QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 614 60V 3A 200KHZ STEP-DOWN CONVERTER WITH BURST MODE LT3434 DESCRIPTION Demonstration circuit 614 is a monolithic step-down to under 100A at most input voltages while main- DC/DC switching converter featuring the LT 3434. taining a regulated output. A power good comparator The board is optimized for 3.3V output at up to 2A and a timing delay can be used for additional system load current for a steady state input voltage range of diagnostics and sequencing. The soft start function 4V to about 42V* with input transients up to 60V . reduces inrush current at soft start and output volt- Minimum on-time restrictions and 3.3V output may age overshoot. An optional Power Good Feedback limit the steady state maximum input voltage to 42V output terminal can be used to monitor or control before pulse skipping occurs. With its wide input power good feedback externally. voltage range, 3A internal power switch, 100A sup- The LT3434 datasheet gives a complete description of ply current (at input voltages above 14V), 200kHz the part, operation and applications information. The switching frequency and thermally enhanced pack- datasheet must be read in conjunction with this Quick age, the LT3434 is a very versatile and powerful IC for Start Guide for demonstration circuit 614. In particu- DC/DC converters that require compact space, high lar, the datasheet section on Thermal Calculations is efficiency at both heavy and light loads and high input important for estimating whether a given applications voltage. combination of input voltage, load current and fre- The LT3434 200kHz switching frequency allows all of quency will cause the LT3434 to exceed its absolute the components to be small, surface mount devices. maximum rated junction temperature. The LT3434 is Synchronization with an external clock of up to assembled in a small 16-pin thermally enhanced 700kHz is possible. The current-mode control topol- package with exposed pad where proper board layout ogy creates fast transient response and good loop is essential for maximum thermal performance. See stability with a minimum number of external compo- the datasheet section Layout Considerations. nents. The low resistance internal power switch Design files for this circuit board are available. Call (0.1 ) achieves high efficiencies of up to 80%. The the LTC factory. shutdown pin can be used to program undervoltage LT is a trademark of Linear Technology Corporation lockout or place the part in micropower shutdown, reducing supply current to less than 1A by driving the pin low. Burst Mode reduces zero load current QUICK START PROCEDURE Demonstration circuit 614 is easy to set up to evalu- be left floating (disconnected) if their functions are ate the performance of the LT3434. Refer to Figure 1 not being used. for proper measurement equipment setup and follow NOTE: Do not hot-plug the input voltage terminal VIN. the procedure below: The absolute maximum voltage on VIN is 60V and NOTE: Make sure that the input voltage does not ex- hot-plugging a power supply through wire leads to ceed 60V. the demonstration circuit can cause the voltage on the extremely low-ESR ceramic input capacitor to ring NOTE: The synchronization, shutdown, and power to twice its DC value. This is due to high currents in- good functions are optional and their terminals can stantaneously generated in the inductive supply leads 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 614 60V 3A 200KHZ STEP-DOWN CONVERTER WITH BURST MODE from an input voltage step on the low-ESR ceramic NOTE: If the output voltage is too low, temporarily input capacitor. A bulky higher-ESR capacitor, and an disconnect the load to make sure that the load is additional inductive filter can be added to the circuit not set too high. to dampen hot-plug transient ringing. See Application 2. Once the proper output voltages are established, Note 88 for more details. In order to protect the IC, a adjust the load within the operating range and ob- transient voltage suppressor diode can be added be- serve the output voltage regulation, ripple voltage, tween VIN and GND terminals to absorb any high efficiency and other parameters. voltage transient ringing that may occur due to hot- plugging. NOTE: Connect the power supply (with power off), load, and meters as shown in Figure 1. 1. After all connections are made, turn on input power and verify that the output voltage is 3.3V. Figure 1. Proper Measurement Equipment Setup 2