DEMO MANUAL DC2422A-A, DC2422A-B, DC2422A-C LTC7812EUH Wide V , Step-Up + Step-Down IN DC/DC Converter DESCRIPTION Demonstration circuit DC2422A is a step-up + step-down The LTC7812 buck input is supplied from the boost output DC/DC converter featuring the LTC 7812EUH, a high per- for the DC2422A-A and DC2422A-B only. With this boost- formance dual output (Boost + Buck) synchronous DC/ then-buck topology, the buck output maintains regulation DC switching regulator controller. This board has three over the entire input range. The wide input voltage range different configurations: of 4V to 36V is suitable for automotive or other battery fed applications where low quiescent current is important. n DC2422A-A: Regulated V to 12V OUT The DC2422A-B is designed such that V is partially OUT n DC2422A-B: Quasi regulated V between 10V and OUT regulated between 10V and 16V for higher efficiency 16V (Figure 4a), reduced power loss, and switching noise. n DC2422A-C: Dual outputs: 12V (boost channel) When V is between 10V and 16V, it operates in pass- IN 5V (buck channel) thru mode with the boost synchronous FET fully on and the buck in drop-out with >99% duty cycle. When V is IN This circuit enables a drop-in layout where the total circuit below 10V, the boost is activated and when V is above IN area is only 1 by 1 . The LTC7812EUH is in a 32-lead 16V, the buck is activated as shown in Figure 4b. exposed pad QFN package. The LT7812 data sheet gives a complete description of The main features of the board include rail tracking (buck the part, operation and application information and must channel only), an internal 5V linear regulator for bias, be read in conjunction with this quick start guide. separate RUN pins for each output and a Mode selector that allows the converter to run in CCM, pulse skip or Design files for this circuit board are available at Burst Mode operation. Synchronization to an external DEMO MANUAL DC2422A-A, DC2422A-B, DC2422A-C QUICK START PROCEDURE Demonstration circuit DC2422A is easy to set up to evaluate 3. Turn on the power at the input. the performance of the LTC7812EUH. Refer to Figure 1 NOTE: Make sure that the input voltage is higher than for proper measurement equipment setup and follow the 8V and does not exceed 36V. procedure below: 4. Check for the proper output voltages for different boards. NOTE: When measuring the input or output voltage ripple, DC2422A-A: V = 11.7V to 12.3V, care must be taken to avoid a long ground lead on the OUT1 oscilloscope probe. Measure the input or output voltage DC2422A-B: 9.7V < V < 16.3V, OUT1 ripple by touching the probe tip directly across the V IN DC2422A-C: V = 4.9V to 5.1V V = 11.7V to OUT1 BUS or V and GND terminals or directly across relevant OUT 12.3V. capacitor. See Figure 2 for proper scope probe technique. NOTE: If there is no output, temporarily disconnect the 1. Place jumpers in the following positions: load to make sure that the load is not set too high. JP1: ON 5. Once the proper output voltages are established, adjust JP2: ON the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and JP3: Burst Mode BURST other parameters. 2. With power off, connect the input power supply to V IN and GND. I OUT LOAD + + I OUT + LOAD + I IN + + V SUPPLY IN Figure 1. Proper Measurement Equipment Setup dc2422af 2