micrel, Inc. MIC2289C Ordering Information Marking Code Overoltage Protection Junction Temp. Range Package Lead Finish MIC2289C-34BD6 SM34| 34V –40°C to +125°C 6-Pin Thin SOT-23 Standard MIC2289C-34YD6 SM34| 34V –40°C to +125°C 6-Pin Thin SOT-23 Pb-Free Part Number Note: Marking bars may not be to scale. Pin Configuration FB GND SW 1 2 3 Denotes Pb-Free SM34 Denotes MIC2289C 5 4 6 EN VIN VOUT 6- Pin Thin SOT-23 (D6) Pin Description Pin Number Pin Name 1 SW 2 GND 3 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 EN Enable (Input): Logic high enables regulator. Logic low shuts down regulator. August 2007 Pin Name Switch node (Input): Internal power BIPOLAR collector. Ground (Return): Ground. 5 VIN Supply (Input): 2.7V to 8V for internal circuitry. 6 OUT Output Pin and Overvoltage Protection (Output): Connect to the output capacitor and LEDs. 2 M9999-081507-B Micrel, Inc. MIC2289C Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VIN) .......................................................12V Switch Voltage (VSW)....................................... –0.3V to 34V Enable Pin Voltage (VEN)................................... –0.3V to VIN FB Voltage (VFB)...............................................................6V Switch Current (ISW) .........................................................2A Ambient Storage Temperature (Ts) ...........–65°C to +150°C Schottky Reverse Voltage (VDA).....................................34V EDS Rating(3) .................................................................. 2kV Supply voltage (VIN) ........................................ 2.5V to +10V Output Voltage (VIN) ............................................ VIN to VOVP Junction Temperature (TJ) ........................ –40°C to +125°C Package Thermal Resistance Thin SOT-23-6 (θJA) ........................................177°C/W Electrical Characteristics(4) TA = 25°C, VIN = VEN = 3.6V, VOUT = 10V, IOUT = 20mA, unless otherwise noted. Bold values indicate –40°C< TJ < +125°C. Symbol Parameter Condition Min VIN Supply Voltage Range 2.5 VUVLO Under Voltage Lockout 1.8 Typ 2.1 Max Units 10 V 2.4 V IVIN Quiescent Current VFB > 200mV, (not switching) 2.5 5 mA ISD Shutdown Current VEN = 0V(5) 0.1 1 µA VFB Feedback Voltage (±10%) 95 105 mV IFB 85 Feedback Input Current VFB = 95mV –450 nA Line Regulation(6) 3V ≤ VIN ≤ 5V 0.5 % 5mA ≤ IOUT ≤ 20mA 0.5 % 90 % Load Regulation (6) DMAX Maximum Duty Cycle ISW Switch Current Limit 750 mA VSW Switch Saturation Voltage ISW = 0.5A 450 mV ISW Switch Leakage Current VEN = 0V, VSW = 10V 0.01 VEN Enable Threshold TURN ON TURN OFF IEN Enable Pin Current 85 5 µA 0.4 V V 20 40 µA 1.2 1.35 MHz 0.8 1 V 4 µA 37 V 1.5 VEN = 10V fSW Oscillator Frequency VD Schottky Forward Drop ID = 150mA 1.05 IRD Schottky Leakage Current VR = 30V VOVP Overvoltage Protection MIC2289C-34YD6 only TJ Overtemperature Threshold Shutdown Hysteresis 27 32 150 10 °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. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model. 4. Specification for packaged product only. 5. ISD = IVIN. 6. Guaranteed by design August 2007 3 M9999-081507-B Micrel, Inc. MIC2289C Typical Characteristics 95 94 93 92 91 8 10 0 12 0 2 4 Switch Frequency vs. Temperature 50 45 40 1.2 IENABLE (µA) 1.0 0.8 0.6 0.4 0.2 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 2.5 Schottky Reverse Leakage Current 2 VR = 25V 1.5 1 VR = 16V 0.5 VR = 10V 0 30 40 0 12 0 2 4 I = 3.6V EN 10 5 I = 3.0V EN 0 -50 0 50 TEMPERATURE (°C) 100 8 10 12 700 600 500 400 300 200 100 0 Saturation Voltage vs. Temperature 900 450 400 350 IS W = 500mA 0 40 80 TEMPERATURE (°C) Schottky Forward Voltage Drop SCHOTTKY FORWARD VOLTAGE DROP (mV) 500 600 SATURATION VOLTAGE (mV) EN Pin Bias Current vs. Temperature 300 -40 6 VIN (V) 35 I = 10V 30 E N 25 20 I = 4.2V 15 E N 550 50 60 70 80 90 100 TEMPERATURE (°C) August 2007 10 CURRENT LIMIT (mA) 1.4 8 VIN (V) SATURATION VOLTAGE (mV) SCHOTTKY LEAKAGE CURRENT (µA) SWITCHING FREQUENCY (MHz) VIN (V) 6 750 6 1 650 4 2 550 2 1 3 450 0 2 SCHOTTKY FORWARD CURRENT (mA) 90 3 4 1150 96 4 1050 97 950 98 Quiescent Current vs. Input Current 5 QUIESCENT CURRENT (mA) 5 SHUTDOWN CURRENT (µA) FB VOLTAGE (mV) 100 99 Shutdown Voltage vs. Input Voltage 850 Feedback Voltage vs. Input Voltage 120 Current Limit vs. Temperature 850 800 750 700 650 VIN = 2.5V 600 -40 0 40 80 TEMPERATURE (°C) 120 Switch Saturation Voltage vs. Current 500 400 VIN = 2.5V 300 VIN = 5V 200 100 0 0 100 200 300 ISW (mA) 4 400 500 M9999-081507-B Micrel, Inc. MIC2289C Functional Diagram VIN FB OUT EN OVP SW PWM Generator gm VREF 95mV S 1.2MHz Oscillator GND Ramp Generator MIC2289C 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 95mV 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, maintaining the constant frequency current-mode PWM control. The LED is set by the feedback resistor: Functional Description The MIC2289C is a constant frequency, PWM current mode boost regulator. The block diagram is shown above. The MIC2289C is composed of an oscillator, slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, 500mA bipolar output transistor, and Schottky rectifier diode. 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. August 2007 ILED = 95mW R FB The Enable pin shuts down the output switching and disables control circuitry to reduce input current-toleakage levels. Enable pin input current is zero at zero volts. 5 M9999-081507-B Micrel, Inc. MIC2289C inductor and output capacitor values for various seriesLED applications. External Component Selection The MIC2289C can be used across a wide rage of applications. The table below shows recommended Series LEDs 2 L 22µH 15µH 10µH 6.8µH 4.7µH 3 22µH 15µH 10µH 6.8µH 4.7µH 4 22µH 15µH 10µH 6.8µH 4.7µH 5, 6 22µH 15µH 10µH 6.8µH 4.7µH 7, 8 22µH 15µH 10µH 6.8µH 4.7µH August 2007 Manufacturer LQH32CN220K21 (Murata) NLC453232T-220K(TDK) LQH32CN150K21 (Murata) NLC453232T-150K(TDK) LQH32CN100K21 (Murata) NLC453232T-100K(TDK) LQH32CN6R8K21 (Murata) NLC453232T-6R8K(TDK) LQH32CN4R7K21 (Murata) NLC453232T-4R7K(TDK) LQH43MN220K21 (Murata) NLC453232T-220K(TDK) LQH43MN 150K21 (Murata) NLC453232T-150K(TDK) LQH43MN 100K21 (Murata) NLC453232T-100K(TDK) LQH43MN 6R8K21 (Murata) NLC453232T-6R8K(TDK) LQH43MN 4R7K21 (Murata) NLC453232T-4R7K(TDK) LQH43MN220K21 (Murata) NLC453232T-220K(TDK) LQH43MN 150K21 (Murata) NLC453232T-150K(TDK) LQH43MN 100K21 (Murata) NLC453232T-100K(TDK) LQH43MN 6R8K21 (Murata) NLC453232T-6R8K(TDK) LQH43MN 4R7K21 (Murata) NLC453232T-4R7K(TDK) LQH43MN220K21 (Murata) NLC453232T-220K(TDK) LQH43MN 150K21 (Murata) NLC453232T-150K(TDK) LQH43MN 100K21 (Murata) NLC453232T-100K(TDK) LQH43MN 6R8K21 (Murata) NLC453232T-6R8K(TDK) LQH43MN 4R7K21 (Murata) NLC453232T-4R7K(TDK) LQH43MN220K21 (Murata) NLC453232T-220K(TDK) LQH43MN 150K21 (Murata) NLC453232T-150K(TDK) LQH43MN 100K21 (Murata) NLC453232T-100K(TDK) LQH43MN 6R8K21 (Murata) NLC453232T-6R8K(TDK) LQH43MN 4R7K21 (Murata) NLC453232T-4R7K(TDK) 6 Min COUT 2.2µF 1µF 0.22µF 0.22µF 0.22µF 2.2µF 1µF 0.22µF 0.22µF 0.27µF 1µF 1µF 0.27µF 0.27µF 0.27µF 0.22µF 0.22µF 0.27µF 0.27µF 0.27µF 0.22µF 0.22µF 0.27µF 0.27µF 0.27µF Manufacturer 0805ZD225KAT(AVX) GRM40X5R225K10(Murata) 0805ZD105KAT(AVX) GRM40X5R105K10(Murata) 0805ZD224KAT(AVX) GRM40X5R224K10(Murata) 0805ZD225KAT(AVX) GRM40X5R225K10(Murata) 0805ZD224KAT(AVX) GRM40X5R224K10(Murata) 0805YD225MAT(AVX) GRM40X5R225K16(Murata) 0805YD105MAT(AVX) GRM40X5R105K16(Murata) 0805YD224MAT(AVX) GRM40X5R224K16(Murata) 0805YD224MAT(AVX) GRM40X5R224K16(Murata) 0805YD274MAT(AVX) GRM40X5R224K16(Murata) 0805YD105MAT(AVX) GRM40X5R105K25(Murata) 0805YD105MAT(AVX) GRM40X5R105K25(Murata) 0805YD274MAT(AVX) GRM40X5R274K25(Murata) 0805YD274MAT(AVX) GRM40X5R274K25(Murata) 0805YD274MAT(AVX) GRM40X5R274K25(Murata) 08053D224MAT(AVX) GRM40X5R224K25(Murata) 08053D224MAT(AVX) GRM40X5R224K25(Murata) 08053D274MAT(AVX) GRM40X5R274K25(Murata) 08053D274MAT(AVX) GRM40X5R274K25(Murata) 08053D274MAT(AVX) GRM40X5R274K25(Murata) 08053D224MAT(AVX) GRM40X5R224K25(Murata) 08053D224MAT(AVX) GRM40X5R224K25(Murata) 08053D274MAT(AVX) GRM40X5R274K25(Murata) 08053D274MAT(AVX) GRM40X5R274K25(Murata) 08053D274MAT(AVX) GRM40X5R274K25(Murata) M9999-081507-B Micrel, Inc. MIC2289C 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 on EN pin as shown in Figure 1. The MIC2289C 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 cycle of the PWM signal. Typical 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 MIC2289C through a series resistor as shown in Figure 2. The LED current is decreased proportionally with the amplitude of the control voltage. The LED intensity (current) can be dynamically varied applying a DC voltage to the FB pin. The DC voltage can come from a DAC signal, or a filtered PWM signal. The advantage of this approach is that a high frequency PWM signal (>10kHz) can be used to control LED intensity. Open-Circuit Protection If the LEDs are disconnected from the circuit, or in case an LED fails open, the sense resistor will pull the FB pin to ground. This will cause the MIC2289C to switch with a high duty-cycle, resulting in output overvoltage. This would normally cause the SW pin voltage to exceed its maximum voltage rating, possibly damaging the IC and the external components. However, the MIC2289C has a dedicated OVP monitor to limit the output voltage within safe levels (see Figure 3). VIN VIN OUT GND Figure 3. Thin SOT-23 Package OVP Circuit Start-Up and Inrush Current During start-up, inrush current of approximately double the nominal current flows to set up the inductor current and the voltage on the output capacitor. If the inrush current needs to be limited, a soft-start circuit similar to Figure 4 could be implemented. The soft-start capacitor, CSS, provides over-drive to the FB pin at start-up, resulting in gradual increase of switch duty cycle and limited inrush current. SW OUT EN PWM FB EN VIN VIN SW FB VIN GND CSS Figure 1. PWM Dimming Method VIN 2200pF SW OUT VIN EN GND FB R VIN 10k SW OUT FB EN GND Figure 4. One of Soft-Start Circuit 5.11k 49.9k DC Equivalent Figure 2. Continuous Dimming August 2007 7 M9999-081507-B Micrel, Inc. MIC2289C 6-Series LED Circuit with External Soft-Start OUTPUT VOLTAGE INPUT CURRENT ENABLE (200mA/div) (2V/div) OUTPUT VOLTAGE INPUT CURRENT ENABLE (200mA/div) (2V/div) 6-Series LED Circuit without External Soft-Start L = 10µH CIN = 1µF COUT = 0.22µF VIN = 3.6V IOUT = 20mA 6 LEDs TIME (100µs/div.) IOUT = 20mA 6 LEDs CSS = 2200pF TIME (100µs/div.) Figure 5. 6-Series LED Circuit without External Soft Start August 2007 L = 10µH CIN = 1µF COUT = 0.22µF VIN = 3.6V Figure 6. 6-Series LED Circuit with External Soft Start 8 M9999-081507-B Micrel, Inc. MIC2289C Package Information 6-Pin Thin SOT-23 (D6) 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. © 2005 Micrel, Incorporated. August 2007 9 M9999-081507-B