DC968A-A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 968A-A ISOLATED DC/DC POWER CONVERTER LT1952 DESCRIPTION Demonstration circuit 968A-A is isolated input to the converter efficiency. Therefore, narrow input high current output 1/8th Brick footprint con- voltage range will be more desirable. verter featuring the LT 1952 switching control- The DC968 circuit features soft-start which pre- ler. The DC968 converts isolated 36V to 75V vents output voltage overshoot on startup or input to 3.3V output and provides over 30A of when recovering from overload condition. output current. The converter operates at The DC968 has precise over-current protection 300kHz with efficiency greater than 91%. The circuit that allows for continuous operation un- DC968 can be easily modified to generate out- der short circuit conditions. The low power dis- put voltages in the range from 0.6V to 28V. The sipation under short circuit conditions insures output currents are limited by total output power high reliability even during short circuits. of up to 200W. The other available versions of DC968A are: The LT1952 can be synchronized to an external clock of up to 400kHz. Please refer to LT1952 DC968A-B 18-36Vin to 5V 20A data sheet for design details and applications DC968A-C 36-75Vin to 12V 12A information. DC968A-D 36-75Vin to 28V 4A Design files for this circuit board are avail- Also, the DC968 can be modified for other input able. Call the LTC factory. voltages like 8V-36V, 18V-75V, 44V-52V, and so LT is a trademark of Linear Technology Corporation on. The wider input voltage range will decrease Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage I = 0A to 30A 36V OUT Maximum Input Voltage I = 0A to 30A 75V OUT V V = 36V to 75V, I = 0A to 30A 3.3V 3% OUT IN OUT Typical Output Ripple V V = 36V to 75V, I = 0A to 30A 50mV OUT IN OUT PP Nominal Switching Frequency 300kHz QUICK START PROCEDURE Demonstration circuit 968 is easy to set up to NOTE: When measuring the input or output evaluate the performance of LT1952 circuit. Re- voltage ripple, care must be taken to avoid a fer to Figure 1 for proper measurement long ground lead on the oscilloscope probe. equipment setup and follow the procedure be- Measure the input or output voltage ripple by low: touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2. for proper scope probe technique. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 968A-A ISOLATED DC/DC POWER CONVERTER 1. With power off, connect the input power sup- 4. Once the proper output voltage is estab- ply to Vin and GND. Make sure that the input lished, adjust the load within the operating power supply has sufficient current rating at range and observe the output voltage regula- minimum input voltage for the required output tion, ripple voltage, efficiency and other pa- load. rameters. 2. Turn on the power at the input. 5. The DC968 is equipped with an output ca- pacitor CSYS (470uF) that approximates NOTE: Make sure that the input voltage does typical system rail capacitance. If system not exceed 75V. board already has capacitance of similar 3. Check for the proper output voltage. value CSYS can be removed. Vout = 3.3V. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. Figure 1. Proper Measurement Equipment Setup 2