DEMO CIRCUIT 1432A LTC3851AEUD/ LTC3851AEUD-1 QUICK START GUIDE LTC3851AEUD/ LTC3851AEUD-1 SYNCHRONOUS BUCK CONVERTER DESCRIPTION Demonstration circuit 1432A is a synchronous buck converter featuring the LTC3851AEUD/ LTC3851AEUD-1. The demo circuit is available in two versions. DC1432A-A is configured with LTC3851AEUD which provides ISET function, while the DC1432A-B is configured with LTC3851AEUD-1 which provides PGOOD function. The main features of the board include an internal 5V linear regulator for bias and a Mode selector that allows the converter to run in Forced CCM Mode, Pulse Skip Mode or Burst Mode operation. Synchronization to an external clock is also possible on this board. The demo circuit has an optional DCR sense circuit that allows using the inductor’s DCR as the current sensing Table 1. Performance Summary (TA=25°C) PARAMETER Input Supply Range Output Voltage Range Nominal Switching Frequency Full Load Efficiency (See Figure 3 for efficiency curves) element to save cost, footprint and improve full load efficiency about 2%. The LTC3851AEUD/ LTC3851AEUD-1 datasheet gives a complete description of these parts, operation and application information and must be read in conjunction with this quick start guide for Demonstration circuit 1432A. Design files for this circuit board are available. Call the LTC factory. L, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower SwitcherCAD, Multimode Dimming, No Latency ∆Σ, No Latency Delta-Sigma, No RSENSE, Operational Filter, PanelProtect, PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT, UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products. CONDITIONS MIN 4.5 1.47 VIN = 12V, ILOAD = 15A VIN = 12V, VOUT = 1.5V, ILOAD = 15A TYP 1.5 350 88.9 MAX 14 1.53 UNITS V V kHz % QUICK START PROCEDURE Demonstration circuit 1432A is easy to set up to evaluate the performance of the LTC3851AEUD/ LTC3851AEUD-1. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 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 jumpers in the following positions: FREQ/PLLFLTR 350kHz RUN On MODE/PLLIN CCM 2. With power off, connect the input power supply to Vin and GND. 3. Turn on the power at the input. NOTE. Make sure that the input voltage does not exceed 14V. 1 LTC3851AEUD/ LTC3851AEUD-1 4. Check for the proper output voltage. Vout = 1.470V to 1.530V NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 5. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 6. Different operating modes can be evaluated by changing the position of MODE/PLLIN jumper and are discussed in the next section. Iin A + V Vin + Vin supply - Vout + V Iout - A + Vout load - Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 2 LTC3851AEUD/ LTC3851AEUD-1 FREQUENCY SYNCHRONIZATION AND MODE SELECTION Demonstration circuit 1432A’s Mode selector allows the converter to run in Forced CCM Mode, Pulse Skip Mode or Burst Mode operation by changing position of MODE/PLLIN jumper. For synchronizing to an external clock source, FREQ/PLLFLTR jumper needs to be placed at “EXTCLK” position and MODE/PLLIN jumper needs to be removed. Apply the external clock from the MODE/PLLIN turret to GND. Refer to Table 2 and to the data sheet for more details. Table 2. Mode Selection and Synchronizing Operation Options CONFIGURATION Forced CCM Mode Operation Pulse Skip Mode Operation Burst Mode Operation Synchronize to Ext. clock (Ext. clock apply to MODE/PLLIN turret) MODE/PLLIN JUMPER “CCM” “P.S.” “BURST” Remove Jumper FREQ/PLLFLTR JUMPER “350K” “350K” “350K” “EXTCLK” RAIL TRACKING Demonstration circuit 1432A is configured for an on board soft start circuit. The soft start ramp rate can be adjusted by changing the value of C24. Demonstration Table 3. Output Tracking Options CONFIGURATION Soft Start Without Tracking (Default) Vout Equals External Ramp Vout Tracking Scaled External Ramp circuit 1432A can also be modified to track an external reference. Refer to Table 3 for tracking options and to the data sheet for more details. R32 R35 0Ω OPEN 0Ω OPEN Resistor Divider C24 0.1μF OPEN OPEN TRK/SS PIN OPEN External Ramp External Ramp OPTIONAL INDUCTOR DCR CURRENT SENSING Demonstration circuit 1432A provides an optional circuit for Inductor DCR Current Sensing. Inductor DCR Current Sensing uses the DCR of the inductor to sense the inductor current instead of discrete sense resistors. The advantages of DCR sensing are lower cost, reduced board space and higher efficiency, but the disTable 4. Optional Inductor DCR Current Sensing CONFIGURATION Current Sense Resistor (Default) Inductor DCR Current Sensing RSNSE 2mΩ, 1W 0Ω Copper advantage is a less accurate current limit. If DCR sensing is used, be sure to select an inductor current with a sufficiently high saturation current or use an iron powder type. Refer to Table 4 for Optional Inductor DCR Current Sensing setup and to the datasheet for more details. R10 100 Ω OPEN R9 100 Ω OPEN R1 OPEN 0Ω C30 1nF 100nF R27 OPEN 2k Ω 3 LTC3851AEUD/ LTC3851AEUD-1 Demonstration Circuit 1432A (LTC3851AEUD/LTC3851AEUD-1) Test Efficiency 95 90 Efficiency (%) 85 80 75 Vin=4.5V CCM Vin=12V CCM 70 Vin=14V CCM 65 0 2 4 6 8 10 Load Current (A) 12 14 16 Figure 3. Efficiency Curve for Demonstration Circuit 1432A Demonstration Circuit 1432A (LTC3851AEUD/LTC3851AEUD-1) Test Efficiency 95 90 Efficiency (%) 85 80 75 Vin=12V Current Sensing Resistor 70 Vin=12V Inductor DCR Sensing 65 0 2 4 6 8 10 Load Current (A) 12 14 Figure 4. Efficiency Curve for Demonstration Circuit 1432A with Optional Inductor DCR Current Sensing 4 16 [1] C26 LTC3851AEUD-1 -B 100K OPT R42 OPT U1 OPT C29 R38 49.9K 1% 3 50K C24 R32 0 OPT R42 [1] ILIM 1K R43 PGOOD ISET E9 INTVCC R41 0 R39 43.2K 1% OPT R35 0.1uF 10V JP1 3 R46 7 4 3 2 1 C20 1nF 10nF C22 ILIM FB ITH TK/SS RUN U1 [1] 200K 1% JP3 3 4 B URST P .S . MODE/PLLIN 2 16 INTVCC E XT CL K R31 FREQ/PLLFLTR 1 VIN VOUT C32 470pF C28 OPT R48 OPT R47 97.6K 1% R30 R40 6.49K 1% 3300pF LTC3851AEUD OPT C23 3 OFF -A E9 E2 E1 JP2 ON 1 RUN ASSY [1] TRK/SS RUN E4 2 MODE/PLLIN 2 14 R45 OPT OPT 10 9 11 12 R44 1nF C30 INTVCC BG VIN BOOST 100 C31 4.7uF 10V R9 2.2 R37 0 R36 3 7 8 C25 0.1uF 10V 100 2 4 R10 C27 2.2uF 10V C19 1uF BG TG Q5 OPT Si4816BDY VIN 5 6 1 1 GND 8 13 TG 15 5 FREQ/PLLFLTR GND 17 MODE/PLLIN SENSE- SW SW TG CMDSH-3 2 BG VIN INTVCC D2 INTVCC 1 SW CIN4 OPT 4 4 5 Q1 RJK0305DPB Q2 OPT 4 Q4 OPT 4 Q3 RJK0329DPB 1 2 3 5 1 2 3 5 1 2 3 CCM SENSE+ 6 5 1 2 3 INTVCC CIN3 22uF 25V OPT OPT C18 R1 OPT R29 OPT R27 0.4uH CIN5 OPT OPTI ONAL DCR SENSI NG L1 CIN6 22uF 25V CIN7 OPT 0.002 OHM RSNSE VIN COUT3 47uF 6.3V + COUT1 330uF 2.5V VOUT + CIN1 150uF 16V E8 J4 + COUT2 330uF 2.5V J3 E7 E6 J2 J1 E5 GND GND 1.5V / 15A VOUT VOUT GND GND 4.5V - 14V VIN VIN LTC3851AEUD/ LTC3851AEUD-1 Figure 5. Demonstration Circuit 1432A Schematic 5