DEMO CIRCUIT 1580A QUICK START GUIDE LTC3856EUH HIGH EFFICIENCY POLYPHASE BUCK CONVERTER DESCRIPTION Demonstration circuit 1580A is a high efficiency, polyphase, synchronous buck converter with 4.5V to 14V input range. It can supply 50A maximum load current at 1.5V output. The demo board uses the LTC®3856EUH controller. The LTC3856 is a feature-rich single-output dual-phase synchronous buck controller with on-chip drivers, remote output voltage sensing. This board is setup with sense resistor configuration with optional inductor DCR sensing circuit. Temperature compensation function can guarantee accurate current limit over a wide temperature range with DCR sensing. Stage shedding function allows the controller to decrease the phase number to be one at the light load condition in order to save switching related loss. Adaptive voltage positioning (AVP) can help improve the transient response. The LTC3856 is suitable for input from 4.5V to 38V and output up to 5V. The LTC3856 can provide high efficiency, high power density and versatile power solutions for telecom and datacom systems, industrial and medical instruments, DC power distribution systems and computer systems. The controller is available in 32-pin 5mm × 5mm QFN and 38pin SSOP packages. Table 1. The RUN pin (JP1) provides enable feature. To shut down the converter, one simple way is to force the RUN pin below 1.2V (JP1: OFF). Use JP3 jumper to select burst mode, stage shedding mode or forced continuous mode operation. The phase of CLKOUT is set by JP2. Switching frequency is pre-set at about 400KHz, and it can be easily modified from 250KHz to 770KHz. Please see LTC3856 data sheet for detailed information. Design files for this circuit board are available. Call the LTC factory. Performance Summary (TA = 25°C) PARAMETER CONDITION Input Voltage Range VALUE 4.5V to 14V Output Voltage, VOUT VIN = 4.5-14V, IOUT = 0A to 50A 1.5V ±2% Maximum Output Current, IOUT VIN = 4.5-14V, VOUT = 1.5V 50A Typical Efficiency VIN = 12V, VOUT = 1.5V, IOUT = 50A 87.7% Typical Switching Frequency 400kHz 1 LTC3856EUH QUICK START PROCEDURE Demonstration circuit 1580A is easy to set up to evaluate the performance of the LTC3856EUH. Refer to Figure 1 for the proper measurement equipment setup and follow the procedure below: 1. With power off, connect the input power supply to Vin (4.5V-14V) and GND (input return). 2. Connect the 1.5V output load between Vout and GND (Initial load: no load). 3. Connect the DVMs to the input and outputs. 4. Turn on the input power supply and check for the proper output voltages. Vout should be 1.5V+/-2%. 5. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage and other parameters. Note: When measuring the output or input voltage ripple, do not use the long ground lead on the oscilloscope probe. See Figure 2 for the proper scope probe technique. Short, stiff leads need to be soldered to the (+) and (-) terminals of an output capacitor. The probe’s ground ring needs to touch the (-) lead and the probe tip needs to touch the (+) lead. 2 LTC3856EUH Figure 1. Proper Measurement Equipment Setup + COUT VOUT - GND Figure 2. Measuring Output Voltage Ripple 3 LTC3856EUH Figure 3. Efficiency vs load current 4 E4 E2 E3 COUT2 100uF 6.3V VOUT PGOOD GND EXTVCC SHT 2 EXTVCC SHT 2 ITEMP TRK/SS E9 3 ON O FF C2 0.1uF JP1 1 2 RUN COUT3 100uF 6.3V R46 100K PS 1 COUT4 100uF 6.3V INTVCC JP2 BM MODE EXTVCC C50 1uF 1 DEG DEG DEG 4 + COUT6 330uF 2.5V JP3 4 + COUT8 330uF 2.5V R48 OPT R65 30.1K 20.0K R78 0 OPT R63 C58 + COUT7 330uF 2.5V C51 OPT CCM R31 8.45K C42 47pF 3.3nF R28 OPT R26 OPT C38 OPT VIN C41 PHASMD INTVCC 120 90 60 R2 OPT R3 0 0 2 PLLIN R77 + COUT9 330uF 2.5V OPT R64 9 DIFFP EXTVCC ISET DIFFOUT DIFFN DIFFP PHASMD ITEMP AVP ITH VFB TRK/SS RUN R44 OPT R42 OPT 20 12 11 + COUT12 OPT PGOOD MODE + COUT10 330uF 2.5V INTVCC 49.9k R66 R79 0 10 6 PHASMD DIFFN 5 ITEMP 4 3 ITH AVP 2 1 TRK/SS VFB 30 FREQ RUN LTC3856EUH U1 R7 100K 1% PLLIN CLKOUT ILIM 13 3 27 15 VIN + COUT13 OPT SW1 26 S2+ 7 R39 200 S2- BG2 19 TG2 SW2 8 R9 1nF C14 1nF C15 0 R25 4.7uF INTVCC C11 16 18 17 21 23 BG1 TG1 25 24 S1+ 32 S1- R29 200 31 + COUT14 OPT SENSE2- SENSE2+ BG2 SW2 BOOST2 TG2 INTVCC BG1 BOOST1 SW1 TG1 SENSE1+ SENSE1- 0.1uF C17 R18 2.2 R40 200 0 R30 200 INTVCC INTVCC C21 0.1uF CMDSH-3 D2 CMDSH-3 D1 C20 0.1uF 4 4 Q4 RJK0330DPB 4 Q3 RJK0305DPB 4 Q2 RJK0330DPB 4 Q1 RJK0305DPB 1 2 3 E1 2 29 FRE Q 28 P LLIN MODE 14 CLK OUT PGOOD 22 V IN 5 6 7 8 Q5 RJK0305DPB 4 4 Q7 RJK0305DPB 5 6 7 8 4 Q8 RJK0330DPB 0.22uH L2 22uF 22uF L2- CIN6 CIN4 Q6 RJK0330DPB 0.22uH L1- 22uF 22uF L1 CIN5 CIN3 VIN VIN R67 10 0.001 RS2 0.001 RS1 R68 10 COUT1 100uF 6.3V + COUT11 OPT S2- S2+ S1- S1+ SW2 SW1 TG2 TG1 BG2 BG1 + COUT5 330uF 2.5V VOUT CIN1 + 180uF 16V VIN 1 2 E20 3 1 2 3 1 2 3 1 2 3 PGND 33 1 2 3 5 6 7 8 5 6 7 8 1 2 3 5 6 7 8 5 6 7 8 1 2 3 5 6 7 8 5 6 7 8 1 2 3 1 2 CLKOUT S2- S2+ S1- S1+ VIN+ VIN- GND E13 SHT 2 GND VO_SNS+ VO_SNS- J4 VOUT 1.5V / 50A J3 E6 J2 VIN 4.5V - 14V E14 SW2 SW1 TG2 TG1 BG2 BG1 C32 4.7uF 16V CIN2 + 180uF 16V E5 J1 LTC3856EUH 5 SW2 OPT R51 OPT S2- R53 OPT S1- R47 OPT OPT R62 OPT R61 L2- S2+ SHT 1 L1- S1+ SHT 1 JP5 IOSTEP C53 100uF 6.3V S D Q9 R73 0.005 G R74 10K SUD50N03-09P 1 LOAD STEP CKT R72 0.005 C54 100uF 6.3V VOUT J5 E7 VOUT IOSTEP CLK A ND RS E NS E 2. DO NOT ST UFF R29 ,R30,R39 A ND R4 0 NOT E: WHE N DCR S ENS ING IS IM PL EM E NT E D, SHORT RSE NSE 1 SHT 1 S2- SHT 1 SW2 SHT 1 S1- SHT 1 SW1 R45 2 3 4 5 SHT 1 OFF3 ON 2 VIN BIAS 1 1uF 16V C55 ITEMP JP4 4 5 OPT RNTC OPT R70 SHDN 3 6 1 R75 6.65K FB SW BOOST U2 LT1616ES6 VIN OPT C52 20K R71 D4 B0530W 0.022uF C56 A914BYW-150 L3 15uH D3 CMDSH-3 OPTIONAL BIAS SUPPY OPT R69 ITEMP1 TEMPERATURE COMPENSATION NETWORK FOR DCR SENSING 2 1 OPTIONAL DCR SENSING GND 2 SW1 C57 10uF 10V 0 R76 EXTVCC SHT 1 LTC3856EUH 6