IRDC3898-P1V2 SupIRBuck TM USER GUIDE FOR IR3898 EVALUATION BOARD 1.2Vout DESCRIPTION The IR3898 is a synchronous buck converter, providing a compact, high performance and flexible solution in a small 4mm X 5 mm Power QFN package. Key features offered by the IR3898 include internal Digital Soft Start/Soft Stop, precision 0.5Vreference voltage, Power Good, thermal protection, programmable switching frequency, Enable input, input under-voltage lockout for proper start-up, enhanced line/ load regulation with feed forward, external frequency synchronization with smooth clocking, internal LDO and pre-bias startup. Output over-current protection function is implemented by sensing the voltage developed across the on-resistance of the synchronous rectifier MOSFET for optimum cost and performance and the current limit is thermally compensated. This user guide contains the schematic and bill of materials for the IR3898 evaluation board. The guide describes operation and use of the evaluation board itself. Detailed application information for IR3898 is available in the IR3898 data sheet. BOARD FEATURES • Vin = +12V (+ 13.2V Max) • Vout = +1.2V @ 0- 6A • Fs=400KHz • L= 1.2uH • Cin= 3x10uF (ceramic 1206) + 1X330uF (electrolytic) • Cout=5x47uF (ceramic 0805) 9/11/2012 1 IRDC3898-P1V2 CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 6A load should be connected to VOUT+ and VOUT-. The inputs and output connections of the board are listed in Table I. IR3898 has only one input supply and internal LDO generates Vcc from Vin. If operation with external Vcc is required, then R15 can be removed and external Vcc can be applied between Vcc+ and Vcc- pins. Vin pin and Vcc/LDOout pins should be shorted together for external Vcc operation. The output can track voltage at the Vp pin. For this purpose, Vref pin is to be connected to ground (use zero ohm resistor for R21). The value of R14 and R20 can be selected to provide the desired tracking ratio between output voltage and the tracking input. Table I. Connections Connection Signal Name VIN+ Vin (+12V) VIN- Ground of Vin Vout+ Vout(+1.2V) Vout- Ground for Vout Vcc+ Vcc/ LDO_out Pin Vcc- Ground for Vcc input Enable Enable P_Good Power Good Signal AGnd Analog ground LAYOUT The PCB is a 4-layer board (2.23”x2”) using FR4 material. All layers use 2 Oz. copper. The PCB thickness is 0.062”. The IR3898 and other major power components are mounted on the top side of the board. Power supply decoupling capacitors, the bootstrap capacitor and feedback components are located close to IR3898. The feedback resistors are connected to the output at the point of regulation and are located close to the SupIRBuck IC. To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground current path. 9/11/2012 2 IRDC3898-P1V2 Connection Diagram Vin Gnd Gnd Vout Enable VDDQ Top View Vref Sync S-Ctrl AGnd PGood Vsns Vcc+ Vcc- Bottom View Fig. 1: Connection Diagram of IR3899/98/97 Evaluation Boards 9/11/2012 3 IRDC3898-P1V2 Fig. 2: Board Layout-Top Layer Single point connection between AGnd and PGnd Fig. 3: Board Layout-Bottom Layer 9/11/2012 4 IRDC3898-P1V2 Fig. 4: Board Layout-Mid Layer 1 Fig. 5: Board Layout-Mid Layer 2 9/11/2012 5 PGood N/S C10 N/A 49.9K R17 Vcc+ R28 VCC R14 0 ohm Agnd VDDQ SYNC 4.32K R1 C11 R9 60.4K 1nF 10nF C26 120pF 1 C12 S_Ctrl R13 0 ohm C23 2.2uF VCC S_Ctrl Vp Rt_Sy nc Gnd COMP C32 1.0uF IR3898 R7 R10 R4 PGnd SW PVin R3 2.37K 3.32K R2 C8 Vsns PGND N38703 C7 0.1uF 0.1uF C24 N/S R29 VCC R15 A 20 ohm R6 R12 2.37K N/S B 3.32K R11 1.2uH L1 0 ohm C25 3300pF 11 12 13 0 ohm 100 ohm N/A R18 49.9K N/S N/S 0 ohm R50 + C35 N/S C29 C30 + C36 N/S N/S C28 N/S C27 C4 10uF C3 10uF N/S C20 47uF C19 47uF C18 C17 47uF 47uF C16 47uF C15 1 1 1 1 1 1 Vout+ Vout+ (1.2V) Vin- Vin- Vin+ Vin+ 1 1 Vout- C14 0.1uFVout- Vout C1 + N/S 330uF/25V C2 Input ceramic: 1206 C5 10uF C6 N/A Fig. 6: Schematic of the IR3898 evaluation board 6 16 5 4 3 1 FB N/S U1 C37 R19 7.5K 2 VREF 1 15 Enable R21 N/S 1 Boot 1 1 1 9 Vin PGood 7 Vcc/LDO_OUT 10 14 Vsns 8 GND 17 VREF 1 1 1 1 Enable 1 9/11/2012 1 Vin IRDC3898-P1V2 6 IRDC3898-P1V2 Bill of Materials Item Qty Part Reference Value Description Manufacture r Part Number 1 1 C1 330uF SMD Electrolytic F size 25V 20% Panasonic EEV-FK1E331P 2 3 C3 C4 C5 10uF 1206, 16V, X5R, 20% TDK C3216X5R1C106M 3 3 C7 C14 C24 0.1uF 0603, 25V, X7R, 10% Murata GRM188R71E104KA01B 4 1 C12 1nF Murata GRM1885C1H102JA01D 5 1 C8 3300pF 0603,50V,X7R Murata GRM188R71H332KA01B 6 1 C11 120pF 0603, 50V, NP0, 5% Murata GRM1885C1H121JA01D 7 5 C15 C16 C17 C18 C19 47uF 0805, 6.3V, X5R, 20% TDK C2012X5R0J476M 8 1 C23 2.2uF 0603, 16V, X5R, 20% TDK C1608X5R1C225M 9 1 C26 4.7nF 0603, 25V, X7R, 10% Murata GRM188R71E472KA01J 10 1 C32 1.0uF 0603, 25V, X5R, 10% Murata GRM188R61E105KA12D 11 1 L1 1.2uH SMD 6.36x6.56x3mm, 6.82mΩ Coilcraft XAL6030-122ME 12 1 R1 4.32K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF4321V 13 2 R2 R11 4.53K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF4531V 14 2 R3 R12 3.24K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF3241V 15 1 R4 100 Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF1000V 16 1 R6 20 Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF20R0V 17 1 R9 60.4K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF6042V 18 5 R10 R13 R14 R15 R50 0 Thick Film, 0603,1/10W Panasonic ERJ-3GEY0R00V 19 2 R17 R18 49.9K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF4992V 20 1 R19 7.5K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF7501V 21 1 U1 IR3898 PQFN 4x5mm IR IR3898MPBF 9/11/2012 0603, 50V, 5% 7 IRDC3898-P1V2 TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no airflow Fig. 7: Start up at 6A Load Ch1:Vin, Ch2:Vo, Ch3:PGood Ch4:Enable Fig. 9: Start up with 1V Pre Bias , 0A Load, Ch1:Vo Fig. 11: Inductor node at 6A load Ch2:LX 9/11/2012 Fig. 8: Start up at 6A Load, Ch1:Vin, Ch2:Vo, Ch3:Vcc, Ch4:PGood Fig. 10: Output Voltage Ripple, 6A load Ch1: Vout , Fig. 12: Short circuit (Hiccup) Recovery Ch1:Vout , Ch4:Iout 8 IRDC3898-P1V2 TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no air flow Fig. 13: Transient Response, 0.5A to 3.5A step Ch1:Vout Ch4-Iout 9/11/2012 9 IRDC3898-P1V2 TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no air flow Fig. 14: Bode Plot at 6A load shows a bandwidth of 89.93KHz and phase margin of 50.9 degrees 9/11/2012 10 IRDC3898-P1V2 TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no air flow 90 88 Efficiency [%] 86 84 82 80 78 76 74 72 70 0.6 1.2 1.8 2.4 3 3.6 Io [A] 4.2 4.8 5.4 6 Fig.15: Efficiency versus load current 2.0 1.8 Power Loss [W] 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 0.5 1 1.5 2 2.5 3 3.5 Io [A] 4 4.5 5 5.5 6 Fig.16: Power loss versus load current 9/11/2012 11 IRDC3898-P1V2 THERMAL IMAGES Vin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, No Air flow Fig. 17: Thermal Image of the board at 6A load Test point 1 is IR3898 Test point 2 is inductor 9/11/2012 12 IRDC3898-P1V2 PCB METAL AND COMPONENT PLACEMENT Evaluations have shown that the best overall performance is achieved using the substrate/PCB layout as shown in following figures. PQFN devices should be placed to an accuracy of 0.050mm on both X and Y axes. Self-centering behavior is highly dependent on solders and processes, and experiments should be run to confirm the limits of self-centering on specific processes. For further information, please refer to “SupIRBuck™ Multi-Chip Module (MCM) Power Quad Flat No-Lead (PQFN) Board Mounting Application Note.” (AN1132) Figure 18: PCB Metal Pad Spacing (all dimensions in mm) 9/11/2012 13 IRDC3898-P1V2 SOLDER RESIST IR recommends that the larger Power or Land Area pads are Solder Mask Defined (SMD.) This allows the underlying Copper traces to be as large as possible, which helps in terms of current carrying capability and device cooling capability. When using SMD pads, the underlying copper traces should be at least 0.05mm larger (on each edge) than the Solder Mask window, in order to accommodate any layer to layer misalignment. (i.e. 0.1mm in X & Y.) However, for the smaller Signal type leads around the edge of the device, IR recommends that these are Non Solder Mask Defined or Copper Defined. When using NSMD pads, the Solder Resist Window should be larger than the Copper Pad by at least 0.025mm on each edge, (i.e. 0.05mm in X&Y,) in order to accommodate any layer to layer misalignment. Ensure that the solder resist in-between the smaller signal lead areas are at least 0.15mm wide, due to the high x/y aspect ratio of the solder mask strip. Figure 19: Solder resist 9/11/2012 14 IRDC3898-P1V2 STENCIL DESIGN Stencils for PQFN can be used with thicknesses of 0.100-0.250mm (0.004-0.010"). Stencils thinner than 0.100mm are unsuitable because they deposit insufficient solder paste to make good solder joints with the ground pad; high reductions sometimes create similar problems. Stencils in the range of 0.125mm-0.200mm (0.005-0.008"), with suitable reductions, give the best results. Evaluations have shown that the best overall performance is achieved using the stencil design shown in following figure. This design is for a stencil thickness of 0.127mm (0.005").The reduction should be adjusted for stencils of other thicknesses. Figure 20: Stencil Pad Spacing (all dimensions in mm) 9/11/2012 15 IRDC3898-P1V2 PACKAGE INFORMATION Figure 21: Package Dimensions IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105 TAC Fax: (310) 252-7903 This product has been designed and qualified for the Industrial market Visit us at www.irf.com for sales contact information Data and specifications subject to change without notice.06/11 9/11/2012 16