DEMO CIRCUIT 1479A QUICK START GUIDE LTC3865EUH DUAL 15A SYNCHRONOUS BUCK CONVERTER with PIN SELECTABLE OUTPUTS DESCRIPTION Demonstration circuit 1479A is a dual output synchronous buck DC/DC converter featuring the LTC3865EUH. The input voltage range is from 4.5V to 14V. The outputs are 1.5V/15A and 1.2V/15A. Each output voltage can be precisely programmed to a preset value within 1% error with the VID pins. The demo board uses a high density, two sided drop-in layout. The package of LTC3865EUH is a small, low thermal impedance 5mm x 5mm 32-Lead QFN. The light load operation mode of the converter is determined with the MODE/PLLIN pin. Use JP3 jumper to select burst mode, pulse skipping mode or forced continuous mode operation. Switching frequency is pre-set at about 500KHz. This frequency can be Table 1. modified by changing R7 value at the FREQ pin. The converter can also be externally synchronized from 250kHz to 770kHz through MODE/PLLIN pin (SYNC terminal on the board). The maximum current sense threshold can be adjusted by connecting ILIM pin to SGND, float or INTVcc (with optional R42 and R44). To shut down a channel, force its RUN pin below 1.2V (Jumper: OFF). The power good output (PGOOD terminal) is low when either channel output exceeds +/-10% regulation window. 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, VOUT1 VIN = 4.5-14V, IOUT1 = 0A to 15A 1.5V ±1% (Note) Output Voltage, VOUT2 VIN = 4.5-14V, IOUT2 = 0A to 15A 1.2V ±1% (Note) Maximum Output Current, IOUT1 VIN = 4.5-14V, VOUT1 = 1.5V 15A Maximum Output Current, IOUT2 VIN = 4.5-14V, VOUT2 = 1.2V 15A Typical full load Efficiency, channel 1 VIN = 12V, VOUT1 = 1.5V, IOUT1 = 15A 85% Typical full load Efficiency, channel 2 VIN = 12V, VOUT2 = 1.2V, IOUT2 = 15A 83.4% Typical Switching Frequency 500kHz Note: VOUT1, VOUT2 are measured directly on output capacitors Cout1 and Cout4. 1 LTC3865EUH QUICK START PROCEDURE Demonstration circuit 1479A is easy to set up to evaluate the performance of the LTC3865EUH. Refer to Figure 1 for the proper measurement equipment setup and follow the procedure below: Jumper positions: JP1,2 (RUN1/RUN2): ON JP3 (MODE): CCM the (-) lead and the probe tip needs to touch the (+) lead. Note: 2. Do not apply load from Vo1+ to Vo1- or from Vo2+ to Vo2- turrets. These are only intended to conveniently measure the output voltage. Heavy load currents may damage the sense traces. To accurately measure the output voltages and efficiency, please directly measure Vout1 and Vout2 on output capacitors Cout1 and Cout4. 1. With power off, connect the input power supply to Vin (4.5V-14V) and GND (input return). 2. Connect the load #1 between Vout1 and GND (Initial load: no load); connect the load #2 between Vout2 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. With current VID pin setting, Vout1 should be 1.5V+/-1%; Vout2 should be 1.2V+/-1%. 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. 6. If necessary, change the resistor options on VID pins for another output voltage according to table 2. Note: 1. 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 2 LTC3865EUH OUTPUT VOLTAGE PROGRAMMING The output voltages of both channels can be programmed to preset values. There are two VID pins for each channel: VID11, VID12 for Vout1, and VID21, VID22 for Vout2. See Table 2 for details. Table 2. Output voltage programming VID11/VID21 VID12/VID22 VOUT1/VOUT2 (V) INTVCC INTVCC 5.0 (Vin > 5V) INTVCC FLOAT 3.3 INTVCC GND 2.5 FLOAT INTVCC 1.8 FLOAT FLOAT FLOAT GND 1.5 GND INTVCC 1.2 GND FLOAT 1.0 GND GND 1.1 0.6 or external divider SINGLE OUTPUT / DUAL PHASE OPERATION A single output / dual phase converter may be preferred for high output current applications. The benefits of single output / dual phase operation are lower ripple current through the input and output capacitors, improved load step response and simplified thermal design. To implement single output / dual phase operation, make the following modifications: Tie VOUT1 to VOUT2. Use a piece of heavy copper foil if possible. 1. 2. 3. Tie VFB1 to VFB2 by stuffing 0Ω at R50. 4. Tie TRK/SS1 to TRK/SS2 by stuffing 0Ω at R52. 5. Tie RUN1 to RUN2 by stuffing 0Ω at R55. 6. Remove channel 2 ITH compensation network (C44, R35) and float VID21, VID22 pins. Tie ITH1 to ITH2 by stuffing 0Ω at R49. 3 LTC3865EUH RAIL TRACKING Demonstration circuit 1479A is configured for independent turn-on of VOUT1 and VOUT2. The ramp-rate for VOUT1 is determined by the TRK/SS1 cap at C2 and the ramp-rate for VOUT2 is determined by the TRK/SS2 cap at C47. This board can be modified on the bench to allow VOUT1 to track an external signal. Table 3. VOUT1 Tracking Options (1.5V) CONFIGURATION Soft Start Without Tracking (original board) External Coincident Tracking Table 4. It can also be modified to allow VOUT2 to track VOUT1 or to allow VOUT2 to track an external signal. Tables 3 and 4 cover the rail tracking options for each rail. R3 0Ω 17.8kΩ TRACK1 DIVIDER R2 Not stuffed 20.0kΩ TRK/SS1 CAP C2 0.1uF Not Stuffed VOUT2 Tracking Options (1.2V) CONFIGURATION Soft Start Without Tracking (original board) R36 0Ω TRACK2 DIVIDER R34 R37 Not stuffed Not stuffed TRK/SS2 CAP C47 0.1uF Coincident Tracking to VOUT1 (1.5V) 0Ω 10.0kΩ 20.0kΩ Not Stuffed External Coincident Tracking 10.0kΩ Not stuffed 20.0kΩ Not Stuffed INDUCTOR DCR SENSING Demonstration circuit 1479A provides an optional circuit for DCR sensing. DCR 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 disadvantage 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. Tables 5 and 6 show an example of how to modify the DC1479A for DCR sensing using these parameters: VOUT1 = 1.5V / 15A VOUT2 = 1.2V / 15A VIN = 4.5V to 14V Fsw = 500kHz, typical L1,2 = Vishay IHLP-4040DZERR47M11 (0.47uH, DCR = 1.53mΩ typ, 1.68mΩ max) ILIM = FLOATING (R42,R44 = OPEN) 4 LTC3865EUH Table 5. VOUT1 Configured as a 1.5V/15A Converter Using DCR Sensing or a Discrete Sense Resistor CONFIGURATION DCR Sensing Discrete RSENSE (original board) Table 6. RS1 Short with Cu strip or very short & thick piece of wire 2mΩ L1 IHLP4040DZERR47M11 IHLP4040DZERR47M11 RSENSE FILTER RESISTORS SENSE FIILTER CAP R29,R30 Open 100Ω DCR FILTER/DIVIDER RESISTORS SENSE1- TO L1JUMPER TOP BOTTOM C14 0.22uF R45 1.40kΩ R47 15.4kΩ R61 0Ω 1nF Open Open Open VOUT2 Configured as a 1.2V/15A Converter Using DCR Sensing or a Discrete Sense Resistor CONFIGURATION DCR Sensing Discrete RSENSE (original board) RS2 Short with Cu strip or very short & thick piece of wire 2mΩ L2 IHLP4040DZERR47M11 IHLP4040DZERR47M11 RSENSE FILTER RESISTORS SENSE FIILTER CAP DCR FILTER/DIVIDER RESISTORS TOP BOTTOM SENSE1- TO L1JUMPER R39,R40 Open C15 0.22uF R51 1.40kΩ R53 15.4kΩ R62 0Ω 100Ω 1nF Open Open Open 5 LTC3865EUH Figure 1. Proper Measurement Equipment Setup + COUT VOUT - GND Figure 2. Measuring Output Voltage Ripple 6 LTC3865EUH 95 Efficiency (%) 90 85 1.5Vo 1.2Vo 80 75 70 0 3 6 9 12 15 Load current (A) Figure 3. Efficiency vs load current (Vin=12V, 500kHz, CCM) 7 E4 PGOOD EXTVCC 0.1uF OPT ITH1 100K R46 220pF 15K SHT 2 TRK/SS2 C42 R31 C41 1nF 1uF INTVCC C47 C50 OPT R34 0.1uF C2 R37 OPT R2 SHT 2 SHT 2 TRK/SS1 12K R35 C43 220pF ITH2 SHT 2 1nF C44 R7 162K 1% 10K 4 JP3 30 29 27 12 6 3 RUN2 4 14 20 13 11 TRK/SS2 7 ITH2 ITH1 TRK/SS1 2 RUN1 3 2 VID11 PGOOD EXTVCC ILIM RUN2 TRK/SS2 ITH2 ITH1 TRK/SS1 RUN1 FREQ MODE/PLLIN VID21 VFB1 VFB2 1. DO NOT APPLY LOAD FROM THE VO1+ TO VO1- OR FROM THE VO2+ TO VO2- TURRETS. THESE ARE ONLY INTENDED TO KELVIN SENSE THE OUTPUT VOLTAGE ACROSS COUT1 AND COUT4. NOTES: UNLESS OTHERWISE SPECIFIED, SHT 2 VFB2 SHT 2 VID12 SHT 2 VID11 PGOOD GND E2 ILIM E3 0 C1 OPT R3 0 R1 R36 0 VOUT1 E9 E1 E10 RUN2 EXTVCC SHT 2 SHT 2 TRK/SS2 TRK/SS1 SHT 2 RUN1 SHT 2 VID21 SHT 2 VID22 SHT 2 VFB1 SYNC E19 MODE P S BM CCM 1 INTVCC 1 V ID 22 28 5 V ID 12 v os e ns e1 U1 R27 0 VINF R9 1nF C14 R39 100 S2- S2+ 1nF C15 0 R25 INTVCC S1+ S1- R29 100 R43 0 9 10 15 16 17 18 19 21 22 23 24 25 26 31 32 OPT R33 SENSE2- SENSE2+ SW2 TG2 BOOST2 PGND BG2 INTVCC VIN BG1 BOOST1 TG1 SW1 SENSE1+ SENSE1- LTC3865EUH v os ens e2 8 R40 100 0.1uF C17 R18 0 R30 100 SHT 2 VIN S2- SHT 2 S2+ SHT 2 0.1uF C21 CMDSH-3 D2 4.7uF C11 2.2 CMDSH-3 D1 0.1uF C20 SW1 SHT 2 S1- S1+ SHT 2 BG1 SHT 2 4 4 SW2 SHT 2 TG2 SHT 2 BG2 SHT 2 INTVCC TG1 SHT 2 4 Q1 RJK0305DPB 4 VIN Q3 RJK0305DPB Q2 RJK0330DPB Q4 RJK0330DPB 10uF L1 0.47uH L2 0.47uH 10uF CIN2 CIN3 VIN VL2- VL1- 0.002 RS2 0.002 RS1 COUT4 100uF 6.3V COUT1 100uF 6.3V + COUT5 220uF 4V + COUT2 220uF 4V CIN1 180uF 16V + COUT6 220uF 4V VOUT2 + COUT3 220uF 4V VOUT1 VIN 1 + C36 4.7uF 6.3V C32 4.7uF 6.3V 2 R4 5 6 7 8 1 2 3 SGND 33 5 6 7 8 1 2 3 5 6 7 8 1 2 3 5 6 7 8 1 2 3 INTVCC VIN+ VIN- GND GND VOUT1 1.5V / 15A VO1+ VO2+ GND VO2- E14 J6 VOUT2 1.2V / 15A J5 E13 VO1- E12 J4 J3 E11 E6 J2 VIN 4.5V-14V J1 E5 LTC3865EUH 8 BG1 TG2 SW2 BG2 SHT 1 SHT 1 SHT 1 SHT 1 SHT 1 SHT 1 SHT 1 4 Q8 OPT 4 Q6 OPT 4 4 OPT R69 Q7 OPT Q5 OPT VID22 VID12 VID21 VID11 E17 E18 E15 E16 R67 10K INTVCC R70 10K R68 OPT INTVCC R63 OPT INTVCC R66 OPT R64 OPT INTVCC R65 10K VID22 VID12 VID21 VID11 SW1 SHT 1 SHT 1 TG1 SHT 1 5 6 7 8 1 2 3 5 6 7 8 1 2 3 5 6 7 8 1 2 3 5 6 7 8 1 2 3 VIN OPT CIN4 OPT CIN5 VIN SHT 1 S2- SW2 SHT 1 S1- NOT E: WHEN DCR SENSING IS IM PLEM ENT ED, SHORT RSENSE1 A ND RS ENS E2. DO NOT S T UFF R29,R30,R39 A ND R40 OPT IONAL DCR SE NSING R45 OPT R51 OPT GND GND SW1 FLOAT INTVCC GND FLOAT INTVCC GND GND GND FLOAT FLOAT FLOAT INTVCC FLOAT INTVCC INTVCC INTVCC VID12/VID22 VID11/VID21 S2- OPT R53 S1- OPT R47 R62 OPT OPT R61 1.1 1.0 1.2 1.5 VL2- S2+ SHT 1 VL1- S1+ SHT 1 0.6 or external divider 1.8 2.5 3.3 5.0 (Vin > 5V) VOUT1/VOUT2 (V) JP2 3 1 2 RUN1 SHT 1 TRK/SS1 SHT 1 VFB1 OPT OPT R55 OPT R52 RUN2 SHT 1 TRK/SS2 SHT 1 VFB2 ITH2 SHT 1 R49 OPT R50 ITH1 SHT 1 R44 OPT OPT R42 OPT OPT OPT R38 OPT R28 R41 VIN OPT C38 OPT R26 C48 OPT IONAL JUM PE RS FOR SINGLE OUT PUT /DUAL PHA SE OPERAT ION INTVCC ON OFF 3 JP1 RUN2 OFF ON 1 2 RUN1 VIN ILIM SHT 1 RUN2 SHT 1 RUN1 SHT 1 LTC3865EUH 9