QUICK START GUIDE FOR DC1235 LOW QUIESCENT CURRENT DUAL SYNCHRONOUS BUCK CONVERTER LTC3826EG-1 DESCRIPTION Demonstration circuit 1235 is a dual-output stepdown power supply. The input voltage is from 4.5V to 32V. The supply has two outputs: 3.3V/5AMAX and 8.5V/3.5AMAX. When the input voltage is close to the output voltage, the supply is in dropout mode. The design features the LTC3826-1, the low quiescent current, 2-phase, dual-output synchronous buck regulator. Table 1. Performance Summary PARAMETER CONDITION VALUE Input Voltage Range If the input voltage must exceed 32V, use higher voltage rating input capacitors. The IC works up to 36V. Minimum of 9V input is needed for 8.5V output regulation at 3A load. 4.5V to 32V Outputs VOUT1 = 3.3V, 0A to 5A 3.3V ± 2% VOUT2 = 8.5V, 0A to 3.5A, Vin>9V 8.5V ± 2% Typical Output Ripple (VOUT1) 20MHz BW, 5A load, VIN = 32V, frequency = 390kHz 35mVP-P Typical Output Ripple (VOUT2) 20MHz BW, 3.5A load, VIN = 32V, frequency = 390kHz 30mVP-P Typical Operating Frequency PLLLPF floating (position JP1 to 390Khz) 390kHz Typical input current@no load CH1 on, no load, CH2 off, frequency=390kHz, Vin=16V. Burst Mode 55 uA Efficiency for Vout1 VIN=12V, Vout1=3.3V at 3.5A, Fs=390KHz 94% Efficiency for Vout2 VIN=12V, Vout2=8.5V at 2.5A, Fs=390kHz 98% - TEST PROCEDURE Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. Set the power supply jumper’s as shown on Table 2 below. JP1 JP2 JP3 JP4 JP5 JP6 FREQ PLL/MODE RUN1 RUN2 TRACK1 TRACK2 390kHz BURST ON ON SS1 SS2 3.With the input voltage set at approximately 20 volts, check that the input current is below 100uA (Typically 85uA). 4. Connect the desired loads to the 3.3V (5 amps) and 8.5V (3.5 amps) terminals and their closest PGND terminals on the board. 5. Measure the output voltages. They should be 3.3V ±0.066V and 8.5V ±0.17V at 0 amps and full load. Table 2 Default Jumper setting 6.Input current with both outputs at full load should be about 2.5A with 20 Vin. 2. Connect the input power supply to the VIN and GND terminals on the right, center of the board. 7.Check the default jumper position after finishing the test evaluation of the board. NOTE: Do not increase VIN over 32V. The maximum load at 3.3V is 5A, and the maximum at 8.5V is 3.5A. NOTE: 1 QUICK START GUIDE FOR DC1235 LOW QUIESCENT CURRENT DUAL SYNCHRONOUS BUCK CONVERTER Load + A V Power supply + V + A V + A Load Figure 1. Proper Measurement Equipment Setup 1 QUICK START GUIDE FOR DC1235 LOW QUIESCENT CURRENT DUAL SYNCHRONOUS BUCK CONVERTER Figure 2. LTC3826 demo circuit DC1235 circuit schematic 2