Linear Technology LT3437IFE Manuals

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1232 HIGH VOLTAGE 500mA 200kHz BUCK CONVERTER WITH BURST MODE 1 LT3437IFE DESCRIPTION Demonstration Circuit 1232 is a high voltage 500mA 200kHz buck converter with burst mode featuring the LT®3437IFE. The board is optimized for 3.3V output at up to 400mA load current for a steady state input voltage range of 3.7V to 60V* with input transients up to 80V. *Minimum on-time restrictions and 3.3V output may limit the steady state maximum input voltage to 42V before pulse skipping occurs. Up to 60V DC input is allowable for the LT3437, but with higher output voltages than 3.3V. 80V input is allow- able for a short transient regardless of output voltage. With its wide input voltage range, 500mA internal power switch, 100uA supply current (at input volt- ages above 14V), 200kHz switching frequency and thermally enhanced package, the LT3437IFE is a very versatile and powerful IC for DC/DC converters that require compact space, high efficiency at both heavy and light loads and high input voltage. The LT3437 200kHz switching frequency allows all of the components to be small, surface mount devices. Synchronization with an external clock of up to 700kHz is possible. The current-mode control topol- ogy creates fast transient response and good loop stability with a minimum number of external compo- nents. The low resistance internal power switch (0.8Ω) achieves high efficiencies of up to 81%. The shutdown pin can be used to program undervoltage lockout or place the part in micropower shutdown, reducing supply current to less than 1µA. Burst Mode™ reduces zero load current to under 100µA at most input voltages while maintaining a regulated output. Burst Mode can be defeated or enabled by setting the Burst Mode jumper position. When Burst Mode is defeated, the IC runs at constant frequency without skipping pulses at light load. This provides low output ripple at light load, but the quiescent cur- rent (1-2mA) is higher than in burst mode. The soft start function reduces inrush current and output volt- age overshoot during startup. The LT3437 datasheet gives a complete description of the part, operation and applications information. The datasheet must be read in conjunction with this Quick Start Guide for demonstration circuit 1232. The LT3437IFE is assembled in a small 16-pin thermally enhanced package with exposed pad where proper board layout is essential for maximum thermal per- formance. See the datasheet section ‘Layout Consid- erations’. Design files for this circuit board are available. Call the LTC factory. LT is a trademark of Linear Technology Corporation QUICK START PROCEDURE Demonstration circuit 1232 is easy to set up to evalu- ate the performance of the LT3437. Refer to Figure 5 for proper measurement equipment setup and follow the procedure below: NOTE: The synchronization and shutdown functions are optional and their terminals can be left floating (disconnected) if they are not being used. NOTE: Do not hot-plug the input voltage terminal VIN. The absolute maximum voltage on VIN is 80V and hot-plugging a power supply through wire leads to the demonstration circuit can cause the voltage on the extremely low-ESR ceramic input capacitor to ring to twice its DC value. This is due to high currents in- stantaneously generated in the inductive supply leads from an input voltage step on the low-ESR ceramic input capacitor. A bulky higher-ESR capacitor and an additional inductive filter can be added to the circuit to dampen hot-plug transient ringing. See Application Note 88 for more details. In order to protect the IC, a