STLD40D White led power supply for large display backlight General Features ■ Inductor switches boost controller ■ PFM mode control ■ High efficiency over wide range of input voltage from 3.0V to 5.5V ■ Overvoltage protection with automatic restart ■ Adjustable peak current limit ■ Enable pin with possibility of PWM dimming control ■ Low shutdown current <1uA ■ Small external component ■ Good load and line regulation ■ QFN 3mm x 3mm x 1mm 8 leads QFN8 (3mm x 3mm) high as 37V and can drive up to 10 white LEDs in series. The converter is a PFM (pulse frequency modulation) inductor switches and can work in discontinuous (DCM) mode operation. A minimum OFF time of the embedded boost switch TSW is fixed internally and allows limiting the switching frequency. The output current capability is 20mA with an output voltage of 37V. Application The regulation is done by sensing the led current through the resistor RLED. ■ White Led supply for LCD backlight ■ Mobile phone ■ PDA and organizers ■ Any handsets powered form 3.0V to 5.5V The device can be turned ON/OFF through the logic enable signal pin EN. By applying a low frequency PWM signal the LEDs can be dimmed. The maximum peak inductor current can be programmed by connected a resistor RSET to the pin RSET. Description STLD40D is a boost converter that operates from 3.0V to 5.5V and can provide an output voltage as Order code April 2006 Part number Package Comments STLD40DPMR QFN8L (3mm x 3mm) 4500 parts per reel Rev. 2 1/14 www.st.com 14 STLD40D Contents Contents 1 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.1 Boost controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.2 Adjustable peak inductor current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3 Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.4 OVP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6 Typical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2/14 STLD40D 1 Pin configuration Pin configuration Figure 1. Pin configuration (Top View ) Table 1. Pin description PlN N° 1 2 3 4 5 6 7 8 9 SYMBOL VI RSET GND FB N/C VO EN SW PGND NOTE Supply voltage Peak inductor current adjust Analog Ground Feedback for the LED current regulation Not connected Output voltage for LED supply IC enable signal Boost switch drain Power Ground 3/14 STLD40D Maximum ratings 2 Maximum ratings Table 2. Absolute maximum ratings Symbol Parameter Value Unit V VBSW, VBO Breakdown voltage at VO and SW pin EN VI Maximum voltage applied on pin EN 44 VI Supply voltage range 6 V VESD ESD ratings - (HBM MIL STD 883C) 2 kV TOP Operating temperature -40 to 85 °C TSTG Storage temperature range -65 to 150 °C Figure 2. 4/14 V Block diagram STLD40D 3 Electrical characteristics Electrical characteristics Table 3. Electrical characteristics (TJ=-40°C to 85°C, VI=3.6V, VEN=3V, CI=2.2µF, CO=4.7µF, L=4.7µH, RLED=8Ω VO=32V, Typ. values @ 25°C, unless otherwise specified) Symbol Parameter VI Input voltage range VO Output voltage range IO Regulated output current ISD Stand-by current IQ Quiescent current RDSON ILIM-ADJ ILIM VFB Line FB TON_MAX Boost switch RDSON BVDS Breakdown voltage Maximum peak inductor limit adjust range Note: 1 Maximum peak inductor limit when RSET = VI Note: 1 Test Conditions VEN Typ. 3.0 VI VO = 36V (10 White Leds) Max. Unit 5.5 V 37 V 20 VEN = Low, VI = 3.6V, TJ = 25°C mA 1 VEN = Low, VI = 3V to 4.2V 3 10 VI = 3V to 4.2V, TJ = 25°C 0.4 0.8 VI = 5.5V, TJ = 25°C 0.8 1.2 VI = 5.5V, I = 100mA 0.4 VI = 4.2V, I = 100mA 0.4 VI = 3.0V, I = 100mA 0.5 µA mA Ω 38 V RSET = 12kΩ to 100kΩ 0.2 1 A VI = 3V to 5.5V 0.75 1.1 A Feedback voltage VI = 3.6V 130 Line feedback voltage VI = 3V to 5.5V Maximum ON Time VI = 4.2V TOFF_MIN Minimum OFF Time VI = 4.2V Efficiency at VI = 3.0VDC Note: 1 IO = 20 mA, VO = 36VDC υ Efficiency at VI = 5.5VDC Note: 1 IO = 20 mA, VO = 36VDC OVP OVHYS Min. Overvoltage protection Overvoltage hysteresis 165 200 mV 5 35 mV 5.5 µs 250 ns 75 % 80 36 42 1.5 Enable input logic low Disable Low VIL Enable input logic high Enable High VIH 0.3 1.2 V V V Note: 1 Guaranteed by design 5/14 STLD40D Typical performance characteristics 4 Typical performance characteristics [VI=3.6V, VEN=3V, CI=2.2µF, CO=4.7µF, L=4.7µH, RLED=8Ω VO=32V, 10W Leds load (VO=32V) Typ. values @ 25°C, unless otherwise specified] Figure 3. ILED vs RLED Figure 4. ILED vs VI Figure 5. IQ vs Temperature Figure 6. ISD vs VI Figure 7. RDSON vs VI Figure 8. ILIMIT vs RSET 6/14 STLD40D Figure 9. Typical performance characteristics VFB vs Temperature Figure 11. Efficiency Vs VI Figure 10. VEN vs Temperature Figure 12. VOVP vs Temperature Figure 13. ILED vs Duty cycle EN pin (Dimming) 7/14 Functional description 5 Functional description 5.1 Boost controller STLD40D The STLD40D is a Boost converter operating in PFM (pulsed frequency modulation) mode. The converter monitors the LED current through the resistor RLED and when the feedback voltage falls below the reference voltage REF2, the boost switch TSW turns ON and the current ramps up. The inductor current is measured by sensing the temperature compensated drain voltage of the boost MOSFET. The boost turns off when its drain voltage reaches the internally reference REF1, the main switch remains off until the minimum off time (250ns typical) has passed and the feedback voltage is below the reference again. A maximum ON time of 4µs typical prevents the switch TSW to stay ON during a too long period of time. 5.2 Adjustable peak inductor current limit The peak inductor current is monitored by sensing the drain voltage of the switch TSW. Since it exceeds the temperature compensated and supply voltage compensated reference REF1, the RS Flip flop is reset and TSW is turned OFF. By connecting a resistance to the pin RSET the peak current limit can be adjusted. from 200mA to 1A. When RSET resistor value is about 12kΩ is connected directly to GND, the default value is 1A. 5.3 Enable The ENABLE pin is a high logic input signal and allows turning on/off the controller without cutting the input voltage from the boost regulator circuit. The pin ENABLE can be used to dim the LED by applying a low frequency PWM signal. 5.4 OVP If the regulation loop is cut, there is no signal at the feedback pin, the PFM controller will then continue to switch without control and generate an output voltage at the SW, and VO pin exceeding the breakdown value VBSW, and VBO. The Over Voltage Protection (OVP) senses the voltage at the VO pin. When the voltage exceed 38V Min the controller is automatically turned OFF. A hysteresis control allows the device restarting automatically since the output voltage drops down of 1.5V. 8/14 STLD40D 6 Typical application Typical application Figure 14. Application circuit Table 4. Symbol D External component proposal (see Figure 14) Parameter Boost schottky diode Test Conditions VRRM VF at IF = 300mA, TJ = 25°C Min. Typ. IR at VR = 10V, TJ = 25°C RLED RSET CI CO L Feedback LED current regulation ILED = 20mA resistor IPEAK = 0.2A to 1A Current peak setting resistor Ceramic Type Capacitance Output capacitance: ceramic low Voltage ESR ESR Inductance DCR Boost inductor (height < 2mm) ISATRSET = GND Max. Unit 0.5 V V 30 µA 40 Ω 8 12 Input filtering capacitor 100 kΩ 1.6 4.7 1 1 µF µF V Ω µH Ω A 2.2 4.7 35 The external components proposal should be considered as a design reference guide.The performances mentioned in the electrical characteristics table are not guaranteed for all the possible electrical parameters of the components included in this list. On an other hand the operation of STLD40D is not limited with the use of components included in this list 9/14 Package mechanical data 7 STLD40D Package mechanical data In order to meet environmental requirements, ST offers these devices in ECOPACK® packages. These packages have a Lead-free second level interconnect. The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com. 10/14 STLD40D Package mechanical data QFN8 (3x3) MECHANICAL DATA DIM. A mm. inch MIN. TYP MAX. MIN. TYP. MAX. 0.80 0.90 1.00 0.032 0.035 0.039 0.03 0.05 0.001 0.002 A1 A2 0.65 0.70 0.75 0.026 0.028 0.030 A3 0.15 0.20 0.25 0.006 0.008 0.010 b 0.29 0.31 0.39 0.011 0.012 0.015 b1 0.17 0.30 0.007 D D2 3.00 1.92 E E2 2.02 0.118 2.12 0.076 3.00 1.11 e 1.21 0.012 0.080 0.084 0.118 1.31 0.044 0.65 0.048 0.052 0.026 K 0.20 0.008 L 0.20 0.29 0.45 0.008 0.011 0.018 L1 0.16 0.24 0.40 0.006 0.009 0.016 L2 0.13 0.005 r 0.15 0.006 r1 0.15 0.006 7517789 11/14 STLD40D Package mechanical data Tape & Reel QFNxx/DFNxx (3x3) MECHANICAL DATA mm. inch DIM. MIN. TYP A MIN. TYP. 330 13.2 MAX. 12.992 C 12.8 D 20.2 0.795 N 60 2.362 T 12/14 MAX. 0.504 0.519 18.4 0.724 Ao 3.3 0.130 Bo 3.3 0.130 Ko 1.1 0.043 Po 4 0.157 P 8 0.315 STLD40D 8 Revision history Revision history Table 5. Document revision history Date Revision Changes 20-Mar-2006 1 Initial release. 04-Apr-2006 2 Add RSET in table 4 and fig 2 has been updated. 13/14 STLD40D Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. 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