Freescale Semiconductor User Guide Document Number: KT34713UG Rev. 4.0, 1/2009 Using the 5.0A 1.0MHz Fully Integrated Single Switch-Mode Power Supply (KIT34713EPEVBE) 1 Introduction This User’s Guide will help the designer become better acquainted with the 34713 IC and Evaluation board. It contains a procedure to configure each block of the 34713 in a practical way, which is based on a working Evaluation Board designed by Freescale (KIT34713EPEVBE). 2 34713 Specification The 34713 is a highly integrated, space-efficient, low cost, single synchronous buck switching regulator with integrated N-channel power MOSFETs. It is a high performance point-of-load (PoL) power supply, with the ability to track an external reference voltage in different configurations. The 34713 has a high efficient 5.0 A continuous output current capability combined with its voltage tracking/sequencing ability and tight output regulation. © Freescale Semiconductor, Inc., 2007-2009. All rights reserved. Contents 1 2 3 4 5 6 7 8 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 34713 Specification. . . . . . . . . . . . . . . . . . . . . 1 Application Diagram . . . . . . . . . . . . . . . . . . . . 2 Board’s Specifications . . . . . . . . . . . . . . . . . . 2 Component Selection for 34713 Eval Board. 3 Layout Design . . . . . . . . . . . . . . . . . . . . . . . . 13 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . 17 References. . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Application Diagram 3 Application Diagram 3.0 to 6.0 V VIN PVIN CIN VMASTER 0.1μF BOOT SW VIN VOUT R3 VREFIN R4 RILH RFQH RFQL 0.1μF RILL INV VDDI FREQ CBOOT L RS VOUT R1 CO CS RF CX R2 CF COMP 34713 ILIM GND PGND VIN 1kΩ PG SD Microcontroller Figure 1. Application diagram for 34713 4 Board’s Specifications The Board was designed to have an operating range defined by: PVIN_MIN = 3.0 V Pvin_max = 6.0 V VOUT_MIN = 0.7 V VOUT_MAX = 3.6 V IOUT_MIN = 0A IOUT_MAX = 5A Using the 34713, Rev. 4.0 2 Freescale Semiconductor Component Selection for 34713 Eval Board 5 Component Selection for 34713 Eval Board 5.1 I/O Parameters: Vin = Pvin = 3.3V (typical) VREFIN = 1 V Vo = 1.8 V Io = 3 A FSW = 1 MHz 5.2 Configuring the Output Voltage: The channel SW of the 34713 is a general purpose DC-DC converter. The resistor divider to the INV1 node is responsible for setting the output voltage. The equation is: Where VREF could be the voltage in the VREFIN terminal or the internal reference VBG=0.7V, VREF is chosen as follows: VREF = VREFIN when VREFIN < 0.7V. For a regulated output at 1.8 V, we choose R1 = 20kΩ, and R2 is calculated as: V R1 R 2 = REF = 12.72 KΩ Vo − V REF Using the 34713, Rev. 4.0 Freescale Semiconductor 3 Component Selection for 34713 Eval Board 5.3 Switching Frequency Configuration The switching frequency will have a default value of 1.0 MHz, by connecting the FREQ terminal to the GND terminal. If the lowest frequency value of 200 KHz is desired, then connect the FREQ terminal to VDDI. To program the switching frequency to another value, connect an external resistor divider to the FREQ terminal to achieve the voltages given by the Frequency Selection Table. Frequency Khz Voltage applied to pin FREQ [V] 200 2.341 – 2.500 253 2.185 - 2.340 307 2.029 - 2.184 360 1.873 - 2.028 413 1.717 – 1.872 466 1.561 – 1.716 520 1.405 - 1.560 573 1.249 - 1.404 627 1.093 - 1.248 680 0.936 - 1.092 733 0.781 - 0.936 787 0.625 - 0.780 840 0.469 - 0.624 893 0.313 - 0.468 947 0.157 - 0.312 1000 0.000 - 0.156 Table 1. Frequency Selection Table The EVB frequency was set to 1 MHz by connecting the FREQ terminal directly to GND. Using the 34713, Rev. 4.0 4 Freescale Semiconductor Component Selection for 34713 Eval Board 5.4 Selecting Inductor Inductor calculation is straightforward. The equation is the following: L = D'MAX ∗T ∗ (Vo + I 0 * ( Rds(on) _ ls + r _ w)) ΔI o Maximum Off time percentage T = 1μs Rds (on) _ ls = 45mΩ Switching period Drain – to – source resistance of FET Winding resistance of Inductor Output current ripple L = 1.15uH Freescale has selected L = 1 .5 μ H to allow some operating margin. 5.5 Input Capacitors The input capacitor selection should be based on the current ripple allowed on the input line. The input capacitor should provide the ripple current generated during the inductor charge time. This ripple is dependent on the output current sourced by 34713 so that: I RMS = Io d (1 − d ) Where: IRMS is the RMS value of the input capacitor current, I0 is the output current, and d= VO/VIN is the duty cycle. For a buck converter, IRMS has its maximum at Vin = 2VO Since: I RMS_MAX = PMAX ESR Where PMAX is the maximum power dissipation of the capacitor, and is a constant, based on its physical size (generally given in the datasheets under the heading AC power dissipation). Freescale derives that the lower the ESR, the higher the ripple current capability. In other words, Using the 34713, Rev. 4.0 Freescale Semiconductor 5 Component Selection for 34713 Eval Board a low ESR capacitor (i.e., with high ripple current capability) can withstand high ripple current levels without overheating. Therefore, for greater efficiency and because the overall voltage ripple on the input line also depends on the input capacitor ESR, we recommend using low ESR capacitors. Cin MIN = 0.5 * L * ( I RMS ) 2 ΔVo * Vin For a ΔVO = 0.5*VIN, Then CinMIN = 35μF The EVB input capacitor of 300μF was selected to assure less input voltage ripple and have better regulation. 5.6 Selecting the Output Filter Capacitor The following output capacitor considerations are the most important and not the actual Farad value: the physical size, the ESR of the capacitor, and the voltage rating. Calculate the minimum output capacitor using the following formula ΔI 0 C 0 = ------------------------------8 ⋅ F SW ⋅ ΔV 0 However, a more significative calculation must include the transient response, in order to calculate the real minimum capacitor value, and to assure a good performance. Transient Response percentage: TR_% = 3% Maximum Transient Voltage: TR_V_dip = Vo*TR_% = 0.75*.03=0.054V Maximum current step: ΔIo _ step = (Vin _ min − Vo ) * D _ max =0.72A Fsw * L T * Io Inductor Current rise time: dt _ I _ rise = ΔIo _ step = 4.7μs Co = Io * dt _ I _ rise = 296.3μF TR _ V _ dip To find the Maximum allowed ESR, the following formula was used: ESR max = ΔVo * Fsw * L = 8mΩ Vo (1 − D min) An array of capacitors in parallel were used, with 3 Low ESR Ceramic capacitors of 100 μF. Using the 34713, Rev. 4.0 6 Freescale Semiconductor Component Selection for 34713 Eval Board 5.7 Bootstrap Capacitor Freescale recommends a 0.1μF capacitor. 5.8 Soft Start Table 2 shows the voltage that should be applied to the terminal ILIM to get the desired configuration of the soft start timing. SoftStart [ms] Voltage applied to ILIM 3.2 1.25 - 1.49V 1.6 1.50 - 1.81V 0.8 1.82 - 2.13V 0.4 2.14 - 2.50V Table 2. Soft Start Configuration The ILIM pin remains connected to VDDI to achieve the minimum soft start timing (0.4ms). 5.9 Compensation Network 1. Choose a value for R1 = 20kΩ 2. Using a Crossover frequency of 50 kHz, set the Zero pole frequency to Fcross/10 1 1 = 5.0kHz FP 0 = Fcross = 10 2π * R1C F 3. Knowing the LC frequency, the Frequency of Zero 1 and Zero 2 in the compensation network are equal to FLC: 1 1 FZ 1 = FZ 2 = 2π * RF C F 2π * R1C S RF = 1 1 = 14.66 KΩ C S = = 1.06 nF 2π * C F FZ 1 2π * R1 FZ 2 4. Calculate RS by placing the first pole at the ESR zero frequency: 1 FP1 = 2π * RS C S RS = 1 = 570Ω 2π * FP1C S Using the 34713, Rev. 4.0 Freescale Semiconductor 7 Component Selection for 34713 Eval Board 5. Set the second pole at ten times the Crossover Frequency to achieve a faster response and a proper phase margin. 1 = 500 kHz FP 2 = Cmargin. Cx a proper phase F 2π * R F CF + Cx CX = CF = 24 pF 2π * R F C F FP 2 − 1 The Actual values used on the EVB might change due to the precision of L and C components. Thus, on EVB where selected as follows. CF = 1.9 nF RF = 15 kΩ Cs = 1 nF Rs = 300 Ω Cx = 20 pF 1 10 100 1000 Hz 10000 100000 1000000 10000000 100000000 120 100 80 60 40 20 dB/Deg 0 -20 -40 -60 -80 -100 -120 -140 -160 -180 -200 Open Loop Gain and phase User Values Gain (dB) Phase (Degrees) Figure 2. Compensated Open Loop Bode Plot Using the 34713, Rev. 4.0 8 Freescale Semiconductor Component Selection for 34713 Eval Board 5.10 Tracking Configurations This device allows two tracking configurations: Ratiometric and Co-incidental Tracking. Figure 3. Ratiometric Tracking Figure 4. Co-incidental Tracking Circuit Configuration: The master voltage (VM) feedback resistor divider network will be used in place of R3 and R4, as shown below. The slave output (VS) is connected through its own feedback resistor divider network to the INV- terminal, resistors R1 and R2 below. All four resistors will affect the accuracy of the system, and they need to be 1% accurate resistors. To achieve this tracking configuration, the master voltage must be connected as in Figure 5, on page 10 and cannot be directly connected to the VREFIN terminal. Using the 34713, Rev. 4.0 Freescale Semiconductor 9 Component Selection for 34713 Eval Board V MASTER VBG VRE FIN R3 R4 To INV - of Vmas ter Reference selector V SLAVE Rs + EA - I NV R1 Cs CX RF CF CO R2 COMP Figure 5. Ratiometric Tracking Circuit Connections Equations: • VM = VBG_M(1+R3/R4) • VREFIN = VM * R4/(R3+R4) • VREFOUT = VREFIN • VS = VREFOUT(1+R1/R2) = VM* R4/(R3+R4)*(R2+R1)/R2, if VREFOUT < VBG_S • VS = VBG_S(1+R1/R2), if VREFOUT ≥ VBG_S Figure 6. Ratiometric Tracking Plot Circuit Configuration: Connect a three resistor divider to the master voltage (VM) and route the upper tap point of the divider to the VREFIN terminal, resistors R3, R4, and R5, as shown in Figure 7, on page 11. This resistor divider must be the same ratio as the slave output’s (VS) feedback resistor divider, which in turn connects to the INV- terminal, and resistors R1 and R2 in Figure 7 (Condition: R1 = R3 and R2 = R4 + R5). The master’s feedback resistor divider would be Using the 34713, Rev. 4.0 10 Freescale Semiconductor Component Selection for 34713 Eval Board (R3+R4) and R5. All five resistors will affect the accuracy of the system and they need to be 1% accurate resistors. To achieve this tracking configuration, the master voltage must be connected in the way shown and cannot be directly connected to the VREFIN terminal. V MASTER VBG VRE FIN R3 R4 Referenc e selec tor To INV- of V mas ter R5 V SLAVE Rs I NV + EA - R1 Cs CX RF CF CO R2 COMP Figure 7. Co-incidental Tracking Circuit Connections Equations: VM = VBG_M[1+(R3+R4)/R5] VREFIN = VM*(R4+R5)/(R3+R4+R5) VREFOUT = VREFIN VS = VREFOUT(1+R1/R2) = VM*(R4+R5)/(R3+R4+R5)*(R2+R1)/R2 = VM if VREFOUT < VBG_S VS = VBG_S(1+R1/R2), if VREFOUT ≥ VBG_S Figure 8. Co-incidental Tracking Plot When no tracking is needed, VREFIN should be attached to a DC voltage higher than 0.7 V. For instance, it can be attached to the VDDI pin. Using the 34713, Rev. 4.0 Freescale Semiconductor 11 Component Selection for 34713 Eval Board 5.11 EVB Schematic Design VIN BOOT VIN BOOT VDDI C15 I/O SIGNALS SW VDDI 0.1uF PVIN 4.7_nopop PVIN R10 10k J3 ILIM GND VMASTER VOUT R11 10k 3 2 1 R13 10k_nopop FREQ ILIM 19 PVIN 20 PVIN BOOT 22 VIN 24 R12 10k_nopop FREQ VDDI VIN GND PVIN 3 2 1 VIN R16 U1 23 C14 0.1uF 21 J2 1 SGND PVIN 18 2 FREQ SW 17 3 ILIM SW 16 SW SW MC34713 PG PG SW 15 5 N/C GND 14 6 SD GND 13 R7 1k R8 10k GND 12 GND VOUT N/C INV 11 10 9 VIN 8 SD COMP SD 7 VMASTER 4 VREFIN VMASTER PGOOD LED PG VREFIN VREFIN C11 VREFIN D1 LED C13 0.1uF 0.1uF R9 10k VOUT LED INV INV COMP C12 0.1uF COMP JUMPERS BUCK CONVERTER VOUT1 VOUT VOUT2 J1 L1 SW 1 VOUT 2 1.5uH D2 PVIN VMASTER STBY_nopop LED R3 4.7_nopop C6 100uF C7 100uF 1 2 1 2 C8 100uF 1 3 5 7 9 2 4 6 8 10 VREFIN PG SD PMEG2010EA_nopop C9 1nF_nopop CON10A SD COMPENSATION NETWORK PVIN CAPACITORS OPTIONAL nopop VOUT VDDI PVIN ILIM C20 1nF 15k C3 100uF C4 100uF C5 100uF C19 FREQ R6 POT_50K_nopop R5 POT_50K_nopop R14 300 0.02nF R15 C2 1uF R1 20k INV C18 COMP C1 0.1uF VIN CAPACITORS R2 12.7k VIN 12.7k 1.9nF C17 10uF C16 0.1uF Figure 9. EVB Schematic Design Using the 34713, Rev. 4.0 12 Freescale Semiconductor Layout Design 6 Layout Design Figure 10. PCB Layout Top View Figure 11. PCB Layout Inner Layer Using the 34713, Rev. 4.0 Freescale Semiconductor 13 Layout Design Figure 12. PCB Layout Bottom Layer 6.1 • • • • • • • • • • • PCB Layout Recommendations Place decoupling capacitors as close as possible to their corresponding pad(s). Try to place all components on just one Layer. Do not place a Ground Plane on component and routing side. Create a Ground plane layer and tie it to ground signals with vias. To effectively transfer heat from the center thermal pad on the top layer to the ground plane, vias need to be used in the center pad. Use 5 to 9 vias spaced evenly with a finished diameter of 0.3mm. Place Test vias as close as possible to the IC to ensure a good measurement value. PVIN, VIN, VOUT signals have to be tracked with a wide and straight copper area. Never trace the Feedback signal in parallel to the SW signal. Ensure the SW Inductor is placed as close as possible to its pads. SW track has to be as thin and short as possible. Make sure the I/O connectors are capable of managing the Load current. Note: Freescale does not recommend connecting the PGND pins to the thermal pad. The thermal pad is connected to the signal ground and should not be used to make the connection from the PGND pins to the ground plane. Doing so can cause ground bounce on the signal ground from the high di/dt switch current and parasitic trace inductance. Using the 34713, Rev. 4.0 14 Freescale Semiconductor Layout Design 6.2 Item Bill of Materials Quantity Reference Value Description Footprint 1 16 VREFOUT, VREFIN, VOUT, VIN, VDDI, SW, STBY, SD, PVIN, PG, INV, ILIM, GND, FREQ, COMP, BOOT not populated PC test point miniature SMT TP1 2 1 C2 1μF Cap Cer 1.0μF 6.3V 10% X5R 0603 SM/C_0603 3 6 C3, C4, C5, C6, C7, C8 100μF Cap Cer 100μF 10% X5R 1210 SM/C_1210 4 1 C9 not populated 5 7 C1, C11, C12, C13 , C14 C15, C16 0.1μF Cap Cer 0.1μF 50V 10% X7R 0603 SM/C_0603 6 1 C17 10μF Cap Cer 10μF 6.3V 20% X5R 0603 SM/C_0603 7 1 C18 20pF Cap Cer 20pF50V 5% C0G 0603 SM/C_0603 8 1 C19 1.8nF Cap Cer 1800pF 50V 5% C0G 0603 SM/C_0603 9 1 C20 1nF Cap Cer 1000pF 25V 5% C0G CC0603 SM/C_0603 10 1 D1 LED LED Green 0603 SM/C_0603 11 1 D2 not populated 12 1 J1 Pin Header (2X5) 13 2 100mils jumpers Jumpers 14 1 J2 not populated 15 1 J3 not populated 16 1 L1 1.5μH Inductor Power 1.5μH 7.0A SMD B82464G 17 1 R1 20k Res MPF 20k ohm 1/10W 5% 0603 SM/C_0603 18 1 R2 12.7k Res 12.7k ohm 1/10W 1% 0603 SMD SM/C_0603 19 2 R3,R16 not populated SM/C_0603 20 2 R5,R6 not populated TRIMPOT 21 1 R7 1k SMC HDR 2X5 TH 100MIL CTR 330H AU 0.1” (2.54mm) 100 mils Res MF 1.0k 1/10W 1%0603 SM/C_0603 Using the 34713, Rev. 4.0 Freescale Semiconductor 15 Layout Design 22 2 R12,R13 not populated SM/C_0603 23 3 R8, R9, R10 10k Res MF 10.0k 1/10W 1% 0603 SM/C_0603 24 1 R11 10k Res MF 10.0k 1/10W 1% 0603 SM/C_0603 25 1 R14 300 Res MF 300 Ohm 1/10W 5% 0603 SM/C_0603 26 1 R15 15k Res MF 15.0k 1/10W 1% 0603 SM/C_0603 27 1 SD Push_button Switch tact mini 200GF SLV GWING 28 1 U1 MC34713 29 1 STBY not populated QFN_24 Switch tact mini 200GF SLV GWING Notes: Freescale does not assume liability, endorse, or warrant components from external manufacturers that are referenced in circuit drawings or tables. While Freescale offers component recommendations in this configuration, it is the customer’s responsibility to validate their application. Using the 34713, Rev. 4.0 16 Freescale Semiconductor Conclusion 7 Conclusion With this User’s Guide, the designer is capable of configuring the 34713 as a general purpose switching power supply for devices that can make use of the capabilities the 34713 offers. The board is fully configured to work at any desirable reference voltage within 0 and 2.5 V. However, it is highly recommended to calculate all components for the specific application situation, in order to assure a better efficiency and stability of the IC. 8 References • • • 34713 Datasheet, “5A, 1MHz Fully Integrated Single Switch-Mode Power Supply”; Freescale semiconductor, Inc. Similar network compensation calculations are available in Application Note “AN1989 MC34701 and MC34702 Component Selection Guide”; Freescale Semiconductor, Inc. Sanjaya Maniktala, “Switching Power Supplies A to Z”, Newnes, 2006. Using the 34713, Rev. 4.0 Freescale Semiconductor 17 How to Reach Us: Home Page: www.freescale.com RoHS-compliant and/or Pb-free versions of Freescale products have the functionality and electrical characteristics of their non-RoHS-compliant and/or non-Pb-free counterparts. For further information, see http://www.freescale.com or contact your Freescale sales representative. Web Support: http://www.freescale.com/support For information on Freescale’s Environmental Products program, go to http://www.freescale.com/epp. USA/Europe or Locations Not Listed: Freescale Semiconductor, Inc. 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