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SP6648LED Evaluation Board Manual
Easy evaluation for SP6648 performance of driving 1W LumiLED. Plug & Light ON Self Protection Programmable Inductor Peak Current High Efficiency: up to 94% SOIC Package & SMT components for small, low profile Power Supply
DESCRIPTION AND BOARD SCHEMATIC The SP6648LED Evaluation Board is designed to help the user evaluate the performance of the SP6648 for use as a dual cell input to drive a 1W LumiLED. The evaluation board is a completely assembled and tested surface mount board which provides easy probe access points to all SP6648 inputs and outputs so that the user can quickly connect and measure electrical characteristics and waveforms.
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USING THE EVALUATION BOARD 1) Powering Up the SP6648LED Circuit The SP6648LED Evaluation Board can be powered from inputs from a +1.8V to +3.2V power supply or from 2 alkaline cells. Connect with short leads directly to the "VIN" and "GND" posts. Plug the 1W LumiLED between the "VOUT" and "REF" posts. Unlike other boost regulators, the part has self-protection feature. It will not be damaged when the output is open as long as there is a low resistance from FB to GND. As shown in Figures 1 and 2, if the board is powered up before the LumiLED is plugged in, the circuit will bring the Feedback pin to 0V and the SP6648 has a feature to set the output voltage to be 3.3V. Once the LumiLED is plugged in, the Feedback pin will go up to 1.25V and begin to regulate. The output voltage will go from 3.3V to 3.68V (=VF+0.61V) accordingly (as shown in Fig. 1), where VF is the forward voltage of the LumiLED. When the LumiLED is open, the Feedback pin voltage will go to 0V and the output voltage will go to 3.3V which will protect the part (as shown in Fig 2).
VOUT
VOUT
VREF
VREF
Fig 1. Plug in the LumiLED
Fig. 2. Unplug the LumiLED
2) Using the J1 Jumper: Enabling the SP6648 Output and using the Shutdown Mode The SP6648 output will be enabled if the J1 Jumper is in the top or pin 1 to 2 position. If J1 is in the pin 2 to 3 position, the Shutdown pin is brought to GND, which puts the SP6648 in the low quiescent Shutdown Mode. 3) Selecting the Bias Resistor In the white LEDs application, the SP6648 is generally programmed as a current source. The bias resistor is used to set the operating current of the white LED as equation V R b = REF IF where VREF is around 0.61V, IF is the operating current of the Lumiled. To set the operating current to be about 350mA, Rb is selected as 1.8 Ohm as shown in the schematic. 4) Vout Programming The SP6648 can be programmed as either a voltage source or a current source. To program the SP6648 as voltage source, the SP6648 requires 2 feedback resistors R6 & R7 to control the output voltage. To set Vout in the voltage mode, use the equation: V R 6 = out - 1 * R 7 0.61
5) Using the Rlim Function The peak inductor current, IPEAK, is programmed externally by the R LIM resistor connected between the RLIM pin and GND. The peak inductor current is defined by: IPEAK = 1400/RLIM The SP6648 datasheet specifications for RLIM give a range of 1.87K to 4K ohms. Using the IPEAK equation above gives an IPEAK range of 350 to 750mA. The saturation current specified for the inductor needs to be greater then the peak current to avoid saturating the inductor, which would result in a loss in efficiency and could damage the inductor. The SP6648 evaluation board uses a Rlim value of 1.87K for an Ipeak = 750mA to allow the circuit to deliver up to 180mA for 1.3V input and 400mA for 2.6V input. Other values could be selected using the above relationships. 6) Using the LBON - Low Battery Output Function The SP6648 will regulate the output current until the input battery is completely discharged. To provide an early low battery warning, the Low Battery Output function of the SP6648 switching regulator can be used. LBON is programmed externally by the R 1 and R2 resistor divider connected between VIN, the LBI input pin and GND. When the LBI comparator falling threshold of 0.61V is reached, D1 switches on, indicating low battery condition. Low battery detect trip point can be calculated by the following formula:
VLOWBAT = 0.61 R1 + R 2 R2
The SP6648 evaluation board R1 & R2 resistors have been set to trip for a falling battery threshold of about 2.0V. Using this relationship, other low battery threshold values can be set by the user. 7) Brightness Control One approach to control LED brightness is to apply a PWM signal to the SHDN input of the SP6648. In this case, the output current will be equal to the product of 350mA and the average duty cycle at the SHDN pin. An additional 10K potentiometer (R5) may also be used for dimming LED. LED current is varied by the potentiometer between almost zero and full 350mA. POWER SUPPLY DATA For the standard evaluation board, The efficiency curve is shown in the figure below.
100 95 90 Efficiency (%) 85 80 75 70 65 60 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 Battery Voltage (V)
Fig.3 Efficiency curve of the SP6648LED evaluation board
EVALUATION BOARD LAYOUT
FIGURE 1: SP6648LEDEB COMPONENT PLACEMENT
FIGURE 2: SP6648LEDEB PC LAYOUT TOP SIDE
FIGURE 3: SP6648LEDEB PC LAYOUT BOTTOM SIDE
TABLE1: SP6648LEDEB LIST OF MATERIALS
Ref. Des. SP6648LED Evaluation Board List of Materials Qty. Manufacturer Part Number Layout Size Component LxWxH 1 Sipex Corp. 146-6510-00 1"x2.14" SP6648LED Eval PC Board 1 Sipex Corp. SP6648EU MSOP-10 10 PIN High Efficiency Boost Regulato 2 TDK Corp TDKC3216X5R0J106K 1206 10uF/6.3V/X5R/10% Ceramic 1 TDK Corp TDKC1608X5R0J105K 603 1uF/6.3V/X5R/10% Ceramic 1 Sumida CD43-100 4x4.5x3.2mm 10uH, 1.04A, 0.18 Ohm, SM inductor 1 Rohm MCR03EZPFX1003 603 100K 1/16W 1% 0603 SM 1 Rohm MCR03EZPFX4322 603 43.2K 1/16W 1% 0603 SM 1 Rohm MCR03EZPFX1501 603 Open 1 Rohm MCR03EZPFX1622 603 16.2K 1/16W 1% 0603 SM 1 Rohm MVR32HXBRN103 3x3.6x1.3mm 0 Ohm between pin 1 and pin 3 1 Rohm Open 1 Rohm Open 1 Rohm MCR03EZPFX1871 603 1.87K 1/16W 1% 0603 SM 1 Rohm MCR25JZHJ1R8 1210 1.8 Ohm 1/4W 5% 1210 SM 1 Stanley BR1101W-TR 3x1.5x1.5mm Open 1 Diode Inc. 1N4148W-7 SOD-123 75V 150mA SM Diode 7 Mill-Max 0300-115-01-4701100 .042 Dia Test Point Female Pin 1 Sullins PTC36SAAN .23x.12 2-Pin Header Vendor Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662 Future 888-589-3662
U1 C1,C3 C2 L1 R1 R2 R3 R4 R5 R6 R7 Rlim Rb D1 D2 TP J1
ORDERING INFORMATION Model Temperature Range Package Type
SP6648LEDEB............................. -40C to +85C...................SP6648LED Evaluation Board SP6648EU.....................................-40C to +85C...................................... 10-pin SOIC

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