QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER LTC3857EUH/LTC3858EUH DESCRIPTION Demonstration circuit 1381A is a Low Quiescent Current, Dual Output Synchronous Buck Converter featuring the LTC3857EUH/LTC3858EUH. The circuit is single sided layout, while the package style for the LTC3857/8EUH is a 32 lead (5mm x 5mm) QFN package The main features of the board include rail tracking (LTC3857EUH only), an internal 5V linear regulator for bias, RUN pins for each output, a PGOOD signal (CH1 only) and a Mode selector that allow the converter to run in CCM, pulse skip or Burst Mode operation. Synchronization to an external clock is also possible. Two versions of the board are available. DC1381A-A is for the LTC3857EUH, while the DC1381A-B is for the LTC3858EUH. The Table 1. LTC3857EUH offers lower quiescent current and smaller burst mode ripple, while the LTC3858EUH offers latch-off protection and increased burst mode efficiency. The wide input voltage range of 4.5V to 36V is suitable for automotive or other battery fed application where low quiescent current is important. The LT3857EUH and LTC3858EUH datasheets give a complete description of these parts, operation and application information. The datasheets must be read in conjunction with this quick start guide for demo circuit 1381A. Design files for this circuit board are available. Call the LTC factory. Burst Mode is a trademark of Linear Technology Corporation Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE # Minimum Input Voltage 4.5V Maximum Input Voltage 36V Output Voltage VOUT1 VIN = 4.5V to 36V, IOUT1 = 0A to 5A 3.3V ±2% Output Voltage VOUT2 VIN = 9V to 36V, IOUT2 = 0A to 3A 8.5V ±2% Nominal Switching Frequency 350kHz VIN = 24V VIN = 36V VOUT1 = 3.3V, IOUT1 = 5A 92.5%* Typical 90.4%* Typical VOUT2 = 8.5V, IOUT1 = 3A 96.6%* Typical 95.4%* Typical Efficiency, DC1381A-A/B See Figures 3 to 6 for efficiency curves * Measured at bulk output capacitor # Minimum input voltage required for 8.5Vout regulation is 9Vin QUICK START PROCEDURE Demonstration circuit 1381A is easy to set up to evaluate the performance of the LTC3857EUH/LTC3858EUH. 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 probing directly across the bulk Vin or Vout capacitor. See Figure 2 for proper scope probe technique. 1. Place jumpers in the following positions: 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER JP2 Burst Mode JP3 On JP4 JP5 On JP6 SS 4. NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high. SS 2. With power off, connect the input power supply to Vin and GND. 3. Turn on the power at the input. NOTE: Make Check for the proper output voltages. Vout1 = 3.234V to 3.366V, Vout2 = 8.330V to 8.670V 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 position of jumper JP3. sure that the input voltage does not exceed 26V. Iout1 + A Vout1 Vout1 load - V + - Iin A + V - Vin + Vin supply - Vout2 load + - V + Vout2 A Iout2 Figure 1. Proper Measurement Equipment Setup 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER Figure 2. Measuring Input or Output Ripple Directly Across Bulk Capacitor RAIL TRACKING Demonstration circuit 1381 is setup for independent soft start without tracking. The soft start ramp-rate is determined by the value of the SS capacitors C1 and C23. This board can also be operated in coincident tracking mode with either Table 2. output as master or both can slave an external ramp Refer to Table 2 for tracking options and to the data sheet for more details. Output Tracking Options TRACK/SS JUMPERS CONFIGURATION JP3 JP4 TERMINALS TRACK1 TRACK2 Soft Start Without Tracking Vout1 SS Vout2 No connection / Don’t care SS No connection / Don’t care Coincident Tracking: Vout1 tracking External Ramp TRACK Vout2 tracking External Ramp Connect external ramp TRACK Connect external ramp Vout2 tracking Vout1 SS TRACK No connection / Don’t care Connect to Vout1 Vout1 tracking Vout2 TRACK SS Connect to Vout2 No connection / Don’t care 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER INDUCTOR DCR SENSING AND RESISTOR SENSING The DCR sense circuit uses the resistive voltage drop across the inductor to estimate the current. In contrast to the traditional sense resistor current feedback, the DCR sensing circuit offers lower cost and higher efficiency, but results in less accurate current limit due to the large variation of the inductor DC resistance. Furthermore, this indirect current sensing method cannot detect inductor saturation and requires the use of ‘soft’ saturating inductors (such as powder iron) Table 3. resulting in increased core losses or ‘hard’ saturating inductors (such as ferrite) with sufficiency high current ratings resulting in increased inductor size. For modifying the demo board for DCR sensing, please refer to Table 3. A full load efficiency improvement of between 0.25% – 0.75% is still possible with optional DCR sensing, but since the inductors are ferrite based, short circuit performance may be compromised. DCR sensing component selection REMOVE RSENSE NETWORK DCR NETWORK Vout1 R8, R9 = Open, R10 = Short R28 = 1.37kΩ R30 = 2.74kΩ R29 = 0Ω C6 = 0.47µF Vout2 R20, R21 = Open, R17 = Short R32 = 1.91kΩ R31 = 1.54kΩ R33 = 0Ω C18 = 0.47µF FREQUENCY SYNCHRONIZATION Demonstration circuit 1381’s Mode selector allows the converter to run in CCM, pulse skip or Burst Mode operation by changing position of jumper JP2. For synchronizing to an external clock source, remove jumper JP2 entirely and apply the external clock signal to the PLLIN/MODE pin. Please refer to datasheet for details on external clock signal requirements. 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER LTC3857EUH Figure 3. Typical Efficiency vs. Load Current for A-A board – 24Vin, 3.3Vout and 8.5Vout LTC3857EUH Figure 4. Typical Efficiency vs. Load Current for A-A board – 36Vin, 3.3Vout and 8.5Vout 5 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER LTC3858EUH Figure 5. Typical Efficiency vs. Load Current for A-B board – 24Vin, 3.3Vout and 8.5Vout LTC3858EUH Figure 6. Typical Efficiency vs. Load Current for A-B board – 36Vin, 3.3Vout and 8.5Vout 6 TRACK2 14V MAX 5 3 1 E 15 1 2 3 OFF RUN1 R22 R41 OPT R40 OPT JP8 60 90 120 VIN R37 [1] R35 [1] OPT C29 1 SS 0.1uF C1 97.6K 1% R24 3 2 R25 10K 1% 3 T RA CK JP6 T RA CK 2 CLKOUT PHASE INTVCC 3 OFF OPT C28 1 2 RUN2 JP4 0 3 INTVCC R38 OPT R7 JP5 T RACK1 T RACK R3 11.5K ON 35.7K R2 INTVCC R36 OPT R34 OPT VOUT2 VIN BURS T M ODE PULSE SK IP CCM 2.2uF JP3 0 INTVCC OPT R26 C19 ON 6 4 2 EXTVCC JP2 M ODE C22 4.7uF 10V E3 E9 E 17 E4 E2 E 10 VOUT2 E 16 1 R4 0.1uF C23 SS 1% R18 102K 1% 57.6K C15 VOUT1 R23 0 OPT C6 ITH2 R21 0 * * EXTVCC R13 2.2 R1 200K C27 C16 0.1uF R15 2.2 100pF 15 16 17 18 19 20 21 22 23 24 25 26 27 14 SNS2+ R20 0 1000pF TG2 SW2 BOOST2 BG2 INTVCC EXTVCC PGND VIN BG1 BOOST1 SW1 TG1 PGOOD1 C18 TRACK/SS2 PHSMD ILIM CLKOUT GND RUN2 RUN1 SGND PLLIN/MODE FREQ C26 100pF * R9 0 PGOOD2 1000pF * R8 0 TRACK/SS1 ITH1 VOUT2 12 13 3 28 4 33 8 7 6 5 2 29 30 [1] U1 0 R6 C21 R19 976K 1% 47pF 3300pF C14 R16 15K 4700pF R11 8.2K C4 C3 22pF 182K 1% R5 C2 10pF R39 200K D2 D3 SW2 SHT 2 TG2 SHT 2 C13 47uF 50V R14 0 INTVCC 4 4 Q3 BSZ097N04LS INTVCC INTVCC C12 0.1uF CMDSH-4E CMDSH-4E 10V C11 4.7uF 0.1uF C10 TG1 SHT 2 VIN + BG2 SHT 2 Q4 BSZ097N04LS 4 VIN 4 BG1 SHT 2 Q2 BSZ097N04LS BSZ097N04LS Q1 VIN SW1 SHT 2 * 2 R28 OPT OPT R30 CDEP 105-3R2M L1 3.2uH SNS1+ SNS1- R29 OPT CDE P105-7R2M L2 7.2uH R32 OPT OPT R31 0.005 * R10 * R17 0.008 R33 OPT SNS2- SNS2+ 4.7uF 50V 4.7uF 50V GND VIN VIN GND GND GND 10uF 16V GND GND E14 COUT4 + OPT J6 8.5V / 3A VOUT2 VOUT2 J5 E13 E6 J4 4.5V - 36V J3 E5 E12 J2 3.3V / 5A VOUT1 VOUT1 C20 COUT2 + 68uF 10V C7 + C5 OPT C17 + COUT1 220uF 4V J1 VOUT2 VIN COUT3 100uF 6.3V VOUT1 E11 NOTE: WHEN DCR SENSING IS IMPLEMENTED, SHORT R10 AND R17, DO NOT STUFF R8,R9,R20 AND R21 OPTIONAL DCR SENSING: ]2 [ EXTVCC SGND CLKOUT PLLIN / MODE 100K R27 INTVCC INTVCC TRACK1 PGOOD2 2 PGOOD1 S NS 11 S NS 1- S NS 1+ 32 E1 1 4 5 6 7 8 1 2 3 31 V FB 1 VFB2 11 S N S 29 SN S2- 5 6 7 8 1 2 3 S NS 1+ S N S 2+ 10 G N SI N SE 5 6 7 8 R C D LA N IO TP O 1 2 3 G N SI N ES 1 2 3 R C D LA N IO TP O 5 6 7 8 INTVCC QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER 9V > IN V N IO T A L U G E R R O F ]2 [ 1 U 1][ 73 R T P O K .72 1 53 R T P O K .56 6 H U E 75 83 C T L H U E 85 83 C T L YS SA A - B - 7