SP6682UEB

SP6682UEB Evaluation Board Manual Low-profile, inductor-less White LED Driver Automatic Transition from X1.5 to X2 mode for highest efficiency PWM dimming control >100mA output current @ 2.8V input Less than 1.5uA shutdown current 10 pin MSOP SP6682 Evaluation Board Schematics LEDA C2 2.2uF 1 J1 SP6682 Vout C1P Vin Vmode FB C2P C1N GND C2N EN/PWM 10 9 8 7 6 C5 2.2uF J2 C4 2.2uF C6 0.1uF D1 D2 LED D3 LED D4 LED LED Vin: 2.7-4.2V R1 158K C1 2.2uF R2 100K 2 3 4 5 LEDK Open C3 Rfb 5.1 R6 20 R7 20 R8 20 R9 20 0.1uF Regulate 60mA total output current VMODE R3 1.0M GND ENABLE/PWM USING THE EVALUATION BOARD 1) Powering Up the SP6682 Circuit The SP6682 Evaluation Board c an 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 Jumpers and posts There are two jumpers (J1 and J2) and seven posts on the Evaluation Board. The output of SP6682 is open as the default. If the customer has discrete white LEDs, the 5.1 ohm “RFB” resistor needs to be removed from the board first. Then the discrete white LEDs should be soldered to the D1-D4 positions and bias resistors should be soldered to the R6-R9 positions. For selection of the bias resistors, please refer to 3). If the customer has a white LED module, they can plug the two terminals of the module to the “LEDA” and “LEDK” posts. Note that a 5.1ohm bias resistor was put on the “RFB” position to regulate a 60mA output current as the default. If the output current is not 60mA in the customer’s application, an appropriate bias resistor should be selected to replace the 5.1ohm resistor. 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) (1) R FB = VFB I LED _ Total = 0.3V 60mA = 5Ω Where ILED_Total is the total output current. R 6−9 = VFB I LED _ D1− 4 = 0.3V 15mA = 20Ω (2) Where ILED_D1-D4 is the operating current of D1-D4. 4) Selecting of Vmode and Divider Resistor SP6682 can automatically change from X1.5 mode to X2 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 SP6682 will work in X1.5 mode, when the input voltage drops to Vth threshold voltage, it will switch to X2 mode automatically. The Vth threshold voltage for mode change can be calculated by (3) Vth = (VF + 0.3 + m ⋅ I LED ⋅ R out ) 1.5 (3) Where VF and m are the forward voltage and number of the white LEDs, Rout is the output resistance of the SP6682. The equation for the voltage divider R1 and R2 with Vmode=1.25V is: Vth = 1.25V ⋅ (1 + R1 R 2 ) (4) which can be expressed as R1: R 1 = (Vth 1.25 − 1)⋅ R 2 (5) For the typical Sp6682 Evaluation Board, using VF =3.6V, m=4, I L E D = 1 5 m A , Rout=16ohms, the Vth will be 3.24V. Select R2=100kohm, then R1=158kohm. 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 2.2uF ceramic capacitors. Input and output ripple could be further reduced by using larger low ESR input and output capacitor. 6) Brightness Control Dimming control can 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 recommended frequency range of the PWM signal is from 60Hz to 200Hz. A repetition rate of at least 60Hz is required to prevent flicker. 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 ripples when the input voltage is 2.7V (SP6682 is in X2 mode), Figure 2 shows the input and output voltage ripple when the input voltage is 3.3V (SP6682 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. X2 Mode Voltage Ripple @ 2.7V Figure 2. X1.5 Mode Voltage Ripple @ 3.3V 90 80 70 Efficiency (%) 60 50 40 30 20 10 0 2.7 3 3.3 3.6 3.9 4.2 Battery Voltage (V) Figure 3. Efficiency vs Input Voltage Evaluation Board Layout FIGURE 4: SP6682 COMPONENT PLACEMENT FIGURE 5: SP6682 PC LAYOUT TOP SIDE FIGURE 6: SP6682 PC LAYOUT BOTTOM SIDE TABLE1: SP6682 BILL OF MATERIALS SP6682 Evaluation Board List of Materials Qty. Manufacturer Part Number Layout Size Component LxWxH 1 Sipex Corp. 146-6483-01 1"x1.5" SP6682 Eval PC Board U1 1 Sipex Corp. SP6682EU MSOP-10 10 PIN High Efficiency Charge Pump Regulator C1,C2,C4,C5 4 TDK Corp TDKC2012X5R1A225K 805 2.2uF/10V/X5R/10% Ceramic C3,C6 2 TDK Corp TDKC1608X7R1E104K 603 0.1uF/10V/X7R/10% Ceramic D1-D4 Open R1 1 603 154K/ 63mW/1% R2 1 603 100K/ 63mW/1% R3 1 603 1.0M/ 63mW/5% R6-R9 603 Open Rfb 1 603 5.1 Ohm/63mW/5% TP 7 Mill-Max 0300-115-01-4727100 .042 Dia Test Point Female Pin J1,J2 1 Sullins PTC36SAAN .23x.12 2-Pin Header 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 800-Digi-Key