DEMO MANUAL DC1998A LTC3892 60V, Low I Dual Output High Q Voltage Step-Down Converter Description Demonstration circuit 1998A is a high input voltage, high of 200kHz and can be adjusted to frequencies between efficiency synchronous dual output buck converter featur- 50kHz and 900kHz. ing the LTC 3892. The DC1998A has a wide input voltage The DC1998A is designed to support multiple footprints range of 6V to 60V. The output voltages are set to 5V and of input/output capacitors and inductors to accommodate 12V, however, the output voltage can be set almost as high a variety of applications. as the input voltage (99% V ), with certain modifica- IN The LTC3892 features an adjustable gate drive voltage. tions. This demo board is capable of delivering up to 8A The DC1998A is preset to provide a 10V gate drive voltage from the 5V output and up to 5A from the 12V output. (DRVCC) for the switching MOSFETs and has 7.5V/6.7V The DC1998A supports three operation modes: forced rising/falling undervoltage lockout (UVLO) thresholds. continuous mode, pulse-skipping and Burst Mode op- In addition, the LTC3892 features a continuously adjust- eration. Forced continuous mode, reduces output voltage able gate drive voltage (5V to 10V) and selectable UVLO ripple and yields a low noise switching spectrum. Burst thresholds that allow the use and optimization of both Mode operation employs a variable frequency switching logic-level and standard threshold MOSFETs. See the algorithm that minimizes the no-load input quiescent cur- LTC3892 data sheet for a more complete description of rent and improves efficiency at light loads. its functionality and applications. The LTC3892 data sheet The DC1998A consumes less than 4A of quiescent current must be read in conjunction with this demo board manual during shutdown and below 0.15 mA no-load quiescent for demonstration circuit 1998A. current when in Burst Mode operation with an input Design files for this circuit board are available at voltage above 14V. However, if Ch2 is in shutdown and DEMO MANUAL DC1998A Quick s p D Demonstration circuit 1998A is easy to set up to evaluate voltage should be regulating. Measure V , it should OUT1 the performance of the LTC3892. For proper measurement measure 5V 2% (do not apply more than the rated equipment configuration, set up the circuit according to maximum voltage of 60V to the board or the part the diagram in Figure 1. Before proceeding to test, insert may be damaged). Vary the V load, which should OUT1 shunts into JP2, JP3 (RUN1, 2) into OFF position, which not exceed 8A. Vary the input voltage from 6V to 55V. connects the RUN pins to ground (GND), and thus shuts V should measure 5V 2%. OUT1 down the outputs. Set jumper JP1 (MODE) into FC (forced 3. Turn on V of the circuit by inserting the shunt in OUT2 continuous mode) position. header JP3 (RUN2) into the ON position. The output NOTE: When measuring the input or output voltage ripple, voltage should be regulating. Measure V , it should OUT2 care must be taken to avoid a long ground lead on the measure 12V 2% (do not apply more than the rated oscilloscope probe. Measure the input or output voltage maximum voltage of 60V to the board or the part may ripple by touching the probe tip directly across the V or be damaged). Vary the V load, which should not IN OUT2 V and GND terminals. See Figure 2 for proper scope exceed 5A. Vary the input voltage from 16V to 55V. OUT probe technique. V should measure 12V 2%. OUT2 1. With the DC1998A set up according to the proper 4. Set output current to zero and move jumper JP1 (MODE) measurement and equipment in Figure 1, apply 20V at into BURST MODE position and measure V and OUT1 V . Measure V it should read 0V. If desired, one V . IN OUT OUT2 can measure the shutdown supply current at this point. 5. Set output current to zero and move jumper JP1 (MODE) The supply current will be approximately 5A, or less, into PLS SKIP position and measure V and V . OUT1 OUT2 in shutdown. 2. Turn on V of the circuit by inserting the shunt in OUT1 header JP2 (RUN1) into the ON position. The output dc1998afb 2 ure roce tart