SC4505 High Efficiency Boost Converter for Backlight/Flash LED Driver POWER MANAGEMENT Description Features Two independent current sources for dual LED strands with optimal current/light matching. Backlight up to 75mA, Flash up to 125mA Wide input range from 2.6V to 12V Adaptive output voltage up to 28V with OVP protection against open circuit conditions Low shutdown current (<1µA ) Internal Flash/Torch mode with flash timeout to protect LEDs 1MHz Fixed Frequency Current-Mode Control Internal 2A current limit for driving large numbers of LEDs Supports PWM Dimming from 50Hz to 50kHz Internal undervoltage lockout Small, low profile, thermally enhanced 16-MLPQ package is fully WEEE and RoHS compliant The SC4505 is a high-frequency PWM current-mode stepup switching regulator with an integrated 2A power transistor. Its high switching frequency (1MHz) allows the use of tiny surface-mount external passive components. The internal switch is rated at 36V which makes the converter ideal for multiple LED series operation with optimal current matching. Two programmable independent current source structure allows dual panel LED backlight and flash operation. The operating frequency of the SC4505 is set at 1MHz. The selected operating frequency gives the SC4505 design flexibility for size, cost and efficiency optimization. The SC4505 is available in thermally enhanced 16-pin MLPQ package (3x3x0.9mm) with embedded over temperature protection. Applications Typical Application Circuit D1 2 IHLP-2525CZ-01-1R5-M-01 1 10BQ015 C2 C1 2.2u PGND Boost Converter Efficiency vs Input Voltage (2 String of 3 LEDs @30mA) LED: SML-LX0603UWD L1 VIN: 2.6V ~ 6.0V White LED power supplies Flat screen LCD bias supplies TFT bias supplies Dual panel Handset/Liquid Crystal Display Monitor Portable media players Digital video cameras Digital still cameras 87 D3 LED D2 LED 2.2uF FL_TRB 16 C3 0.33uF 15 14 EN_FL 13 EN_BL 12 AGND 11 RO1SET 6.98k 10 9 RO2SET 1.54k VIN FTO PGND PGND FL_TRB SW EN_FL SW EN_BL VO IO1SET IO2 IO2SET IO1 AGND COMP 0 1 85 D5 LED D4 LED Efficiency (%) SC4505 0 0 2 3 4 D6 LED 5 D7 LED 83 81 6 7 R1 8 1.47k C5 C4 C6 12n 0 Power Ground 79 12n (Optional) 12n (Optional) 77 0 0 Analog Ground 2.5 3 3.5 4 4.5 5 Input Voltage (V) All Capacitors are Ceramic. Figure 1. SC4505 Application Circuit for Backlight and Flashlight LED Driver Revision: December 15, 2006 1 www.semtech.com SC4505 POWER MANAGEMENT Absolute Maximum Rating Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device reliability. Parameter Symbol Typ Units VIN -0.3 to 20 V VSW, VO, VIO1, VIO2 -0.3 to 36 V I0SET Voltage VIO1SET,VIO2SET -0.3 to 2 V FTO Voltage VFTO -0.3 to VIN + 0.3 V VEN_BL, VEN_FL VFL_TRB -0.3 to VIN + 0.3 V Thermal Resistance Junction to Ambient θJ A 37 °C/W Maximum Junction Temperature TJ 150 °C Storage Temperature Range TSTG -65 to +150 °C IR Reflow (Soldering) 10s to 30s TPKG 260 °C ESD Rating (Human Body Model) ESD 1 kV Supply Voltage SW Voltage, Output Voltage, Current Source Voltage EN_BL, EN_FL, FL_TRB Voltage Electrical Characteristics Unless specified: VIN = 3.6V, -40°C < TA = TJ < 85°C, RO1SET=6.98KΩ, RO2SET=1.54KΩ Parameter Test Conditions VIN rising 2.45 UVLO Hysteresis VIN Supply Current VIN Supply Current in Shutdown Switching Frequency Typ 2.6 Supply Input Voltage VIN UVLO Threshold Min Not switching Maximum Duty Cycle V 2.59 V 1.7 mA 0.8 1 85 90 1.0 µA 1.2 MHz % 0 Switch Current Limit 1.75 2.25 V S W = 28V 0.01 Switch Saturation Voltage ISW = 1A 300 EN_FL, FL_TRB, EN_BL High Voltage VIN = 2.6V to 4.7V EN_FL, FL_TRB, EN_BL Low Voltage VIN = 2.6V to 4.7V 2006 Semtech Corp. 12 mV Minimum Duty Cycle Switch Leakage Current Unit 50 EN_FL = FL_TRB = EN_BL = 0 TJ = 25°C Max 2 % A 1 µA mV 2 V 0.4 V www.semtech.com SC4505 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: VIN = 3.6V, -40°C < TA = TJ < 85°C, RO1SET=6.98KΩ, RO2SET=1.54KΩ Parameter EN_FL, FL_TRB, EN_BL Input Current Test Conditions Min VEN_FL = 0V to 4.7V Typ Max Unit 0.01 1 µA EN_BL PWM Dimming Control Frequency Note 1 50 50K Hz EN_BL PWM Dimming Control Duty Cycle Note 1 0 100 % FTO Sourcing Current EN_FL = FL_TRB = 1 1.2 µA 1.25 V 2.6 mA Overvoltage Protection 28 V Thermal Shutdown Temperature 155 °C Thermal Shutdown Hysteresis 10 °C FTO Trip Threshold Voltage FTO Pull Down Current Backlight Current Accuracy ( I O1 ) EN_FL = 1, FL_TRB = 0 EN_BL = 1 TJ = 25°C, RO1SET =6.98KΩ 19 Max Backlight Current ( I O1 ) Flash Current Accuracy ( I O2 ) 20 21 75 EN_FL = FL_TRB = 1 TJ = 25°C, RO2SET =1.54KΩ Max Flash Current ( I O2 ) 92 100 mA mA 108 mA 125 mA EN_FL=1, FL_TRB=0 TJ = 25°C, RO2SET =1.54KΩ 18 mA IO1 Off Leakage Current VIO1 =28V 0.1 1 µA IO2 Off Leakage Current VIO2 =28V 0.1 1 µA Torch Output Current ( I O2 ) VO Pulldown in Overvoltage Fault 7 KΩ Note 1: Guaranteed by Design 2006 Semtech Corp. 3 www.semtech.com SC4505 POWER MANAGEMENT Pin Configurations Ordering Information TOP VIEW Device(1)(2) SC4505MLTRT P ackag e Temp. Range( TA) MLPQ-16 -40 to 85°C S C 4505E V B EVALUATION BOARD Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant. (16 Pin - MLPQ) Block Diagram VCC VO OVP VOUT S Thermal Shutdown Q R Rsense5mOhm Sense Amp OSC Reference& Internal Regulator Comparator Error signal selection and summation ADJ1 COMP ADJ1 EN_BL IO1 ADJ2 EN_FL BL Setpoint ADJ2 UVLO IO2 FL Setpoint FL_TRB IO1SET IO2SET RO1SET RO2SET PGND AGND 2006 Semtech Corp. 4 www.semtech.com SC4505 POWER MANAGEMENT Pin Descriptions Block Diagram Pin Pin Name Pin Function 1,2 PGND Power ground. 3,4 SW Collector of the internal power transistor. Connect to the boost inductor and the rectifying diode. 5 VO Boost output voltage pin. Internal overvoltage protection also monitors the voltage at this pin. Connect the output capacitor and the anode of the LED strings to this pin. 6 IO2 Provides constant source current to LED string 2. 7 IO1 Provides constant source current to LED string 1. 8 COMP The output of the internal transconductance error amplifier. This pin is used for loop compensation. 9 AGND Analog ground. 10 IO2SET Current source IO2 value set pin. By selecting the resistor connected from this pin to GND, the corresponding maximum current on string 2 is set. 11 IO1SET Current source IO1 value set pin. By selecting the resistor connected from this pin to GND, the corresponding maximum current on string 1 is set. 12 EN_BL Enable and Brightness control pin for LED backlight string 1. (See Table 2 for logic). 13 EN_FL 14 FL_TRB 15 FTO Flash time out pin. By selecting the capacitor connected to this pin, the time out duration is determined. By pulling this pin to AGND, the FTO function is disabled. 16 VIN Power Supply Pin. Bypassed with capacitors close to the pin. Enable and Brightness control pin for LED flash light string 2. (See Table 1 for logic). Exposed Pad The exposed pad must be soldered to the analog ground plane on the PCB for good thermal conduction. E N _B L Status Status E N _F L F L _T R B 0 0 Flash disable 0 Backlight disable 0 1 Flash disable 1 Backlight enable 1 0 20% max. output current set by external resistor, RO2SET 1 1 100% max. output current set by external resistor, RO2SET Table 2 Table 1 Note: When EN_FL = 0 FL_TRB = 0 EN_BL = 0 The boost is turned OFF and disabled. 2006 Semtech Corp. 5 www.semtech.com SC4505 POWER MANAGEMENT Overview The states of the two LED current regulators are chosen by a three-bit digital input. Either or both of the current regulators can be on at any given time. The converter automatically shuts down to zero-current shutdown mode if all pins are low. The SC4505 contains a 1MHz fixed-frequency, currentmode boost converter, and two independent LED current regulators. The LED current setpoints are chosen using external resistors, and the PWM controller operates independently to keep the two currents in regulation. Since the SC4505 receives feedback from both of the LED current regulators, either or both LED strands can be on at any given time. Additionally, different numbers of LED can be used in the two strands with no resistor ballasting, or preset output voltage setpoint. EN_BL – Enable Backlight regulator (IO1). EN_FL – Enable Flash/Torch regulator (IO2) FL_TRB – Select flash or torch mode for IO2. The current in torch mode is approximately 1/5 of the current in flash mode. Flash mode when FL_TRB = 1. A typical application would use 3-6 backlight LED, driven with 20mA, and 2-6 flash LED, driven with 20mA during torch mode (video recording), and driven with 100mA during flash mode (for photographs). Usually only the backlight LED are used, but during some cases both strands must be on at the same time. As the output voltage is different for each case, a designer is often forced to use lossy ballast resistors to balance the LED currents, or to use two separate converter ICs, greatly increasing component count and BOM cost. The SC4505 solves these issues by controlling the boost converter set point based on instantaneous requirements of the two current regulators. Therefore, only a single inductor and power switch is needed to provide power to the entire lighting subsystem, increasing efficiency and reducing part count. A digital interface allows independent control of all LED currents with no converter “babysitting”. Interface to output control is highbandwidth, supporting digital PWM dimming on any channel at 50Hz to 50kHz dimming frequency, while aggressively shutting the entire IC down to less than 1µA shutdown mode when all LED strands are turned off. In shutdown mode, leakage through the current regulator outputs is also < 1µA, keeping the output capacitor charged and ready for instant activation of the LED strands. 1 MHz switching speed provides high output power using a tiny 1.0mm high inductor, maximizing efficiency for space-constrained and cost-sensitive applications. In addition, converter and output capacitor are protected from open-LED conditions by overvoltage protection, and flash LED are protected from burnout by a user-settable time-out feature. 2006 Semtech Corp. 6 www.semtech.com SC4505 POWER MANAGEMENT Applications Information An important note is that continuous operation of mismatched LED strands deteriorates the efficiency of the overall lighting subsystem because the extra voltage must be dropped across that output of the current regulator. Fortunately, for the cases of high mismatch such as the backlight/flashlight example previously mentioned, the time duration in which both heavily mismatched LEDs strands are “on” is very short. Furthermore, the sacrifice of 5-10% efficiency loss is negligiable when compared to the overall cost reduction of the single-IC and single-inductor solution. Boost Converter Setup The SC4505 is a fixed-frequency, current mode step-up DC-DC converter that is ideal for driving LEDs in the applications in which both backlighting and flashlighting are needed. Unlike the ballasting resistor scheme, multiple strands can be independently controlled, or shut off entirely without leaking current from a charged output capacitor or causing false-lighting with low LED count and high VIN. It also enables regulation of several output setpoints using a single inductor. For example, if a user has three Backlight LEDs and four Flash LEDs, output may need to be as high as 16V during flash mode, or as low as 10V during backlight mode. If both of the strands can be “on” at the same time, it is impossible to regulate using the FB ballast method unless an additional resistor is used to take up the 6V mismatch. This forces the output voltage to the full 16V which is not needed in the nominal case. Typically, two separate converters are used in this case. Neither of these cases is suitable in cost or efficiency-conscious applications. Inductor Selection Selection of power-stage components for system optimal performance is often a lengthy and tedious process. Much effort has been put into the straightforward implementation of the SC4505. The converter operates preferably in DCM, to reap the advantages of small inductance and quick transient response while avoiding the bandwidth-limiting instability of the RHP zero found in CCM boost converters. Using this strategy, the loop bandwidth is extended to over 100 kHz, allowing the converter to lock into regulation even when dimming with PWM frequencies as high as 50 kHz. The SC4505 boost converter receives information from both of the LED current regulators, and drives the output to the proper setpoint with no user intervention. The controller quickly drives to one of three separate limit cases, based on voltage requirement of the strands (number of LED, and LED current), which is shown in Table 3. In the table, it is assumed that the forward voltage drops of all the LEDs are the same. And the assumption applies to the the rest of analysis in the data sheet. C ase C ondition Operation Si ngle Strand One Strand Only Regulate to C urrent Strand Backli ght Li mi ted Number of Backli ght LE D s > Number of Flashli ght LE D s Flashli ght Li mi ted Number of Backli ght LE D s < Number of Flashli ght LE D s In many cases, the required output currents from a tiny inductor footprint limit the designer to very small values of inductance (0.8 - 2.2µH). Inductor selection, for SC4505 based applications, begins with estimation of output current and step-up ratios. Design example of four backlight LEDs with three flash LEDs. Backlight only: Largest step up: 2.7V to 14.4V @20mA (81% Duty) Flashlight only: Largest step up: 2.7V to 12V @ 100mA (78% Duty) Servos to the Number of Backli ght LED s. Flashli ght i s sti ll Regulated to IO2 Set Value Both Strands: It requires: 14.4V @120mA Suppose the efficiency of the boost converter is about 80%, the Maximum average input current is: Servos to the Number of Flashli ght LED s. Backli ght i s sti ll Regulated to IO1Set Value 14.4V x 120mA / (2.7V x 80%) = 0.8A. Suppose a 1.5µH inductor is used, the peak inductor current would be: Table 3. SC4505 Operation States 2006 Semtech Corp. 7 www.semtech.com SC4505 POWER MANAGEMENT Applications Information Although the mechanics of regulation and frequency dependence may be complex, actual selection of output capacitor can be simplified to two boundary conditions, minimum output current and maximum output current. Output capacitor is chosen to keep ripple voltage between 10mV & 200mV under all loads. 2.7V 1 × 1µ S × 81% × = 1.5A IPK = 0.8A + 2 1.5 µ H When using tiny inductors for size-sensitive applications, only a few limited selections are available that fulfill this need, and all are within the low µH range of inductance. We select a Coiltronics 1.5µH SD3114 series, presently the only 3mmx3mmx1.5mm inductor that can provide the required current in the microminiature size required in space-constrained applications. Design example for Backlight=20mA, Flashlight=100mA: Minimum Load Current: 20mA (Backlight Only) Maximum Load Current: 120mA (Backlight and Flash) All other cases (Torch mode only, Flash mode only, Backlight and Torch) fall within these two boundary conditions, so they are automatically satisfied by the selected output capacitor. Table 4 shows a list of several low profile inductor manufacturers. Please consult the manufacturers for detailed information on their entire selection of power inductors. PART L (µH) MAX DCR (Ω ) MAX HEIGHT (mm) VENDOR SD3112-1R0 SD3114-1R5 SD3114-4R7 1.0 1.5 4.7 0.069 0.057 0.147 1.2 1.45 1.45 Coiltronics www.cooperet.com LQH3C4R7M24 LQH3C100M24 4.7 10 0.260 0.300 2.2 2.2 Murata www.murada.com LB2016B4R7 LB2016B100 4.7 6.8 0.250 0.350 1.6 1.6 Taiyo Yuden www.t-yuden.com CMD4D06-4R7 CLQ4D10-4R7 CLQ4D10-6R8 4.7 4.7 6.8 0.216 0.162 0.195 0.8 1.2 1.2 Sumida www.sumida.com IHLP2525CZ1R5 IHLP2525CZ3R3 IHLP2525CZ4R7 1.5 3.3 4.7 0.014 0.028 0.037 3.0 3.0 3.0 Since the load is a constant current, the capacitor ∆V can be solved for the output equation ∆I = C ⋅ ∆T ripple. ∆VOUT = At 1MHz switching frequency and with the assumption of the worse case analysis (D=0), an even simpler relationship can be applied: ∆VOUT = Vishay www.vishay.com IOUT × 1µ S COU T where COUT is in µF. Table 4. Recommended Inductors For worse case analysis, We see that our typical case of 20mA, 120mA can be immediately converted into its corresponding ripple relationships of: Output Capacitor Selection ∆VOUTMIN = 20mV/COUT where COUT is in µF. The next task in SC4505 design is targeting the proper amount of ripple voltage due to the constant-current LED loads. The two error amplifiers that control the PWM converter sense the delta between requested current and actual current in each output current regulator. On a cycle-by-cycle basis, a small amount of output ripple ensures good sensing and tight regulation, while the output current regulators keep each LED current at a fixed value. Overall, this allows usage of small output caps while ensuring precision LED current regulation. 2006 Semtech Corp. IOUT × 1µ S × (1- D) COU T ∆VOUTMAX = 120mV/COUT where COUT is in µF. For the example, if 1µF output capacitor were used, the 20mV/120mV boundary conditions are well within the suggested guidelines. Recommended ceramic capacitor manufacturers are listed in Table 5. 8 www.semtech.com SC4505 POWER MANAGEMENT Applications Information IO1SET Resistor Selection Chart PHONE WEBSITE KEMET 408-986-0424 www.kemet.com Murata 814-237-1431 www.murada.com Taiyo Yuden 408-573-4150 www.t-yuden.com 160 140 IO1SET Resistor (kΩ ) VENDOR Table 5. Recommended Ceramic Capacitor Manufacturers 120 100 80 60 40 20 0 Output Rectifying Diode Selection 0 20 40 60 80 100 IO1 Current (mA) Schottky diodes are the ideal choice for SC4505 due to their low forward voltage drop and fast switching speed. Table 6 shows several different Schottky diodes that work well with the SC4505. Make sure that the diode has a voltage rating greater that the possible maximum ouput voltage. The diode conducts current only when the power switch is turned off. So a 1A diode will be sufficient for most designs. VENDOR S S 13 S S 14 Vishay www.vishay.com 10BQ015 International Rectifier www.irf.com IO2SET Resistor Selection Chart 160 140 IO2SET Resistor (kΩ ) PART Figure 2. IO1SET Resistor Selection Chart 120 100 80 60 40 20 0 0 Table 6. Recommended Rectifying Diodes 40 60 80 100 120 140 IO2 Current (mA) Figure 3. IO2SET Resistor Selection Chart PWM Dimming Output Current Programming The SC4505 features two independent LED current regulators. The LED current setpoints are chosen using external resistors. The relationships between the programming resistors and the two channel output current setpoints are shown as in the Figure 2 and Figure 3 below. Either of the enable pins can be toggled by external circuitry to allow PWM dimming. In a typical application, a microcontroller sets a register or counter that varies the pulsewidth on a GPIO pin. The SC4505 allows dimming over two decades in frequency (50Hz-50 kHz) in order to allow compatibility with a wide range of devices, including newest dimming strategies that avoid the audio band by using high frequency PWM dimming. In this manner, a wide range of illumination can be generated while keeping the instantaneous LED current at its peak value for luminescent efficiency and color purity. Furthermore, advanced lighting effects such as backlight “dim-on” or photographic red-eye reduction can be implemented as the SC4505 can resolve PWM from 10% to 90% duty at its highest frequency. The relationships between the programming resistor value and the output current setpoint can be described as follows: R O1SET = (140 V) / IO1 R O2SET = (154 V) / IO2 Where RO1SET and RO2SET are in Ohms. IO1 and IO2 are in Amperes. 2006 Semtech Corp. 20 9 www.semtech.com SC4505 POWER MANAGEMENT Applications Information An additional advantage of PWM dimming comes to customers who prefer to avoid inrush currents when filling the boost output capacitor – simply PWM the device at 10% duty for a millisecond or two, reducing inrush current to less than 50mA. This dim time will vary based on number of LED and size of output capacitor, but can be easily determined on the bench, and programmed into the uC firmware. The relationship between the EN_FL, FL_TRB, FTO pin voltage and the current flowing through the IO2 pin is illustrated in Figure 4 below. EN_FL For an example, suppose the current flowing through the IO1 channel is programmed at 20mA by RO1SET. A 1kHz PWM signal with the duty ratio of 20% is applied to the EN_BL pin of the SC4505. Then the average current flowing through the IO1 channel is FL_TRB However, since PWM is always linear, offset can be easily corrected in software. The offset correction factor can be described as: DCORRECTION = 100 × 1.6 µ S × FPWM FPWM is in KHz. For an example, at 20kHz, DCORRECTION = 3%. So for 50% of the nominal LED current in IO1 channel, the PWM signal should have a duty ratio of 53%. Flash Timeout Programming When Channel IO2 is in flash mode, a timer is available to prevent LED overstress. The timer is only active in Flash mode – not active in torch mode. The capacitor tied between the FTO pin and the AGND sets the time duration of the flash mode. In flash mode, an external capacitor is charged with 1.2µA. When the voltage on this capacitor reaches the 1.25V threshold Channel 2 is turned off. The timer can be reset by entering torch mode or turning off channel 2. The FTO pin can simply be grounded to disable this feature, as would be necessary when using IO2 for sub display. 2006 Semtech Corp. t 0 1.25V FTO IO1AVG = 20% × 20mA = 4mA A startup delay time between the enable signal goes high and the internal current regulator actually turns on is about 1.6µs, which causes a small offset dependent on PWM frequency. As the PWM signal frequency goes higher, the effect of the delay will get more obvious to customers. t 0 0 t IO2MAX IO2 t 0 20% x IO2MAX Figure 4. Relationship between RN_FL, FL_TRB, FTO and IO2 Current To calculate the FTO capacitor needed for a desired timeout, a simple formula can be used as shown below: C = 0.862 ⋅ 10 -6 ⋅ t Where C is in Farads, and t is in Seconds. Over Voltage Protection (OVP) SC4505 includes a built-in overvoltage protection circuit to prevent damage to the IC and output capacitor in the event of open-circuit condition. The output voltage of the boost converter is detected at the VO pin, and divided down by an internal resistor strand of 500kΩ. If the voltage at the VO pin exceeds 28V, the boost converter will be shut down, and a strong pulldown will be applied to the VO pin to quickly discharge the output capacitor. This additional level of protection prevents a condition where the output capacitor and Schottky diode must endure high voltage for an extended period of time, which can pose a reliability risk for the user’s system. The boost OVP triggering point can be adjusted by adding an external resistor divider at VO pin as shown in Figure 5. 10 www.semtech.com SC4505 POWER MANAGEMENT Applications Information VIN VOUT L1 D1 SW COUT SC4505 R3 VO R1 COMP R2 R4 I2 I1 VOVP Figure 5. OVP Tweaking As shown in Figure 5, R1 and R2 are the internal resistor divider. R3 and R4 are external resistor divider for OVP triggering point adjustment. It is noted that the resistance of the internal resistor divider formed by R1 and R2 is around 500kΩ. When OVP happens, a strong pulldown will be applied to VO pin to quickly discharge the output capacitor. Any large value of R 3 will slow down the discharge process at OVP condition. Generally speaking, small value of R3 is preferred in applications. However, small value of the resistor divider formed by R3 and R4 would cause additional power loss. People often use R4=100kΩ and then select R3 according to the OVP specification. In this case, the OVP triggering threshold estimation equation can be rewritten as follows: R //500KΩ + R 3 VOVP = 4 × 28V R 4 //500K Ω Set R 4 = 100K Ω We can get V R3 = OVP − 1 × 83.3KΩ 28V The tolerance of the R3 and R4 should also be considered in determining the OVP triggering point. Usually there is about 5%~8% difference between the calculated value and the measure OVP triggering threshold. 2006 Semtech Corp. 11 www.semtech.com SC4505 POWER MANAGEMENT Applications Information As shown in Figure 6a, C1 serves as decoupling capacitor for the SC4505. It should be placed close to the VIN and PGND of SC4505 to achieve the best performance. C2 is the input power filtering capacitor for the boost converter power train. L1 is the boost converter input inductor. D5 is the output rectifying diode. It is recommended that a schottky diode is used for fast reverse recovery. Layout Guideline The SC4505 contains a boost converter. The placements of the power components outside the SC4505 should follow the guideline of general boost converter layout. The application circuit (Figure 7a) will be used as an example. The layout illustration diagram is shown as in Figure 6a and Figure 6b. R2 R3 R4 C7 EN_BL 9 12 8 13 EN_FL C8 D9 D8 D7 D6 D3 D2 D1 FL_TRB SC4505 D4 5 16 VIN VOUT 1 C1 4 D5 PGND C2 VIN L1 Figure 6a Layout Illustration -- Top Layer C4 SC4505 C6 VIN PGND C3 C5 VOUT VIN Figure 6b Layout Illustration -- Bottom Layer 2006 Semtech Corp. 12 www.semtech.com SC4505 POWER MANAGEMENT Applications Information To minimize switching noise for boost converter, the output capacitor, C3, should be placed right at the bottom as displayed in Figure 6b so that loop formed by C3, D5 and the SC4505 internal switch is the smallest. The output of the boost converter is used to power up the LEDs. The backlight LED string includes D6, D7, D8 and D9. The flashligh/torch-light string is composed of D1, D2, D3 and D4. C5 and C6 are the filtering capacitors for the IO2 and IO1 pins and they are optional to customers. If they are adopted, C5 should be placed as close as possible to IO2 and PGND and C6 should be placed as close as possible to IO1 and PGND. R2, C7 and C8 form the compensation network for the boost converter. C7 should return to analog ground. C4, on the bottom layer, determines the flash timeout duration. It should be connected to analog ground. R3 and R4 are the output current programming resistors for IO1 and IO2 respectively. R3 and R4 should return to analog ground. Since there is pad at the bottom of the SC4505 for heat dissipation, as shown in Figure 6a, a copper area right underneath the pad is used for better heat spreading. On the bottom layer of the board, another square copper area, connected through vias to the top layer, is used for better thermal performance. The pad at the bottom of the SC4505 should be tied to the analog ground of the SC4505. The analog ground should be kelvin connected to the power ground near the input filtering capacitors for better noise immunity as shown in Figure 6a. 2006 Semtech Corp. 13 www.semtech.com SC4505 POWER MANAGEMENT Typical Application Circuits P1 Vin=2.6~4.6V 10BQ015 D5 L1 2 LED: SML-LX0603UWD 1 IHLP-2525CZ-01-1R5-M-01 D1 LED C2 C1 C3 2.2u 2.2u 2.2uF D7 D2 P2 LED 0 0.33uF C4 R1 100 16 15 14 13 12 11 10 9 R6 10k R5 10k R3 6.98k SC4505 VIN PGND FTO PGND FL_TRB SW EN_FL SW EN_BL VO IO1SET IO2 IO2SET IO1 AGND COMP D3 1 LED D8 LED 2 D6 LED LED 0 0 3 D4 4 LED 5 D9 LED 6 7 8 R2 1.47k R4 1.54k C7 open 0 Analog Ground C5 12n (Optional) C6 12n (Optional) C8 12n Power Ground 0 0 Figure 7a Backlight and Flashlight LED driver for IO1=20mA and IO2=100mA Boost Converter Efficiency vs Input Voltage ( Backlight Mode: 4 LEDs @ IO1=20m A) 83 Efficiency (%) 82 81 80 79 78 2.5 3 3.5 4 4.5 5 Input Voltage (V) Figure 7b Efficiency Curve for Backlight LEDs Driver Application 2006 Semtech Corp. 14 www.semtech.com SC4505 POWER MANAGEMENT Outline Drawing - MLPQ - 16 A D B DIM PIN 1 INDICATOR (LASER MARK) A A1 A2 b D D1 E E1 e L N aaa bbb E A2 A SEATING PLANE aaa C DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX .031 .040 .000 .002 (.008) .007 .009 .012 .114 .118 .122 .061 .067 .071 .114 .118 .122 .061 .067 .071 .020 BSC .012 .016 .020 16 .003 .004 0.80 1.00 0.00 0.05 (0.20) 0.18 0.23 0.30 2.90 3.00 3.10 1.55 1.70 1.80 2.90 3.00 3.10 1.55 1.70 1.80 0.50 BSC 0.30 0.40 0.50 16 0.08 0.10 C A1 D1 e/2 LxN E/2 E1 2 1 N e bxN D/2 bbb C A B NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS. 3. DAP IS 1.90 x 1.90mm. Land Pattern - MLPQ - 16 H R DIM (C) K G DIMENSIONS INCHES MILLIMETERS C G H K P R X Y Z Z Y X P (.114) .083 .067 .067 .020 .006 .012 .031 .146 (2.90) 2.10 1.70 1.70 0.50 0.15 0.30 0.80 3.70 NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. 2. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD SHALL BE CONNECTED TO A SYSTEM GROUND PLANE. FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE. Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804 2006 Semtech Corp. 15 www.semtech.com