DEMO MANUAL DC2447A LTC3896 High Voltage, Low I , Synchronous Q Inverting DC/DC Controller Description Demonstration circuit 2447A is a high voltage, high ef- driver to drive the gate of an external N-channel MOSFET ficiency synchronous inverting converter featuring the which acts as a linear regulator to power the IC. LTC 3896. This demo board has a wide input voltage The LTC3896 can support a wide output voltage range range from 7V to 72V and produces a 12V output voltage. from 0.8V to 60V. However, the voltage difference The DC2447A is capable of delivering up to 5A of output between the input voltage and output voltage should not current. Note that the thermal stress increases at lower exceed the maximum voltage of the switching semicon- input voltages due to increased input current. ductors (100V for DC2447A) and shown by the equation V +V <V . OUT IN DS This demo board supports four operation modes consist- ing of fixed-frequency modulation, pulse skipping, Burst The DC2447A is set to provide a 10V gate drive voltage Mode Operation (default mode) and adjustable Burst Mode (DRV ) for the switching MOSFETs. It has an UVLO of CC operation. During a light load condition, fixed-frequency 7.5V rising and 6.7V falling. However, the gate drive volt- mode reduces output voltage ripple and yields the lowest age and UVLO voltages can be adjusted lowered. See the noise spectrum. Burst mode operation employs a variable LTC3896 data sheet for details. frequency algorithm that minimizes the no-load quiescent The DC2447A was designed to support multiple footprints current and improves light load efficiency. of input and output capacitors, and inductors to accom- The DC2447A consumes less than 12A of current in modate a variety of applications. shutdown and consumes only 100A of quiescent current The LTC3896 data sheet gives a complete description of when the output is in regulation, unloaded and configured the part, contains operating and application information, for Burst Mode operation which helps extend the run-time and must be read in conjunction with this data sheet. in battery powered applications. This demo board oper- Design files for this circuit board are available at ates at a 300kHz switching frequency and can easily be DEMO MANUAL DC2447A Quick s tart p D Demonstration circuit 2447A is easy to set up to evaluate voltage should be regulating. Measure VOUT and it the performance of the LTC3896. For proper measurement should measure 12.0V 2% (Do not apply more than equipment configuration, set up the circuit according to the maximum voltage of 72V to the board or the part the diagram in Figure 1. Before proceeding to test, insert may be damaged). Vary the VOUT load, which should shunt into JP1 (RUN) into OFF position, which connects not exceed 5A. Vary the input voltage from 7V to 72V, the RUN pin to ground (GND) and shuts down the output. the VOUT, it should measure 12.0V 2%. Set jumper JP2 (MODE) into the FCM (Forced Continuous 3. Set output current to zero and move jumper JP2 (MODE) Conduction Mode) position. into Burst Default position and measure VOUT. It NOTE: When measuring the input or output voltage ripple, should be 12.0V 2%. Vary the VOUT load, which care must be taken to avoid a long ground lead on the should not exceed 5A. Vary the input voltage from 7V oscilloscope probe. Measure the input or output voltage to 72V, the VOUT, it should measure 12.0V 2%. ripple by touching the probe tip directly across the V or IN 4. Set output current to zero and move jumper JP2 (MODE) VOUT and GND terminals. See Figure 2 for proper scope into Pulse Skip position and measure VOUT. It should probe technique. be 12.0V 2%. Vary the VOUT load, which should 1. With the DC2447A set up according to the proper not exceed 5A. Vary the input voltage from 7V to 72V, measurement and equipment in Figure 1, apply 16V the VOUT, it should measure 12.0V 2%. at V . Measure VOUT it should read 0V. If desired, IN DC2447A supports synchronization to external clock one can measure the shutdown supply current at this referenced to input GND use PLLIN terminal for point. The supply current will be approximately 12A, synchronization. PGOOD signal also referenced to or less, in shutdown. input GND. To activate PGOOD functionality, connect 2. Turn on VOUT of the circuit by inserting the shunt external voltage source to terminals V PGOOD and in header JP1 (RUN) into the ON position. The output GND. DC2447A also supports EXTV function, however CC EXTV is referenced to VOUT. CC 80V DC/DC + POWER SUPPLY + LOAD DC2447 F01 Figure 1. Proper Measurement Equipment Setup dc2447af 2 ure roce