SEMTECH SC4505

SC4505 High Efficiency Boost Converter for Backlight/Flash LED Driver POWER MANAGEMENT Features Description The SC4505 is a high-frequency PWM current-mode step- ‹ Two independent current sources for dual LED strands up switching regulator with an integrated 2A power tran- with optimal current/light matching. Backlight up to 75mA, Flash up to 125mA sistor. Its high switching frequency (1MHz) allows the use of tiny surface-mount external passive components. The ‹ Wide input range from 2.6V to 12V internal switch is rated at 36V which makes the con- ‹ Adaptive output voltage up to 28V with OVP protec- verter ideal for multiple LED series operation with opti- tion against open circuit conditions mal current matching. Two programmable independent ‹ Low shutdown current (<1µA ) ‹ Internal Flash/Torch mode with flash timeout to pro- current source structure allows dual panel LED backlight and flash operation. tect LEDs ‹ 1MHz Fixed Frequency Current-Mode Control The operating frequency of the SC4505 is set at 1MHz. ‹ Internal 2A current limit for driving large numbers of The selected operating frequency gives the SC4505 de- LEDs ‹ Supports PWM Dimming from 50Hz to 50kHz sign flexibility for size, cost and efficiency optimization. The SC4505 is available in thermally enhanced 16-pin ‹ Internal undervoltage lockout MLPQ package (3x3x0.9mm) with embedded over tem- ‹ Small, low profile, thermally enhanced 16-MLPQ pack- perature protection. age is fully WEEE and RoHS compliant Applications ‹ 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 Typical Application Circuit Boost Converter Efficiency vs Input Voltage LED: SML-LX0603UWD (2 String of 3 LEDs @30mA) L1 VIN: 2.6V ~ 6.0V D1 2 1 IHLP-2525CZ-01-1R5-M-01 10BQ015 D3 87 D2 C2 LED LED C1 2.2u PGND 2.2uF 85 SC4505 D5 D4 0 0 16 1 VIN PGND LED LED C3 15 2 0 FTO PGND 83 0.33uF FL_TRB 14 3 FL_TRB SW EN_FL 13 4 EN_FL SW D6 D7 LED LED EN_BL 12 5 81 EN_BL VO AGND 11 6 IO1SET IO2 RO1SET 10 7 IO2SET IO1 79 6.98k C5 R1 C4 9 8 AGND COMP 12n C6 3.01k 12n RO2SET (Optional) (Optional) 12n 1.54k 77 0 0 0 2.5 3 3.5 4 4.5 5 Power Analog Ground Ground Input Voltage (V) All Capacitors are Ceramic. Figure 1. SC4505 Application Circuit for Backlight and Flashlight LED Driver Revision: December 12, 2007 1 www.semtech.com Efficiency (%) 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. Pl arameter Sp ymbo Ts y Unit SV upply Voltage -V 0.3 to 20 IN SV W Voltage, Output Voltage, Current Source Voltage , V , V , V -V 0.3 to 36 SW O IO1 IO2 IVV oltage V -V 0.3 to 2 0SET IO1SET, IO2SET FV TO Voltage -0.3 to V+V 0.3 FTO IN V , V EN_BL EN_FL EN_BL, EN_FL, FL_TRB Voltage -0.3 to V+V 0.3 IN V FL_TRB Thermal Resistance Junction to Ambient 3W 7 °C/ θ JA MT aximum Junction Temperature 1C 50 ° J ST torage Temperature Range -C 65 to +150 ° STG IT R Reflow (Soldering) 10s to 30s 2C 60 ° PKG ED SD Rating (Human Body Model) E1 S kV Electrical Characteristics Unless specified: V = 3.6V, -40°C < T = T < 85°C, R =6.98KΩ, R =1.54KΩ IN A J O1SET O2SET Ps arameter Tn est Condition Mp i Tx y Mt a Uni Supply Input Voltage V 22 .6 1V IN UV VLO Threshold r5 ising 29 .4 2V .5 IN UVLO Hysteresis 5V 0 m VSg upply Current N7 ot switchin 1A . m IN VS0 upply Current in ShutdownE0 N_FL = FL_TRB = EN_BL = 1A . µ IN ST witching Frequency =8 25°C 01 . 1z .2 MH J Maximum Duty Cycle 80 5 9 % Minimum Duty Cycle 0% Switch Current Limit 15 .752A .2 V=1 28V 01 .0 µA Switch Leakage Current SW I=0 1A 3V 0 m Switch Saturation Voltage SW EN_FL, FL_TRB, EN_BL V=2 2.6V to 4.7V V IN High Voltage EN_FL, FL_TRB, EN_BL V=4 2.6V to 4.7V 0V . IN Low Voltage  2007 Semtech Corp. www.semtech.com 2 SC4505 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: V = 3.6V, -40°C < T = T < 85°C, R =6.98KΩ, R =1.54KΩ IN A J O1SET O2SET Ps arameter Tn est Condition Mp i Tx y Mt a Uni EN_FL, FL_TRB, EN_BL V=1 0V to 4.7V 01 .0 µA EN_FL Input Current EN_BL PWM Dimming N0 ote 1 5K5z 0 H Control Frequency EN_BL PWM Dimming F=2 32kHz , Note 1 101% 0 PWM Control Duty Cycle F1 TO Sourcing Current E2 N_FL = FL_TRB = 1A . µ FTO Trip Threshold Voltage 1V .25 F0 TO Pull Down Current E6 N_FL = 1, FL_TRB = 2A . m Overvoltage Protection 2V 8 Thermal Shutdown Temperature 1C 55 ° Thermal Shutdown Hysteresis 1C 0 ° EN_BL = 1 BI acklight Current Accuracy ( ) 10 9 212A m O1 T = 25°C, R =6.98KΩ J O1SET Max Backlight Current ( I)57A m O1 EN_FL = FL_TRB = 1 Flash Current Accuracy ( I ) 90 2 18 0 1A 0 m O2 T = 25°C, R =1.54KΩ J O2SET Max Flash Current ( I ) 1A 25 m O2 EN_FL=1, FL_TRB=0 Torch Output Current ( I ) 1A 8 m O2 T = 25°C, R =1.54KΩ J O2SET IOV ff Leakage Current =1 28V 01 . µA O1 IO1 IOV ff Leakage Current =1 28V 01 . µA O2 IO2 V Pulldown in Overvoltage Fault 7KΩ O Note 1: Guaranteed by Design  2007 Semtech Corp. 3 www.semtech.com SC4505 POWER MANAGEMENT Pin Configurations Ordering Information TOP VIEW (1)(2) DevicePT ackage Temp. Range( ) A S6 C4505MLTRTMC LPQ-1 -40 to 85° (3) SC4505EVB 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. (3) Consult factory for all other available options. (16 Pin - MLPQ) Block Diagram VCC VO OVP VOUT S Q Thermal UVLO Shutdown R Sense Rsense- Amp 5mOhm OSC Reference& Comparator Internal Regulator Error signal selection COMP and summation IO1 IO2 ADJ1 ADJ2 EN_FL EN_BL BL Setpoint FL Setpoint FL_TRB IO1SET IO2SET RO1SET RO2SET PGND AGND  2007 Semtech Corp. www.semtech.com 4 ADJ1 ADJ2 SC4505 POWER MANAGEMENT Block Diagram Pin Descriptions Pe inPn in Nam Pin Functio 1D ,2P. GN Power ground 3W ,4 S Collector of the internal power transistor. Connect to the boost inductor and the rectifying diode. Boost output voltage pin. Internal overvoltage protection also monitors the voltage at this pin. 5O V Connect the output capacitor and the anode of the LED strings to this pin. 62I. O Provides constant source current to LED string 2 71I. O Provides constant source current to LED string 1 The output of the internal transconductance error amplifier. This pin is used for loop 8P COM compensation. 9DA. GN Analog ground Current source IO2 value set pin. By selecting the resistor connected from this pin to GND, the 1T 0 IO2SE corresponding maximum current on string 2 is set. Current source IO1 value set pin. By selecting the resistor connected from this pin to GND, the 1T 1 IO1SE corresponding maximum current on string 1 is set. 1L 2 EN_B Enable and Brightness control pin for LED backlight string 1. (See Table 2 for logic). 1L 3 EN_F Enable and Brightness control pin for LED flash light string 2. (See Table 1 for logic). 1B 4 FL_TR Flash time out pin. By selecting the capacitor connected to this pin, the time out duration is 1O 5 FT determined. By pulling this pin to AGND, the FTO function is disabled. Power Supply Pin. Bypassed with capacitors close to the pin. 1N 6 VI Exposed Pad The exposed pad must be soldered to the analog ground plane on the PCB for good thermal conduction. EB N_FLFs L_TR Statu Es N_BL Statu 0e Backlight disabl 00 Flash disable 01 Flash disable 1e Backlight enabl 10 20% max. output current set by Table 2 external resistor, RO2SET 11 100% max. output current set by external resistor, RO2SET Table 1 Note: When EN_FL = 0 FL_TRB = 0 EN_BL = 0 The boost is turned OFF and disabled.  2007 Semtech Corp. 5 www.semtech.com SC4505 POWER MANAGEMENT Overview The states of the two LED current regulators are chosen The SC4505 contains a 1MHz fixed-frequency, current- mode boost converter, and two independent LED current by a three-bit digital input. Either or both of the current regulators. The LED current setpoints are chosen using regulators can be on at any given time. The converter external resistors, and the PWM controller operates automatically shuts down to zero-current shutdown mode if all pins are low. 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 EN_BL – Enable Backlight regulator (I ). O1 be on at any given time. Additionally, different numbers EN_FL – Enable Flash/Torch regulator (I ) O2 of LED can be used in the two strands with no resistor FL_TRB – Select flash or torch mode for I . The current O2 in torch mode is approximately 1/5 of the current in flash ballasting, or preset output voltage setpoint. 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 high- bandwidth, 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.  2007 Semtech Corp. www.semtech.com 6 SC4505 POWER MANAGEMENT Applications Information An important note is that continuous operation of Boost Converter Setup mismatched LED strands deteriorates the efficiency of the overall lighting subsystem because the extra voltage The SC4505 is a fixed-frequency, current mode step-up must be dropped across that output of the current DC-DC converter that is ideal for driving LEDs in the regulator. Fortunately, for the cases of high mismatch applications in which both backlighting and flashlighting such as the backlight/flashlight example previously are needed. mentioned, the time duration in which both heavily mismatched LEDs strands are “on” is very short. Unlike the ballasting resistor scheme, multiple strands Furthermore, the sacrifice of 5-10% efficiency loss is can be independently controlled, or shut off entirely negligiable when compared to the overall cost reduction without leaking current from a charged output capacitor of the single-IC and single-inductor solution. or causing false-lighting with low LED count and high VIN. It also enables regulation of several output setpoints Inductor Selection using a single inductor. For example, if a user has three Backlight LEDs and four Flash LEDs, output may need to Selection of power-stage components for system optimal be as high as 16V during flash mode, or as low as 10V performance is often a lengthy and tedious process. during backlight mode. If both of the strands can be Much effort has been put into the straightforward “on” at the same time, it is impossible to regulate using implementation of the SC4505. The converter operates the FB ballast method unless an additional resistor is preferably in DCM, to reap the advantages of small used to take up the 6V mismatch. This forces the output inductance and quick transient response while avoiding voltage to the full 16V which is not needed in the nominal the bandwidth-limiting instability of the RHP zero found case. Typically, two separate converters are used in this in CCM boost converters. Using this strategy, the loop case. Neither of these cases is suitable in cost or bandwidth is extended to over 100 kHz, allowing the efficiency-conscious applications. 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 In many cases, the required output currents from a tiny to the proper setpoint with no user intervention. The inductor footprint limit the designer to very small values controller quickly drives to one of three separate limit of inductance (0.8 - 2.2µH). Inductor selection, for cases, based on voltage requirement of the strands SC4505 based applications, begins with estimation of (number of LED, and LED current), which is shown in output current and step-up ratios. Table 3. In the table, it is assumed that the forward voltage drops of all the LEDs are the same. And the Design example of four backlight LEDs with three flash assumption applies to the the rest of analysis in the LEDs. data sheet. Cn aseCn onditio Operatio Backlight only: Largest step up: 2.7V to 14.4V @20mA (81% Duty) Single One Strand Regulate to Current Strand Strand Only Flashlight only: Number of Largest step up: 2.7V to 12V @ 100mA (78% Duty) Backlight Servos to the Number of Backlight LEDs > Backlight LEDs. Flashlight is Limited Number of still Regulated to I Set Value O2 Both Strands: It requires: 14.4V @120mA Flashlight LEDs Suppose the efficiency of the boost converter is about Number of Backlight 80%, the Maximum average input current is: Servos to the Number of Flashlight LEDs < Flashlight LEDs. Backlight is Limited Number of still Regulated to I Set Value O1 14.4V x 120mA / (2.7V x 80%) = 0.8A. Flashlight LEDs Suppose a 1.5µH inductor is used, the peak inductor Table 3. SC4505 Operation States current would be:  2007 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,  2.7V  1 I = 0.8A +  × 1 µ S× 81% × =1.5A minimum output current and maximum output current. PK   1.5 µ H 2   Output capacitor is chosen to keep ripple voltage between 10mV & 200mV under all loads. When using tiny inductors for size-sensitive applications, only a few limited selections are available that fulfill this Design example for Backlight=20mA, Flashlight=100mA: need, and all are within the low µH range of inductance. We select a Coiltronics 1.5µH SD3114 series, presently Minimum Load Current: 20mA (Backlight Only) the only 3mmx3mmx1.5mm inductor that can provide Maximum Load Current: 120mA (Backlight and Flash) the required current in the microminiature size required in space-constrained applications. All other cases (Torch mode only, Flash mode only, Backlight and Torch) fall within these two boundary Table 4 shows a list of several low profile inductor conditions, so they are automatically satisfied by the manufacturers. Please consult the manufacturers for selected output capacitor. detailed information on their entire selection of power inductors. Since the load is a constant current, the capacitor MAX MAX L ΔV   PART DCR HEIGHT VENDOR (µH) ΔI = C⋅ equation   can be solved for the output (Ω) (mm) ΔT   SD3112-1R0 1.0 0.069 1.2 Coiltronics SD3114-1R5 1.5 0.057 1.45 ripple. www.cooperet.com SD3114-4R7 4.7 0.147 1.45 I OUT ΔV = × 1 µ S× (1-D) OUT LQH3C4R7M24 4.7 0.260 2.2 Murata C OU T LQH3C100M24 10 0.300 2.2 www.murada.com LB2016B4R7 4.7 0.250 1.6 Taiyo Yuden At 1MHz switching frequency and with the assumption LB2016B100 6.8 0.350 1.6 www.t-yuden.com of the worse case analysis (D=0), an even simpler CMD4D06-4R7 4.7 0.216 0.8 relationship can be applied: Sumida CLQ4D10-4R7 4.7 0.162 1.2 www.sumida.com CLQ4D10-6R8 6.8 0.195 1.2 I OUT ΔV = × 1 µ S IHLP2525CZ1R5 1.5 0.014 3.0 OUT Vishay C IHLP2525CZ3R3 3.3 0.028 3.0 OU T www.vishay.com IHLP2525CZ4R7 4.7 0.037 3.0 where C is in µF. OUT 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 ΔV = 20mV/C OUTMIN OUT The next task in SC4505 design is targeting the proper where C is in µF. OUT amount of ripple voltage due to the constant-current LED loads. The two error amplifiers that control the PWM ΔV = 120mV/C OUTMAX OUT converter sense the delta between requested current where C is in µF. OUT and actual current in each output current regulator. On a cycle-by-cycle basis, a small amount of output ripple For the example, if 1µF output capacitor were used, the ensures good sensing and tight regulation, while the 20mV/120mV boundary conditions are well within the output current regulators keep each LED current at a suggested guidelines. fixed value. Overall, this allows usage of small output caps while ensuring precision LED current regulation. Recommended ceramic capacitor manufacturers are listed in Table 5.  2007 Semtech Corp. www.semtech.com 8 SC4505 POWER MANAGEMENT Applications Information I Resistor Selection Chart O1SET 160 VENDOR PHONE WEBSITE 140 KEMET 408-986-0424 www.kemet.com 120 Murata 814-237-1431 www.murada.com 100 80 Taiyo Yuden 408-573-4150 www.t-yuden.com 60 Table 5. Recommended Ceramic Capacitor 40 Manufacturers 20 0 0 20 40 60 80 100 Output Rectifying Diode Selection I Current (mA) O1 Schottky diodes are the ideal choice for SC4505 due to Figure 2. I Resistor Selection Chart their low forward voltage drop and fast switching speed. O1SET Table 6 shows several different Schottky diodes that I Resistor Selection Chart O2SET work well with the SC4505. Make sure that the diode has a voltage rating greater that the possible maximum 160 ouput voltage. The diode conducts current only when 140 the power switch is turned off. So a 1A diode will be 120 sufficient for most designs. 100 80 PR ART VENDO 60 SS13 Vishay SS14 www.vishay.com 40 20 International Rectifier 10BQ015 www.irf.com 0 0 20 40 60 80 100 120 140 Table 6. Recommended Rectifying Diodes I Current (mA) O2 Figure 3. I Resistor Selection Chart Output Current Programming O2SET PWM Dimming The SC4505 features two independent LED current regulators. The LED current setpoints are chosen using Either of the enable pins can be toggled by external external resistors. The relationships between the circuitry to allow PWM dimming. In a typical application, programming resistors and the two channel output a microcontroller sets a register or counter that varies current setpoints are shown as in the Figure 2 and Figure the pulsewidth on a GPIO pin. The SC4505 allows 3 below. dimming over two decades in frequency (50Hz-50 kHz) in order to allow compatibility with a wide range of The relationships between the programming resistor devices, including newest dimming strategies that avoid value and the output current setpoint can be described the audio band by using high frequency PWM dimming. as follows: In this manner, a wide range of illumination can be generated while keeping the instantaneous LED current R = (140 V) / I O1SET O1 at its peak value for luminescent efficiency and color R = (154 V) / I O2SET O2 purity. Furthermore, advanced lighting effects such as backlight “dim-on” or photographic red-eye reduction can Where R and R are in Ohms. I and I are in O1SET O2SET O1 O2 be implemented as the SC4505 can resolve PWM from Amperes. 12% to 90% duty at 32kHz.  2007 Semtech Corp. 9 www.semtech.com I Resistor (kΩ ) O2SET I Resistor (k ) O1SET Ω SC4505 POWER MANAGEMENT Applications Information An additional advantage of PWM dimming comes to The relationship between the EN_FL, FL_TRB, FTO pin customers who prefer to avoid inrush currents when filling voltage and the current flowing through the IO2 pin is the boost output capacitor – simply PWM the device at illustrated in Figure 4 below. 12% 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 EN_FL easily determined on the bench, and programmed into t the uC firmware. 0 For an example, suppose the current flowing through FL_TRB the I channel is programmed at 20mA by R . A 1kHz t O1 O1SET 0 PWM signal with the duty ratio of 20% is applied to the 1.25V EN_BL pin of the SC4505. Then the average current FTO t flowing through the I channel is 0 O1 I O2MAX I = 20% × 20mA = 4mA I O1AVG O2 t 0 A startup delay time between the enable signal goes high 20% x I O2MAX and the internal current regulator actually turns on is about 1.6µs, which causes a small offset dependent on Figure 4. Relationship between RN_FL, FL_TRB, FTO PWM frequency. As the PWM signal frequency goes and I Current O2 higher, the effect of the delay will get more obvious to customers. To calculate the FTO capacitor needed for a desired timeout, a simple formula can be used as shown below: However, since PWM is always linear, offset can be easily -6 corrected in software. The offset correction factor can C = 0.862 ⋅10 ⋅ t be described as: Where C is in Farads, and t is in Seconds. D = 100 × 1.6 µ S× F CORRECTION PWM F is in KHz. PWM Over Voltage Protection (OVP) For an example, at 20kHz, D = 3%. So for 50% CORRECTION SC4505 includes a built-in overvoltage protection circuit of the nominal LED current in I channel, the PWM signal O1 to prevent damage to the IC and output capacitor in the should have a duty ratio of 53%. event of open-circuit condition. The output voltage of the boost converter is detected at the VO pin, and divided Flash Timeout Programming down by an internal resistor strand of 500kΩ. If the voltage at the VO pin exceeds 28V, the boost converter When Channel IO2 is in flash mode, a timer is available will be shut down, and a strong pulldown will be applied to prevent LED overstress. The timer is only active in to the VO pin to quickly discharge the output capacitor. Flash mode – not active in torch mode. The capacitor This additional level of protection prevents a condition tied between the FTO pin and the AGND sets the time where the output capacitor and Schottky diode must duration of the flash mode. In flash mode, an external endure high voltage for an extended period of time, which capacitor is charged with 1.2µA. When the voltage on can pose a reliability risk for the user’s system. this capacitor reaches the 1.25V threshold Channel 2 is turned off. The timer can be reset by entering torch mode The boost OVP triggering point can be adjusted by adding or turning off channel 2. The FTO pin can simply be an external resistor divider at VO pin as shown in Figure grounded to disable this feature, as would be necessary 5. when using I for sub display. O2  2007 Semtech Corp. www.semtech.com 10 SW SC4505 POWER MANAGEMENT Applications Information VIN VOUT L1 D1 C OUT SC4505 R 3 VO I 2 R 4 R 1 I 1 R 2 COMP V OVP Figure 5. OVP Tweaking As shown in Figure 5, R and R are the internal resistor 1 2 divider. R and R are external resistor divider for OVP 3 4 triggering point adjustment. It is noted that the resistance of the internal resistor divider formed by R and R is 1 2 around 500kΩ. When OVP happens, a strong pulldown will be applied to VO pin to quickly discharge the output will slow down the capacitor. Any large value of R 3 discharge process at OVP condition. Generally speaking, small value of R is preferred in applications. 3 However, small value of the resistor divider formed by R and R would cause additional power loss. People 3 4 often use R =100kΩ and then select R3 according to 4 the OVP specification. In this case, the OVP triggering threshold estimation equation can be rewritten as follows: R //500KΩ +R 4 3 V = × 28V OVP R //500KΩ 4 Set R = 100KΩ 4 We can get V   OVP R = −1 × 83.3KΩ   3 28V   and R should also be considered The tolerance of the R 3 4 in determining the OVP triggering point. Usually there is about 5%~8% difference between the calculated value and the measure OVP triggering threshold.  2007 Semtech Corp. 11 www.semtech.com 13 16 SC4505 POWER MANAGEMENT Applications Information As shown in Figure 6a, C1 serves as decoupling capacitor Layout Guideline for the SC4505. It should be placed close to the VIN and PGND of SC4505 to achieve the best performance. The SC4505 contains a boost converter. The placements C2 is the input power filtering capacitor for the boost of the power components outside the SC4505 should converter power train. L1 is the boost converter input follow the guideline of general boost converter layout. inductor. D5 is the output rectifying diode. It is The application circuit (Figure 7a) will be used as an recommended that a schottky diode is used for fast example. The layout illustration diagram is shown as in reverse recovery. Figure 6a and Figure 6b. R2 R3 R4 C7 EN_BL C8 EN_FL D9 D8 D7 D6 FL_TRB SC4505 D4 D3 D2 D1 VIN VOUT 1 4 C1 D5 PGND C2 VIN L1 Figure 6a Layout Illustration -- Top Layer C4 SC4505 C5 C6 VIN C3 PGND VOUT VIN Figure 6b Layout Illustration -- Bottom Layer  2007 Semtech Corp. www.semtech.com 12 5 8 12 9 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 I and I O1 O2 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.  2007 Semtech Corp. 13 www.semtech.com SC4505 POWER MANAGEMENT Typical Application Circuits 10BQ015 D5 LED: SML-LX0603UWD Vin=2.6~4.6V P1 L1 2 1 IHLP-2525CZ-01-1R5-M-01 D6 D1 LED LED C2 C1 C3 2.2u 2.2u 2.2uF D7 D2 P2 LED LED 0 D3 SC4505 D8 0.33uF 16 1 C4 VIN PGND LED LED R1 15 2 100 FTO PGND 0 14 3 0 FL_TRB SW D4 D9 13 4 EN_FL SW LED LED 12 5 EN_BL VO 11 6 IO1SET IO2 10 7 IO2SET IO1 9 8 AGND COMP R2 3.01k R3 R4 C5 C6 R6 R5 6.98k 1.54k C7 12n 12n 10k 0 10k open (Optional) (Optional) C8 Analog Ground Power Ground 12n 0 0 Figure 7a Backlight and Flashlight LED driver for I =20mA and I =100mA O1 O2 Boost Converter Efficiency vs Input Voltage ( Backlight Mode: 4 LEDs @ I =20mA) O1 83 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  2007 Semtech Corp. www.semtech.com 14 Efficiency (%) SC4505 POWER MANAGEMENT Outline Drawing - MLPQ - 16 DIMENSIONS A D B INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX - - A .031 .040 0.80 1.00 - - A1 .000 .002 0.00 0.05 - - - - A2 (.008) (0.20) PIN 1 b .007 .009 .012 0.18 0.23 0.30 E INDICATOR D .114 .118 .122 2.90 3.00 3.10 (LASER MARK) D1 .061 .067 .071 1.55 1.70 1.80 E .114 .118 .122 2.90 3.00 3.10 E1 .061 .067 .071 1.55 1.70 1.80 e .020 BSC 0.50 BSC L .012 .016 .020 0.30 0.40 0.50 A2 N 16 16 aaa .003 0.08 A bbb .004 0.10 SEATING PLANE aaa C 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 DIMENSIONS DIM INCHES MILLIMETERS C (.114) (2.90) G .083 2.10 (C) Z K G H .067 1.70 K .067 1.70 P .020 0.50 R .006 0.15 Y X .012 0.30 Y .031 0.80 X Z .146 3.70 P 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  2007 Semtech Corp. 15 www.semtech.com