MIC2287 Micrel MIC2287 1.2MHz PWM White LED Driver with OVP in 2mm × 2mm MLF™ and Thin SOT-23 General Description Features The MIC2287 is a 1.2MHz pulse width modulated (PWM), boost-switching regulator that is optimized for constantcurrent, white LED driver applications. With a maximum output voltage of 34V and a switch current of over 500mA, the MIC2287 easily drives a string of up to 8 white LEDs in series, ensuring uniform brightness and eliminating several ballast resistors. The MIC2287 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 as opposed to variable frequency topologies is much lower noise and input ripple injected back to the battery source. To optimize efficiency, the feedback voltage is set to only 95mV. This reduces the power dissipation in the current set resistor and allows the lowest total output voltage, hence minimal current draw from the battery. The MIC2287 is available with 3 levels of overvoltage protection, 15V, 24V, and 34V. This allows designers to choose the smallest possible external components with the appropriate voltage ratings for their applications. The MIC2287 is available in low profile Thin SOT-23 5-lead and an 8-lead 2mm × 2mm MLF™ package options. The MIC2287 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. • • • • • • • • • • • • • • 2.5V to 10V input voltage Output voltage up to 34V Over 500mA switch current 1.2 MHz PWM operation 95mV feedback voltage Output Overvoltage Protection (OVP) Options for 15V, 24V, and 34V OVP <1% line and load regulation <1µA shutdown current Over-temperature protection UVLO Low profile Thin SOT-23-5 package option 8-lead 2mm × 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 • Photo flash LED driver • LED flashlights • Constant current power supplies Typical Application CMDSH-3 10µH MIC2287BD5 5 1-Cell Li Ion VIN SW MIC2287-34BML 1 1µF 4 FB EN CMDSH-3 10µH 1-Cell Li Ion 0.22µF 3 1µF VIN SW EN OVP 95mV FB GND 2 GND 6.3Ω 0.22µF 95mV 6.3Ω 3-Series White LED Driver in Thin SOT-23 6-Series White LED Driver with Output OVP in 2mm × 2mm MLF™-8 MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc. Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com August 2004 1 M0510-081104 MIC2287 Micrel Ordering Information Part Number Marking Code Overvoltage Protection Junction Temp. Range Package Lead Finish MIC2287BD5 SGAA N/A –40°C to 125°C Thin SOT-23-5 Standard MIC2287YD5 Thin SOT-23-5 Lead Free SGAA N/A –40°C to 125°C MIC2287-15BML SLA 15V –40°C to 125°C 2mm x 2mm MLF™ Standard MIC2287-15YML SLA 15V –40°C to 125°C 2mm x 2mm MLF™ Lead Free MIC2287-24BML SLB 24V –40°C to 125°C 2mm x 2mm MLF™ Standard MIC2287-24YML SLB 24V –40°C to 125°C 2mm x 2mm MLF™ Lead Free MIC2287-34BML SLC 34V –40°C to 125°C 2mm x 2mm MLF™ Standard MIC2287-34YML SLC 34V –40°C to 125°C 2mm x 2mm MLF™ Lead Free Pin Configuration FB GND SW 1 2 3 4 EN 5 VIN TSOT-23-5 (BD5) OVP 1 8 PGND VIN 2 7 SW EN 3 6 FB AGND 4 5 NC EP 8-Pin MLF™ (BML) (Top View) Fused Lead Frame Pin Description Pin Number Pin Number TSOT-23-5 2mm ×2mm MLF™ 1 7 2 Pin Name SW GND Pin Function Switch node (Input): Internal power BIPOLAR collector. Ground (Return): Ground. 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 3 EN Enable (Input): Logic high enables regulator. Logic low shuts down regulator. 5 2 VIN Supply (Input): 2.5V to 10V for internal circuitry. — 1 OVP Overvoltage protection (Input): Connect to the output. — 4 AGND Analog ground. — 8 PGND Power ground. — 5 NC No connect (no internal connection to die). — EP GND Ground (Return): Exposed backside pad. M0510-081104 2 August 2004 MIC2287 Micrel Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VIN) ..................................................... 12V Switch Voltage (VSW) ..................................... –0.3V to 34V Enable Pin Voltage (VEN) ................................... –0.3 to VIN FB Voltage (VFB) ............................................................. 6V Switch Current (ISW) ....................................................... 2A Ambient Storage Temperature (TS) ......... –65°C to +150°C ESD Rating(3) ................................................................ 2kV Supply Voltage (VIN) ........................................ 2.5V to 10V Junction Temperature Range (TJ) ........... –40°C to +125°C Package Thermal Impedance 2mm × 2mmMLF™ (θJA) ..................................... 93°C/W Thin SOT-23-5 (θJA) .......................................... 256°C/W Electrical Characteristics(4) 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 VIN Supply Voltage Range 2.5 VUVLO Under Voltage Lockout 1.8 IVIN Quiescent Current VFB > 200mV, (not switching) 0V(5) Typ Max Units 10 V 2.1 2.4 V 2.5 5 mA 0.1 1 µA 95 100 mV ISD Shutdown Current VEN = VFB Feedback Voltage (±5%) IFB Feedback Input Current VFB = 95mV Line Regulation 3V ≤ VIN ≤ 5V 0.5 1 % Load Regulation 5mA ≤ IOUT ≤ 20mA 0.5 2 % DMAX Maximum Duty Cycle ISW Switch Current Limit VSW Switch Saturation Voltage ISW VEN 90 –450 90 % 750 mA ISW = 0.5A 450 mV Switch Leakage Current VEN = 0V, VSW = 10V 0.01 Enable Threshold TURN ON TURN OFF IEN Enable Pin Current fSW Oscillator Frequency VOVP Overvoltage Protection TJ Overtemperature Threshold Shutdown 85 nA 5 µA 0.4 V V 20 40 µA 1.05 1.2 1.35 MHz 13 21 30 14 22.5 32 16 24 34 V V V 1.5 VEN = 10V MIC2287BML- 15 only MIC2287BML- 24 only MIC2287BML- 34 only 150 10 Hysteresis °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. Specification for packaged product only. 5. ISD = IVIN. August 2004 3 M0510-081104 MIC2287 Micrel Typical Characteristics Feedback Voltage vs. Input Voltage Shutdown Current vs. Input Voltage SHUTDOWN CURRENT (µA) 97 96 95 94 93 92 0 2 4 6 8 10 5 4 3 2 1 0 12 0 2 4 VIN (V) EFFICIENCY (%) EFFICIENCY (%) 80 78 74 VIN = 4.2V L = 10µH COUT = 0.22µF 70 0 5 10 15 IOUT (mA) 20 80 78 VIN = 3.0V 76 74 L = 10µH C = 0.22µF 72 70 25 OUT 0 5 15 I EN = 3.6V 10 5 I = 3.0V 0 EN 0 50 -50 TEMPERATURE (°C) 10 15 IOUT (mA) 20 25 100 6 8 10 12 1 0.8 0.6 0.4 0.2 0 -40 500 850 450 400 350 ISW = 500mA 0 40 80 TEMPERATURE (°C) 0 40 80 TEMPERATURE (°C) 120 Current Limit vs. Temperature 900 300 -40 4 1.2 550 CURRENT LIMIT (mA) SATURATION VOLTAGE (mV) IENABLE (µA) 35 I = 10V 30 EN 25 2 1.4 Saturation Voltage vs. Temperature 50 45 40 IEN = 4.2V 0 Switch Frequency vs. Temperature VIN = 3.6V EN Pin Bias Current vs. Temperature 20 1 VIN (V) 82 VIN = 3.0V 72 2 0 12 VIN = 4.2V 84 76 10 3 6 Series LED Efficiency 84 VIN = 3.6V 8 4 VIN (V) 3 Series LED Efficiency 82 6 SWITCHING FREQUENCY (MHz) FB VOLTAGE (mV) 99 98 QUIESCENT CURRENT (mA) 5 100 91 90 Quiescent Current vs. Input Voltage 120 800 750 700 650 V = 2.5V 600 IN -40 0 40 80 TEMPERATURE (°C) 120 Switch Saturation Voltage vs. Current SATURATION VOLTAGE (mV) 600 M0510-081104 500 400 VIN = 2.5V 300 VIN = 5V 200 100 0 0 100 200 300 ISW (mA) 4 400 500 August 2004 MIC2287 Micrel Functional Diagram VIN FB OVP* EN OVP* SW PWM Generator gm VREF 95mV Σ 1.2MHz Oscillator GND Ramp Generator *OVP available on MLFTM package option only MIC2287 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 MIC2287 is a constant frequency, PWM current mode boost regulator. The block diagram is shown above. The MIC2287 is composed of an oscillator, slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, and a 500mA 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. August 2004 95mv ILED = RFB The Enable pin shuts down the output switching and disables control circuitry to reduce input current-to-leakage levels. Enable pin input current is zero at zero volts. 5 M0510-081104 MIC2287 Micrel The table below shows recommended inductor and output capacitor values for various series-LED applications. External Component Selection The MIC2287 can be used across a wide rage of applications. Series LEDs L Manufacturer Min COUT Manufacturer 2 22µH LQH32CN220K21 (Murata) NLC453232T-220K(TDK) 2.2µF 0805ZD225KAT(AVX) GRM40X5R225K10(Murata) 15µH LQH32CN150K21 (Murata) NLC453232T-150K(TDK) 1µF 0805ZD105KAT(AVX) GRM40X5R105K10(Murata) 10µH LQH32CN100K21 (Murata) NLC453232T-100K(TDK) 0.22µF 0805ZD224KAT(AVX) GRM40X5R224K10(Murata) 6.8µH LQH32CN6R8K21 (Murata) NLC453232T-6R8K(TDK) 0.22µF 0805ZD225KAT(AVX) GRM40X5R225K10(Murata) 4.7µH LQH32CN4R7K21 (Murata) NLC453232T-4R7K(TDK) 0.22µF 0805ZD224KAT(AVX) GRM40X5R224K10(Murata) 22µH LQH43MN220K21 (Murata) NLC453232T-220K(TDK) 2.2µF 0805YD225MAT(AVX) GRM40X5R225K16(Murata) 15µH LQH43MN 150K21 (Murata) NLC453232T-150K(TDK) 1µF 0805YD105MAT(AVX) GRM40X5R105K16(Murata) 10µH LQH43MN 100K21 (Murata) NLC453232T-100K(TDK) 0.22µF 0805YD224MAT(AVX) GRM40X5R224K16(Murata) 6.8µH LQH43MN 6R8K21 (Murata) NLC453232T-6R8K(TDK) 0.22µF 0805YD224MAT(AVX) GRM40X5R224K16(Murata) 4.7µH LQH43MN 4R7K21 (Murata) NLC453232T-4R7K(TDK) 0.27µF 0805YD274MAT(AVX) GRM40X5R224K16(Murata) 22µH LQH43MN220K21 (Murata) NLC453232T-220K(TDK) 1µF 0805YD105MAT(AVX) GRM40X5R105K25(Murata) 15µH LQH43MN 150K21 (Murata) NLC453232T-150K(TDK) 1µF 0805YD105MAT(AVX) GRM40X5R105K25(Murata) 10µH LQH43MN 100K21 (Murata) NLC453232T-100K(TDK) 0.27µF 0805YD274MAT(AVX) GRM40X5R274K25(Murata) 6.8µH LQH43MN 6R8K21 (Murata) NLC453232T-6R8K(TDK) 0.27µF 0805YD274MAT(AVX) GRM40X5R274K25(Murata) 4.7µH LQH43MN 4R7K21 (Murata) NLC453232T-4R7K(TDK) 0.27µF 0805YD274MAT(AVX) GRM40X5R274K25(Murata) 22µH LQH43MN220K21 (Murata) NLC453232T-220K(TDK) 0.22µF 08053D224MAT(AVX) GRM40X5R224K25(Murata) 15µH LQH43MN 150K21 (Murata) NLC453232T-150K(TDK) 0.22µF 08053D224MAT(AVX) GRM40X5R224K25(Murata) 10µH LQH43MN 100K21 (Murata) NLC453232T-100K(TDK) 0.27µF 08053D274MAT(AVX) GRM40X5R274K25(Murata) 6.8µH LQH43MN 6R8K21 (Murata) NLC453232T-6R8K(TDK) 0.27µF 08053D274MAT(AVX) GRM40X5R274K25(Murata) 4.7µH LQH43MN 4R7K21 (Murata) NLC453232T-4R7K(TDK) 0.27µF 08053D274MAT(AVX) GRM40X5R274K25(Murata) 22µH LQH43MN220K21 (Murata) NLC453232T-220K(TDK) 0.22µF 08053D224MAT(AVX) GRM40X5R224K25(Murata) 15µH LQH43MN 150K21 (Murata) NLC453232T-150K(TDK) 0.22µF 08053D224MAT(AVX) GRM40X5R224K25(Murata) 10µH LQH43MN 100K21 (Murata) NLC453232T-100K(TDK) 0.27µF 08053D274MAT(AVX) GRM40X5R274K25(Murata) 6.8µH LQH43MN 6R8K21 (Murata) NLC453232T-6R8K(TDK) 0.27µF 08053D274MAT(AVX) GRM40X5R274K25(Murata) 4.7µH LQH43MN 4R7K21 (Murata) NLC453232T-4R7K(TDK) 0.27µF 08053D274MAT(AVX) GRM40X5R274K25(Murata) 3 4 5, 6 7, 8 M0510-081104 6 August 2004 MIC2287 Micrel 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 MIC2287 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 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 MIC2287 through a series resistor as shown in Figure 2. 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 a high frequency PWM signal (>10kHz) that can be used to control LED intensity. with options for 15V, 24V, or 34V (see Figure 3). The reason for the three OVP levels is to let users choose the suitable level of OVP for their application. For example, a 3-LED application would typically see an output voltage of no more than 12V, so a 15V OVP option would offer a suitable level of protection. This allows the user to select the output diode and capacitor with the lowest voltage ratings, as well as smallest size and lowest cost. The OVP will clamp the output voltage to within the specified limits. For the Thin SOT-23-5 package, an OVP pin is not available. An external zener diode can be connected from the output of the converter to FB pin as shown in Figure 4. to implement similar protection. VIN VIN SW EN FB GND OVP Figure 3. MLF™ Package OVP Circuit VIN VIN PWM VIN SW EN FB VIN SW EN FB GND GND Figure 4. Thin SOT-23 Package OVP Circuit Figure 1. PWM Dimming Method 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 5 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 inrush current. VIN VIN SW EN FB 5.11k 49.9k GND VIN DC Equivalent CSS 2200pF Figure 2. Continuous Dimming 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 MIC2287 to switch with a high duty-cycle, resulting in output overvoltage. This may cause the SW pin voltage to exceed its maximum voltage rating, possibly damaging the IC and the external components. To ensure the highest level of protection, the MIC2287 has 3 product options in the 8-lead 2mm × 2mm MLF™ with overvoltage protection (OVP). The extra pins of the 8-lead 2mm × 2mm MLF™ package allow a dedicated OVP monitor August 2004 5.11k VIN SW EN FB GND R 10k Figure 5. Soft-Start Circuit 7 M0510-081104 MIC2287 Micrel 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.) M0510-081104 L = 10µH CIN = 1µF COUT = 0.22µF VIN = 3.6V IOUT = 20mA 6 LEDs CSS = 2200pF R = 10kΩ TIME (100µs/div.) 8 August 2004 MIC2287 Micrel Package Information All Dimensions are in millimeters 5-Pin TSOT (BD5) 8-Pin MLF™ (BML) August 2004 9 M0510-081104 MIC2287 Micrel ×2 8 Lead Recommended Land Pattern for MLF™ 2× MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB USA 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. © 2004 Micrel, Incorporated. M0510-081104 10 August 2004