STEVAL-TLL010V1

STLA02 White LED driver for display backlight Features ■ Boost DC-DC converter ■ Drives up to 6 LEDs with a total current up to 20 mA ■ Output power capability up to 500 mW ■ Input voltage range 2.5 V to 18 V ■ Output current control ■ 2.3 MHz switching frequency ■ PWM input for the output current dimming with 300:1 dimming range ■ 350 mA integrated switch ■ Overvoltage protection ■ Chip overtemperature detection and protection ■ Soft-start implemented ■ Package DFN6 2 x 2 mm DFN6 (2 x 2 mm) on/off by the logic signal connected to the EN pin and this pin is also dedicated for the PWM dimming of the output current. Current mode control of the regulation allows a fast response to a change of the enable pin voltage level. Applications ■ PDA and handheld devices ■ Cellular phones ■ MP3 players Description STLA02 is a boost converter that operates from 2.5 V to 18 V and can provide an output voltage as high as 27 V and can drive up to 6 white LEDs connected in series. The total output current capability is 20 mA at an output voltage of 24 V. The total output power capability is up to 500 mW. The regulation is done by the internal error amplifier which works with the feedback voltage from the sensing resistor connected in high side sensing configuration. The device can be turned Table 1. Device summary Part number Order code Package STLA02 STLA02PUR DFN6 (2 x 2 mm) February 2011 Doc ID 010005 Rev 1 1/23 www.st.com 23 Contents STLA02 Contents 1 Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6 Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.1 PWM input (EN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.2 Selection of the external components . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2/23 Doc ID 010005 Rev 1 STLA02 Diagram 1 Diagram Figure 1. Block diagram VIN VLX EN/ PWM OVP LOGIC BIAS VOUT VBG STEP-UP CONTROL 12 V/5 V CONV ILIM FB SENSING REFERENCE ILIM VSET FB VSET VBG GND Doc ID 010005 Rev 1 AM07827v1 3/23 Pin configuration STLA02 2 Pin configuration Figure 2. Pin connections (top view) Table 2. Pin description Pin n° Symbol 1 VIN 2 GND 3 LX 4 VOUT Output voltage pin 5 FB Feedback voltage 6 EN/PWM Exposed pad GND 4/23 Name and function Supply voltage pin Ground Switching pin Enable pin or PWM control input for dimming Ground Doc ID 010005 Rev 1 STLA02 Maximum ratings 3 Maximum ratings Table 3. Absolute maximum ratings Symbol Parameter VIN Signal supply voltage VLX Inductor connection FB Feedback connection EN/PWM Logic pin/PWM input VOUT (1) Output voltage connection Value Unit - 0.3 to 19 V - 0.3 to 30 V - 0.3 to 30 V - 0.3 to 12 V - 0.3 to 30 V 530 mW °C)(1) PTOT Continuous power dissipation (at TA = 70 TOP Operating ambient temperature range - 40 to 85 °C Junction temperature - 40 to 150 °C Storage temperature range - 65 to 150 °C TJ TSTG 1. The maximum acceptable difference between the VOUT pin potential and feedback pin potential is 5 V. Note: Absolute maximum ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is not implied. Table 4. Thermal data Symbol RthJA Parameter Thermal resistance junction-ambient Value Unit 102 °C/W (1) 1. Power dissipation is dependent on PCB. The recommended PCB design is included in this document (TBD). Table 5. ESD Symbol Parameter HBM Human body model MM Machine model Doc ID 010005 Rev 1 Value Unit 2 kV 200 V 5/23 Application STLA02 4 Application Figure 3. Application schematic L VLX VIN VIN CIN EN/PWM VOUT RFB STLA02 EN/PWM FB GND ILED COUT AM07828v1 Table 6. List of external components Component Manufacturer Part number Value Size CIN MURATA GRM216R61E105KA12 1 µF / 25 V 0805 COUT MURATA GRM216R61E105KA12 1 µF / 25 V 0805 MURATA LQH3NPN100NJ0L 10 µH 3x3x0.9 mm TDK VLF3012ST-100MR59 10 µH 3x2.8x1.2 mm RFB TYCO CPF0402B10RE 10 Ω 0402 LED OSRAM LWL283-Q1R2-3K8L-1-Z 20 mA / 3.1 V 0603 L Note: 6/23 Above listed components refer to a typical application with maximum performance settings. Operation of the STLA02 is not limited to the choice of these external components. Doc ID 010005 Rev 1 STLA02 5 Electrical characteristics Electrical characteristics VEN = VIN = 3 V TA = - 40 °C to 85 °C unless otherwise specified. Typical values are at TA = 25 °C, unless otherwise specified. Table 7. Symbol VIN Electrical characteristics Parameter Test conditions Input operating supply voltage Min. Typ. 2.5 VEN = VIN, VOUT = 24 V, VFB = 23 V 2 VEN = GND 10 IS Supply current IO Output current adjustment VIN = 2.5 V to 18 V, RFB = 10 Ω VOUT Regulated voltage range VIN = 2.5 V to 18 V IPEAK Inductor peak current VIN = 2.5 V VIN+1 Max. Unit 18 V 4 mA µA 20 mA 27 V 300 400 550 mA 190 200 210 mV VFB Feedback voltage (VOUT VEN = VIN, RFB = 10 Ω VFB) IFB FB bias current VEN = VIN, VOUT = 24 V, VFB = 24 V ILX(leak) N-MOS leakage current VEN = 0, VLX = VOUT = 24 V ΔIO Output current tolerance VIN = 3 V, IOUT = 0.2 V / RFB -5 fs Switching frequency VIN = 2.5 V, TA = 25 °C 1.7 2 DMAX Maximum duty cycle VEN = VIN, VOUT = 24 V, VFB = 24 V 88 92 % 0.8 Ω RDSon-N 6 Internal N-channel RDSon ILX = 20 mA µA 0.1 µA 5 % 2.3 MHz ν Efficiency of the chip itself VIN = 10 V, IO = 20 mA, VO = 6 x VFLED_max + VRSENSE = 24 V (1) 85 % ν Efficiency of the whole application VIN = 10 V, IO = 20 mA, VO = 6 x VFLED_max + VRSENSE = 24 V (1) 83 % OVP Output overvoltage protection VIN = 3 V, no load 28 V TSHDN Thermal shutdown 150 °C THYS Thermal shutdown hysteresis 15 °C VIL VIH Low and high level input logic signal on EN pin 130 VIN = 2.5 V to 18 V, VENMAX = 12 V 0 1.5 1.8 VIN V TEN LED current rise time ILED VIN = 9 V, VEN = 0 V to 3 V 6 LEDs in = 0 to ILED = 20 mA series (1) 0.2 ms TRESPONSE LED current rise time ILED VIN = 9 V, VEN = 0 V to 3 V, 6 LEDs in = 0 mA to ILED = 20 mA series (1), VOUT precharged 60 µs 1. Guaranteed by design, but not tested in production. Doc ID 010005 Rev 1 7/23 Typical performance characteristics STLA02 6 Typical performance characteristics Figure 4. Efficiency at 20 mA current load STLA02 20 mA / 18 V eff. IN [mA] AM07819v1 Eff [%] 92 89 86 83 80 77 74 71 68 65 62 59 56 53 50 200 150 100 I IN [mA] 50 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 VIN [V] Figure 5. Quiescent current vs. VIN AM07820v1 IIN [µA] 20 15 10 5 0 0 2 4 6 8 10 12 VIN [V] 8/23 Doc ID 010005 Rev 1 14 16 18 20 STLA02 Figure 6. Typical performance characteristics STLA02 driver current consumption vs. VIN +85°C -40°C 25°C AM07821v1 1.80 IIN [mA] 1.60 1.40 1.20 1.00 0.80 0.60 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 VIN [V] Figure 7. Switching frequency vs. temperature 2 AM07822v1 F [MHz] 98 1, 96 1, 94 1, 92 1, -60 -40 -20 9 1, 0 20 40 60 80 100 Temp [°C] Doc ID 010005 Rev 1 9/23 Typical performance characteristics Figure 8. STLA02 Switching frequency vs. VIN @ POUT = 0.36 W AM07823v1 2.0 1.9 1.8 1.7 1.6 F [MHz] 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 2 3 4 5 6 7 8 9 10 11 12 13 14 VIN [V] Figure 9. Overvoltage protection threshold vs. VIN AM07824v1 30.0 29.5 29.0 VOUT [V] 28.5 28.0 27.5 27.0 26.5 26.0 25.5 25.0 2 3 4 5 6 7 8 9 10 11 VIN [V] 10/23 Doc ID 010005 Rev 1 12 13 14 15 16 17 18 STLA02 Typical performance characteristics Figure 10. Overvoltage protection threshold vs. temp -40 -30 -20 -10 25 .0 25 .5 26 .0 26 .5 27 .0 27 .5 VOUT [V] 28 .0 28 .5 29 .0 29 .5 30 .0 AM07825v1 0 10 20 30 40 50 60 70 80 Temp [°C] IOUT [mA] Figure 11. Output current regulation vs. VIN AM07826v1 21.0 20.8 20.6 20.4 20.2 20.0 19.8 19.6 19.4 19.2 19.0 18.8 18.6 18.4 18.2 18.0 17.8 17.6 17.4 17.2 17.0 0 2 4 6 8 10 12 14 16 18 VIN [V] Doc ID 010005 Rev 1 11/23 Typical performance characteristics STLA02 Figure 12. Switching waveform at VIN = 2.5 V Figure 13. Switching waveform at VIN = 7 V IL IL IOUT IOUT VOUT VOUT VLX Figure 14. VLX Switching waveform at VIN = 12 V Figure 15. Overvoltage function IL IOUT VOUT IL VOUT VLX VLX Figure 16. Line transient response VIN = 3.4 V to 4 V step VIN IL IOUT VLX 12/23 Doc ID 010005 Rev 1 STLA02 Typical performance characteristics Figure 17. Direct PWM dimming 300 Hz at VBAT = 2.5 V, VEN = 0 to 3 V step Doc ID 010005 Rev 1 13/23 Introduction 7 STLA02 Introduction The STLA02 is a boost converter dedicated to powering and controlling the current of white LEDs in an LCD backlight. The device operates at a typical constant switching frequency of 2.3 MHz. It steps an input voltage ranging from 2.5 V to 18 V, up to 27 V. The output current is adjustable by the resistor RFB connected between the VOUT and FB pins. The STLA02 device contains high side sensing to simplify the PCB layout in terms of connection of the LEDs. The output current is dimmable by the PWM signal applied to the EN pin with minimum PWM frequency equal 100 Hz. 7.1 PWM input (EN) Light intensity can be dimmed by a signal applied to the PWM (EN) input. The PWM signal is directly connected to the enable pin of the STLA02. It is recommended to use the frequency of the PWM signal in the range of 100 Hz to 1 kHz and amplitude of the signal 1.8 V min. The result of the direct PWM dimming method (300 Hz PWM and VEN = 1.8 V) is shown in Figure 17. Note: When the device is required to operate in a constant current mode with the EN pin connected to the voltage higher than 1.8 V, then the delay between rise times of VIN voltage of the device and the EN voltage is mandatory to guarantee the proper internal reset of the logic of the device during ramping of the VIN. It is recommended to delay the EN voltage rise time by 2 ms after the rise time on VIN appears. 7.2 Selection of the external components CIN selection It is recommended to use 1 µF as the input capacitor to achieve good stability of the device and low noise on the VIN track. COUT selection It is recommended to use 1 µF as the optimal value of output capacitor to get the best compromise between output voltage ripple and load transients response. The output ripple can be checked according to the equation for step-up architecture: Equation 1 VPK −PK = ( ) IOUT(MAX ) ∗ VOUT − VIN(MIN) * 100 2 C OUT ∗ VOUT ∗ f [V; A, V,F,Hz] Inductor selection A thin shielded inductor with a low DC series winding resistance is recommended for this application. To achieve a good efficiency in step-up mode, it is recommended to use an inductor with a DC series resistance RDCL = RD/10 [Ω; Ω; 1], where RD is the dynamic resistance of the LED [Ω; Ω; 1]. 14/23 Doc ID 010005 Rev 1 STLA02 Introduction For nominal operation, the peak inductor current can be calculated by the formula: Equation 2 ⎧⎪⎛ I IPEAK = ⎨⎜ OUT ⎪⎩⎝ ν [ ⎞ (VOUT − VIN ) ∗ VIN ⎟+ 2 2 ∗ L ∗ f ∗ VOUT ⎠ 2 ]⎫⎪⎬ ∗ V OUT ⎪⎭ VIN where: IPEAK Peak inductor current IOUT Current sourced at the VOUT pin ν Efficiency of the STLA02 VOUT Output voltage at the VOUT pin VIN Input voltage at the VIN pin L Inductance value of the inductor f Switching frequency For the optimal function of the STLA02 device, it is recommended to use the inductor value 10 µH and higher with low serial resistance and relevant saturation current calculated from the equation above. RFB value RFB = VFB / ILED In the case of a typical setting ILED = 20 mA, VFB = 200 mV, and RSENSE = 10 Ω. The resistor must be rated for a power dissipation of 10 x 0.02² W = 0.004 W. PCB layout STLA02 is a powerful switched device, the PCB must be designed in line with rules for designing switched supplies. It is recommended to use a two layer PCB. The power wirings must be as short as possible and wide. Place all external components close to the STLA02. High-energy switched loops should be as small as possible to reduce EMI. Most LEDs need cooling, which may be done by a defined area of copper on the PCB. Use the reference guide of each LED to design the heatsink. Place the RFB resistor as close as possible to pin 4 and 5. When a change of PCB layer is needed, use enough vias. During routing the PCB must be focused on the minimum area of the application ground - the smaller the ground area of the DC-DC converter (a), the better stability and lower noise issues are achieved. It is recommended to place the copper plate, connected through the vias to the Exposed pad, on the bottom layer to create the heatsink of the device. a. The application ground area is represented by the area which is created by the ground pins of the CIN, COUT, ground of the DEVICE and GND connection of the load. Doc ID 010005 Rev 1 15/23 Introduction STLA02 Figure 18. Top layer Figure 19. Bottom layer 16/23 Doc ID 010005 Rev 1 STLA02 Introduction Figure 20. Top overlay Doc ID 010005 Rev 1 17/23 Package mechanical data 8 STLA02 Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK specifications, grade definitions, and product status are available at www.st.com. ECOPACK is an ST trademark. 18/23 Doc ID 010005 Rev 1 STLA02 Table 8. Package mechanical data DFN6 (2 x 2 mm.) mechanical data mm. Dim. Min. Typ. Max. A 0.70 0.75 0.80 A1 0 0.02 0.05 A3 0.20 b 0.18 0.25 0.30 D 1.90 2.00 2.10 D2 1.35 1.50 1.60 E 1.90 2.00 2.10 E2 0.15 0.30 0.40 e L 0.50 0.25 0.35 0.45 Figure 21. DFN6 (2 x 2 mm.) drawing 7733060D Doc ID 010005 Rev 1 19/23 Package mechanical data Table 9. STLA02 DFN6 (2 x 2 mm.) tape and reel mechanical data mm. inch. Dim. Min. Typ. A Max. Typ. 180 C 12.8 D 20.2 N 60 13.2 Max. 7.087 0.504 0.519 0.795 2.362 T 14.4 0.567 Ao 2.3 0.091 Bo 2.3 0.091 Ko 1.0 0.039 Po 4 0.157 P 8 0.315 Figure 22. DFN6 (2 x 2 mm.) tape and reel drawing 20/23 Min. Doc ID 010005 Rev 1 STLA02 Package mechanical data Figure 23. DFN6 (2 x 2 mm) footprint recommended data Doc ID 010005 Rev 1 21/23 Revision history STLA02 9 Revision history Table 10. Document revision history Date Revision 22-Feb-2011 1 22/23 Changes Initial release Doc ID 010005 Rev 1 STLA02 Please Read Carefully: Information in this document is provided solely in connection with ST products. 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