SC604AIMLTR

Low Noise, High Efficiency Regulated White LED Driver POWER MANAGEMENT OBJECTIVE -NOVEMBER Description Features 9, 2000 is a very high efficiency charge pump white Very high efficiency over 90% of battery life The SC604A LED driver driver from the mAhXLifeTM family of products, optimized for Li-Ion battery applications. The four (4) LED outputs are current matched for consistent LED brightness. Extremely low battery current is achieved by automatically reconfiguring the charge pump to match circuit conditions. Using four LEDs, each at 20mA for a total IOUT= 80mA, the SC604A can use less than 83mA from the supply for most of the battery life. Patented low noise mode switching circuitry and constant output current allow the use of extremely small input and output capacitors. SC604A Peak efficiency over 92% Current regulation for up to 4 LEDs Digital 3 bit output control logic Current matching tolerance of ±3% typical Wide current range per LED [0.5mA - 30mA] High available total LED current = 4 ILED = 120mA Low Shutdown Current: 1µA typical Soft start / In-rush current limiting Short circuit protection MLP-16 [4x4] Package Fixed frequency 250kHz 1x, 1.5x and 2x charge pump modes of operation Applications Cellular phones LED backlighting PDA power supplies Portable devices Electronic books Wireless web appliances LCD Modules Typical Application Circuit Patent Pending VIN BATTERY 1µ F VOUT 1µ F SC604A EN CTRL0 CTRL1 CTRL2 GND C1+ 1µF ILED1 ILED2 ILED3 ILED4 ISET C1C2+ 1µF C2- June 27, 2005 1 United States Patents: 6,504,422, 6,794,926 www.semtech.com SC604A POWER MANAGEMENT Absolute Maximum Ratings 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. Parameter Sup p ly Voltage Outp ut Voltage VOUT Shor t Circuit Duration Thermal Resistance, Junction to Ambient Op erating Ambient Junction Temp erature Range Storage Temp erature Range IR Reflow Temp erature SC604AIMLTR IR Reflow Temp erature SC604AIMLTRT Note: (1) By JESD51 standards (1) Symbol V IN VOUT SC θJ A TA TJ TSTG T LE A D T LE A D Maximum -0.3 to +7.0 -0.3 to +7.0 Indefinite 40 -40 to +85 -40 to +150 -65 to +150 240 260 Units V V s °C/W °C °C °C °C °C Electrical Characteristics Unless specified: TA = -40°C to 85°C, VIN= 2.85V to 5.5V, C1 = C2 = 1.0µF (ESR = 0.03Ω). Typical values @ TA=25°C, LED VF = 3.4V. This device is ESD sensitive. Use of standard ESD handling precautions is required. Parameter Inp ut Sup p ly Voltage Current into LEDs 1, 2, 3 and 4 Symbol V IN IL E D Conditions Min 2.5 Typ Ma x 6.5 Units V mA mA RSET = 24.0kΩ RSET = 94.0kΩ 2.7V < VIN < 5.5V 3.1V < VIN < 5.5V 0.5 0.5 20 5.0 20 30 1500 1 ±5 ±3 3.796 2000 7 mA mA µA µA % % V Quiescent Current IQ IOUT = 5mA Enable = 0V ILED Accuracy Current Matching 1x mode to 1.5x mode transition voltage (VIN falling) 1.5x mode to 2x mode transition voltage (VIN falling) Oscillator Frequency Outp ut Over Voltage Protection (1)  2005 Semtech Corp. ILED-ERR ILED-LED-ERR VTRANS1X VTRANS1.5X fOSC VOVP 0.5mA ≤ ILED ≤ 30mA 0.5mA ≤ ILED ≤ 30mA VLED = 3.6V, IOUT = 80mA, ILED = 20mA VLED = 3.6V, IOUT = 80mA, ILED = 20mA 212.5 Op en circuit at any LED that is p rogrammed to be in the On state 2 3.320 250 287.5 V kHz V www.semtech.com 5.0 SC604A POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: TA = -40°C to 85°C, VIN= 2.85V to 5.5V, C1 = C2 = 1.0µF (ESR = 0.03Ω). Typical values @ TA=25°C, LED VF = 3.4V. Parameter Inp ut Current Limit Inp ut High Threshold Inp ut Low Threshold Inp ut High Current Inp ut Low current Notes: (1) Guaranteed by design Symbol IL IM IT V IH V IL I IH I IL Conditions Shor t circuit ap p lied from VOUT to GN D Inp ut high logic threshold Inp ut low logic threshold VIH= VIN VIL= GN D Min Typ 220 Ma x 850 Units mA V 1.3 0.4 10 10 V µA µA  2005 Semtech Corp. 3 www.semtech.com SC604A POWER MANAGEMENT Definitions ILED Accuracy The LED current is determined by the RSET resistor (ILED vs. RSET data is found on pages 9 and 10). This term does not include the tolerance of the resistor RSET. If maximum accuracy is required, a precision resistor is needed. To calculate the error ILED-ERR[%], use the formula ILED-ERR [%] = ± Input Current The total input current of the SC604A is a function of the sum of the LED currents, the charge pump mode and the quiescent current. The quiescent current trend is charted on page 12 and used to calculate IIN in the following examples. IIN = IOUT Mode + IQ = 100 % (I LED ) MEASURED I LED - I LED (ILED1+ILED2+ILED3+ILED4 ) Mode + IQ Example 1: Mode = 1x, IQ = 2.4mA, ILED1+ILED2+ILED3+ILED4 = 4 15mA = 60mA Answer 1: IIN = IOUT 62.4mA Example 2: Mode = 1.5x, IQ = 2.4mA, ILED1+ILED2+ILED3+ILED4 = 4 15mA = 60mA Mode + IQ = 60mA 1 + 2.4mA = Current Matching Current Matching refers to the difference in current from one LED to the next. The ∆I between any two LEDs will meet this requirement. To calculate the error ILED-LED-ERR , first identify the highest and lowest value of the 4 LED currents, and use the formula: ILED-LED-ERR [%] = IMAX IMAX + IMIN 2 -1 100% or IMIN IMAX + IMIN 2 -1 100% which reduces to ± IMAX IMIN IMAX + IMIN 100% Answer 2: IIN = IOUT Mode + IQ = 60mA 1.5 + 2.4mA = 1x Mode, 1.5x Mode and 2x Mode 1x Mode, 1.5x Mode and 2x Mode all refer to the charge pump configuration. These modes boost the battery input voltage and ensure there is enough voltage at VOUT so that the regulated current will flow through the LEDs and return via the ILED pins. 92.4mA Mode Transition Voltage Mode transition voltage refers to the input voltage at the point just before the charge pump changes from a weaker mode to a stronger mode. V TRANS1X i s the transition from 1x to 1.5x mode, and VTRANS1.5X is the transition from 1.5x to 2x mode. Equations for VTRANS1X and VTRANS1.5X are given on page 7.  2005 Semtech Corp. 4 www.semtech.com SC604A POWER MANAGEMENT Pin Configuration TOP VIEW ILED1 ILED2 ILED3 ILED4 16 15 14 13 12 11 10 T 5 6 7 8 9 Ordering Information DEVICE SC604AIMLTR GND C2+ C2C1- PACKAGE(1) MLP-16 MLP-16 Evaluation Board EN CTRL0 CTRL1 CTRL2 1 2 3 4 SC604AIMLTRT(2) SC604EVB TOP VIEW Notes: (1) Available in tape and reel only. A reel contains 3000 devices. (2) Available in lead-free package only. This product is fully WEEE and RoHS compliant. ISET VOUT VIN C1+ MLPQ16: 4X4 16 LEAD Pin Descriptions Pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 T Pin Name EN CTRL0 CTRL1 CTRL2 ISET VOUT V IN C1+ C1C2C2+ GN D ILED4 ILED3 ILED2 ILED1 Pin Function Active high enable Outp ut control bit 0 (see Table 1 on p age 6) Outp ut control bit 1 (see Table 1 on p age 6) Outp ut control bit 2 (see Table 1 on p age 6) LED current is set by the value of the resistor RSET connected from the ISET p in to ground. Do not shor t the ISET p in. VISET is typ ically 1.22V Voltage outp ut source for connection to the LED anodes Voltage inp ut Positive terminal of bucket cap acitor 1 N egative terminal of bucket cap acitor 1 N egative terminal of bucket cap acitor 2 Positive terminal of bucket cap acitor 2 Ground Current sink for LED 4 [lf not in use, p in must be left op en](1) Current sink for LED 3 [lf not in use, p in may be left op en, grounded, or connected to VIN](1) Current sink for LED 2 [lf not in use, p in may be left op en, grounded, or connected to VIN](1) Current sink for LED 1 [lf not in use, p in may be left op en, grounded, or connected to VIN](1) Thermal Pad Pad for heatsinking p urp oses. Connect to ground p lane using multip le vias. N ot connected Internally www.semtech.com 5 Note: (1) The CTRL word must match the outputs in use.  2005 Semtech Corp. SC604A POWER MANAGEMENT Block Diagram C1+ 8 C19 C210 C2+ 11 ILED4 13 ILED3 14 ILED2 15 ILED1 16 VOUT 6 Current Brightness Control mAhXLifeTM Fractional Charge Pump [1x, 1.5x, 2x] Current Sense FETs and Amplifier(s) 12 GND VIN 7 Current Set Detect 250kHz Oscillator & Delay Clk Mode Select [1x, 1.5x, 2x Startup, Shutdown] Ouput Selection Logic 5 ISET 1.22V Bandgap Voltage EN 1 Schmitt Buffer Schmitt Buffer Schmitt Buffer Schmitt Buffer 2 CTRL0 3 CTRL1 4 CTRL2 Table 1 - LED Enable Logic Control Inputs CTR L2 0 0 0 0 1 1 1 1 CTR L1 0 0 1 1 0 0 1 1 (1) Output Status CTR L0 0 1 0 1 0 1 0 1 LED4 OFF OFF OFF ON OFF OFF ON OFF LED3 OFF OFF ON OFF OFF ON ON OFF LED2 OFF ON OFF OFF ON ON ON OFF LED1 ON OFF OFF OFF ON ON ON OFF Notes: (1) The sequencing of Enable and logic state CTRL{2,1,0} = [1, 1, 1] will affect quiescent state current. IQ = 100µA if Enable transitions high before CTRL{2,1,0} transitions to [1, 1, 1]. IQ = 400µA if Enable transitions high after CTRL{2,1,0} transitions to [1, 1, 1]. If Enable = high and CTRL{2,1,0}= [1, 1, 1] is to be used for an extended period of time, it is recommended that Enable = High when change to the [1, 1, 1] state to achieve the lower IQ level.  2005 Semtech Corp. 6 www.semtech.com SC604A POWER MANAGEMENT Applications Information Detailed Description The SC604A contains a fractional charge pump, mode selection circuit, output selection logic, current setting detection circuit, and four current sense circuits. All are depicted in the block diagram on page 6. The fractional charge pump multiplies the input voltage a multiple of 1, 1.5 or 2 times the input voltage. The charge pump switches at a fixed 250kHz whenever the mode is 1.5x or 2x. The charge pump does not switch during 1x mode, saving power and improving efficiency. The mode selection circuit automatically selects the mode as 1x, 1.5x or 2x based on circuit conditions such as LED voltage, input voltage and load current. 1x is the most efficient mode, followed by 1.5x and 2x modes. At lower voltages a stronger mode may be needed to maintain regulation, if so, the mode will change first to 1.5x and then to 2x. 2x mode usually operates for a much shorter run time compared to 1x mode, and 2x mode maintains the output until the battery is discharged to 2.85V or less. The LED requiring the highest voltage drop will determine the output voltage needed to drive all outputs with adequate bias. Comparing all cathodes and regulating VOUT for the LED with the lowest cathode voltage ensures sufficient bias for all LEDs. Output selection logic enables control over the LED outputs for on and off functions with eight (8) different output states. The states are defined in Table 1 on page 6. The current set and detection circuit uses an external resistor and a 1.22V reference to program the LED current. Four (4) current regulating circuits sink matched currents from the LEDs. LEDs with matched forward voltage will produce the best possible matched currents. For best matching performance it is recommended that the ∆Vf between LEDs be under 250mV. (For more information on ∆ Vf considerations refer to Semtech application notes). Designing for Lowest Possible Battery Current The SC604A efficiency and battery current are shown in the plots that follow on page 8. For this example, 4 LEDs are matched at 15mA each. The battery current remains low at 63mA well into the Li-Ion battery range as indicated in the plot by a boundary box. The SC604A uses 1x mode (IIN=IOUT+IQ) for part of the input voltage range, conserving significant energy from the battery. A similar four (4) output device uses only 1.5x mode (IIN= IOUT 1.5+IQ) over the input voltage range. This means that the SC604A will have about 25% higher efficiency than a 1.5x only charge pump. Where the competition drops off at 3V, the SC604A uses 2x mode to extend the operating range down to a battery voltage of only 2.85V. The input voltages at which the mode transitions occur are dependent on the forward voltage VF of the LED used and the LED current ILED. To keep the battery current low and in the 1x mode for as long as possible, it is best to choose an LED with a lower VF. The mode transition voltages VTRANS1X and VTRANS1.5X can be estimated by the following equations: VTRANS1X = VF + VILED + [(# of LEDs used) ILED 1.2] VTRANS1.5X = VF + VILED + [(# of LEDs used) ILED 16] 1.5 where, VF is the forward LED voltage measured from anode to cathode, VILED is the voltage at the ILED pin, typically VILED = 100mV, ILED is the LED current. Power efficiency can now be estimated for comparison with the intended battery voltage range. Efficiency [%] = VOUT IOUT 100% VIN (IOUT Mode + IQ (  2005 Semtech Corp. 7 www.semtech.com SC604A POWER MANAGEMENT Battery Current Comparison for 4 LEDs at 15mA Each with LED = 3.5V 110 100 Competition 1.5x mode Battery Current [mA] 90 Semtech 1.5x mode 80 70 Semtech 1x mode 60 50 4.2 4.1 4.0 3.9 90% of Li-Ion battery life 3.8 VIN [V] 3.7 3.6 3.5 3.4 3.3 3.2 100 Efficiency Comparison for 4 LEDs with 15mA Each and LED = 3.5V Semtech 1x mode 90 80 Efficiency [%] 70 Semtech 1.5x mode 60 Competition 1.5x mode 50 40 4.2 4.1 4.0 3.9 90% of Li-Ion battery life 3.8 3.7 3.6 3.5 3.4 3.3 3.2 VIN [V]  2005 Semtech Corp. 8 www.semtech.com SC604A POWER MANAGEMENT Methods for Setting LED Current There are four methods for setting and adjusting the LED current outlined here. The methods are: 1) RSET only 2) Analog Reference VADJ 3) NMOS switched parallel resistors 4) PWM Input Method 1. The most basic means of setting the LED current is with a resistor connected from ISET to GND, as shown in the application circuit on Page 1. The resistor RSET establishes the reference current needed for a constant LED current. Values of RSET for a fixed LED current are given in Table 2 and also in the below graph, “Typical RSET Resistance vs. LED Current”. Methods 2 and 3 on page 10 are for setting the LED current allow for brightness control. Table 2 - Resistor Value Selection RSET Value ILED[mA] 0.5 1 2 3 5 10 15 20 30 [k RSET[kΩ] 931 471 237 155 94.0 47.5 31.83 24.0 16.5 N earest kΩ Standard Value 931 470 237 154 93.1 47.5 31.6 24.0 16.5 Standard Value % Difference 0.0% -0.2% 0.0% -0.6% -1.0% 0.0% -0.7% 0.0% 0.0% Typical R SET R esistance vs. LED Current 1000 950 900 850 800 750 700 R SET Resistance [kΩ] 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 LED Current [mA] 9 6.5 7 7.5 8 8.5 9 9.5 10  2005 Semtech Corp. www.semtech.com SC604A POWER MANAGEMENT Methods for Setting LED Current (Cont.) Method 2. The example circuit in Figure 1 uses a 16.5kΩ resistor and an analog input DC voltage, VADJ , which varies from 1.2V to 0V to control LED current from 1mA to 30mA. Table 3 shows the resulting output. If necessary, the analog VADJ voltage can be sourced from a voltage higher than 1.2V, but the source must be divided down so that the VADJ mode will not exceed 1.2V. For lower current applications and for higher resolution, a larger resistor may be substituted in this circuit. PWM applications are also possible with this circuit by application of RC filtering. (Consult with Semtech for detailed application support). Figure 1 - Analog Voltage for LED Current Control Method 3. The circuit in Figure 2 uses open drain NMOS transistors to set an equivalent resistance for RSET. Parallel combinations are switched on and off for R1, R2 and R3. R4 is always connected, so that a minimum value of LED current can be maintained at 1.5mA. Figure 2 - 3 Bit LED Current Control with Open Drain Table 3 - Analog Voltage for LED Current Control VADJ [V] 0.000 0.100 0.200 0.300 0.400 0.500 ILED [mA] 30.2 27.7 25.1 22.5 20.0 17.3 VADJ [V] 0.600 0.700 0.800 0.900 1.000 1.150 ILED [mA] 14.8 12.3 9.7 7.1 2.1 1.0  2005 Semtech Corp. 10 www.semtech.com SC604A POWER MANAGEMENT Methods for Setting LED Current (Cont.) Method 4. LED current may also be controlled by applying a PWM signal to any of the CTRL2, CTRL1 and CTRL0 inputs. The circuit in Figure 3 turns 4 LEDs on and off by applying a PWM signal to the CTRL0 input. This circuit uses resistor RSET to set the on state current and the average LED current is then proportional to the percentage of on-time when the CTRL0 pin is a logic low. Average LED current is approximately equal to: IAVG = (tON ILED_ON)/(tON + tOFF) The recommended PWM frequency is between 100Hz and 500Hz. Due to start up delay and ramp up time, frequency >500Hz will result in error in the average value of ILED. Frequency