DC974A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 974 HIGH VOLTAGE PROGRAMMABLE FREQUENCY STEP-DOWN CONVERTER LT3844 DESCRIPTION Demonstration Circuit 974 is a 100kHz 500kHz pro- circuit can increase the overall efficiency by reducing the grammable frequency, high voltage, current-mode power lost in the LT3844. The demonstration board has DC/DC step-down converter featuring the LT3844. The also been layed out with the option for a second switch- operating frequency can be synchronized up to 600kHz. ing MOSFET to facilitate higher output currents. The cir- cuit design can be modified for a Boost converter con- The board operates from a Vin range of 15V 60V and figuration. outputs 12Vout 4.2A (50W). A soft-start feature con- trols the output voltage slew rate at start-up, reducing This board is suitable for a wide range of Industrial con- current surges and voltage overshoots. The Burst Mode trol and automotive applications. of operation that improves the efficiency at light loads Note: Its best to Ground the SYNC pin if the SYNC func- can be enabled with a jumper. tion is not being used. An Optional Boost Bias circuit is provided on the bottom Design files for this circuit board are available. Call side of the board for back-driving the LT3844 internal the LTC factory. regulator from the output voltage. Customers might want to use this optional circuit with modified applica- tions that have relatively high input voltages and low (~ 5V) output voltages. In such applications, the optional Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Vin Input Voltage Range 15V 60Vin 48Vin, 0.1Aout 76.5% Efficiency 48Vin, 1.0Aout 79.5% 48Vin, 4.2Aout 87.5% Switching Frequency 100kHz 600kHz.. Output Voltage 0 4.2Aout 12V Vout ripple pp ~ 75mV 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 974 HIGH VOLTAGE PROGRAMMABLE FREQUENCY STEP-DOWN CONVERTER QUICK START PROCEDURE DC974 is easy to set up to evaluate the performance of 3. Connect a 0 - 60V Power Supply (or better) across the LT3844. Refer to Figure 1 for proper measurement the Vin/Gnd turrets. Typically its best to set the Cur- equipment setup and follow the procedure below: rent Limit of this Power Supply to its maximum set- ting. The power supply must be capable of providing the required start-up power. If using a bench power 1. Apply a 0 4.2A Load across the Vout/Gnd turrets. supply, a 60V/15A rated (or better) supply is recom- mended. Set Vin to 15V 60Vin for start-up. Make 2. Connect Voltmeters and Ammeters as shown in Fig- sure the SHDN/RUN jumper is in the RUN position. ure 1. 2