DEMO MANUAL DC1999A LTC3111EDHD 15V, 1.5A Synchronous Buck-Boost DC/DC Converter DESCRIPTION Demonstration circuit 1999A is a fixed frequency syn- Typical demo board efficiency is shown in Figure 2 for chronous buck-boost converter with an extended input several loads. The demo board has the provision to set an and output range. The unique 4-switch, single inductor accurate run threshold. Consult the LTC3111data sheet for architecture provides low noise and seamless operation more information. The transient response of the converter from input voltages above, below, or equal to the output to a 100mA to 600mA transient at input voltages of 3.5V voltage. and 12V are presented in Figures 3 and 4. The LTC 3111 features selectable PWM or Burst Mode The LTC3111 data sheet has detailed information about operation, and an easily synchronizable oscillator. Jumper the operation, specifications, and applications of the part. JP1 is provided to enable the converter. The demo board The data sheet should be read in conjunction with this is configured for 800kHz. A jumper, JP2, is provided to Quick Start Guide. select PWM, or Burst Mode operation. A clock signal can Design files for this circuit board are available at also be applied to JP2 if synchronization is desired. DEMO MANUAL DC1999A QUICK START PROCEDURE Using short twisted-pair leads for any power connections 3. Connect the load to VOUT as shown in Figure 1. Again, and with all loads and power supplies off, refer to Figure1 connect an ammeter if accurate current measurement for the proper measurement and equipment setup. The or monitoring is desired. power supply should not be connected to the circuit until 4. Turn on the power supply and slowly increase voltage told to do so in the procedure below. until the voltage at VIN is 2.5V. Move Jumper JP1 to When measuring the input or output voltage ripple, care ON. must be taken to avoid a long ground lead on the oscil- 5. Verify VOUT is ~5.0V. loscope probe. 6. V can now be varied between 2.5V and 15.0V. V IN OUT 1. JP1, JP2 and Load Settings to start: should remain in regulation. JP1 (RUN) = OFF 7. I can also be varied from 0A to 1.5A. For V < 5.0V, OUT IN JP2 (PWM) = 800kHz (Fixed Frequency) maximum I is reduced. This reduction is due to I OUT IN LOAD = 0.1A/50 10W Resistor increasing as V decreases. Once the input current IN 2. With power OFF connect the power supply as shown in limit is reached, V will fall out of regulation. OUT Figure 1. If accurate current measurements are desired Note: If V drops out of regulation, check to be sure OUT (for efficiency calculations for example) then connect the maximum load has not been exceeded, or that V is IN an ammeter in series with the supply as shown. The not below the minimum value (2.5V). ammeter is not required however. Figure 1. Measurement Setup dc1999af 2