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SP7615 Evaluation Board Manual
Cost Effective LED driver Constant current output ideal for Driving LED strings Four Channel LED Driver provides matched LED current Current adjusted via an external resistor PWM dimming possible by using either the ENABLE or the ISET pin Small 2mm x 3mm DFN power package Outputs can be connected in parallel to increase drive Constant current for wide cathode voltage range (0.5V to 16V) Highly integrated design, minimal components Thermal shutdown protects the driver
DESCRIPTION AND BOARD SCHEMATIC The SP7615 Evaluation Board is designed to help the user evaluate the performance of the SP7615 for use as a single Luxeon 1W LED Driver or 4 LED Driver with matched currents. The evaluation board is a completely assembled and tested surface mount board which provides easy probe access points to all SP7615 inputs and outputs so that the user can quickly connect and measure electrical characteristics and waveforms. Two versions of the Evaluation Board schematic diagram are shown at Figure 1 and Figure 2. The SP7615 is a linear constant current driver designed to drive multiple LEDs in series from a high input voltage rail or single high current LED. The driver acts as a high current matched four channel current source ensuring constant LED current for a range of input voltage. The SP7615 allows implementing the lowest cost LED driver for a variety of applications. Internal circuitry maintains the pre-set constant current output for a wide voltage range at the LED outputs (LED1, 2, 3, 4). LED current can be adjusted up to 125mA per string with an external resistor R1. The dimming can be achieved by controlling the ISET input or by feeding a PWM signal to the EN pin. Fast EN turn-on and turn-off time allows for very fast PWM dimming frequencies completely eliminating flickering. The built-in thermal protection automatically adjusts LED current to prevent overheating.
Figure 1. SP7615 Evaluation board with a single Luxeon 1W LED
Rev Aug24-06
SP7615 Evaluation Board Manual
(c) 2006 Sipex Corporation
Figure 2. SP7615 Evaluation board with four LED with matched currents Capacitor C1 is a decoupling capacitor. Resistor R2 is used to turn device on at power on. The SP7615 has internal pull down resistor at EN input and will be in the Sleep Mode if EN pin isn't connected to Vin voltage. If EN pin isn't used for modulation, it may be connected to Vin voltage directly.
USING THE EVALUATION BOARD 1) Powering Up the SP7615 Circuit
The SP7615 Evaluation Board can be powered from a 4.5V power supply or from 3 alkaline cells. Connect 4.5V source pin with short lead directly to the "Vin" and -4.5V /GND pin to the "GND" posts.
2) Selecting the Bias Resistor
LED current can be adjusted up to 125mA per string with an external resistor R1. The R1 value may be determined as R1 = 1.26 * 1000/IOUT, kohm, where 1.26 is a typical ISET pin voltage, 1000 is a typical current multiplication ratio, and IOUT is a required one string current in mA.
3) Dimming
The device has an enable function that is designed for TTL level inputs. This input will also track the VCC pin so levels up to VCC are acceptable. The enable pin can also be used to control the LED brightness with a pulse width modulated control signal. Duty Cycle or PWM control of the LED current maintains constant LED color while brightness is changing. The SP7615 responds in less than 10s to PWM signals applied to this pin. To change LED brightness apply 70Hz - 1kHz PWM rectangle pulse TTL level to EN post in respect to GND. Logic one turns the device on and logic zero turns it off.
5.5 5 Voltage, V, Current x100mA 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 2.5 3 3.5 4 Vin Voltage, V Vdiode_f Vcat Iin x100mA Idiode x100mA Iquies x100mA 4.5 5 5.5
Graph 1. LED Forward Voltage (Vdiode_f), LED cathode voltage (Vcat), Evaluation Board Input Current (Iin), sum of LED Currents (Idiode), and Quiescent Current (Iquies) vs. Input Voltage at R1 = 10k
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Graph 2. LED Cathode Voltage (black curve) vs. 100 and 1000Hz PWM signal (blue) applied to EN pin
700 600 LED Current. mA 500 400 300 200 100 0 0 50 100 150 200 250 R1 Value, kohm
Graph 3. LED Current vs. resistor R1 value at Vin = 4.5V Table 1. LED Current vs. resistor R1 value at Vin = 4.5V R1, kohm LED Current. mA 6.34 651.2 11.8 377.8 24.9 198.2 49.9 100.9 75 65.63 100 49.01 205 23.8
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EVALUATION BOARD LAYOUT
Figure 3. SP7615 Evaluation Board Layout top and bottom side Table2. SP7615EB List of Materials Reference C1 D1* D2, D3, D4, D5* R1 R2 U1 Quantity 1 1 4 1 1 1 Value 1nF 10% Type 06033D102KAT2 LXHLMW1D SML-LX2832UWC-TR M11251031%P5 M11251031%P5 SP7615ER Manufacturer AVX Luxeon Vishay Vishay Vishay Sipex
10k 1% 10k 1%
* Board may contain only D1 or D2 - D5 depend on modification
ORDERING INFORMATION Model Temperature Range Package Type
SP7615EB............................... -40C to +85C.................... SP7615 Evaluation Board Configurable for 1 or 4 LED SP7615ER/TR..........................-40C to +85C................... 8-pin DFN (2 x 3 mm)
/TR = Tape and Reel Pack quantity is 3000 for DFN. Available in lead free packaging. To order add "-L" suffix to part number. Example: SP7615ER/TR = standard; SP7615ER-L/TR = lead free
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