STLD20D ® WHITE LED POWER SUPPLY ASD™ PRELIMINARY DATA FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ APPLICATION High efficiency above 80% Can drive up to 4 LEDs in series from 2.8V supply Constant LED current regulation Integrated LED disconnect switch that cuts the LEDs branch in shutdown mode Constant switching frequency Stable current regulation across the total input voltage range Supply voltage rejection Inherent soft start by limiting the peak inductor current Peak inductor current adjustability (STLD20DC8 only) Shutdown pin with possibility of PWM dimming control Over voltage and over temperature protection with automatic restart Low shutdown current < 1µA Small external inductor (10µH, height < 2mm) Tiny ceramic external capacitor Can be supplied by a Li-ion battery - VIN range: 2.5Vdc to 5Vdc ■ ■ ■ ■ White Led supply for LCD backlight Mobile phone PDA and organizers Any handsets powered from 2.8V to 4.2V DESCRIPTION The STLD20D is a constant switching frequency boost regulator with specific features to supply up to 4 white LEDs in series. A stable LED current regulation, from 2.8V to 4.2V, is achieved by sensing the LED current through a low ohmic shunt resistor RLED (see figure 1). The device also includes a supply rejection circuit that prevent any kind of flickering effect on the display during dynamic supply voltage variation. A LED disconnect switch cut the LED branch to reduce the current consumption in shutdown mode. The maximum peak inductor current can be programmed. The STLD20D includes often numerous features and innovative design circuit that allows getting an efficiency above 80% across the total supply voltage range. Figure 2: Efficiency versus input voltage (ILED=20mA; Tamb=25°C) Figure 1: Basic connection Efficiency (%) 88 D L = 10µH VBATT 87 86 Cin = 2.2µF 85 Cout = 1µF 84 VOUT SW 83 RSET (*) 82 ILED = 20mA RSET VIN STLD20D 81 LDS 80 FB 79 SHDN RLED GND 78 2.5 D: STM BAT20J L: Murata LQH32CN100K33 (*) STLD20D-C8 only 3 3.5 4 4.5 5 Input voltage (Vdc) Table 1: Order Codes Part Number STLD20D-C8 STLD20D-DEF October 2004 Marking L2D L2D Package SOT23-8L QFN 3x3 8L REV. 2 1/8 This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice. STLD20D Figure 3: STLD20D-C8 Pin-Out Designation (SOT23-8L top view) SHDN LDS RSET FB GND VIN VIN VOUT 3 4 SHDN RSET SW EXPOSED PAD VIN 2 GND SW GND 1 Figure 4: STLD20D-DEF Pin-Out Designation (QFN 8L top view) SHDN N/C VOUT LDS FB 5 6 7 8 1 2 3 4 5 6 7 8 FB LDS VOUT SW GND VIN SHDN N/C FB LDS VOUT SW Figure 5: Block Diagram SW OTP OSCILLATOR VIN OVP RAMP OSCILLATOR COMPENSATION VOUT POWER FAULT ENABLE VIN S + - SW Q R PWN COMP. SHDN + - T° VIN DRAIN CURRENT REFERENCE RSET (*) LED DISCONNECT LDS VIN SHDN LDS FB + LED CURRENT REFERENCE GND (*) STLD20D-C8 only 2/8 STLD20D Table 2: External Components Pproposal (note 1) - Referred basic connection (figure 1) Symbol Parameter RLED LED current resistance CIN Input filtering capacitor COUT L Test Conditions Value Min. Typ. Max. Ceramic type Output capacitance Boost inductor (height < 2mm) 15 Ω 2.2 µF 1 Inductance 10 Resistance at 500kHz D Boost diode (STMicroelectronics BAT20J type) Unit µH 1 Ω Isat (RSET = 100kΩ) 300 mA VRRM 23 Vdc IF (peak forward current) 1 A VF @ IF = 0.1A Tj = 25°C 0.35 0.4 V IR @ Tj = 25°C VR = 15V 3 12 µA IR @ Tj = 85°C VR = 15V 120 250 Note 1: 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 STLD20D is not limited with the use of components included in this list. Table 3: Absolute Maximum Ratings Symbol VIN Parameter Test conditions Supply voltage range Value Min. Typ. Max. 2.5 5 Unit V VESD ESD ratings TOP Operating temperature - 40 + 85 °C Tstg Storage temperature - 65 150 °C HBM MIL STD 883C BVDS Breakdown voltage at pin SW and TSS and VOUT SHDN Maximum voltage applied on SHDN pin 2 kV 20 V VIN V 3/8 STLD20D Table 4: Electrical Characteristics (for VIN = 2.8 to 4.2V and Tj = 25°C) Symbol Parameter Test conditions VIN Operating Input voltage range IOUT Average regulated current IOUT = 20mA ISD Stand-by current SHDN = low VIN = 4.2V IQ Quiescent current consumption SHDN = high VIN = 4.2V SW LDS Boost switch RDSON Line Eff 2.8 RLED = 15Ω 19 V 21 mA 1 µA 0.43 0.6 mA 0.6 Ω 20 0.51 VIN = 4.2V 0.45 0.49 QFN Tj = 25°C ISW = 250mA VIN = 2.8V 0.65 VIN = 4.2V 0.55 Load disconnect switch SOT23-8L Tj = 25°C RDSON ILDS = 20mA VIN = 2.8V 5.5 6.1 VIN = 4.2V 4.7 5.2 Tj = 25°C ILDS = 20mA VIN = 2.8V 6.2 VIN = 4.2V 5.3 Feedback voltage 0.285 0.300 0.315 Variation of the LED current versus the input voltage: RLED = 15Ω Efficiency with 4 LEDS Vout = 16V Circuit configuration (figure 1) L: Murata LQH32CN100K33 Diode: BAT20J VIN = 2.8V 80 VIN = 4.2V Minimum duty cycle % 500 600 kHz 22 25 % 640 mA 20 Vdc Peak current boost switch L = 10µH RSET = GND (STLD20D-C8) OVP Overvoltage protection 17.5 18.5 HystOV Overvoltage hysteresis 0.7 Vdc 110 HystOT Over temperature protection hysteresis SHDN Shutdown signal logic °C 5 Disable Low VIL Enable high VIH V 85 400 Over temperature protection Ω 0.9 mA/V ILIM OTP Unit 4.2 VIN = 2.8V Switching frequency DCMIN Min. Typ. Max. SOT23-8L Tj = 25°C ISW = 250mA QFN FB Value °C 0.3 V 1.2 Table 5: Thermal Characteristics Symbol Rth(j-a) 4/8 Parameter Mounted on epoxy board without copper heatsink Value Min. Typ. Max. SOT23-8L 300 QFN 350 Unit °C/W STLD20D FUNCTIONAL DESCRIPTION Figure 6: LED current versus input voltage ILED(mA) 21.00 1. BOOST CONTROLLER: The STLD20D is a PWM mode control boost converter operating at 500kHz in discontinuous mode. An automatic compensation of the oscillation ramp allows rejection of the battery voltage transient. The LED constant regulation (referred figure 4 ) is done by sensing the LED current through the resistance RLED (figure 1). The voltage across RLED is used by the feedback loop of the controller (pin FB). 20.80 20.60 20.40 20.20 20.00 19.80 19.60 19.40 19.20 19.00 2.5 3 3.5 4 4.5 5 VIN(V) 2. PEAK INDUCTOR CURRENT LIMITATION AND SOFT START FUNCTION: An integrated current sensor senses the peak drain current of the switch SW in order to keep the inductor current below its saturation level. Since the peak drain current exceeds 590mA (if RSET = GND for STLD20D-C8), the RS flip flop turns off the switch SW. During start up, this peak drain current limitation acts inherently like a soft start function . 3. PEAK INDUCTOR CURRENT ADJUSTABILITY (STLD20D-C8 ONLY) The peak current of the boost inductor should always be below the saturation current. In order to provide flexibility in the selection of the inductor, the maximum peak inductor current can be adjusted by connecting a resistor at the pin RSET. The figure 5 gives the value of the resistance RSET versus the peak inductor current limit ILMAX at 25°C. If a low ripple is espected on the battery voltage bus, then the maximum peak inductor current should be reduced. Figure 7: RSET (kΩ) versus ILMAX (A) RSET(kΩ) RSET = f(ILmax) 120 VIN=3.2V 100 VIN=4.2V 80 60 40 20 0 0.3 0.4 0.5 ILmax(A) 0.6 0.7 4. SHUTDOWN: The SHDN pin is a low logic input signal and allows turning off the controller without cutting the input voltage from the boost regulator circuit. An integrated LED disconnect switch LDS disconnects the LEDs branch in shutdown mode .This arrangement allows eliminating the DC current path that normally exists with traditional boost regulator in shutdown mode. 5. BRIGHTNESS CONTROL: The brightness of the Led is adjusted by pulsing the shutdown pin with a low frequency PWM signal. By using such a PWM signal the controller is alternatively ON and OFF and the LED current changes from full current to zero. The duty cycle allows to regulate the average LED current . This scheme ensures that when the LEDs are ON they are driven at the full current without risk of color change. 6. OTP: An integrated temperature sensor senses the temperature of the junction of the controller. when this temperature exceeds 110°C min fixed internally the controller is automatically turned OFF . When the temperature is reduced the operation of the device automatically recovers. 5/8 STLD20D 7. OVER VOLTAGE PROTECTION (OVP): In case of failure and if the LED branch is cut, then there is no signal at the feedback pin FB (figure 1), the PWM controller will then switches with a maximum duty cycle. This will generate a voltage at the pin SW and VOUT that can exceed the maximum rating of the device. The overvoltage protection bloc senses the output voltage at the pin VOUT (figure 1). If the voltage exceeds 18.5Vdc typical the controller is automatically turned OFF. When the voltage is reduced of 0.7V, the operation of the device automatically recovers. 8. EFFICIENCY (Figure 1 & 2) The efficiency takes into account these following losses: ■ RLED ohmic losses ■ ■ ■ ■ ■ Boost switch SW losses LED disconnect switch LDS Boost inductor losses Boost diode losses Total driver consumption. Figure 8: SOT23-8L Package Mechanical Data DIMENSIONS REF. < Min. GAUGE PLANE A1 L D e1 c e 0.25 SEATING PLANE c Inches Max. Min. Max. A 1.45 0.057 A1 0.15 0.006 A2 0.90 1.30 0.035 0.051 b 0.22 0.38 0.008 0.015 c 0.08 0.22 0.003 0.008 D 2.80 3 0.110 0.118 E 2.60 3 1.102 0.118 E1 1.50 1.75 0.059 0.069 E1 E 6/8 Millimeters A2 A b e 0.65 typ. 0.026 typ. e1 1.95 typ. 0.077 typ. L 0.30 0.60 0.012 0.024 < 0° 8° 0° 8° STLD20D Figure 9: QFN 3x3 8L Package Mechanical Data REF. L2 E L2 D1 A2 A A3 A1 b e L r b1 E2 L1 k r1 D2 A A1 A2 A3 b b1 D D2 E E2 e K L L1 L2 r r1 DIMENSIONS Millimeters Inches Min. Typ. Max. Min. Typ. 0.80 0.90 1.00 0.031 0.035 0.03 0.03 0.001 0.65 0.70 0.75 0.026 0.028 0.15 0.20 0.25 0.006 0.008 0.29 0.31 0.39 0.011 0.012 0.17 0.30 0.007 3.00 0.118 1.92 2.02 2.12 0.076 0.079 3.00 0.118 1.11 1.21 1.31 0.044 0.048 0.65 0.026 0.20 0.008 0.20 0.29 0.45 0.008 0.011 0.16 0.24 0.40 0.006 0.009 0.13 0.15 0.006 0.15 0.006 Max. 0.039 0.002 0.030 0.010 0.015 0.012 0.083 0.051 0.018 0.016 0.005 Figure 10: QFN Foot Print Dimensions (in millimeters) 0.65 0.41 0.39 0.34 4.00 1.21 2.02 4.00 - Exposed pad is not connected to the ground of the dice. - Connect exposed pad to pin one. 7/8 STLD20D Table 6: Ordering Information Part Number Marking Package Weight Base qty STLD20D-C8 STLD20D-DEF L2D L2D SOT23-8L QFN 3x3 8L 0.2 g 0.22 g 3000 3000 Delivery mode Tape & reel Tape & reel Table 7: Revision History Date Revision Description of Changes August-2004 1 First issue 12-Oct-2004 2 Table 4 on page 4 following parameters values updated: . IOUT (min), IQ (min), SW (QFN max), LDS (QFN max), ILIM, HystOT . FB VAR symbol changed to Line and value changed from 0.7 to 0.9 mA/V Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement 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 STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners © 2004 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com 8/8