STCF02 High power white led driver General features ■ Buck-boost DC/DC Converter ■ Drives one power white led: up to 600mA between 2.7 to 4.5V ■ Led temperature protection ■ Output current control ■ 1.8 MHz (typ) fixed frequency PWM Description ■ Synchronous rectification ■ High efficiency across the total input voltage range ■ Operational modes: - Shutdown mode - Shutdown mode with NTC - Flash mode up to 600 mA - Medium flash mode - Torch mode: up to 250 mA ■ Adjustable current in all three modes The STCF02 is a high efficiency power supply solution to drive a single flash LED in camera phone, PDAs and other hand-held devices. It is a buck-boost converter that guarantees a proper LED current control over the battery voltage (particularly in the case, when the output voltage is lower than the input voltage); the output current control ensures a good current regulation over the forward voltage spread characteristics of the Flash LED. ■ LED disconnected from the battery in shutdown mode ■ Programmable safety shutdown in flash mode ■ LED short and open circuit protection ■ Overvoltage protection ■ < 1µA Shutdown current ■ QFN20 4mm x 4 mm package Applications ■ Cell phone and smart phones ■ Camera flashes/strobes ■ PDAS and digital still cameras QFN20 (4mm x 4mm) Three logic input signals can select 5 modes of operation: Shutdown mode (quiescent current less than 1µA typ), Shutdown mode with NTC active, Torch mode (drives the LED up to 250mA), Flash mode (up to 600mA), and Medium flash mode (reduces the flash current). This highly efficient converter is able to accept input current from the battery (lower than 1.5A), while limiting the peak inductor current to 2.3A (typ). Other features include Soft start control, thermal shutdown, short circuit protection, overvoltage protection, and LED temperature protection. An alternative to LED temperature protection is that a safety flash time-out feature can be implemented instead. This device is available in a QFN20, 4mm x 4mm, no-lead package (height is less than 1mm). Order code Part number Package Packaging STCF02PNR QFN20 (4x4 mm) 4500 parts per reel February 2007 Rev. 6 1/19 www.st.com 19 STCF02 Contents Contents 1 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Pin connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6 Detailed operating description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.2 Buck-Boost converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.3 Flash mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.4 Medium flash mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.5 Torch mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.6 Shutdown mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.7 Soft start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.8 LED Failure Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.9 Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.10 Thermal shutdown protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.11 Sensing of LED temperature by NTC resistor . . . . . . . . . . . . . . . . . . . . . . . . 14 6.12 Safety shutdown in flash mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 7 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2/19 STCF02 1 Application Application Figure 1. Application circuit Table 1. External components Symbol Parameter Min. Typ. Max. Unit RFLASH Sensing flash current resistor - thick film type (0805) 0.27 Ω RTORCH Sensing torch current resistor - thick film type (0603) 6.2 Ω 8200 Ω RMF CI CO L NTC CCOMP RX C1 Note: Setting resistor for middle flash mode - thick film type (0402) Two Input filtering capacitor TDK C1608X5R0J106MT - Ceramic type (0603) 6.3V Output capacitance - Ceramic type 0603 6.3V INDUCTANCE TDKVLF5014A-4R7 DCR Negative thermistor - NCP18WF104J03RB - Thick film type Compensation capacitor - 0402 Reference resistor - 0402 Ceramic Capacitor 10 2x10 µF 820 µF µH Ω kΩ pF 4.7 4.7 0.12 100 100 15 47 kΩ pF - 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 the other hand the operation of STCF02 is not limited with the use of the external components listed above. - The CCOMP is optional and may be used if the error amplifier bandwidth (which by default is set to 2 KHz) has to be decreased because of an unstable driver function. Unstable operation could be caused by using different values of inductor and output capacitor then recommended. 3/19 STCF02 Pin connections 2 Pin connections Figure 2. Pin configuration (bottom view) Table 2. Pin description Pln N° Symbol 1 VLX2 2 RX 3 VO 4 NTC 5 FB1 6 RTBY 7 FB2 8, 10 GND 9 COM1 11 COM2 12 13 14 VBAT PVBAT VLX1A 15 VLX1B 16 EN3 Enable Pin 3 17 EN2 Enable Pin 2 4/19 Name and function Note External coil is connected between this pin and VLX1. It should be placed as close as possible to the device in order to minimize resistance which cause losses. Rx resistor is connected between this pin and ground to set LED over Rx Resistor connection temperature threshold. Output voltage Anode of the LED is connected to this pin. This pin is used for the LED temperature sensing using an external NTC Resistor connection NTC resistor. Feedback pin for torch This pin is used for current sensing in Torch mode – Cathode of the mode Flash LED and RTorch resistor are connected to this pin. This pin is used to short-circuit the RTORCH during FLASH and RTORCH Bypass MIDDLE FLASH MODE. This pin is used to sense the voltage across RFLASH. It must be Feedback pin for flash directly connected to the non-grounded terminal of RFLASH. mode Inductor connection Signal ground Compensation connection Compensation connection Supply voltage Power supply voltage Inductor connection This is the signal ground pin related to digital and analog signals and must be connected as close as possible to the sensing resistor. Optional external compensation should be connected to these pins. Optional external compensation should be connected to these pins. Supply pin of the device. Power supply pin of the device. External coil is connected between these pins and VLX2. They should be placed as close as possible to the device in order to minimize resistance which causes losses. It is mandatory to connect VLX1A and VLX1B together. Digital input that allows selection of the operational modes of the device (refer to truth table). Digital input that allows selection of the operational modes of the device (refer to truth table). STCF02 Pin connections Pln N° Symbol 18 PGND Power ground 19 RMFL Middle flash resistor connection 20 EN1 Enable Pin 1 Exppad PGND Power ground Figure 3. Name and function Note Power ground pin for power analog circuit. To be connected to the PCB ground plane. This pin is used for the current setting in Middle Flash Mode – RMF resistor is connected to this pin. Digital input that allow selecting the operational modes of the device (refer to truth table). To be connected to the PCB Ground Plane for optimal electrical and thermal performance. Block diagram 5/19 STCF02 Maximum ratings 3 Maximum ratings Table 3. Absolute maximum ratings Symbol Parameter VBAT PVBAT EN1,2,3 VO Signal supply voltage Power supply voltage Enable input Output voltage VLX1A-VLX1B Inductor connection 1 VLX2 FB1 FB2 RTBY RX RMFL NTC COM1,COM2 TOP Inductor connection 2 Feedback for torch current Feedback for flash current MOS Switch connection Connection for reference resistor Connection for setting resistor for middle flash LED temperature sensing connection Compensation connection TSTG Ambient operating temperature (1) Storage temperature range VESD ESD rating Value Unit -0.3 to 6 -0.3 to 6 -0.3 to 6 -0.3 to 6 -0.3 to VI + 0.3 V V V V -0.3 to VO + 0.3 V V V V V V V V °C -0.3 to 3 -0.3 to 3 -0.3 to 3 -0.3 to 3 -0.3 to 6 -0.3 to 6 -0.3 to 3 -40 to + 85 V -65 to + 150 °C 2 KV 1. STCF02 is guaranteed to meet specification from 0°C to 70°C – specifications over the -40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process control. Table 4. Thermal data Symbol RthJA Parameter Thermal resistance junction-ambient (*) (*) Typical Application on a two layer board. 6/19 Value Unit 59 °C/W STCF02 4 Characteristics Characteristics Table 5. Electrical characteristics (All typical values are referred to TA = 25°C, VI = 3.6V) Symbol Min. Typ. Max. Unit 2.7 616 590 555 5.1 686 688 660 5.5 757 733 728 5.3 V Torch mode Medium flash mode Flash mode VI rising VI falling 5.1 5.3 Output Current Adjustment Range, IFLASH Flash mode for VI = 2.7V to 4.5V RFLASH_MIN=1.6Ω to RFLASH_MAX=0.27Ω 100 600 Output Current Adjustment Range, IMFLASH Medium flash mode for VI = 2.7V to 4.5V RMFLASH_MIN=1.1kΩ to RMFLASH_MAX=500kΩ 25% IFLASH IFLASH Output Current Adjustment Range, ITORCH Torch mode VI = 2.7V to 4.5V RTORCH+RFLASH=6.4Ω to RTORCH+RFLASH=0.64Ω 25 250 ∆IO Output current variation Flash and medium flash mode (1) Torch mode VO Regulated voltage range Feedback Voltage VI Parameter Input Operating Voltage ICC VUVLO IO FB1,2 IQ f Under voltage lockout threshold Quiescent Current in Stand By Frequency e1 Efficiency e2 IPK OVP OTP OTHYST Test Conditions Inductor peak current Flash Mode EN1=EN2=EN3=0 EN1=EN2=0 EN3=X (NTC ON) VI = 2.7V 160 1 3 1.8 5.1 170 mA % % V mV µA MHz 78 85 % Application Circuit Figure 2 VI = 3.2 V to 4.2V, IO=25mA 72 75 % 1.23 A 140 °C VI = 2.7V, IO=600mA Over voltage protection VI = 4.2V No load VI = 2.7V to 4.5V (Note: 1) Overtemperature hysteresis VI = 2.7V to 4.5V (Note: 1) EN1, EN2, Logic signals level EN3 2.5 150 V Application Circuit Figure 2 VI = 3.2 V to 4.2V, IO=600mA Over temperature protection NTC Voltage Reference NTCHYST Hysteresis NTCLEAK Voltage Reference leakage ±10 ±5 µA 5.2 VI = 4V, INTC = 2mA max 20 °C 1.192 V 0.3 V ±1 EN1=EN2=0, EN3=X Disable Low VIL Enable High VIH V 0.4 1.4 µA V I_ENx Enable input current ±1 µA TFL/TR Transition time from PIN (Flash) to PIN (Torch) (see Figure 11) PIN (IO=600mA) to PIN (IO=100mA) (Note: 1) 30 µs TON Led current rise time ILED = 0 to ILED = max (see Figure 13) EN1=EN2=0 to EN1=0 & EN2=1 or EN1=EN2=1 (Note 1) 2 ms 1. Not include tolerance of sensing resistor Note: 1 Guaranteed by design 7/19 STCF02 Characteristics Table 6. Truth table selection mode EN1 EN2 EN3 ILED ILED_MAX (mA) Mode NTC 0 1 0 1 0 0 1 1 X 1 X 1 0 0 ITORCH=160mV/ (RTORCH+RFLASH) 0 0 Shutdown Shutdown OFF ON 250 Torch ON 1 0 0 IMFLASH = f (IFLASH,RMFLASH) 500 Medium Flash ON 0 IFLASH = 160mV/RFLASH 600 Flash ON 1 8/19 1 STCF02 Typical characteristics 5 Typical characteristics Figure 4. IIN vs VIN in torch mode Figure 5. IO vs VIN in torch mode 25 mA Figure 6. IO vs VIN in flash mode 600 mA Figure 7. VFB1 vs temp in torch mode Figure 8. Efficiency vs IO in torch mode Figure 9. Start-up to torch mode 25 mA at VBATT = 3.6V 9/19 Typical characteristics Figure 10. Start-up to flash mode 600 mA at VBATT = 3.6V 10/19 STCF02 STCF02 Detailed operating description 6 Detailed operating description 6.1 Introduction The STCF02 is a buck-boost converter, dedicated to power and control the current of a Power White Led in a camera cell Phone. The device operates at a constant switching frequency of 1.8MHz typ. It provides an output voltage down to 2.5V and up to 5.1 V, from a single cell 2.7 V to 5.5 V lithium-ion battery. The flash current is adjustable from 100mA to 600mA for the input voltage range from 2.7V to 4.5V. Torch current is adjustable from 25mA to 250mA. The device also includes a medium flash mode with the current set between the 25% of flash current and flash current. The device contains a pin for connection of NTC which senses the temperature of the LED. 6.2 Buck-Boost converter Regulation of the PWM controller is made by sensing the current of the led through the RFLASH resistor (see Figure 2). Depending on the forward voltage of the Flash LED, the device can automatically change the operation mode between buck (step down) and boost (step up) mode. Three case can occur: Boost region (VO > VBAT): this configuration is used in most cases, as the output voltage (VO = VfLED + ILED x RFLASH) is higher than VBAT; Buck region (VO < VBAT); Buck / Boost region (VO ~ VI). 6.3 Flash mode To select Flash mode the Enable pins have to be connected as follows: EN1=1, EN2=1, EN3=0. The STCF02 operates continuously to supply maximum current to the flash LED (up to 600 mA). The flash current can be adjusted by the RFLASH resistor. The control loop uses the FB2 pin to sense the voltage across RFLASH. The flash current is then programmed at: IFLASH= 160mV / RFLASH. For a flash current programmed at 600mA, the sensing resistor is equal to 0.27Ω. During this operation mode the MOS Switch between FB1 and RTBY pins is closed. If the EN3 is forced to High during Flash mode operation, the current is reduced to that of Torch mode. Such reduction of input power during transition from Flash to Torch mode is achieved within less than 30µs. The NTC divider for measuring LED temperature is active. 11/19 Detailed operating description STCF02 Figure 11. Reducing power during the EN3 6.4 Medium flash mode To select this operating mode the Enable pins have to be connected as follows: EN1=1, EN2=0, EN3=0 In medium flash mode the current is set between the Torch and the flash mode levels and can be adjusted by connecting a resistor between the RMFL pin and the ground: The medium flash current is then programmed using the following equation: IMF=10-5/RFL • [3000+(13000•RMF/13000+RMF)]. (See Figure 12). 12/19 STCF02 Detailed operating description Figure 12. Middle Flash Current (as a percentage of flash current) vs RMF 6.5 Torch mode To select this operating mode the Enable pins have to be connected to any one of the follow states: EN1 = 0, EN2 = 1, EN3 = x EN1 = 1, EN2 = 1, EN3 = 1. The STCF02 can continuously provide a torch current adjustable between 25mA and 250mA. The torch current adjustment is made by resistor RTORCH (Figure 2). The control loop uses the FB1 pin to sense the voltage across RFLASH+RTORCH. The torch current is then programmed using the following equation: ITORCH=160mV/(RFLASH+RTORCH). If the programmed Flash current is 600mA (RFLASH = 0.27Ω) and a 250mA Torch current is needed, the RTORCH resistance is equal to 0.37Ω. During Torch operation mode the MOS Switch between FB1 and RTBY pins is opened. The NTC divider for measuring LED temperature is active. 6.6 Shutdown mode When the device is not used, two shutdown modes are available. They can be selected by the enable pins: EN1=0, EN2=0, EN3=X With this combination the NTC divider for measuring of LED temperature is not active. The quiescent current is less than 1µA. EN=1, EN2=0, EN3=1 This combination of enable pins provides shutdown modes with an active NTC divider for sensing LED temperature. This Mode is useful for measuring the temperature before starting both TORCH and FLASH MODE operations. 13/19 Detailed operating description 6.7 STCF02 Soft start To avoid spikes the battery during start-up sequence, a soft start function has been implemented. This soft start is achieved by progressively increasing the feedback voltage reference. In the worst case scenario the start up time as defined below (IO = IMAX) will not exceed 6ms. Figure 13. Start up - LED current rise time 6.8 LED Failure Protection The device is self protected when the LED fails as a result of a short or open circuit. Such performances are tested using a standard mobile phone Lithium battery with internal resistance 170mΩ typ. 6.9 Overvoltage protection The device includes a power switch protection that stops the operation of the PWM controller when the voltage at the pin VO exceeds the OVP threshold. 6.10 Thermal shutdown protection Internal thermal shutdown protection will switch off the device when the junction temperature exceeds 140°C typical. The hysteresis comparator allows for the automatic restart of the PWM controller, when the temperature is reduced by 20°C. 6.11 Sensing of LED temperature by NTC resistor The device is able to switch off the power circuit, if high temperature on the LED is detected (see Figure 14). 14/19 STCF02 6.12 Detailed operating description Safety shutdown in flash mode To avoid LED burning during flash mode, which could be brought on by a micro-controller fault, a simple programmable RC circuit is possible to shutdown the device after a selected time through the RX Pin (see Figure 15). Figure 14. Typical application of LED temperature sensing by NTC resistor Figure 15. Typical Application of Safety Shutdown EN1 EN2 0 0 1 1 0 1 0 1 Mode TimeOut All OFF Torch Mid-Flash Full-Flash N/A NO YES YES 15/19 Package mechanical data 7 STCF02 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. 16/19 STCF02 Package mechanical data QFN20 (4x4) MECHANICAL DATA mm. mils DIM. MIN. TYP MAX. MIN. TYP. MAX. 0.8 0.9 1.00 31.5 35.4 39.4 A1 0.02 0.05 0.8 2.0 A2 0.65 1.00 25.6 39.4 A3 0.25 A 9.8 b 0.18 0.23 0.30 7.1 9.1 11.8 D 3.875 4.00 4.125 152.6 157.5 162.4 D2 0.75 1.7 2.25 29.5 66.9 88.6 E 3.875 4.00 4.125 152.6 157.5 162.4 E2 0.75 1.7 2.25 29.5 66.9 88.6 e 0.45 0.50 0.55 17.7 19.7 21.7 L 0.35 0.55 0.75 13.8 21.7 25.9 ddd 0.08 3.1 7169619-D 17/19 STCF02 Revision history 8 Revision history Table 7. Revision history Date Revision 10-Nov-2005 1 First release. 19-Dec-2005 2 Document updating. 29-Jun-2006 3 The table 5 has been updated and add typical characteristics. 27-Jul-2006 4 Mistake on table 5 figure reference TFL/TR parameter. 18-Oct-2006 5 Text updates. 09-Feb-2007 6 Mistake value of IO test condition RMFLASH_MAX = 500Ω ==> 500kΩ on Table 5. 18/19 Changes STCF02 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. 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