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SC4505 High Efficiency Boost Converter for Backlight/Flash LED Driver
POWER MANAGEMENT Description
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.
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 (<1A ) 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
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
Boost Converter Efficiency vs Input Voltage (2 String of 3 LEDs @30mA) 87
Typical Application Circuit
L1 IHLP -2525CZ-01-1R5-M-01 C2 PGND 2.2u C1
VIN: 2.6 V ~ 6.0V
LED: SML-LX0603UWD
2 D1 1 D2 L ED D3 L ED 10BQ015
2.2u F
0
C3 0 .33uF
SC4505 16 15 14 13 12 11 VIN FTO FL_TRB EN_FL EN_BL IO1SET IO2SET AGND PGND PGND SW SW VO IO2 IO1 COMP 1 2 3 4 5 6 7 8 R1 3.0 1k C6 12n
85
D5 L ED
0 0
Efficiency (%)
C5 12n (Optional)
D4 L ED
FL_TRB EN_FL EN_BL AGND RO1SET 6.9 8k
83
D6 L ED
D7 L ED
81
10 9 RO2SET 1.5 4k
C4 12n (Optional)
79
0
0
0
77 2.5 3 3.5 4 4.5 5 Input Voltage (V)
Power Ground
Analog Ground
All Capacitors are Ceramic. Figure 1. SC4505 Application Circuit for Backlight and Flashlight LED Driver
Revision: December 12, 2007
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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 Supply Voltage SW Voltage, Output Voltage, Current Source Voltage I0SET Voltage FTO Voltage EN_BL, EN_FL, FL_TRB Voltage Thermal Resistance Junction to Ambient Maximum Junction Temperature Storage Temperature Range IR Reflow (Soldering) 10s to 30s ESD Rating (Human Body Model)
Symbol VIN VSW, VO, VIO1, VIO2 VIO1SET,VIO2SET VFTO VEN_BL, VEN_FL VFL_TRB J A TJ TSTG TPKG ESD
Typ -0.3 to 20 -0.3 to 36 -0.3 to 2 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 37 150 -65 to +150 260 1
Units V V V V V C/W C C C kV
Electrical Characteristics
Unless specified: VIN = 3.6V, -40C < TA = TJ < 85C, RO1SET=6.98K, RO2SET=1.54K
Parameter Supply Input Voltage VIN UVLO Threshold UVLO Hysteresis VIN Supply Current VIN Supply Current in Shutdown Switching Frequency Maximum Duty Cycle Minimum Duty Cycle Switch Current Limit Switch Leakage Current Switch Saturation Voltage EN_FL, FL_TRB, EN_BL High Voltage EN_FL, FL_TRB, EN_BL Low Voltage
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Test Conditions
Min 2.6
Typ
Max 12
Unit V V mV mA
VIN rising
2.45 50
2.59
Not switching EN_FL = FL_TRB = EN_BL = 0 TJ = 25C 0.8 85
1.7 1.0 1 90 0 1.75 2.25 0.01 300 2 0.4 1 1.2
A MHz % % A A mV V V
V S W = 28V ISW = 1A VIN = 2.6V to 4.7V VIN = 2.6V to 4.7V
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SC4505
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: VIN = 3.6V, -40C < TA = TJ < 85C, RO1SET=6.98K, RO2SET=1.54K
Parameter EN_FL, FL_TRB, EN_BL Input Current EN_BL PWM Dimming Control Frequency EN_BL PWM Dimming Control Duty Cycle FTO Sourcing Current FTO Trip Threshold Voltage FTO Pull Down Current Overvoltage Protection Thermal Shutdown Temperature Thermal Shutdown Hysteresis Backlight Current Accuracy ( I O1 ) Max Backlight Current ( I O1 ) Flash Current Accuracy ( I O2 ) Max Flash Current ( I O2 ) Torch Output Current ( I O2 ) IO1 Off Leakage Current IO2 Off Leakage Current VO Pulldown in Overvoltage Fault
Note 1: Guaranteed by Design
Test Conditions VEN_FL = 0V to 4.7V Note 1 FPWM=32kHz , Note 1 EN_FL = FL_TRB = 1
Min
Typ 0.01
Max 1 50K 100
Unit A Hz % A V mA V C C
50 12 1.2 1.25
EN_FL = 1, FL_TRB = 0
2.6 28 155 10
EN_BL = 1 TJ = 25C, RO1SET =6.98K
19
20 75
21
mA mA
EN_FL = FL_TRB = 1 TJ = 25C, RO2SET =1.54K
92
100 125
108
mA mA mA
EN_FL=1, FL_TRB=0 TJ = 25C, RO2SET =1.54K VIO1 =28V VIO2 =28V
18 0.1 0.1 7 1 1
A A K
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SC4505
POWER MANAGEMENT Pin Configurations
TOP VIEW
Ordering Information
Device(1)(2) SC4505MLTRT SC4505EVB(3) P ackag e MLPQ-16 Temp. Range( TA) -40 to 85C
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
UVLO
Thermal Shutdown
S R OSC
Q
Sense Amp Comparator
Rsense5mOhm
Reference& Internal Regulator
COMP
Error signal selection and summation
ADJ1
ADJ1 EN_BL BL Setpoint
IO1 EN_FL FL Setpoint FL_TRB
ADJ2
ADJ2
IO2
IO1SET RO1SET PGND AGND
IO2SET RO2SET
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SC4505
POWER MANAGEMENT Pin Descriptions Block Diagram
Pin 1,2 3,4 5 6 7 8 9 10 11 12 13 14 15 16 Pin Name PGND SW VO IO2 IO1 COMP AGND IO2SET IO1SET EN_BL EN_FL FL_TRB FTO VIN Exposed Pad Pin Function Power ground. 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. Connect the output capacitor and the anode of the LED strings to this pin. Provides constant source current to LED string 2. Provides constant source current to LED string 1. The output of the internal transconductance error amplifier. This pin is used for loop compensation. Analog ground. 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. 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. Enable and Brightness control pin for LED backlight string 1. (See Table 2 for logic). Enable and Brightness control pin for LED flash light string 2. (See Table 1 for logic). 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. Power Supply Pin. Bypassed with capacitors close to the pin. The exposed pad must be soldered to the analog ground plane on the PCB for good thermal conduction.
E N _F L 0 0 1 1
F L _T R B 0 1 0 1
Status Flash disable Flash disable 20% max. output current set by external resistor, RO2SET 100% max. output current set by external resistor, RO2SET
E N _B L 0 1
Status Backlight disable Backlight enable
Table 2
Table 1 Note: When EN_FL = 0 FL_TRB = 0 EN_BL = 0 The boost is turned OFF and disabled.
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SC4505
POWER MANAGEMENT Overview
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. 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 1A shutdown mode when all LED strands are turned off. In shutdown mode, leakage through the current regulator outputs is also < 1A, 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. 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. 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.
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SC4505
POWER MANAGEMENT Applications Information
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. 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 Si ngle Strand C ondition One Strand Only Number of Backli ght LE D s > Number of Flashli ght LE D s Number of Backli ght LE D s < Number of Flashli ght LE D s Operation Regulate to C urrent Strand
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. 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. In many cases, the required output currents from a tiny inductor footprint limit the designer to very small values of inductance (0.8 - 2.2H). 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) Both Strands: It requires: 14.4V @120mA Suppose the efficiency of the boost converter is about 80%, the Maximum average input current is: 14.4V x 120mA / (2.7V x 80%) = 0.8A. Suppose a 1.5H inductor is used, the peak inductor current would be:
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Backli ght Li mi ted
Servos to the Number of Backli ght LED s. Flashli ght i s sti ll Regulated to IO2 Set Value
Flashli ght Li mi ted
Servos to the Number of Flashli ght LED s. Backli ght i s sti ll Regulated to IO1Set Value
Table 3. SC4505 Operation States
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SC4505
POWER MANAGEMENT Applications Information
2.7V 1 IPK = 0.8A + 1.5 H x 1 S x 81% x 2 = 1.5A
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 H range of inductance. We select a Coiltronics 1.5H SD3114 series, presently the only 3mmx3mmx1.5mm inductor that can provide the required current in the microminiature size required in space-constrained applications. 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 SD3112-1R0 SD3114-1R5 SD3114-4R7 LQH3C4R7M24 LQH3C100M24 LB2016B4R7 LB2016B100 CMD4D06-4R7 CLQ4D10-4R7 CLQ4D10-6R8 IHLP2525CZ1R5 IHLP2525CZ3R3 IHLP2525CZ4R7 L (H) 1.0 1.5 4.7 4.7 10 4.7 6.8 4.7 4.7 6.8 1.5 3.3 4.7 MAX DCR ( ) 0.069 0.057 0.147 0.260 0.300 0.250 0.350 0.216 0.162 0.195 0.014 0.028 0.037 MAX HEIGHT (mm) 1.2 1.45 1.45 2.2 2.2 1.6 1.6 0.8 1.2 1.2 3.0 3.0 3.0 VENDOR
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. 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. Since the load is a constant current, the capacitor
V can be solved for the output equation I = C T
ripple.
Coiltronics www.cooperet.com Murata www.murada.com Taiyo Yuden www.t-yuden.com Sumida www.sumida.com Vishay www.vishay.com
VOUT =
IOUT x 1 S x (1- D) COU T
At 1MHz switching frequency and with the assumption of the worse case analysis (D=0), an even simpler relationship can be applied:
VOUT =
where COUT is in F.
IOUT x 1 S COU T
Table 4. Recommended Inductors
Output Capacitor Selection 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.
For worse case analysis, We see that our typical case of 20mA, 120mA can be immediately converted into its corresponding ripple relationships of: VOUTMIN = 20mV/COUT where COUT is in F. VOUTMAX = 120mV/COUT where COUT is in F. For the example, if 1F output capacitor were used, the 20mV/120mV boundary conditions are well within the suggested guidelines. Recommended ceramic capacitor manufacturers are listed in Table 5.
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SC4505
POWER MANAGEMENT Applications Information
IO1SET Resistor Selection Chart
VENDOR KEMET Murata Taiyo Yuden
PHONE 408-986-0424 814-237-1431 408-573-4150
WEBSITE
IO1SET Resistor (k )
160 140 120 100 80 60 40 20 0 0 20 40 60 80 100
www.kemet.com www.murada.com www.t-yuden.com
Table 5. Recommended Ceramic Capacitor Manufacturers Output Rectifying Diode Selection 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.
PART S S 13 S S 14 10BQ015 VENDOR Vishay www.vishay.com International Rectifier www.irf.com
IO1 Current (mA)
Figure 2. IO1SET Resistor Selection Chart
IO2SET Resistor Selection Chart 160 140 IO2SET Resistor (k ) 120 100 80 60 40 20 0 0 20 40 60 80 100 120 140 IO2 Current (mA)
Table 6. Recommended Rectifying Diodes 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. 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
Figure 3. IO2SET Resistor Selection Chart PWM Dimming 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 12% to 90% duty at 32kHz.
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Where RO1SET and RO2SET are in Ohms. IO1 and IO2 are in Amperes.
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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 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 easily determined on the bench, and programmed into the uC firmware. 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
IO1AVG = 20% x 20mA = 4mA
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 0
t
FL_TRB 1.25V FTO
0
t
0
t
IO2MAX
IO2 0 20% x IO2MAX
A startup delay time between the enable signal goes high and the internal current regulator actually turns on is about 1.6s, 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. However, since PWM is always linear, offset can be easily corrected in software. The offset correction factor can be described as:
DCORRECTION = 100 x 1.6 S x FPWM
t
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 500k. 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.
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 1.2A. 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.
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SC4505
POWER MANAGEMENT Applications Information
VIN L1
SW
VOUT D1 COUT
SC4505
VO
R3
R1
COMP
R4
I2
R2 VOVP
I1
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 500k. 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=100k and then select R3 according to the OVP specification. In this case, the OVP triggering threshold estimation equation can be rewritten as follows: R //500K + R 3 VOVP = 4 x 28V R 4 //500K Set
R 4 = 100K
We can get
V R3 = OVP - 1 x 83.3K 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.
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SC4505
POWER MANAGEMENT Applications Information
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. 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.
R2 R3 EN_BL C8
9 12
R4 C7
EN_FL FL_TRB
VIN C1 PGND C2 VIN L1
1 4
5
13
8
D9
D8
D7
D6
SC4505
D4
16
D3
D2
D1
VOUT
D5
Figure 6a Layout Illustration -- Top Layer
C4
SC4505
VIN
C6
C5
PGND
C3
VOUT
VIN
Figure 6b Layout Illustration -- Bottom Layer
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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.
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SC4505
POWER MANAGEMENT Typical Application Circuits
P1 Vin=2.6~4.6V L1 2 IHLP-252 5CZ-01- 1R5 -M-01 10BQ015 D5 1 D1 LED C2 2.2 u P2 C1 2.2 u C3 2.2uF D2 LED D7 LED D6 LED LED: SML-LX0603UWD
0
R1 100 0.33uF C4 16 15 14 13 12 11 10 9 V IN FTO FL_TRB EN_FL EN_ BL IO1SET IO2SET AGND
SC4505 PGND PGND SW SW VO IO2 IO1 COMP 1 2 3 4 5 6 7 8 R2 3.01k
D3 LED
D8 LED
0 0
D4 LED D9 LED
R6 10k
R5 10k
R3 6.98k
R4 1.54k
0
Analog Ground Power Ground C8 12n
C7 ope n
C5 12n (Op tiona l)
C6 12n (Op tiona l)
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
82 Efficiency (%)
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
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SC4505
POWER MANAGEMENT Outline Drawing - MLPQ - 16
A
D
B
DIM
A A1 A2 b D D1 E E1 e L N aaa bbb
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
PIN 1 INDICATOR (LASER MARK)
E
A2 A aaa C A1 C D1 e/2 LxN E/2 E1
2 1 N
SEATING PLANE
e bxN D/2
NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
bbb
CAB
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 Z
DIMENSIONS INCHES MILLIMETERS
(.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
Y
X P
NOTES: 1.
C G H K P R X Y Z
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

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