SP7600EB MaxLinear

SP7600 Evaluation Board Manual FEATURES Wide Input Voltage Range 4.5V 29V 3 Amps Max Continuous Output Current Internal Compensation Input Feedforward Control improves Transient and Regulation 1200kHz Constant Frequency Operation Low 0.2V Reference Voltage High output setpoint accuracy of 2.5% PWM Dimming Capable Small SO8-EP Thermally Enhanced Package Lead Free, RoHS Compliant Package DESCRIPTION The SP7600 Evaluation Board is designed to help the user evaluate the performance of the SP7600 for use as a LED Driver. The evaluation board is a completely assembled and tested surface mount board which provides easy probe access points to all SP7600 inputs and outputs so that the user can quickly connect and measure electrical characteristics and waveforms. The Evaluation Board schematic diagram is shown in Figure 1. BOARD SCHEMATIC Figure 1.The SP7600 Evaluation Board Schematic Diagram Rev 12/06/07 SP7600 Evaluation Board Manual Copyright 2007 Exar Corporation USING THE EVALUATION BOARD 1) Powering Up the SP7600 Circuit The SP7600 Evaluation Board can be powered from a 4.5V to 29V power supply. Connect the power supply with short leads directly to the Vin and GND posts. 2) Setting the output current Externally connected LEDs need to be connected anode to the VOUT pin and cathode to the Vfb pin. Asmany as 6 series connected LEDs may be used, depending on the input voltage range available. The maximum output current is 3A but the user should take care not to exceed the maximum junction temperature, 125C. Up to 2A maximum is possible in almost all conditions. The board also has SMT pads available for LEDs to be mounted in the LED1 position for a Luxeon K2 LED, and LED2, LED3 and LED4 positions for Luxeon Rebel LEDs. The total output current of the SP7600 is controlled by the VFB pin voltage setpoint of 200mV. Use a resistor at RA to set the output current by the formula: Iout = Vfb/RA where RA is the parallel combination of Ra and any of the resistors Rb, Rc or Rd. If Ra, Rb, Rc and Rd are used then RA = 1/(1/Ra + 1/Rb + 1/Rc + 1/Rd) Standard SP7600EB Evaluation Board Example: Iout = Vfb/RA = 200mV/0.22ohm = 1A 3) Dimming The SP7600 can be pulse width modulated using a signal applied to the DIM post. The DIM signal connects to the VFB pin through a 1N4148 diode and will shutdown the SP7600 when DIM = H and turn- on the SP7600 when DIM = L. The DIM signal needs to be greater than 600mV minimum to turn-off the SP7600 and less than 200mV to fully turn-on the SP7600. It is recommended to use a signal with DIM = 1V or more for OFF and 0V for ON. The user should note that the logic is reversed relative many other PWM controlled LED drivers. In other words a logic level high at 20% duty cycle will result in approximately a 80% duty cycle for the LED. Recommended modulation frequencies are from 100Hz to 200Hz with 10 90% duty cycle, 500Hz with 10 80% duty cycle, and 1000Hz with 10 70% duty cycle. Figures 2 & 3 show the output response at the maximum PWM DIM signal of 1000Hz. See figure 4 for 100Hz to 1000Hz duty cycle response for two Luxeon K2 LEDs in parallel at 2A total current. 12/04/07 SP7600 Evaluation Board Manual 2007 Exar Corporation Page 2 of 5