TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com 4.5V to 18 V Input, 4-A Synchronous Step-Down SWIFT™ Converter with Eco-Mode™ Check for Samples: TPS54428 FEATURES DESCRIPTION • The TPS54428 is an adaptive on-time D-CAP2™ mode synchronous buck converter. 1 23 • • • • • • • • • • • D-CAP2™ Mode Enables Fast Transient Response Low Output Ripple and Allows Ceramic Output Capacitor Wide VIN Input Voltage Range: 4.5 V to 18 V Output Voltage Range: 0.76 V to 7.0 V Highly Efficient Integrated FETs Optimized for Lower Duty Cycle Applications – 70 mΩ (High Side) and 53 mΩ (Low Side) High Efficiency, Less Than 10 μA at Shutdown High Initial Bandgap Reference Accuracy Adjustable Soft Start Pre-Biased Soft Start 650-kHz Switching Frequency (fSW) Cycle By Cycle Over Current Limit Auto-Skip Eco-mode™ for High Efficiency at Light Load APPLICATIONS • Wide Range of Applications for Low Voltage System – Digital TV Power Supply – High Definition Blu-ray Disc™ Players – Networking Home Terminal – Digital Set Top Box (STB) The TPS54428 enables system designers to complete the suite of various end-equipment power bus regulators with a cost effective, low component count, low standby current solution. The main control loop for the TPS54428 uses the D-CAP2™ mode control that provides a fast transient response with no external compensation components. The adaptive on-time control supports seamless transition between PWM mode at higher load conditions and Eco-mode™ operation at light loads. Eco-mode™ allows the TPS54428 to maintain high efficiency during lighter load conditions. The TPS54428 also has a proprietary circuit that enables the device to adopt to both low equivalent series resistance (ESR) output capacitors, such as POSCAP or SP-CAP, and ultra-low ESR ceramic capacitors. The device operates from 4.5-V to 18 V VIN input. The output voltage can be programmed between 0.76 V and 7.0 V. The device also features an adjustable soft start time. The TPS54428 is available in the 8-pin DDA package,and designed to operate from –40°C to 85°C. . Vout(50mV/div) TPS54428DDA Iout(2A/div) 100us/div 1 2 3 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. D-CAP2 is a trademark of Texas Instruments. Blu-ray Disc is a trademark of Blu-ray Disc Association. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2011–2012, Texas Instruments Incorporated TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. ORDERING INFORMATION (1) (1) (2) (3) TA PACKAGE (2) (3) –40°C to 85°C DDA ORDERABLE PART NUMBER TRANSPORT MEDIA PIN TPS54428DDA Tube 8 TPS54428DDAR Tape and Reel For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI web site at www.ti.com. Package drawings, thermal data, and symbolization are available at www.ti.com/packaging. All package options have Cu NIPDAU lead/ball finish. ABSOLUTE MAXIMUM RATINGS over operating free-air temperature range (unless otherwise noted) (1) VALUE Input voltage range MAX VIN, EN –0.3 20 V VBST –0.3 26 V VBST (10 ns transient) –0.3 28 V VBST (vs SW) –0.3 6.5 V VFB, SS –0.3 6.5 V –2 20 V SW –3 22 V VREG5 –0.3 6.5 V GND –0.3 0.3 V –0.2 0.2 V 2 kV SW (10 ns transient) Output voltage range Voltage from GND to thermal pad, Vdiff Electrostatic discharge UNIT MIN Human Body Model (HBM) 500 V Operating junction temperature, TJ –40 150 °C Storage temperature, Tstg –55 150 °C (1) Charged Device Model (CDM) Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. THERMAL INFORMATION THERMAL METRIC (1) TPS54428 DDA (8 PINS) θJA Junction-to-ambient thermal resistance 42.1 θJCtop Junction-to-case (top) thermal resistance 50.9 θJB Junction-to-board thermal resistance 31.8 ψJT Junction-to-top characterization parameter ψJB Junction-to-board characterization parameter 13.5 θJCbot Junction-to-case (bottom) thermal resistance 7.1 (1) 2 5 UNITS °C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com RECOMMENDED OPERATING CONDITIONS over operating free-air temperature range (unless otherwise noted) VIN Supply input voltage range VBST VI Input voltage range MIN MAX 4.5 18 –0.1 24 VBST (10 ns transient) -0.1 27 VBST(vs SW) –0.1 5.7 SS –0.1 5.7 EN –0.1 18 VFB –0.1 5.5 SW –1.8 18 UNIT V V –3 21 GND –0.1 0.1 –0.1 5.7 V 0 10 mA SW (10 ns transient) VO Output voltage range VREG5 IO Output Current range IVREG5 TA Operating free-air temperature –40 85 °C TJ Operating junction temperature –40 150 °C TYP MAX UNIT ELECTRICAL CHARACTERISTICS over operating free-air temperature range, VIN = 12 V (unless otherwise noted) PARAMETER TEST CONDITIONS MIN SUPPLY CURRENT IVIN Operating - non-switching supply current VIN current, TA = 25°C, EN = 5 V, VFB = 0.8 V 950 1400 μA IVINSDN Shutdown supply current VIN current, TA = 25°C, EN = 0 V 3.0 10 μA LOGIC THRESHOLD VENH EN high-level input voltage EN VENL EN low-level input voltage EN REN EN pin resistance to GND VEN = 12 V 1.6 225 V 450 0.6 V 900 kΩ mV VFB VOLTAGE AND DISCHARGE RESISTANCE TA = 25°C, VO = 1.05 V, IO = 10 mA, Eco-mode™ operation VFBTH IVFB VFB threshold voltage VFB input current 771 TA = 25°C, VO = 1.05 V, continuous mode operation 757 765 773 TA = –40°C to 85°C , VO = 1.05V, continuous mode operation (1) 751 765 779 0 ±0.1 μA 5.5 5.7 V 25 mV 100 mV VFB = 0.8 V, TA = 25°C VREG5 OUTPUT VVREG5 VREG5 output voltage TA = 25°C, 6.0 V < VIN < 18 V, 0 < IVREG5 < 5 mA VLN5 Line regulation 6 V < VIN < 18 V, IVREG5 = 5 mA VLD5 Load regulation 0 mA < IVREG5 < 5 mA IVREG5 Output current VIN = 6 V, VREG5 = 4.0 V, TA = 25°C 60 mA RDS(on)h High side switch resistance 25°C, VBST - SW = 5.5 V 70 mΩ RDS(on)l Low side switch resistance 25°C 53 mΩ 5.2 MOSFET CURRENT LIMIT Iocl (1) Current limit L out = 1.5 µH (1) 4.6 5.3 6.8 A Not production tested. Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 3 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com ELECTRICAL CHARACTERISTICS (continued) over operating free-air temperature range, VIN = 12 V (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT THERMAL SHUTDOWN TSDN Thermal shutdown threshold Shutdown temperature (2) 170 Hysteresis (2) °C 35 ON-TIME TIMER CONTROL tON On time VIN = 12 V, VO = 1.05 V 150 tOFF(MIN) Minimum off time TA = 25°C, VFB = 0.7 V 260 310 ns 7.8 ns SOFT START ISSC SS charge current VSS = 0 V 4.2 6.0 ISSD SS discharge current VSS = 0.5 V 0.1 0.2 Wake up VREG5 voltage 3.45 3.75 4.05 Hysteresis VREG5 voltage 0.19 0.32 0.45 μA mA UVLO UVLO (2) 4 UVLO threshold V Not production tested. Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com DEVICE INFORMATION DDA PACKAGE (TOP VIEW) 1 EN 2 VFB POWER PAD VIN 8 VBST 7 SW 6 GND 5 TPS54428 DDA 3 VREG5 HSOP8 4 SS PIN FUNCTIONS PIN NAME DESCRIPTION NO. EN 1 Enable input control. Active high. VFB 2 Converter feedback input. Connect to output voltage with feedback resistor divider. VREG5 3 5.5 V power supply output. A capacitor (typical 1 µF) should be connected to GND. VREG5 is not active when EN is low. SS 4 Soft-start control. An external capacitor should be connected to GND. GND 5 Ground pin. Power ground return for switching circuit. Connect sensitive SS and VFB returns to GND at a single point. SW 6 Switch node connection between high-side NFET and low-side NFET. VBST 7 Supply input for the high-side FET gate drive circuit. Connect 0.1µF capacitor between VBST and SW pins. An internal diode is connected between VREG5 and VBST. 8 Input voltage supply pin. VIN Exposed Thermal Pad Back side Thermal pad of the package. Must be soldered to achieve appropriate dissipation. Must be connected to GND. Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 5 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com FUNCTIONAL BLOCK DIAGRAM VIN EN Logic EN 1 VIN 8 VREG5 7 Control Logic VBST Ref SS 1 shot SW VFB VREG 5 SGND VO 6 2 XCON VREG5 Ceramic Capacitor 3 SS 5 SW 4 PGND GND ZC Softstart PGND SS SW SGND PGND VIN UVLO VREG 5 UVLO REF 6 TSD Protection Logic Ref Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com OVERVIEW The TPS54428 is a 4-A synchronous step-down (buck) converter with two integrated N-channel MOSFETs. It operates using D-CAP2™ mode control. The fast transient response of D-CAP2™ control reduces the output capacitance required to meet a specific level of performance. Proprietary internal circuitry allows the use of low ESR output capacitors including ceramic and special polymer types. DETAILED DESCRIPTION PWM Operation The main control loop of the TPS54428 is an adaptive on-time pulse width modulation (PWM) controller that supports a proprietary D-CAP2™ mode control. D-CAP2™ mode control combines constant on-time control with an internal compensation circuit for pseudo-fixed frequency and low external component count configuration with both low ESR and ceramic output capacitors. It is stable even with virtually no ripple at the output. At the beginning of each cycle, the high-side MOSFET is turned on. This MOSFET is turned off after internal one shot timer expires. This one shot is set by the converter input voltage, VIN, and the output voltage, VO, to maintain a pseudo-fixed frequency over the input voltage range, hence it is called adaptive on-time control. The one-shot timer is reset and the high-side MOSFET is turned on again when the feedback voltage falls below the reference voltage. An internal ramp is added to reference voltage to simulate output ripple, eliminating the need for ESR induced output ripple from D-CAP2™ mode control. PWM Frequency and Adaptive On-Time Control TPS54428 uses an adaptive on-time control scheme and does not have a dedicated on board oscillator. The TPS54428 runs with a pseudo-constant frequency of 650 kHz by using the input voltage and output voltage to set the on-time one-shot timer. The on-time is inversely proportional to the input voltage and proportional to the output voltage, therefore, when the duty ratio is VOUT/VIN, the frequency is constant. Auto-Skip Eco-Mode™ Control The TPS54428 is designed with Auto-Skip Eco-mode™ to increase light load efficiency. As the output current decreases from heavy load condition, the inductor current is also reduced and eventually comes to point that its rippled valley touches zero level, which is the boundary between continuous conduction and discontinuous conduction modes. The rectifying MOSFET is turned off when its zero inductor current is detected. As the load current further decreases the converter run into discontinuous conduction mode. The on-time is kept almost the same as is was in the continuous conduction mode so that it takes longer time to discharge the output capacitor with smaller load current to the level of the reference voltage. The transition point to the light load operation IOUT(LL) current can be calculated in Equation 1. 1 (VIN - VOUT ) ´ VOUT IOUT(LL) = ´ 2 ´ L ´ fSW VIN (1) Soft Start and Pre-Biased Soft Start The soft start function is adjustable. When the EN pin becomes high, 6-µA current begins charging the capacitor which is connected from the SS pin to GND. Smooth control of the output voltage is maintained during start up. The equation for the slow start time is shown in Equation 2. VFB voltage is 0.765 V and SS pin source current is 6-uA. C6(nF) ´ Vref ´ 1.1 C6(nF) ´ 0.765 ´ 1.1 Tss(ms) = = 6 Iss(m A) (2) The TPS54428 contains a unique circuit to prevent current from being pulled from the output during startup if the output is pre-biased. When the soft-start commands a voltage higher than the pre-bias level (internal soft start becomes greater than feedback voltage VFB), the controller slowly activates synchronous rectification by starting the first low side FET gate driver pulses with a narrow on-time. It then increments that on-time on a cycle-by-cycle basis until it coincides with the time dictated by (1-D), where D is the duty cycle of the converter. This scheme prevents the initial sinking of the pre-bias output, and ensure that the out voltage (VO) starts and ramps up smoothly into regulation and the control loop is given time to transition from pre-biased start-up to normal mode operation. Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 7 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com Current Protection The output over-current protection (OCP) is implemented using a cycle-by-cycle valley detect control circuit. The switch current is monitored by measuring the low-side FET switch voltage between the SW pin and GND. This voltage is proportional to the switch current. To improve accuracy, the voltage sensing is temperature compensated. During the on time of the high-side FET switch, the switch current increases at a linear rate determined by Vin, Vout, the on-time and the output inductor value. During the on time of the low-side FET switch, this current decreases linearly. The average value of the switch current is the load current Iout. The TPS54428 constantly monitors the low-side FET switch voltage, which is proportional to the switch current, during the low-side on-time. If the measured voltage is above the voltage proportional to the current limit, an internal counter is incremented per each SW cycle and the converter maintains the low-side switch on until the measured voltage is below the voltage corresponding to the current limit at which time the switching cycle is terminated and a new switching cycle begins. In subsequent switching cycles, the on-time is set to a fixed value and the current is monitored in the same manner. If the over current condition exists for 7 consecutive switching cycles, the internal OCL threshold is set to a lower level, reducing the available output current. When a switching cycle occurs where the switch current is not above the lower OCL threshold, the counter is reset and the OCL limit is returned to the higher value. There are some important considerations for this type of over-current protection. The load current one half of the peak-to-peak inductor current is higher than the over-current threshold also when the current is being limited, the output voltage tends to fall as the demanded load current may be higher than the current available from the converter. This may cause the output voltage to fall. When the over current condition is removed, the output voltage returns to the regulated value. This protection is non-latching. UVLO Protection Undervoltage lock out protection (UVLO) monitors the voltage of the VREG5 pin. When the VREG5 voltage is lower than UVLO threshold voltage, the TPS54428 is shut off. This protection is non-latching. Thermal Shutdown TPS54428 monitors the temperature of itself. If the temperature exceeds the threshold value (typically 170°C), the device is shut off. This is non-latch protection. TYPICAL CHARACTERISTICS VIN = 12 V, TA = 25°C (unless otherwise noted) 20 1200 Ivccsdn - Shutdown Current - mA ICC - Supply Current - mA 1000 800 600 400 15 10 5 200 0 -50 0 50 100 TJ - Junction Temperature - °C 150 Figure 1. VIN CURRENT vs JUNCTION TEMPERATURE 8 0 -50 0 50 100 TJJunction Temperature - °C 150 Figure 2. VIN SHUTDOWN CURRENT vs JUNCTION TEMPERATURE Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com TYPICAL CHARACTERISTICS (continued) VIN = 12 V, TA = 25°C (unless otherwise noted) 50 1.1 VI = 18 V 45 40 VO - Output Voltage - V EN Input Current - mA 1.075 35 30 25 20 15 VI = 18 V 1.05 VI = 12 V VI = 5 V 1.025 10 5 1 0 5 0 10 EN Input Voltage - V 15 20 0 1 2 3 4 IO - Output Current - A Figure 3. EN CURRENT vs EN VOLTAGE Figure 4. 1.05V OUTPUT VOLTAGE vs OUTPUT CURRENT 1.08 Vout (50 mV/div) VO - Output Voltage - V 1.07 IO = 10 mA 1.06 Iout (2 A/div) IO = 1 A 1.05 1.04 0 5 10 VI - Input Voltage - V 15 20 100 ms/div Figure 5. 1.05V OUTPUT VOLTAGE vs VIN VOLTAGE Figure 6. 1.05V LOAD TRANSIENT RESPONSE 100 EN (10 V/div) 90 VO = 1.8 V Efficiency - % 80 VREG5 (5 V/div) Vout (0.5 V/div) VO = 2.5 V VO = 3.3 V 70 60 50 40 0 1 ms/div Figure 7. START UP WAVEFORM 1 2 3 IO - Output Current - A 4 5 Figure 8. EFFICIENCY vs OUTPUT CURRENT Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 9 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com TYPICAL CHARACTERISTICS (continued) VIN = 12 V, TA = 25°C (unless otherwise noted) 100 900 850 90 VO = 3.3 V fsw - Switching Frequency - kHz 80 VO = 2.5 V Efficiency - % 70 VO = 1.8 V 60 50 40 30 20 10 800 VO = 5 V VO = 3.3 V VO = 2.5 V V = 1.8 V O 750 700 650 VO = 1.5 V 600 VO = 1.2 V VO = 1.05 V 550 500 450 0 0.001 0.01 IO - Output Current - A 400 0.1 5 0 Figure 9. LIGHT LOAD EFFICIENCY vs OUTPUT CURRENT 10 VI - Input Voltage - V 15 20 Figure 10. SWITCHING FREQUENCY vs INPUT VOLTAGE 800 0.78 0.775 600 VO = 1.05 V VO = 1.8 V VO = 3.3 V 0.77 500 Vfb - Voltage - V fsw - Switching Frequency - kHz 700 400 300 0.765 0.76 200 0.755 100 0 0 1 2 IO - Output Current - A 3 4 Figure 11. SWITCHING FREQUENCY vs OUTPUT CURRENT VO = 1.05 V 0.75 -50 0 150 Figure 12. VFB VOLTAGE vs JUNCTION TEMPERATURE VIN (50 mV/div) Vo = 1.5 V Vo (10 mV/div) 50 100 TJ - Junction Temperature - °C SW (5 V/div) SW (5 V/div) 500 ns/div Figure 13. VOLTAGE RIPPLE vs RIPPLE AT OUTPUT (IO = 4A 10 Figure 14. VOLTAGE RIPPLE vs RIPPLE AT INPUT (IO = 4A Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com DESIGN GUIDE Step By Step Design Procedure To • • • • • begin the design process, you must know a few application parameters: Input voltage range Output voltage Output current Output voltage ripple Input voltage ripple 4.5 to 18 V Δ 1 TPS54428DDA 1.05 V 4 A 8200 pF Figure 15. Schematic Diagram for This Design Example. Output Voltage Resistors Selection The output voltage is set with a resistor divider from the output node to the VFB pin. It is recommended to use 1% tolerance or better divider resistors. Start by using Equation 3 to calculate VOUT. To improve efficiency at very light loads consider using larger value resistors, too high of resistance will be more susceptible to noise and voltage errors from the VFB input current will be more noticeable. æ R1 ö VOUT = 0.765 ´ ç 1+ ÷ è R2 ø (3) Output Filter Selection The output filter used with the TPS54228 is an LC circuit. This LC filter has double pole at: 1 FP = 2p LOUT ´ COUT (4) At low frequencies, the overall loop gain is set by the output set-point resistor divider network and the internal gain of the TPS54428. The low frequency phase is 180 degrees. At the output filter pole frequency, the gain rolls off at a –40 dB per decade rate and the phase drops rapidly. D-CAP2™ introduces a high frequency zero that reduces the gain roll off to –20 dB per decade and increases the phase to 90 degrees one decade above the zero frequency. The inductor and capacitor selected for the output filter must be selected so that the double pole of is located below the high frequency zero but close enough that the phase boost provided be the high frequency zero provides adequate phase margin for a stable circuit. To meet this requirement use the values recommended in Table 1. Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 11 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com Table 1. Recommended Component Values C4 (pF) (1) Output Voltage (V) R1 (kΩ) R2 (kΩ) L1 (µH) C8 + C9 (µF) 1 6.81 22.1 1.5 22 - 68 1.05 8.25 22.1 1.5 22 - 68 1.2 12.7 22.1 1.5 22 - 68 1.5 21.5 22.1 1.5 22 - 68 1.8 30.1 22.1 5 - 22 2.2 22 - 68 2.5 49.9 22.1 5 - 22 2.2 22 - 68 3.3 73.2 22.1 5 - 22 2.2 22 - 68 5 124 22.1 5 - 22 3.3 22 - 68 6.5 165 22.1 5 - 22 3.3 22 - 68 (1) Optional For higher output voltages at or above 1.8 V, additional phase boost can be achieved by adding a feed forward capacitor (C4) in parallel with R1 The inductor peak-to-peak ripple current, peak current and RMS current are calculated using Equation 5, Equation 6 and Equation 7. The inductor saturation current rating must be greater than the calculated peak current and the RMS or heating current rating must be greater than the calculated RMS current. Use 650 kHz for fSW. Use 650 kHz for fSW. Make sure the chosen inductor is rated for the peak current of Equation 6 and the RMS current of Equation 7. VIN(MAX) - VO UT VO UT I lP-P = ´ VIN(MA X) LO ´ f SW (5) IlPEA K = IO + IL O(RMS) = IlP-P 2 IO2 + (6) 1 IlP -P 2 12 (7) For this design example, the calculated peak current is 4.51 A and the calculated RMS current is 4.01 A. The inductor used is a TDK SPM6530-1R5M100 with a peak current rating of 11.5 A and an RMS current rating of 11 A. The capacitor value and ESR determines the amount of output voltage ripple. The TPS54428 is intended for use with ceramic or other low ESR capacitors. Recommended values range from 22µF to 68µF. Use Equation 8 to determine the required RMS current rating for the output capacitor. VOx ´ (VIN - VO UT ) ICO(RMS) = 12 ´ VIN ´ L O ´ f SW (8) For this design two TDK C3216X5R0J226M 22µF output capacitors are used. The typical ESR is 2 mΩ each. The calculated RMS current is 0.286A and each output capacitor is rated for 4A. Input Capacitor Selection The TPS54428 requires an input decoupling capacitor and a bulk capacitor is needed depending on the application. A ceramic capacitor over 10µF is recommended for the decoupling capacitor. An additional 0.1 µF capacitor from pin 8 to ground is optional to provide additional frequency filtering. The capacitor voltage rating needs to be greater than the maximum input voltage. Bootstrap Capacitor Selection A 0.1µF ceramic capacitor must be connected between the VBST to SW pin for proper operation. It is recommended to use a ceramic capacitor. 12 Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com VREG5 Capacitor Selection A 1-µF ceramic capacitor must be connected between the VREG5 to GND pin for proper operation. It is recommended to use a ceramic capacitor THERMAL INFORMATION This 8-pin DDA package incorporates an exposed thermal pad that is designed to be directly to an external heatsink. The thermal pad must be soldered directly to the printed board (PCB). After soldering, the PCB can be used as a heatsink. In addition, through the use of thermal vias, the thermal pad can be attached directly to the appropriate copper plane shown in the electrical schematic for the device, or alternatively, can be attached to a special heartsink structure designed into the PCB. This design optimizes the heat transfer from the integrated circuit (IC). For additional information on the exposed thermal pad and how to use the advantage of its heat dissipating abilities, refer to Technical Brief, PowerPAD™ Thermally Enhanced Package, Texas Instruments Literature No. SLMA002 and Application Brief, PowerPAD™ Made Easy, Texas Instruments Literature No. SLMA004. The exposed thermal pad dimensions for this package are shown in Figure 16. 8 5 Exposed Thermal Pad 2,40 1,65 1 3,10 2,65 4 Figure 16. Thermal Pad Dimensions Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 13 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com LAYOUT CONSIDERATIONS 1. Keep the input switching current loop as small as possible. 2. Keep the SW node as physically small and short as possible to minimize parasitic capacitance and inductance and to minimize radiated emissions. Kelvin connections should be brought from the output to the feedback pin of the device. 3. Keep analog and non-switching components away from switching components. 4. Make a single point connection from the signal ground to power ground. 5. Do not allow switching current to flow under the device. 6. Keep the pattern lines for VIN and PGND broad. 7. Exposed pad of device must be connected to PGND with solder. 8. VREG5 capacitor should be placed near the device, and connected PGND. 9. Output capacitor should be connected to a broad pattern of the PGND. 10. Voltage feedback loop should be as short as possible, and preferably with ground shield. 11. Lower resistor of the voltage divider which is connected to the VFB pin should be tied to SGND. 12. Providing sufficient vias for VIN, SW and PGND connection. 13. PCB pattern for VIN, SW, and PGND should be as broad as possible. 14. VIN Capacitor should be placed as near as possible to the device. 15. The TPS54428 can supply relatively large current up to 4A. So heat dissipation may be a concern. The top-side area adjacent to the TPS54428 should be filled with ground as much as possible to dissipate heat. 16. The bottom-side area directly below the IC should a dedicated ground area. It should be directly connected to the thermal pad using vias as shown. The ground area should be as large as practical. Additional internal layers can be dedicated as ground planes and connected to vias as well. Additional Thermal Vias TO ENABLE CONTROL FEEDBACK RESISTORS VIN INPUT BYPASS CAPACITOR VIN INPUT BYPASS CAPACITOR VIN EN VIN VFB VBST VREG5 SW BOOST CAPACITOR VOUT Connection to POWER GROUND on internal or bottom layer BIAS CAP SS SOFT START CAP ANALOG GROUND TRACE EXPOSED POWERPAD AREA PGND Additional Thermal Vias OUTPUT INDUCTOR OUTPUT FILTER CAPACITOR POWER GROUND Figure 17. TPS54428 Layout 14 Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 TPS54428 SLVSB42A – NOVEMBER 2011 – REVISED JANUARY 2012 www.ti.com REVISION HISTORY Changes from Original (November 2011) to Revision A Page • Changed in 6th paragraph, page 1: alsohas to also has ...................................................................................................... 1 • Deleted TA = –20ºC to 85ºC from ELEC CHARA table, CURRENT LIMIT section, Test Conditions statement .................. 3 Submit Documentation Feedback Copyright © 2011–2012, Texas Instruments Incorporated Product Folder Link(s) :TPS54428 15 PACKAGE OPTION ADDENDUM www.ti.com 4-Jan-2012 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Qty Eco Plan (2) Lead/ Ball Finish MSL Peak Temp (3) TPS54428DDA ACTIVE SO PowerPAD DDA 8 75 Green (RoHS & no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR TPS54428DDAR ACTIVE SO PowerPAD DDA 8 2500 Green (RoHS & no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR Samples (Requires Login) (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. 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Addendum-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 5-May-2012 TAPE AND REEL INFORMATION *All dimensions are nominal Device TPS54428DDAR Package Package Pins Type Drawing SO Power PAD DDA 8 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 2500 330.0 12.8 Pack Materials-Page 1 6.4 B0 (mm) K0 (mm) P1 (mm) 5.2 2.1 8.0 W Pin1 (mm) Quadrant 12.0 Q1 PACKAGE MATERIALS INFORMATION www.ti.com 5-May-2012 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) TPS54428DDAR SO PowerPAD DDA 8 2500 366.0 364.0 50.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. 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