QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 473 HIGH EFFICIENCY DUAL OUTPUT POWER SUPPLY LTC1702A DESCRIPTION Demonstration circuit 473A is a high efficiency dual output synchronous buck converter using the constant frequency LTC1702A dual channel switching controller. It operates from a 3V to 7V input and generates 1.8V at 5A and 2.5V at 5A. The LTC1702A operates at 550kHz typical switching frequency and uses voltage mode control to switch a pair of N channel MOSFETs. MOSFET RDS(ON) is used for short circuit protection. For operation at 3.3V, the demo board uses sub-logic level power MOSFETs. Design files for this circuit board are available. Call the LTC factory. QUICK START PROCEDURE Demonstration circuit 473 is easy to set up to evaluate the performance of the LTC1702A. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 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. NOTE: 1. Place jumper JP1 in the CONT posi- tion. 2. With power off, connect the input power supply to Vin and GND. 3. Turn on the power at the input. Make sure the voltage not exceed 7V at turn on. NOTE: will 4. Check for proper output voltages. Vout1 = 1.764V to 1.836V, Vout2 = 2.450V to 2.550V In case of no output, verify that the load is not set too high by temporarily disconnecting the load. 5. Once outputs are established at the proper voltages, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. See Figure 3 to Figure 7 for expected performance. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 473 HIGH EFFICIENCY DUAL OUTPUT POWER SUPPLY POWER SUPPLY 3.0V-7.0V + - + - - - LOAD + - - - + + LOAD + - + Figure 1. + Proper Measurement Equipment Setup GND VIN Figure 2. Scope Probe Placement for Measuring Input or Output Ripple 100 90 80 EFFICIENCY (%) 70 60 Vout = 1.8V 50 Vout = 2.5V 40 30 20 10 0 0 1 2 3 4 5 LOAD (A) Figure 3. 1.8V Output Ripple (VIN = 3.3V, IOUT = 5A) Figure 4. 2.5V Output Ripple (VIN = 3.3V, IOUT = 5A) Figure 5. Efficiency 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 473 HIGH EFFICIENCY DUAL OUTPUT POWER SUPPLY 1.8V RUN/SS1 (SD1) Figure 6. 1.8V Load Transient Response Figure 7. 1.8V Output Voltage Startup Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage 3V Maximum Input Voltage 7V VOUT1 VIN = 3V to 7V, IOUT1 = 0A to 5A 1.8V 2% VOUT2 VIN = 3V to 7V, IOUT1 = 0A to 5A 2.5V 2% Typical Output Ripple VOUT1 VIN = 3.3V, IOUT1 = 5A 15mVP-P Typical Output Ripple VOUT2 VIN = 3.3V, IOUT2 = 5A 20mVP-P Nominal Switching Frequency 550kHz 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 473 HIGH EFFICIENCY DUAL OUTPUT POWER SUPPLY Vin VIN + 2 4 3 3 4 1.8V @ 5A C9 180uF 4V SP R5 1.2K R7 1 2 C13 4700pF 1 C12 820pF R6 10K R8 14K Q1A Si4922DY Burst 5 6 7 2 Cont. JP1 1 Gnd VIN 3 C8 + 1uF 6.3V 7 8 E3 E6 8 C17 1uF 6.3V 9 10 11 12 1.8V C18 27pF R13 8.06K VIN PVCC BOOST1 IMAX2 BOOST2 BG1 BG2 TG1 TG2 SW1 SW2 IMAX1 PWRGD1 PGND PWRGD2 FAULT FCB RUN/SS1 COMP1 RUN/SS2 COMP2 SGND FB2 FB1 VCC U1 LTC1702ACGN R15 47K R17 10K Pwrgd1 2 Gnd D2 MBR0520LT1 R2 14K 24 23 R4 10 22 C7 1uF 6.3V Q2B Si4922DY E2 C5 1uF 6.3V L2 1.5uH IHLP-2525CZ-01-1.5uH 4 Vout2+ 21 20 19 18 C16 1uF 6.3V 17 16 2 Q2A Si4922DY + R9 1 R10 1.6K C14 4700pF C15 680pF R11 10K C10 180uF 4V SP C11 1uF 6.3V E4 2.5V @ 5A Gnd E5 15 14 13 C19 27pF R16 68K C20 680pF 6 5 1 E1 3V-7Vin 3 R3 10 1 C6 1uF 6.3V 8 7 5 6 L1 1.5uH IHLP-2525CZ-01-1.5uH Vout1+ Q1B Si4922DY R1 10 5% 1 D1 MBR0520LT1 C4 1uF 6.3V C3 10uF Cer 1 2 C2 1uF 6.3V C1 150uF 6.3V SP C21 3300pF R12 4.75K VIN R14 10K Pwrgd2 E7 Fault E8 E9 SD1 SD2 E10 E11 SGND Figure 8. PGND Demo Circuit Schematic 4