DATASHEET EL1848 FN7427 Rev 0.00 March 31, 2004 White LED Step-Up Regulator The EL1848 is a constant current boost regulator specially designed for driving white LEDs. It can drive 3 LEDs in series or up to 9 LEDs in parallel/series configuration and achieves efficiency up to 91%. Features The brightness of the LEDs is adjusted through a voltage level on the CNTL pin. When the level falls below 0.1V, the chip goes into shut-down mode and consumes less than 1µA of supply current for VIN less than 5.5V. • Drives up to 9 LEDs, 3 in a series The EL1848 is available in 8-pin TSOT and MSOP packages. The TSOT is just 1mm high, compared to 1.45mm for the standard SOT-23 package. • 1µA maximum shut-down current Ordering Information • Pb-free Available PART NUMBER PACKAGE TAPE & REEL PKG. DWG. # • 2.6V to 13.2V input voltage • 14V maximum output voltage • 1MHz switching frequency • Up to 91% efficiency • Dimming control • 8-pin TSOT and MSOP packages Applications EL1848IWT-T7 8-Pin TSOT 7” (3K pcs) MDP0049 • PDAs EL1848IWT-T7A 8-Pin TSOT 7” (250 pcs) MDP0049 • Cellular phones EL1848IWTZ-T7 (See Note) 8-Pin TSOT (Pb-free) 7” (3K pcs) MDP0049 • Digital cameras EL1848IWTZT7A (See Note) 8-Pin TSOT (Pb-free) 7” (250 pcs) MDP0049 EL1848IY 8-Pin MSOP - MDP0043 EL1848IY-T7 8-Pin MSOP 7” MDP0043 2.6V TO 5.5V C1 EL1848IY-T13 8-Pin MSOP 13” MDP0043 4.7µF • White LED backlighting Typical Connection D L NOTE: Intersil Pb-free products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which is compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J Std-020B. C2 33µH 1µF VIN LX VOUT CS VCTRL C3 CNTL PGND COMP SGND R1 5 0.1µF FN7427 Rev 0.00 March 31, 2004 Page 1 of 12 EL1848 Pinouts EL1848 (8-PIN MSOP) TOP VIEW EL1848 (8-PIN TSOT) TOP VIEW COMP 1 8 VIN CS 1 8 CNTL CNTL 2 7 CS VIN 2 7 COMP VOUT 3 6 SGND PGND 3 6 LX LX 4 5 PGND SGND 4 5 VOUT FN7427 Rev 0.00 March 31, 2004 Page 2 of 12 EL1848 Absolute Maximum Ratings (TA = 25°C) SGND to PGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +0.3V Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C Ambient Operating Temperature . . . . . . . . . . . . . . . .-40°C to +85°C Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Curves Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . 125°C COMP, CNTL, CS to SGND. . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V VIN to SGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+14V VOUT to SGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+14V LX to PGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+16V CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. This part is ESD sensitive. Handle with care. IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typ values are for information purposes only. Unless otherwise noted, all tests areat the specified temperature and are pulsed tests, therefore: TJ = TC = TA Electrical Specifications VIN = 3V, VO = 12V, C1 = 4.7µF, L = 33µH, C2 = 1µF, C3 = 0.1µF, R1 = 5, TA = 25°C, unless otherwise specified. PARAMETER DESCRIPTION CONDITIONS MIN TYP MAX UNIT 13.2 V 1 µA VIN Input Voltage IQ1 Total Input Current at Shut-down VCNTL = 0V IQ1 Quiescent Supply Current at VO Pin VCNTL = 1V, load disconnected 1 1.5 mA ICOMP COMP Pin Pull-up Current COMP connected to SGND 11 20 µA VCOMP COMP Voltage Swing 1.5 2.5 V ICNTL CNTL Shut-down Current 1 µA VCNTL1 Chip Enable Voltage VCNTL2 Chip Disable Voltage 2.6 0.5 CNTL = 0V 240 mV 100 mV IOUT_ACCURACY VCNTL = 1V VCNTL = 1V 14 15 16 mA VOUT1 Over-voltage Threshold VOUT rising 13 14 15 V VOUT2 Over-voltage Threshold VOUT falling, with resistive load 11 12 13 V ILX MOSFET Current Limit RDS_ON MOSFET On-resistance ILEAK MOSFET Leakage Current FS Switching Frequency DMAX Maximum Duty Ratio ICS CS Input Bias Current IO/VIN Line Regulation 400 mA 0.7 VCNTL = 0V, VLX = 12V VCNTL = 2V, IS = 0 800 1000 85 90 1 µA 1200 kHz % 1 VIN = 2.6V - 5.5V 0.03 µA %/V Pin Descriptions PIN NUMBER PIN NAME DESCRIPTION 1 COMP Compensation pin. A compensation cap (4700pF to 1µF) is normally connected between this pin and SGND. 2 CNTL Control pin for dimming and shut-down. A voltage between 250mV and 5.5V controls the brightness, and less than 100mV shuts down the converter. 3 VOUT Output voltage sense. Use for over voltage protection. 4 LX Inductor connection pin. The drain of internal MOSFET. 5 PGND Power Ground pin. The source of internal MOSFET. 6 SGND Signal Ground. Ground pin for internal control circuitry. Needs to connect to PGND at only one point. 7 CS Current sense pin. Connect to sensing resistor to set the LED bias current. 8 VIN Power supply for internal control circuitry. FN7427 Rev 0.00 March 31, 2004 Page 3 of 12 EL1848 Block Diagram 2.6V TO 5.5V CIN VIN 4.7µF REFERENCE GENERATOR 1MHz OSCILLATOR THERMAL SHUTDOWN OVER-VOLTAGE PROTECTION L 33µH VOUT LX COMP + + + CCOMP COUT PWM LOGIC 1µF BOOST I-SENSE 0.1µF I(LED) START-UP CONTROL PWM SIGNAL VCNTL ERROR AMP + - 617K CNTL PGND CS 5 50K SGND Typical Performance Curves All performance curves and waveforms are taken with C1 = 4.7µF, C2 = 1µF, C3 = 0.1µF, L = 33µF, VIN = 3.3V, VCNTL = 1V, R1 = 5, 3 LEDs in a series; unless otherwise specified. 1.05 3.5 3 1.04 VCNTL=0V, 0.1V WHITE LEDs DISCONNECTED IIN (µA) FS (MHz) 2.5 1.03 1.02 2 1.5 1 1.01 1 2.5 0.5 3 3.5 4 4.5 5 VIN (V) FIGURE 1. SWITCHING FREQUENCY vs VIN FN7427 Rev 0.00 March 31, 2004 5.5 0 2.5 4.5 6.5 8.5 10.5 12.5 14.5 VIN (V) FIGURE 2. QUIESCENT CURRENT Page 4 of 12 EL1848 Typical Performance Curves (Continued) All performance curves and waveforms are taken with C1 = 4.7µF, C2 = 1µF, C3 = 0.1µF, L = 33µF, VIN = 3.3V, VCNTL = 1V, R1 = 5, 3 LEDs in a series; unless otherwise specified. VCNTL=1V 35 16 15.8 30 15.6 15.4 20 ILED (mA) ILED (mA) 25 15 10 15 14.8 14.6 14.4 5 0 15.2 14.2 0 0.5 1 1.5 2 2.5 14 2.5 VCNTL (V) FIGURE 3. ILED vs VCNTL 3.5 4.5 4 VIN (V) 5 5.5 FIGURE 4. ILED vs VIN BAT54HT1 L VIN 3 90 33µH 4.7µF 2 LEDs IN A SERIES 1µF VIN=4.2V 8 VIN LX VOUT CS VCTRL 2 1 CNTL PGND COMP SGND EFFICIENCY (%) 85 4 3 7 VIN=2.7V 80 75 5 5 70 6 L=COILCRAFT LPO1704-333CM 5 10 15 0.1µF FIGURE 5A. 2 LEDs IN A SERIES 3 LEDs IN A SERIES 33µH 90 1µF VIN=4.2V LX VOUT CS VCTRL 2 1 CNTL PGND COMP SGND EFFICIENCY (%) 85 VIN 30 FIGURE 5B. EFFICIENCY vs IO FIGURE 5. 4.7µF 8 25 BAT54HT1 L VIN 20 IO (mA) 4 3 7 5 VIN=2.7V 80 75 5 70 6 L=COILCRAFT LPO1704-333CM 5 10 15 20 25 30 IO (mA) 0.1µF FIGURE 6A. 3 LEDs IN A SERIES FN7427 Rev 0.00 March 31, 2004 FIGURE 6. FIGURE 6B. EFFICIENCY vs IO Page 5 of 12 EL1848 Typical Performance Curves (Continued) All performance curves and waveforms are taken with C1 = 4.7µF, C2 = 1µF, C3 = 0.1µF, L = 33µF, VIN = 3.3V, VCNTL = 1V, R1 = 5, 3 LEDs in a series; unless otherwise specified. BAT54HT1 L VIN 90 33µH 4.7µF 2 LEGS OF 2 LEDs IN A SERIES 1µF VIN=4.2V 8 VIN LX VOUT CS 2 VCTRL 1 CNTL PGND COMP SGND EFFICIENCY (%) 85 4 3 7 5 5 VIN=2.7V 80 75 5 70 10 6 L=COILCRAFT LPO1704-333CM 20 30 40 50 60 IO (mA) 0.1µF FIGURE 7A. 2 LEGS OF 2 LEDs IN A SERIES BAT54HT1 L VIN FIGURE 7B. EFFICIENCY vs IO FIGURE 7. 2 LEGS OF 3 LEDs IN A SERIES 33µH 90 4.7µF 1µF VIN=4.2V 8 VIN LX VOUT CS 2 VCTRL 1 CNTL PGND COMP SGND EFFICIENCY (%) 85 4 3 7 5 5 VIN=2.7V 80 75 5 70 10 6 L=SUMIDA CMD13D13-33µH 20 30 FIGURE 8A. 2 LEGS OF 3 LEDs IN A SERIES VIN 50 60 FIGURE 8B. EFFICIENCY vs IO FIGURE 8. BAT54HT1 L 3 LEGS OF 2 LEDs IN A SERIES 95 15µH 1µF 8 VIN LX VOUT CS 2 1 CNTL PGND COMP SGND EFFICIENCY (%) 4.7µF VCTRL 40 IO (mA) 0.1µF 4 3 7 5 90 VIN=4.2V 85 VIN=2.7V 80 75 5 5 5 70 15 6 L=SUMIDA CMD13D13-15µH 35 55 75 95 IO (mA) 0.1µF FIGURE 9A. 3 LEGS OF 2 LEDs IN A SERIES FN7427 Rev 0.00 March 31, 2004 FIGURE 9. FIGURE 9B. EFFICIENCY vs IO Page 6 of 12 EL1848 Typical Performance Curves (Continued) All performance curves and waveforms are taken with C1 = 4.7µF, C2 = 1µF, C3 = 0.1µF, L = 33µF, VIN = 3.3V, VCNTL = 1V, R1 = 5, 3 LEDs in a series; unless otherwise specified. VIN BAT54HT1 L 3 LEGS OF 3 LEDs IN A SERIES 95 15µH 4.7µF 1µF VIN=4.2V 8 VIN LX VOUT CS VCTRL 2 1 CNTL PGND COMP SGND EFFICIENCY (%) 90 4 3 7 5 85 VIN=2.7V 80 75 5 5 5 70 15 6 L=SUMIDA CMD13D13-15µH 35 55 75 95 IO (mA) 0.1µF FIGURE 10A. 3 LEGS OF 3 LEDs IN A SERIES JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 0.6 0.9 0.8 870mW POWER DISSIPATION (W) POWER DISSIPATION (W) 1 MSOP8/10 0.7 JA=115°C/W 0.6 0.5 0.4 0.3 0.2 0.1 0 FIGURE 10B. EFFICIENCY vs IO FIGURE 10. 0.5 486mW 25 50 75 85 100 125 AMBIENT TEMPERATURE (°C) FIGURE 11. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE FN7427 Rev 0.00 March 31, 2004 MSOP8/10 0.4 JA=206°C/W 0.3 0.2 0.1 0 0 JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 0 25 50 75 85 100 125 AMBIENT TEMPERATURE (°C) FIGURE 12. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE Page 7 of 12 EL1848 Waveforms All performance curves and waveforms are taken with C1 = 4.7µF, C2 = 1µF, C3 = 0.1µF, L = 33µF, VIN = 3.3V, VCNTL = 1V, R1 = 5, 4 LEDs in a series; unless otherwise specified. C3=4700pF 50mA/DIV IIN VIN 2V/DIV IIN 50mA/DIV VCNTL 1V/DIV ILED VCNTL 1V/DIV ILED 10mA/DIV 10mA/DIV 0.1ms/DIV 10ms/DIV FIGURE 14. SHUT-DOWN FIGURE 13. START-UP ILED=15mA 2V VCNTL 1V 14.2V 12.9V VO ILED 10mV/DIV VIN IL 100mA/DIV 30mA VLX 10V/DIV 15mA VO 50mV/DIV 1µs/DIV 20ms/DIV FIGURE 15. TRANSIENT RESPONSE FIGURE 16. CONTINUOUS CONDUCTION MODE VCTRL=0.34V, ILED=5mA VIN 10mV/DIV VO (5V/DIV) IL 100mA/DIV VLX 10V/DIV VO 50mV/DIV VCOMP (1V/DIV) 1µs/DIV FIGURE 17. DISCONTINUOUS CONDUCTION MODE FN7427 Rev 0.00 March 31, 2004 FIGURE 18. OVER VOLTAGE PROTECTION (LED DISCONNECTED) Page 8 of 12 EL1848 Detailed Description The EL1848 is a constant current boost regulator specially designed for driving white LEDs. It can drive up to 3 LEDs in series or 9 LEDs in parallel/series configuration and achieves efficiency up to 91%. The brightness of the LEDs is adjusted through a voltage level on the CNTL pin. When the level falls below 0.1V, the chip goes into shut-down mode and consumes less than 1µA of current for VIN less than 5.5V. Steady-State Operation EL1848 is operated in constant frequency PWM. The switching is around 1MHz. Depending on the input voltage, the inductance, the type of LEDs driven, and the LED’s current, the converter operates at either continuous conduction mode or discontinuous conduction mode (see waveforms). Both are normal. Brightness Control LED’s current is controlled by the voltage level on CNTL pin (VCNTL). This voltage can be either a DC or a PWM signal with frequency less than 200Hz (for C3=4700pF). When a higher frequency PWM is used, an RC filter is recommended before the CNTL pin (see Figure 17). hiccough continues until LED is applied or converter is shut down. When designing the converter, caution should be taken to ensure the highest operating LED voltage does not exceed 13V, the minimum shut-down voltage. There is no external component required for this function. Component Selection The input and output capacitors are not very important for the converter to operate normally. The input capacitance is normally 0.22µF - 4.7µF and output capacitance 0.22µF - 1µF. Higher capacitance is allowed to reduce the voltage/current ripple, but at added cost. Use X5R or X7R type (for its good temperature characteristics) of ceramic capacitors with correct voltage rating and maximum height. When choosing an inductor, make sure the inductor can handle the average and peak currents giving by following formulas (80% efficiency assumed): IO VO I LAVG = -----------------------0.8 V IN 1 I LPK = I LAVG + --- I L 2 V IN V O – V IN I L = --------------------------------------------L VO FS where: PWM SIGNAL 100K 0.1µF CNTL • IL is the peak-to-peak inductor current ripple in Ampere COMP • L inductance in µH • FS switching frequency, typical 1MHz FIGURE 19. PWM BRIGHTNESS CONTROL The relationship between the LED current and CNTL voltage level is as follows: V CNTL I LED = ---------------------------13.33 R 1 When R1 is 5, 1V of VCNTL conveniently sets ILED to 15mA. The range of VCNTL is 250mV to 5.5V. A wide range of inductance (6.8µH - 68µH) can be used for the converter to function correctly. For the same series of inductors, the lower inductance has lower DC resistance (DCR), which has less conducting loss. But the ripple current is bigger, which generates more RMS current loss. Figure 9 shows the efficiency of the demo board under different inductance for a specific series of inductor. For optimal efficiency in an application, it is a good exercise to check several adjacent inductance values of your preferred series of inductors. Shut-Down When VCNTL is less than 100mV, the converter is in shut-down mode. The max current consumed by the chip is less than 1µA for VIN less than 5.5V. Over-Voltage Protection When an LED string is disconnected from the output, VO will continue to rise because of no current feedback. When VO reaches 14V (nominal), the chip will shut down. The output voltage will drop. When VO drops below 11V (nominal), the chip will boost output voltage again until it reaches 14V. This FN7427 Rev 0.00 March 31, 2004 Page 9 of 12 EL1848 For the same inductance, higher overall efficiency can be obtained by using lower DCR inductor. 85 The demo board is a good example of layout based on the principle. Please refer to the EL1848 Application Brief for the layout. EFFICIENCY vs IO EFFICIENCY (%) VIN=3.3V FOR DIFFERENT L L=22µH 83 L=33µH L=15µH 81 L=10µH 79 77 L=Coilcraft LPO1704 SERIES 1mm HEIGHT 5 10 15 20 25 30 IO (mA) FIGURE 20. EFFICIENCY OF DIFFERENT INDUCTANCE (4 LEDs IN A SERIES) The diode should be Schottky type with minimum reverse voltage of 20V. The diode's peak current is the same as inductor's peak current, the average current is IO, and RMS current is: I DRMS = I LAVG I O Ensure the diode's ratings exceed these current requirements. White LED Connections One leg of LEDs connected in series will ensure the uniformity of the brightness. 14V maximum voltage enables 3 LEDs can be placed in series. However, placing LEDs into series/parallel connection can give higher efficiency as shown in the efficiency curves. One of the ways to ensure the brightness uniformity is to pre-screen the LEDs. PCB Layout Considerations The layout is very important for the converter to function properly. Power Ground ( ) and Signal Ground ( ) should be separated to ensure the high pulse current in the power ground does not interference with the sensitive signals connected to Signal Ground. Both grounds should only be connected at one point right at the chip. The heavy current paths (VIN-L-LX pinPGND, and VIN-L-D-C2-PGND) should be as short as possible. The trace connected to the CS pin is most important. The current sense resister R1 should be very close to the pin When the trace is long, use a small filter capacitor close to the CS pin. The heat of the IC is mainly dissipated through the PGND pin. Maximizing the copper area around the plane is preferable. In addition, a solid ground plane is always helpful for the EMI performance. FN7427 Rev 0.00 March 31, 2004 Page 10 of 12 EL1848 TSOT Package Outline Drawing FN7427 Rev 0.00 March 31, 2004 Page 11 of 12 EL1848 MSOP Package Outline Drawing NOTE: The package drawing shown here may not be the latest version. To check the latest revision, please refer to the Intersil website at <http://www.intersil.com/design/packages/index.asp> © Copyright Intersil Americas LLC 2004. All Rights Reserved. All trademarks and registered trademarks are the property of their respective owners. For additional products, see www.intersil.com/en/products.html Intersil products are manufactured, assembled and tested utilizing ISO9001 quality systems as noted in the quality certifications found at www.intersil.com/en/support/qualandreliability.html Intersil products are sold by description only. Intersil may modify the circuit design and/or specifications of products at any time without notice, provided that such modification does not, in Intersil's sole judgment, affect the form, fit or function of the product. Accordingly, the reader is cautioned to verify that datasheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com FN7427 Rev 0.00 March 31, 2004 Page 12 of 12