DC909A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 909 MULTI-LED CAMERA LIGHT CHARGE PUMP LTC3217 WARNING: The LEDs on this demo board produce very bright light. Do not look directly at LEDs when power is applied. Serious eye damage may occur. DESCRIPTION play may be adjusted by pressing the EN1, EN2, or Demonstration Circuit 909 is a Multi-LED Camera both buttons. The intensity may be further controlled Light Charge Pump featuring the LTC3217. by pulse width modulating EN2. The LTC3217 is a low noise charge pump designed to An ultra-low dropout current source maintains accu- power four high current LEDs. The LTC3217 requires rate LED current at very low I voltages. Automatic only four small ceramic capacitors plus two resistors LED to form a complete LED power supply and a current mode switching optimizes efficiency by monitoring controller. the voltage across the LED current source and switching modes only when ILED dropout is detected. Built-in soft-start circuitry prevents excessive inrush current during start-up and mode changes. High switching frequency enables the use of small external Design files for this circuit board are available. Call capacitors. Independent high and low current set- the LTC factory. tings are programmed by two external resistors. , LTC and LT are registered trademarks of Linear Technology Corporation. Shutdown mode and current output levels are se- lected via two logic inputs. The intensity of the dis- QUICK START PROCEDURE The DC909 is only intended for continuous operation at a current level of 300mA or less. As a result, the higher current settings should only be used for periods less than 10 seconds. The use of the Demo Circuit 909 requires a DC TABLE 1. Enable Pin Truth Table power supply capable of supplying at least 1A of EN2 EN1 I LED current. 0 0 0 1. Connect the DC power supply across the Vin 0 1 25mA and GND terminals of the board as shown in 1 0 75mA Figure 1. For best stability and noise perform- 1 1 100mA ance, use the shortest leads possible between the board and the supply. Capacitor C5 has The ISET resistors (R1 and R2) may be re- been placed on the board to assist in offsetting placed with different values to achieve other the effects of long power supply leads. current levels. The resistance required 2. Set the output of the supply to a voltage be- (RSET W ) to achieve a desired LED current tween 2.9V and 4.5V. (I A ) may be approximately determined by LED the following equation: 3. Pressing either EN1, EN2, or both of the enable buttons will enable the part and illuminate the RSET=488/I LED LED. The individual LED current settings for the Pulse width modulation may be performed on set enable pins are shown in the table 1. demo circuit 909 by connecting a pulse genera- 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 909 MULTI-LED CAMERA LIGHT CHARGE PUMP LTC3217 WARNING: The LEDs on this demo board produce very bright light. Do not look directly at LEDs when power is applied. Serious eye damage may occur. tor between the EN2 and GND terminals. Set the high pulse voltage to no greater than VIN+0.3V and the low pulse voltage to 0V. The pulse may be varied from a minimum pulse width of 50us and a maximum off time of 1ms to a 100% duty cycle. See the LTC3217 data sheet for more information on this. Figure 1. Proper Measurement Equipment Setup for DC909 2