DEMO MANUAL DC1511A LTM8042, LTM8042-1 1A, 350mA Module LED Driver DESCRIPTION Demonstration circuits 1511A-A and 1511A-B feature the P-channel MOSFET that is necessary for PWM dimming. LTM 8042 and the LTM8042-1, which are respectively com- The RADJ pin/terminal voltage controls the output current. plete 1A and 350mA Module LED drivers. The demonstra- Voltage is either applied directly to the terminal or set by a divider that includes resistor RADJ and the LTM8042s tion circuits are assembled as boost topologies, accepting internal 2V reference and divider resistor. Open LED over- an input voltage from 3V to 30V and supporting an output voltage protection is also included. Consult the LTM8042/ up to 32V (see Table 1). The default switching frequency is LTM8042-1 datasheet for further information on how to 600kHz for DC1511A-A and 950kHz for DC1511A-B, but properly use or modify the circuit. can be adjusted by changing the value of RT. Design files for this circuit board are available at DC1511A is easily configured to support other features, DEMO MANUAL DC1511A QUICK START PROCEDURE Demonstration circuit 1511A is easy to set up to evaluate To use the DC1511A in a buck-boost mode topology, make the performance of the LTM8042EV/LTM8042EV-1. Refer the following modifications to the procedure. to Figure 1 for the proper measurement equipment set- 1. At step 1, connect the cathode of the LED string to up and follow the procedure below for a boost (step-up) the BSTIN/BKLED terminal. The LED forward voltage topology. may be greater than the input voltage for buck-boost 1. Connect a string of LEDs with forward voltage 32V or mode. + less, but greater than the input voltage, to the LED 2. At step 2, refer to the datasheet buck-boost mode (LED anode) and GND (LED cathode) terminals on the applications information table. Preset the DC input PCB, as shown in Figure 1. voltage within the recommended input voltage range 2. With the power off, connect the input power supply for the appropriate forward voltage and current of the to the BSTIN/BKLED and GND terminals within the LED string. ranges specified in Table 1. Preset the DC input volt - To use the DC1511A in a buck mode (step-down) topology, age within the recommended input voltage range for make the following modifications to the procedure. the appropriate forward voltage of the LED string. 1. Remove the 0 jumper at location R8 and instead Table 1. Input Range for Proper Operation (Refer to the install the jumper at location R4. This shorts the V , CC LTM8042/LTM8042-1 Datasheet) TGEN and RUN pins/terminals to BSTOUT/BKIN DC1511A-A LTM8042 DC1511A-B LTM8042-1 instead of BSTIN/BKLED . INPUT VOLTAGE LED STRING INPUT VOLTAGE LED STRING (BSTIN/BKLED VOLTAGE (BSTIN/BKLED VOLTAGE 2. At step 1, connect the cathode of the LED string to + + TO GND) (LED TO GND) TO GND) (LED TO GND) the BSTIN/BKLED terminal. The LED forward voltage 5V to 5.8V 6V to 9V 3.2V to 7V 8V to 12V must be less than the input voltage for buck mode. 6.4V to 7.7V 8V to 12V 4.1V to 10V 12V to 16V 3. At step 2, connect the input power supply to BSTOUT/ 8.6V to 11.3V 12V to 16V 4.8V to 12.3V 15V to 21V BKIN and GND. Refer to the datasheet buck mode 11.3V to 13.8V 15V to 21V 5.8V to 15V 18V to 24V applications information table. Preset the DC input 13.4V to 16.5V 18V to 24V 8.5V to 20.8V 24V to 32V voltage within the recommended input voltage range 20.5V to 22.5V 24V to 32V for the appropriate forward voltage and current of the LED string. 3. Connect the PWM terminal. If PWM is not used, con- nect PWM to a 5V source or to the input voltage. PWM must be pulled high or the LEDs will remain off. 4. Turn the input power supply on. 5. Observe the LED string running at the programmed LED current. 6. For PWM dimming, connect a PWM 100Hz or higher frequency signal to the PWM terminal. 7. Observe the reduction of brightness in the LED string by varying the duty cycle of the PWM signal. dc1511af 2