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Figure 1

   

Introduction

This is a reference design for a 6A step-down LED driver for a portable projector. The reference design is based on the MAX16821, a PWM HB LED driver. This circuit drives a single LED; three MAX16821 devices are required to drive RGB LEDs.

LED Driver Specifications:

• Input supply voltage (V_IN): 10V to 15V
• Output voltage (V_LED): 4.5V to 6V
• Output current (I_LED): 1.5A to 6A with analog control
• Analog control voltage: 1.1V to 2.8V for 1.5A to 6A
• Maximum LED on duty cycle: 50%
• Maximum LED current rise/fall times: < 1µs
• Maximum LED current ripple: < 15% at 6A
  
  

Inputs:

• V_IN (J1 and J2 VIN+, J3 and J4 GND): 10V to 15V input power supply
• On/Off (J8): leave open or drive +5V to enable the driver. Short for disabling the board.
• PWM input (J7): dimming PWM input. Connect a PWM signal with 3V to 5V amplitude. The source should provide rise/fall times less than 500ns with a 300pF load so that the PWM input can drive Q1 and Q7. As output can rise/fall within 1µs, any PWM period three to four times higher than 1µs can be used.
• LED current control (J6): LED current adjust input. Apply 1.1V to 2.8V to adjust LED current from 1.5A to 5A.
  
  

Outputs:

• LED+ (J9, J10): connect anode of LED.
• LED- (J11, J12): connect cathode of LED.
• Inductor current output (J5): provides a signal proportional to the LED current. The voltage at OUTV will be 135x the voltage across R9.