DEMO CIRCUIT 9 8 6 LT3496EUFD Q UICK S TA RT G UIDE L T3 4 9 6 EUF D Trip le S te p -Do w n L ED Driv e r DESCRIPTION WARNING! Do not look directly at operating LED. This circuit produces light that can damage eyes. Demonstration circuit 986 is a Triple Step-Dow n LED Driver featuring the LT3496EU FD. The LT3496 is a triple output DC/DC converter designed to operate as current sources for driving high current LEDs. O n the demo board, the default current for each output channel is 500mA. Setting CTR L voltage to be less than 1V w ill control the current sense voltage to be one-tenth of CTR L voltage, therefore, reduce the LED current. The output current should not exceed the rated current of the LEDs used. The LED current thermal derating should be considered to protect the LEDs. The maximum voltage of an LED string the demo board can drive is limited by the duty cycle and the input voltage of the LT3496. The demo board default sw itching frequency is 2.1M H z. At this frequency, the maximum duty cycle is 70% (M IN ). Low er the sw itching frequency results in higher maximum duty cycle. PERF ORM A NCE SU M M A RY SYM BO L PVIN VIN VLED ILED FSW η POUT PWM D PAR AM ETER Pow er Input Supply * Chip Bias Input Supply ** O utput LED Voltage, per O utput O utput LED Current, per O utput Sw itching Frequency Conversion Efficiency M aximum Total O utput Pow er PWM Dimming R atio The maximum pow er input voltage (PVIN ) is 45V. As a result, each channel of the demo board can drive up to ~31V total LED voltage. Adjustable sw itching frequency allow s optimization of the efficiency and the external component size. At 2.1M H z, 93% efficiency can be achieved at 500mA w ith minimum solution size. Each of the three regulators on the demo board is independently operated. The PWM dimming feature of the LT3496 allow s True Color PWM dimming w ith the dimming ratio of 5000:1. Additional analog dimming is possible. The LT3476 datasheet gives complete description of the part, operation and application information. The datasheet must be read in conjunction w ith this quick start guide for w orking on or modifying the demo circuit 986. Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks ofLinear Technology Corporation. Specifications are at TA = 25°C CO N DITIO N S M IN TYP 3 PVIN = 45V, ILED = 500mA, Fsw =2.1M H z FADJ=VR EF ILED = 500mA, PVIN =33V, VIN =3.3V, 10 R ed LEDs ILED = 500mA PWM Frequency = 100H z, PVIN =33V, VIN =3.3V, 3 White LEDs at 300mA, 2.1M H z 485 1.9 500 2.1 93 M AX 45 5.5 31 515 2.3 45 U N ITS V V V mA M Hz % W 5000:1 * 45V is the absolute maximum rating ofthe LT3496. This rating should not be exceeded under any condition. ** VIN of the demo board is limited by the choice of the input capacitor. The LT3496 input range is 3V-30V w ith transient protection to 40V. 1 LT3496EUFD Q U ICK STA RT PROCEDU RE Demonstration circuit 986 is easy to set up to evaluate the performance of the LT3496EU FD. R efer to Figure 1 for proper measurement equipment setup and follow the procedure below : LED to the LEDn+. Connect the cathode of the last LED to the LEDn-. All three channels can operate simultaneously or individually. 5. Turn on PVIN pow er supply. 6. Turn on VIN pow er supply. 1. With pow er off, connect an input pow er supply to VIN and G N D. To achieve highest efficiency, a low voltage supply, such as 3.3V or 5V, is recommended. 2. With pow er off, connect a second input pow er supply to PVIN and G N D. The PVIN absolute maximum rating is 45V. 3. If an output channel n is not used, the PWM n should be tied to G N D. 4. With pow er off, connect as LED string to an output channel interested. Connect the anode of the first 2 7. Check for the proper LED current and LED string voltage. NOTE. Ifthere is no output, turn offthe pow er supplies. Check all connections. 8. O nce the proper output current/voltage are established, adjust the parameters w ithin the operating range and observe the output current regulation, efficiency and other parameters. 9. To observe PWM dimming, turn off all pow er supplies. Connect the PWM n to a pulse generator. Then repeat step 5 – 8. LT3496EUFD Figure 1. Proper M easurem ent Equipm ent Setup 3 LT3496EUFD 4