DC1316A Analog Devices

DEMO CIRCUIT 1316 LT1913 QUICK START GUIDE LT1913EMSE 3.5A,25V Step-down Switching Regula- tor with SYNC Function DESCRIPTION Demonstration circuit 1316 is a monolithic step- RUN/SS pin can be used to set the part in micro- down DC/DC switching regulator featuring LT1913. power shutdown mode, reducing the supply cur- The LT1913 can be synchronized over a 250 KHz rent to less than 1uA. The RUN/SS pin can also be to 2 MHz range. The demo board is designed for used to program soft start. In this mode, the 5V output from a 6.5V to 25V input. The wide input RUN/SS pin is driven through an external RC filter range of the LT1913 allows a variety of input to create a voltage ramp on this pin. The soft start sources. The typical sources are automotive bat- function reduces the input current surge during teries, wall adaptors and industrial supplies. start-up. An optional EMC filter at the input is provided on The LT1913 datasheet gives a complete descrip- the bottom of the board, which greatly reduces the tion of the part, operation and application informa- conductive EMI noise at the input side. Customers tion. The datasheet must be read in conjunction can use this optional circuit by cutting the input with this quick start guide for demo circuit 1316. trace on the bottom of the board and install the Note: It is best to ground the SYNC pin if the components. The current mode control scheme SYNC function is not being used. creates fast transient response and good loop sta- Design files for this circuit board are available. bility. The gate drive of the internal switch is Call the LTC factory. boosted to a voltage that is higher than the Vin to ensure saturation of the switch. The LT1913s inte- , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and PowerPath are trademarks of Linear Technology Corporation. grated boost diode reduces the parts count. The o Performance Summary for Step-down Switching Regulator ( T = 25 C ) A PARAMETER FOR BUCK REGULATOR CONDITION VALUE Minimum Input Voltage 6.5V Maximum Input Voltage 25V Output Voltage V 5V +/- 4% OUT Maximum Output Current 3.5A Typical Switching Frequency 800kHz QUICK START PROCEDURE NOTE. When measuring the input or output voltage ripple, care Demonstration circuit 1316 is easy to set up to must be taken to avoid a long ground lead on the oscilloscope evaluate the performance of the LT1913. Refer to probe. Measure the input or output voltage ripple by touching the Figure 1 for proper measurement equipment setup probe tip directly across the Vin or Vout and GND terminals. See and follow the procedure below: Figure 2 for proper scope probe technique. 1 GND VIN L T1913 1. Place JP1 on the RUN position. 5. Once the proper output voltage is established, adjust the load within the operating range and 2. With power off, connect the input power supply observe the output voltage regulation, ripple to Vin and GND. voltage, efficiency and other parameters. 3. Turn on the power at the input. 6. An external clock can be added to the SYNC pin 4. Check for the proper output voltage. when SYNC function is used. See synchroniza- tion section in the datasheet for details. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. + A + + A V + + V + Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2 Load