QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 965A SINGLE 5A HIGH FREQUENCY STEP-DOWN DC/DC CONVERTER LTC3835EGN-1 DESCRIPTION Demonstration circuit 965A is a single output high frequency step-down DC/DC converter featuring the low quiescent current LTC®3835 in a 16-pin GN package. The DC965A is programmed to generate a regulated 3.3V@5A output from a 4.5V to 36V input voltage. To maximize battery usage, the demo circuit allows low dropout operation when the input voltage is close to the output voltage. Its selectable burst mode operation reduces the IC supply current at light loads to extend battery life. The phase-lockable frequency allows the LTC3835 to be synchronized by an external signal. The output voltage of the LTC3835 can track an external ramp voltage signal during power-up and power-down. Also, the built-in current foldback prevents the overheating of output MOSFETs during short-circuit. All these features make the circuit a high performance solution for applications in automotive and batteryoperated systems, telecom and distributed DC power systems. Design files for this circuit board are available. Call the LTC factory. LTC is a registered trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION MINIMUM Input Voltage Range Maximum Output Current 4.5V < VIN < 36V Output Voltage VOUT 0A < IOUT < 5A Output Ripple VOUT IOUT = 5A (20MHz BW) VIN = 36V, FSW = 400kHz MAXIMUM 36V 5A 3.234V 3.3V 3.366V 36mVP–P Nominal Switching Frequency Efficiency TYPICAL 4.5V 400kHz VIN = 14V, IOUT = 3.5A, 400kHz Switching Frequency 91.5% QUICK START PROCEDURE Demonstration circuit 965A is easy to set up to evaluate the performance of the LTC3835EGN-1. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: MODE jumper (JP3) in desired Mode (Burst, CCM or DCM) position. Table 2 shows the default setting for DC965A. JP1 TRACK/SS NOTE: When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe technique. 1. Place VOUT jumper in the OFF position, the PLLPF jumper (JP2) at the selected frequency and the SS JP2 PLLPF JP3 MODE JP4 400kHz DCM VOUT ON Table 2. Default Jumper Settings 2. With power off, connect a 4.5V-36V, 6A power supply to VIN and GND. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 965A SINGLE 5A HIGH FREQUENCY STEP-DOWN DC/DC CONVERTER 3. Connect a load to VOUT and GND (maximum load is 5A). 4. Move the VOUT jumper to the ON position. 5. Turn on the power at the input. 7. NOTE: Make sure that the input voltage is above 4.5V, but does not exceed 36V. 6. NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high. Once proper output voltages are established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. Check for proper output voltages. VOUT should measure 3.3V (could vary from 3.234V to 3.366V). Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 965A SINGLE 5A HIGH FREQUENCY STEP-DOWN DC/DC CONVERTER 3