SP6683UEB

SP6683EB Evaluation Board Manual Low-profile, inductor-less White LED Driver, drives up to 8 WLEDs Automatic Transition from X1 to X1.5 mode for highest efficiency Build in 1.2 MHz oscillator enables using 1uF ceramic caps at 200mA output. PWM dimming control 1uA shutdown current Space Saving 10-pin DFN Package SP6683 Evaluation Board Schematics Vout C2 1uF 1 SP6683 Vout C1P Vin Vmode FB C2P C1N GND C2N EN/PWM 10 9 8 7 6 C4 1uF 2 3 C5 1uF D1 LED D2 LED D3 LED D4 LED D5 LED D6 LED Vin: 2.7-4.2V C1 1uF R1 192K 4 5 R2 100K C3 0.1uF R4 20 R5 R6 R7 R8 R9 Vfb R3 1.0M GND EN/PWM USING THE EVALUATION BOARD 1) Powering Up the SP6683 Circuit The SP6683 Evaluation Board can be powered from inputs from a +2.7V to +5.5V battery or a power supply. Connect with short leads directly to the “VIN” and “GND” posts. 2) Using the evaluation board The Evaluation Board was set up for a 4 15mA LED application even though there are 6 LED spots on the board. The output of SP6683 was open as default. If the customer has discrete white LEDs, then the discrete white LEDs should be soldered to the D1-D6 positions and bias resistors should be soldered to the R4-R9 positions. Selection of the bias resistors please refers to 3). If the customer has white LED module, they can plug the two terminals of the module to the “VOUT” and “Vfb” posts, and use R4 as the bias current to regulate the total current. The value of the bias resistor could be calculated by equation (1). 3) Selecting the Bias Resistor The bias resistor could be estimated by (1) RTotal = VFB I LED _ Total = 0.3V 60mA = 5Ω (1) Where ILED_Total is the total output current. R4−9 = VFB I LED _ D1−6 = 0.3V 15mA = 20Ω (2) Where ILED_D1-D6 is the operating current of D1-D6. 4) Selecting of Vmode and Divider Resistor SP6683 can automatically change from X1 mode to X1.5 mode for highest efficiency. To use this feature, divider resistors should be chosen according to the specific application. The guideline for divider resistor selections is as follows. For high input voltage, the SP6683 will work in X1 mode, when the input voltage drops to Vth threshold voltage, it will switch to X1.5 mode automatically. The Vth threshold voltage for mode change can be calculated by (3) Vth = (VF + 0.3 + m ⋅ I LED ⋅ Rout ) (3) Where VF and m are the forward voltage and number of the white LEDs, Rout is the output resistance of the SP6683. The equation for the voltage divider R1 and R2 with Vmode=1.25V is: Vth = 1.25V ⋅ (1 + R 1 R 2 ) (4) which can be expressed as R1: R1 = (Vth 1.25 − 1) ⋅ R 2 (5) For the typical Sp6683 Evaluation Board, using VF=3V, m=4, ILED=15mA, Rout=6ohms, the Vth will be 3.7V. Select R2=100kohm, then R1=192kohm. 5) Selecting of Capacitors Ceramic capacitors are used on the evaluation board due to their inherently low ESR, which will help produce low peak to peak output ripple, and reduce high frequency spikes. Selection of the flying capacitor is a trade-off between the output voltage ripple and the output current capability. Decreasing the flying capacitor will reduce the output voltage ripple because less charge will be delivered to the output capacitor. However, smaller flying capacitor leads to larger output resistance, thus decrease the output current capability and the circuit efficiency. In the evaluation board, the input, output and flying capacitors are selected as 1uF ceramic capacitors. Input and output ripple could be further reduced by using larger low ESR input and output capacitor. 6) Brightness Control Obvious dimming control could be achieved by applying a PWM control signal to the ENABLE/PWM pin. The brightness of the white LEDs is controlled by increasing and decreasing the duty cycle of The PWM signal. The recommend frequency range of the PWM signal is from 60Hz to 700Hz. A repetition rate of at least 60Hz is required to prevent flicker. 2 POWER SUPPLY DATA For a 4x15mA White LEDs application, in which the output current is 60mA, the power supply data is provided as Fig 1 to Fig 3. The white LEDs used here were from LUMEX (Part Number SML-LX2832UWC-TR). Figure 1 shows the input and output voltage ripple when the input voltage is 3.9V (SP6683 is in X1 mode), Figure 2 shows the input and output voltage ripple when the input voltage is 3.3V (SP6683 is in X1.5 mode). Figure 3 shows the typical efficiency curve in the input voltage range. Channel 1 is the input ripple and the channel 2 is the output ripple. Other applications, such as 80mA output current application (4 20mA white LEDs in parallel), have the similar characteristic. Vin Vin Vout Vout Figure 1. X1 Mode Voltage Ripple @ 3.9V Figure 2. X1.5 Mode Voltage Ripple @ 3.3V 100.0 90.0 80.0 70.0 Efficiency (%) 60.0 50.0 40.0 30.0 20.0 10.0 0.0 2.7 3.0 3.3 Vin (V) 3.6 3.9 4.2 Figure 3. Efficiency vs Input Voltage 3 Evaluation Board Layout FIGURE 4: SP6683 COMPONENT PLACEMENT FIGURE 5: SP6683 PC LAYOUT TOP SIDE FIGURE 6: SP6683 PC LAYOUT BOTTOM SIDE 4 TABLE1: SP6683 BILL OF MATERIALS SP6683 Evaluation Board List of Materials Qty. Manufacturer Part Number Layout Size Component LxWxH 1 Sipex Corp. 1"x1.6" SP6683 Eval PC Board, 146-6548-00 1 Sipex Corp. SP6683ER DFN-10 10 PIN High Efficiency Charge Pump Regulator U1 4 TDK Corp TDKC1608X5R1A105K 603 1uF/10V/X5R/10% Ceramic C1,C2,C4,C5 2 TDK Corp TDKC1608X7R1E104K 603 0.1uF/10V/X7R/10% Ceramic C3 D1-D6 Open R1 1 603 191K/ 63mW/1% R2 1 603 100K/ 63mW/1% 1 603 1.0M/ 63mW/5% R3 603 20Ohms/63mV/1% R4-R9 6 Mill-Max 0300-115-01-4727100 .042 Dia Test Point Female Pin TP Ref. Des. Vendor Sipex 978-667-8700 Sipex 978-667-8700 TDK 847-803-6100 TDK 847-803-6100 800-Digi-Key 800-Digi-Key 800-Digi-Key 800-Digi-Key 800-Digi-Key ORDERING INFORMATION Model Temperature Range Package Type SP6683UEB ............................. -40°C to +85°C...................SP6683 Evaluation Board SP6683ER.....................................-40°C to +85°C...................................... 10-pin DFN 5