LMZ10505 LMZ10505 5A SIMPLE SWITCHER(R) Power Module with 5.5V Maximum Input Voltage Literature Number: SNVS633D LMZ10505 5A SIMPLE SWITCHER(R) Power Module with 5.5V Maximum Input Voltage Easy to Use 7 Pin Package Performance Benefits Operates at high ambient temperatures High efficiency up to 96% reduces system heat generation Low radiated emissions (EMI) complies with EN55022 class B standard (Note 4) Passes 10V/m radiated immunity EMI test standard EN61000 4-3 Low output voltage ripple of 10 mV allows for powering noise-sensitive transceiver and signaling ICs Fast transient response for powering FPGAs and ASICs 30107402 TO-PMOD 7 Pin Package 10.16 x 13.77 x 4.57 mm (0.4 x 0.39 x 0.18 in) JA = 20C/W, JC = 1.9C/W (Note 3) RoHS Compliant System Performance Current Derating (VOUT = 3.3V) Electrical Specifications 25W maximum total output power Up to 5A output current Input voltage range 2.95V to 5.5V Output voltage range 0.8V to 5V 1.63% feedback voltage accuracy over temperature Efficiency up to 96% Key Features 30107413 Integrated shielded inductor Flexible startup sequencing using external soft-start, Efficiency (VOUT = 3.3V) tracking, and precision enable Protection against in-rush currents and faults such as input UVLO and output short-circuit -40C to +125C junction temperature operating range Single exposed pad and standard pinout for easy mounting and manufacturing Pin-to-pin compatible with LMZ10503 (3A/15W max) LMZ10504 (4A/20W max) Fully enable for WEBENCH(R) and Power Designer 30107471 Radiated Emissions (EN 55022, Class B) Applications Point-of-load conversions from 3.3V and 5V rails Space constrained applications Extreme temperatures/no air flow environments Noise sensitive applications (i.e. transceiver, medical) 30107412 Note 1: JA measured on a 2.25" x 2.25" (5.8 cm x 5.8 cm) four layer board. Refer to PCB Layout Diagrams or Evaluation Board Application Note: AN-2022. Note 2: EN 55022:2006, +A1:2007, FCC Part 15 Subpart B: 2007. See Figure 5 and layout for information on device under test. (c) 2011 National Semiconductor Corporation 301074 www.national.com LMZ10505 5A SIMPLE SWITCHER(R) Power Module with 5.5V Maximum Input Voltage June 16, 2011 LMZ10505 Typical Application Circuit 30107401 Connection Diagram 30107472 Top View 7-Lead TO-PMOD Ordering Information Order Number Supplied As LMZ10505TZE-ADJ 45 Units in a Rail LMZ10505TZ-ADJ 250 Units in Tape and Reel LMZ10505TZX-ADJ 500 Units in Tape and Reel Package Type NSC Package Drawing Package Marking TO-PMOD-7 TZA07A LMZ10505TZ-ADJ Pin Descriptions Pin Number Name Description 1 VIN Power supply input. A low ESR input capacitance should be located as close as possible to the VIN pin and exposed pad (EP). 2 EN Active high enable input for the device. 3 SS Soft-start control pin. An internal 2 A current source charges an external capacitor connected between SS and GND pins to set the output voltage ramp rate during startup. The SS pin can also be used to configure the tracking feature. 4 GND Power ground and signal ground. Provide a direct connection to the EP. Place the bottom feedback resistor as close as possible to GND and FB pin. 5 FB Feedback pin. This is the inverting input of the error amplifier used for sensing the output voltage. Keep the copper area of this node small. www.national.com 2 Name Description 6, 7 VOUT The output terminal of the internal inductor. Connect the output filter capacitor between VOUT pin and EP. EP Exposed Pad Exposed pad is used as a thermal connection to remove heat from the device. Connect this pad to the PC board ground plane in order to reduce thermal resistance value. EP must also provide a direct electrical connection to the input and output capacitors ground terminals. Connect EP to pin 4. 3 www.national.com LMZ10505 Pin Number LMZ10505 Storage Temperature Range Peak Reflow Case Temperature (30 sec) Absolute Maximum Ratings (Note 5) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN, VOUT, EN, FB, SS to GND ESD Susceptibility (Note 6) Power Dissipation Junction Temperature Operating Ratings -0.3V to 6.0V 2 kV Internally Limited 150C -65C to 150C 245C (Note 5) VIN to GND Junction Temperature (TJ) 2.95V to 5.5V -40C to 125C Electrical Characteristics Specifications with standard typeface are for TJ = 25C only; limits in bold face type apply over the operating junction temperature range TJ of -40C to 125C. Minimum and maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. VIN = VEN = 3.3V, unless otherwise indicated in the conditions column. Symbol Parameter Conditions Min (Note 7) Typ (Note 8) Max (Note 7) Units SYSTEM PARAMETERS V FB Total Feedback Voltage Variation Including Line and Load Regulation VIN = 2.95V to 5.5V VOUT = 2.5V IOUT = 0A to 5A 0.78 0.8 0.82 V V FB Feedback Voltage Variation VIN = 3.3V, VOUT = 2.5V IOUT = 0A 0.787 0.8 0.812 V V FB Feedback Voltage Variation VIN = 3.3V, VOUT = 2.5V IOUT = 5A 0.785 0.798 0.81 V 2.6 2.95 V 1.55 3 mA 267 500 A 7.3 8.7 A VIN(UVLO) Input UVLO Threshold (Measured at VIN Rising pin) Falling ISS Soft-Start Current Charging Current IQ Non-Switching Input Current VFB = 1V ISD Shut Down Quiescent Current VIN = 5.5V, VEN = 0V IOCL Output Current Limit (Average Current) VOUT = 2.5V fFB Frequency Fold-back In current limit 1.95 2.4 2 5.1 A 250 kHz PWM SECTION fSW Drange Switching Frequency 750 PWM Duty Cycle Range 1000 0 1160 kHz 100 % 1.8 V ENABLE CONTROL VEN-IH EN Pin Rising Threshold VEN-IF EN Pin Falling Threshold 1.23 1.06 V TJ for Thermal Shutdown 145 C Hysteresis for Thermal Shutdown 10 C 0.8 THERMAL CONTROL TSD TSD-HYS THERMAL RESISTANCE JA Junction to Ambient (Note 3) 20 C/W JC Junction to Case No air flow 1.9 C/W www.national.com 4 Symbol Parameter Conditions Min (Note 7) Typ (Note 8) Max (Note 7) Units PERFORMANCE PARAMETERS VOUT Output Voltage Ripple Refer to Table 3 VOUT = 2.5V Bandwidth Limit = 2 MHz 10 mVpk-pk VOUT Output Voltage Ripple Refer to Table 5 Bandwidth Limit = 20 MHz 5 mVpk-pk Feedback Voltage Line Regulation VIN = 2.95V to 5.5V 0.04 % 0.04 % VFB / VFB IOUT = 0A VOUT / VOUT Output Voltage Line Regulation VIN = 2.95V to 5.5V IOUT = 0A, VOUT = 2.5V VFB / VFB VOUT / VOUT Feedback Voltage Load Regulation IOUT = 0A to 5A 0.25 % Output Voltage Load Regulation IOUT = 0A to 5A VOUT = 2.5V 0.25 % VOUT = 3.3V 96.1 VOUT = 2.5V 94.8 VOUT = 1.8V 93.1 VOUT = 1.5V 92 VOUT = 1.2V 90.4 VOUT = 0.8V 86.8 VOUT = 2.5V 95.7 VOUT = 1.8V 94.1 VOUT = 1.5V 93.0 VOUT = 1.2V 91.6 VOUT = 0.8V 88.3 VOUT = 3.3V 93.1 VOUT = 2.5V 91.2 VOUT = 1.8V 88.5 VOUT = 1.5V 86.7 VOUT = 1.2V 84.1 VOUT = 0.8V 78.2 VOUT = 2.5V 89.8 VOUT = 1.8V 86.9 VOUT = 1.5V 85.1 VOUT = 1.2V 82.5 VOUT = 0.8V 76.2 Efficiency Peak Efficiency (1A) VIN = 5V Peak Efficiency (1A) VIN = 3.3V Full Load Efficiency (5A) VIN = 5V Full Load Efficiency (5A) VIN = 3.3V % % % % Note 3: JA measured on a 2.25" x 2.25" (5.8 cm x 5.8 cm) four layer board, with one ounce copper, thirty six 10mil thermal vias, no air flow, and 1W power dissipation. Refer to PCB Layout Diagrams or Evaluation Board Application Note: AN-2022. Note 4: EN 55022:2006, +A1:2007, FCC Part 15 Subpart B: 2007. See Table 9 and layout for information on device under test. Note 5: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 6: The human body model is a 100 pF capacitor discharged through a 1.5 k resistor into each pin. Test method is per JESD22-AI14S. Note 7: Min and Max limits are 100% production tested at an ambient temperature (TA) of 25C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. Limits are used to calculate National's Average Outgoing Quality Level (AOQL). Note 8: Typical numbers are at 25C and represent the most likely parametric norm. 5 www.national.com LMZ10505 Electrical Characteristics Specifications with standard typeface are for TJ = 25C only; limits in bold face type apply over the operating junction temperature range TJ of -40C to 125C. Minimum and maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. VIN = VEN = 3.3V, unless otherwise indicated in the conditions column. LMZ10505 Typical Performance Characteristics Unless otherwise specified, the following conditions apply: VIN = VEN = 5.0V, CIN is 47 F 10V X5R ceramic capacitor; TAMBIENT = 25C for efficiency curves and waveforms. Load Transient Response VIN = 3.3V, VOUT = 2.5V, IOUT = 0.5A to 4.5A to 0.5A step 20 MHz Bandwidth Limited Refer to Table 5 for BOM, includes optional components Load Transient Response VIN = 5.0V, VOUT = 2.5V, IOUT = 0.5A to 4.5A to 0.5A step 20 MHz Bandwidth Limited Refer to Table 5 for BOM, includes optional components 30107462 30107463 Output Voltage Ripple VIN = 3.3V, VOUT = 2.5V, IOUT = 5A, 20 mV/DIV Refer to Table 5 for BOM Output Voltage Ripple VIN = 5.0V, VOUT = 2.5V, IOUT = 5A, 20 mV/DIV Refer to Table 5 for BOM 30107465 30107464 Efficiency VOUT = 3.3V Efficiency VOUT = 2.5V 30107471 www.national.com 30107470 6 LMZ10505 Efficiency VOUT = 1.8V Efficiency VOUT = 1.5V 30107469 30107411 Efficiency VOUT = 1.2V Efficiency VOUT = 0.8V 30107468 30107467 Current Derating VIN = 5V, JA = 20C / W Current Derating VIN = 3.3V, JA = 20C / W 30107414 30107415 7 www.national.com LMZ10505 Radiated Emissions (EN 55022, Class B) VIN = 5V, VOUT = 2.5V, IOUT = 5A Evaluation Board Startup VOUT = 2.5V, IOUT = 0A 30107456 30107412 Pre-biased Startup VOUT = 2.5V, IOUT = 0A 30107455 www.national.com 8 LMZ10505 Block Diagram 30107417 6. Follow the PCB design guideline. 7. Learn about the LMZ10505 features such as enable, input UVLO, soft-start, tracking, pre-biased startup, current limit, and thermal shutdown. General Description The LMZ10505 SIMPLE SWITCHER(R) power module is a complete, easy-to-use DC-DC solution capable of driving up to a 5A load with exceptional power conversion efficiency, output voltage accuracy, line and load regulation. The LMZ10505 is available in an innovative package that enhances thermal performance and allows for hand or machine soldering. The LMZ10505 can accept an input voltage rail between 2.95V and 5.5V and deliver an adjustable and highly accurate output voltage as low as 0.8V. One megahertz fixed frequency PWM switching provides a predictable EMI characteristic. Two external compensation components can be adjusted to set the fastest response time, while allowing the option to use ceramic and/or electrolytic output capacitors. Externally programmable soft-start capacitor facilitates controlled startup. The LMZ10505 is a reliable and robust solution with the following features: lossless cycle-by-cycle peak current limit to protect for over current or short-circuit fault, thermal shutdown, input under-voltage lock-out, and pre-biased startup. Design Example For this example the following application parameters exist. * VIN = 5V * VOUT = 2.5V * IOUT = 5A * VOUT = 20 mVpk-pk * Vo_tran = 20 mVpk-pk Input Capacitor Selection A 22 F or 47 F high quality dielectric (X5R, X7R) ceramic capacitor rated at twice the maximum input voltage is typically sufficient. The input capacitor must be placed as close as possible to the VIN pin and GND exposed pad to substantially eliminate the parasitic effects of any stray inductance or resistance on the PC board and supply lines. Neglecting capacitor equivalent series resistance (ESR), the resultant input capacitor AC ripple voltage is a triangular waveform. The minimum input capacitance for a given peakto-peak value (VIN) of VIN is specified as follows: Design Guideline And Operating Description Design Steps LMZ10505 is fully supported by Webench(R) and offers the following: component selection, performance, electrical, and thermal simulations as well as the Build-It board, for a reduced design time. On the other hand, all external components can be calculated by following the design procedure below. 1. Determine the input voltage and output voltage. Also, make note of the ripple voltage and voltage transient requirements. 2. Determine the necessary input and output capacitance. 3. Calculate the feedback resistor divider. 4. Select the optimized compensation component values. 5. Estimate the power dissipation and board thermal requirements. where the PWM duty cycle, D, is given by: If VIN is 1% of VIN, this equals to 50 mV and fSW = 1 MHz 9 www.national.com LMZ10505 RESR is the total output capacitor ESR, L is the inductance value of the internal power inductor, where L = 1.5 H, and fSW = 1 MHz. Therefore, per the design example: A second criteria before finalizing the Cin bypass capacitor is the RMS current capability. The necessary RMS current rating of the input capacitor to a buck regulator can be estimated by The minimum output capacitance requirement due to the PWM ripple voltage is: With this high AC current present in the input capacitor, the RMS current rating becomes an important parameter. The maximum input capacitor ripple voltage and RMS current occur at 50% duty cycle. Select an input capacitor rated for at least the maximum calculated ICin(RMS). Additional bulk capacitance with higher ESR may be required to damp any resonance effects of the input capacitance and parasitic inductance. Three miliohms is a typical RESR value for ceramic capacitors. The following equation provides a good first pass capacitance requirement for a load transient: Output Capacitor Selection In general, 22 F to 100 F high quality dielectric (X5R, X7R) ceramic capacitor rated at twice the maximum output voltage is sufficient given the optimal high frequency characteristics and low ESR of ceramic dielectrics. Although, the output capacitor can also be of electrolytic chemistry for increased capacitance density. Two output capacitance equations are required to determine the minimum output capacitance. One equation determines the output capacitance (CO) based on PWM ripple voltage. The second equation determines CO based on the load transient characteristics. Select the largest capacitance value of the two. The minimum capacitance, given the maximum output voltage ripple (VOUT) requirement, is determined by the following equation: Where Istep is the peak to peak load step (10% to 90% of the maximum load for this example), VFB = 0.8V, and Vo_tran is the maximum output voltage deviation, which is 20 mV. Therefore the capacitance requirement for the given design parameters is: In this particular design the output capacitance is determined by the load transient requirements. Table 1 lists some examples of commercially available capacitors that can be used with the LMZ10505. Where the peak to peak inductor current ripple (iL) is equal to: www.national.com 10 CO (F) Voltage (V), RESR (m) Make Manufacturer Part Number Case Size 22 6.3, < 5 Ceramic, X5R TDK C3216X5R0J226M 1206 47 6.3, < 5 Ceramic, X5R TDK C3216X5R0J476M 1206 47 6.3, < 5 Ceramic, X5R TDK C3225X5R0J476M 1210 47 10.0, < 5 Ceramic, X5R TDK C3225X5R1A476M 1210 100 6.3, < 5 Ceramic, X5R TDK C3225X5R0J107M 1210 100 6.3, 50 Tantalum AVX TPSD157M006#0050 D, 7.5 x 4.3 x 2.9 mm 100 6.3, 25 Organic Polymer Sanyo 6TPE100MPB2 B2, 3.5 x 2.8 x 1.9 mm 150 6.3, 18 Organic Polymer Sanyo 6TPE150MIC2 C2, 6.0 x 3.2 x 1.8 mm 330 6.3, 18 Organic Polymer Sanyo 6TPE330MIL D3L, 7.3 x 4.3 x 2.8 mm 470 6.3, 23 Niobium Oxide AVX NOME37M006#0023 E, 7.3 x 4.3 x 4.1 mm operation is 30 to 60 of phase margin, with a bandwidth of 100 kHz 20 kHz. Output Voltage Setting A resistor divider network from VOUT to the FB pin determines the desired output voltage as follows: Rfbt is defined based on the voltage loop requirements and Rfbb is then selected for the desired output voltage. Resistors are normally selected as 0.5% or 1% tolerance. Higher accuracy resistors such as 0.1% are also available. The feedback voltage (at VOUT = 2.5V) is accurate to within -2.5% / +2.5% over temperature and over line and load regulation. Additionally, the LMZ10505 contains error nulling circuitry to substantially eliminate the feedback voltage variation over temperature as well as the long term aging effects of the internal amplifiers. In addition the zero nulling circuit dramatically reduces the 1/f noise of the bandgap amplifier and reference. The manifestation of this circuit action is that the duty cycle will have two slightly different but distinct operating points, each evident every other switching cycle. 30107408 TABLE 2. LMZ10505 Compensation Component Values VIN CO (F) (V) Loop Compensation 5.0 The LMZ10505 preserves flexibility by integrating the control components around the internal error amplifier while utilizing three small external compensation components from VOUT to FB. An integrated type II (two pole, one zero) voltage-mode compensation network is featured. To ensure stability, an external resistor and small value capacitor can be added across the upper feedback resistor as a pole-zero pair to complete a type III (three pole, two zero) compensation network. The compensation components recommended in Table 2 provide type III compensation at an optimal control loop performance. The typical phase margin is 45 with a bandwidth of 80 kHz. Calculated output capacitance values not listed in Table 2 should be verified before designing into production. A detailed application note is available to provide verification support, AN-2013. In general, calculated output capacitance values below the suggested value will have reduced phase margin and higher control loop bandwidth. Output capacitance values above the suggested values will experience a lower bandwidth and increased phase margin. Higher bandwidth is associated with faster system response to sudden changes such as load transients. Phase margin changes the characteristics of the response. Lower phase margin is associated with underdamped ringing and higher phase margin is associated with overdamped response. Losing all phase margin will cause the system to be unstable; an optimized area of 3.3 ESR (m) Rfbt Min Max Ccomp (pF) Rcomp (k) 22 2 20 200 27 1.5 47 2 20 124 56 1.4 100 1 10 82.5 120 1 150 1 5 63.4 180 1.21 150 10 25 63.4 220 16.5 150 26 50 44.2 220 23.7 220 15 30 63.4 220 23.7 220 31 60 76.8 220 57.6 22 2 20 118 39 9.09 (k) 47 2 20 76.8 82 8.45 100 1 10 49.9 180 4.12 150 1 5 40.2 330 2.0 150 10 25 43.2 330 11.5 150 26 50 49.9 270 25.5 220 15 30 40.2 390 15.4 220 31 60 48.7 330 35.7 Note: In the special case where the output voltage is 0.8V, it is recommended to remove Rfbb and keep Rfbt, Rcomp, and Ccomp for a type III compensation. 11 www.national.com LMZ10505 TABLE 1. Recommended Output Filter Capacitors LMZ10505 Estimate Power Dissipation And Board Thermal Requirements Use the current derating curves in the typical performance characteristics section to obtain an estimate of power loss (PIC_LOSS). For the design case of VIN = 5V, VOUT = 2.5V, IOUT = 5A, TA(MAX) = 85C , and TJ(MAX) = 125C, the device must see a thermal resistance from case to ambient (CA) of less than: 30107453 FIGURE 1. High Current Loops 1. Minimize area of switched current loops. From an EMI reduction standpoint, it is imperative to minimize the high di/dt current paths. The high current that does not overlap contains high di/dt, see Figure 1. Therefore physically place input capacitor (Cin1) as close as possible to the LMZ10505 VIN pin and GND exposed pad to avoid observable high frequency noise on the output pin. This will minimize the high di/dt area and reduce radiated EMI. Additionally, grounding for both the input and output capacitor should consist of a localized top side plane that connects to the GND exposed pad (EP). 2. Have a single point ground. The ground connections for the feedback, soft-start, and enable components should be routed only to the GND pin of the device. This prevents any switched or load currents from flowing in the analog ground traces. If not properly placed, poor grounding can result in degraded load regulation or erratic output voltage ripple behavior. Provide the single point ground connection from pin 4 to EP. 3. Minimize trace length to the FB pin. Both feedback resistors, Rfbt and Rfbb, and the compensation components, Rcomp and Ccomp, should be located close to the FB pin. Since the FB node is high impedance, keep the copper area as small as possible. This is most important as relatively high value resistors are used to set the output voltage. 4. Make input and output bus connections as wide as possible. This reduces any voltage drops on the input or output of the converter and maximizes efficiency. To optimize voltage accuracy at the load, ensure that a separate feedback voltage sense trace is made at the load. Doing so will correct for voltage drops and provide optimum output accuracy. 5. Provide adequate device heat-sinking. Use an array of heat-sinking vias to connect the exposed pad to the ground plane on the bottom PCB layer. If the PCB has multiple copper layers, thermal vias can also be employed to make connection to inner layer heat-spreading ground planes. For best results use a 6 x 6 via array with minimum via diameter of 10mils (254 m) thermal vias spaced 59mils (1.5 mm). Ensure enough copper area is used for heat-sinking to keep the junction temperature below 125C. Given the typical thermal resistance from junction to case (JC) to be 1.9C/W (typ.). Continuously operating at a TJ greater than 125C will have a shorten life span. To reach CA = 27.5C/W, the PCB is required to dissipate heat effectively. With no airflow and no external heat, a good estimate of the required board area covered by 1oz. copper on both the top and bottom metal layers is: As a result, approximately 18 square cm of 1oz. copper on top and bottom layers is required for the PCB design. The PCB copper heat sink must be connected to the exposed pad (EP). Approximately thirty six, 10mils (254 m) thermal vias spaced 59mils (1.5 mm) apart must connect the top copper to the bottom copper. For an extended discussion and formulations of thermal rules of thumb, refer to AN-2020. For an example of a high thermal performance PCB layout with JA of 20C/W, refer to the evaluation board application note AN-2022 and for results of a study of the effects of the PCB designs, refer to AN-2026. PC Board Layout Guidelines PC board layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance of a DCDC converter and surrounding circuitry by contributing to EMI, ground bounce and resistive voltage drop in the traces. These can send erroneous signals to the DC-DC converter resulting in poor regulation or instability. Good layout can be implemented by following a few simple design rules. www.national.com 12 ENABLE The LMZ10505 features an enable (EN) pin and associated comparator to allow the user to easily sequence the LMZ10505 from an external voltage rail, or to manually set the input UVLO threshold. The turn-on or rising threshold and hysteresis for this comparator are typically 1.23V and 0.15V respectively. The precise reference for the enable comparator allows the user to guarantee that the LMZ10505 will be disabled when the system demands it to be. The EN pin should not be left floating. For always-on operation, connect EN to VIN. SOFT-START CAPACITOR Determine the soft-start capacitance with the following relationship where VFB is the internal reference voltage (nominally 0.8V), ISS is the soft-start charging current (nominally 2 A) and CSS is the external soft-start capacitance. Thus, the required soft-start capacitor per unit output voltage startup time is given by ENABLE AND UVLO Using a resistor divider from VIN to EN as shown in the schematic diagram below, the input voltage at which the part begins switching can be increased above the normal input UVLO level according to CSS = 2.5 nF / ms For example, a 4 ms soft-start time will yield a 10 nF capacitance. The minimum soft-start capacitance is 680 pF. TRACKING The LMZ10505 can track the output of a master power supply during soft-start by connecting a resistor divider to the SS pin. In this way, the output voltage slew rate of the LMZ10505 will be controlled by a master supply for loads that require precise sequencing. When the tracking function is used, a small value soft-start capacitor should be connected to the SS pin to alleviate output voltage overshoot when recovering from a current limit fault. For example, suppose that the required input UVLO level is 3.69V. Choosing Renb = 10 k, then we calculate Rent = 20 k. 30107444 Alternatively, the EN pin can be driven from another voltage source to cater to system sequencing requirements commonly found in FPGA and other multi-rail applications. The following schematic shows an LMZ10505 that is sequenced to start based on the voltage level of a master system rail (VOUT1). 30107457 TRACKING - EQUAL SOFT-START TIME One way to use the tracking feature is to design the tracking resistor divider so that the master supply output voltage, VOUT1, and the LMZ10505 output voltage, VOUT2, both rise together and reach their target values at the same time. This is termed ratiometric startup. For this case, the equation governing the values of tracking divider resistors Rtrkb and Rtrkt is given by 30107445 The above equation includes an offset voltage, of 200 mV, to ensure that the final value of the SS pin voltage exceeds the reference voltage of the LMZ10505. This offset will cause the LMZ10505 output voltage to reach regulation slightly before the master supply. A value of 33 k 1% is recommended for Rtrkt as a compromise between high precision and low quiescent current through the divider while minimizing the effect of the 2 A soft-start current source. SOFT-START The LMZ10505 begins to operate when both the VIN and EN, voltages exceed the rising UVLO and enable thresholds, respectively. A controlled soft-start eliminates inrush currents during startup and allows the user more control and flexibility when sequencing the LMZ10505 with other power supplies. 13 www.national.com LMZ10505 In the event of either VIN or EN decreasing below the falling UVLO or enable threshold respectively, the voltage on the soft-start pin is collapsed by discharging the soft-start capacitor by a 14 A (typ.) current sink to ground. Additional Features LMZ10505 For example, if the master supply voltage VOUT1 is 3.3V and the LMZ10505 output voltage was 1.8V, then the value of Rtrkb needed to give the two supplies identical soft-start times would be 14.3 k. A timing diagram for this example, the equal soft-start time case, is shown below. PRE-BIAS STARTUP CAPABILITY At startup, the LMZ10505 is in a pre-biased state when the output voltage is greater than zero. This often occurs in many multi-rail applications such as when powering an ASIC, FPGA, or DSP. The output can be pre-biased in these applications through parasitic conduction paths from one supply rail to another. Even though the LMZ10505 is a synchronous converter, it will not pull the output low when a pre-bias condition exists. The LMZ10505 will not sink current during startup until the soft-start voltage exceeds the voltage on the FB pin. Since the device does not sink current it protects the load from damage that might otherwise occur if current is conducted through the parasitic paths of the load. CURRENT LIMIT When a current greater than the output current limit (IOCL) is sensed, the on-time is immediately terminated and the low side MOSFET is activated. The low side MOSFET stays on for the entire next four switching cycles. During these skipped pulses, the voltage on the soft-start pin is reduced by discharging the soft-start capacitor by a current sink on the softstart pin of nominally 14 A. Subsequent over-current events will drain more and more charge from the soft-start capacitor, effectively decreasing the reference voltage as the output droops due to the pulse skipping. Reactivation of the soft-start circuitry ensures that when the over-current situation is removed, the part will resume normal operation smoothly. 30107459 TRACKING - EQUAL SLEW RATES Alternatively, the tracking feature can be used to have similar output voltage ramp rates. This is referred to as simultaneous startup. In this case, the tracking resistors can be determined based on the following equation OVER-TEMPERATURE PROTECTION When the LMZ10505 senses a junction temperature greater than 145C (typ.), both switching MOSFETs are turned off and the part enters a standby state. Upon sensing a junction temperature below 135C (typ.), the part will re-initiate the soft-start sequence and begin switching once again. and to ensure proper overdrive of the SS pin VOUT2 < 0.8 x V OUT1 For the example case of VOUT1 = 5V and VOUT2 = 2.5V, with Rtrkt set to 33 k as before, Rtrkb is calculated from the above equation to be 15.5 k. A timing diagram for the case of equal slew rates is shown below. 30107461 www.national.com 14 This section provides several application solutions with an associated bill of materials. The compensation for each solution was optimized to work over the full input range. Many applications have a fixed input voltage rail. It is possible to modify the compensation to obtain a faster transient response for a given input voltage operating point. 30107454 FIGURE 2. TABLE 3. Bill of Materials, VIN = 3.3V to 5V, VOUT = 2.5V, IOUT (MAX) = 5A, Optimized for Electrolytic Input and Output Capacitance Designator Description Case Size Manufacturer Manufacturer P/N Quantity U1 SIMPLE SWITCHER (R) TO-PMOD-7 National Semiconductor LMZ10505TZ-ADJ 1 Cin1 150 F, 6.3V, 18 m C2, 6.0 x 3.2 x 1.8 mm Sanyo 6TPE150MIC2 1 CO1 330 F, 6.3V, 18 m D3L, 7.3 x 4.3 x 2.8 mm Sanyo 6TPE330MIL 1 Rfbt 100 k 0603 Vishay Dale CRCW0603100KFKEA 1 Rfbb 47.5 k 0603 Vishay Dale CRCW060347K5FKEA 1 Rcomp 15 k 0603 Vishay Dale CRCW060315K0FKEA 1 Ccomp 330 pF, 5%, C0G, 50V 0603 TDK C1608C0G1H331J 1 CSS 10 nF, 10%, X7R, 16V 0603 Murata GRM188R71C103KA01 1 TABLE 4. Bill of Materials, VIN = 3.3V, VOUT = 0.8V, IOUT (MAX) = 5A, Optimized for Solution Size and Transient Response Designator Description Case Size Manufacturer Manufacturer P/N Quantity U1 SIMPLE SWITCHER (R) TO-PMOD-7 National Semiconductor LMZ10505TZ-ADJ 1 Cin1, CO1 47 F, X5R, 6.3V 1206 TDK C3216X5R0J476M 2 110 k 0402 Vishay Dale CRCW0402100KFKED 1 Rcomp 1.0 k 0402 Vishay Dale CRCW04021K00FKED 1 Ccomp 27 pF, 5%, C0G, 50V 0402 Murata GRM1555C1H270JZ01 1 CSS 10 nF, 10%, X7R, 16V 0402 Murata GRM155R71C103KA01 1 Rfbt In the case where the output voltage is 0.8V, it is recommended to remove Rfbb and keep Rfbt, Rcomp, and Ccomp for a type III compensation. 15 www.national.com LMZ10505 LMZ10505 Application Circuit Schematic and BOMs LMZ10505 30107481 FIGURE 3. TABLE 5. Bill of Materials, VIN = 3.3V to 5V, VOUT = 2.5V, IOUT (MAX) = 5A, Optimized for Low Input and Output Ripple Voltage and Fast Transient Response Designator Description Case Size Manufacturer Manufacturer P/N Quantity U1 SIMPLE SWITCHER(R) TO-PMOD-7 National Semiconductor LMZ10505TZ-ADJ 1 Cin1 22 F, X5R, 10V 1210 AVX 1210ZD226MAT 2 Cin2 220 F, 10V, AL-Elec E Panasonic EEE1AA221AP 1* CO1 4.7 F, X5R, 10V 0805 AVX 0805ZD475MAT 1* CO2 22 F, X5R, 6.3V 1206 AVX 12066D226MAT 1* CO3 100 F, X5R, 6.3V 1812 AVX 18126D107MAT 1 Rfbt 75 k 0402 Vishay Dale CRCW040275K0FKED 1 34.8 k 0402 Vishay Dale CRCW040234K8FKED 1 Rcomp 1.0 k 0402 Vishay Dale CRCW04021K00FKED 1 Ccomp 100 pF, 5%, C0G, 50V 0402 Murata GRM1555C1H101JZ01 1 CSS 10 nF, 10%, X7R, 16V 0402 Murata GRM155R71C103KA01 1 Rfbb * Optional components, include for low input and output voltage ripple. TABLE 6. Output Voltage Setting (Rfbt = 75 k) www.national.com VOUT Rfbb 2.5 V 34.8 k 1.8 V 59 k 1.5 V 84.5 k 1.2 V 150 k 0.9 V 590 k 16 LMZ10505 30107480 FIGURE 4. TABLE 7. Bill of Materials, VIN = 3.3V to 5V, VOUT = 2.5V, IOUT (MAX) = 5A Designator Description Case Size Manufacturer Manufacturer P/N Quantity U1 SIMPLE SWITCHER(R) TO-PMOD-7 National Semiconductor LMZ10505TZ-ADJ 1 Cin1 1 F, X7R, 16V 0805 TDK C2012X7R1C105K 1 Cin2, CO1 4.7 F, X5R, 6.3V 0805 TDK C2012X5R0J475K 2 Cin3, CO2 22 F, X5R, 16V 1210 TDK C3225X5R1C226M 2 Cin4 47 F, X5R, 6.3V 1210 TDK C3225X5R0J476M 1 Cin5 220 F, 10V, AL-Elec E Panasonic EEE1AA221AP 1 CO3 100 F, X5R, 6.3V 1812 TDK C4532X5R0J107M 1 Rfbt 75 k 0805 Vishay Dale CRCW080575K0FKEA 1 Rfbb 34.8 k 0805 Vishay Dale CRCW080534K8FKEA 1 Rcomp 1.1 k 0805 Vishay Dale CRCW08051K10FKEA 1 Ccomp 180 pF, 5%, C0G, 50V 0603 TDK C1608C0G1H181J 1 Ren1 100 k 0805 Vishay Dale CRCW0805100KFKEA 1 CSS 10 nF, 5%, C0G, 50V 0805 TDK C2012C0G1H103J 1 TABLE 8. Output Voltage Setting (Rfbt = 75 k) VOUT Rfbb 2.5 V 34.8 k 1.8 V 59 k 1.5 V 84.5 k 1.2 V 150 k 0.9 V 590 k 17 www.national.com LMZ10505 30107416 FIGURE 5. TABLE 9. Bill of Materials, VIN = 5V, VOUT = 2.5V, IOUT (MAX) = 5A, Complies with EN55022 Class B Radiated Emissions Designator Description Case Size Manufacturer Manufacturer P/N Quantity U1 SIMPLE SWITCHER(R) TO-PMOD-7 National Semiconductor LMZ10505TZ-ADJ 1 Cin1 1 F, X7R, 16V 0805 TDK C2012X7R1C105K 1 Cin2 4.7 F, X5R, 6.3V 0805 TDK C2012X5R0J475K 1 Cin3 47 F, X5R, 6.3V 1210 TDK C3225X5R0J476M 1 CO1 100 F, X5R, 6.3V 1812 TDK C4532X5R0J107M 1 Rfbt 75 k 0805 Vishay Dale CRCW080575K0FKEA 1 Rfbb 34.8 k 0805 Vishay Dale CRCW080534K8FKEA 1 Rcomp 1.1 k 0805 Vishay Dale CRCW08051K10FKEA 1 Ccomp 180 pF, 5%, C0G, 50V 0603 TDK C1608C0G1H181J 1 CSS 10 nF, 5%, C0G, 50V 0805 TDK C2012C0G1H103J 1 TABLE 10. Output Voltage Setting (Rfbt = 75 k) www.national.com VOUT Rfbb 3.3 V 23.7 k 2.5 V 34.8 k 1.8 V 59 k 1.5 V 84.5 k 1.2 V 150 k 0.9 V 590 k 18 LMZ10505 PCB Layout Diagrams The PCB design is available in the LMZ10505 product folder at www.national.com. 30107476 FIGURE 6. Top Copper 30107477 FIGURE 7. Internal Layer 1 (Ground) 19 www.national.com LMZ10505 30107478 FIGURE 8. Internal Layer 2 (Ground and Signal Traces) 30107479 FIGURE 9. Bottom Copper www.national.com 20 LMZ10505 Physical Dimensions inches (millimeters) unless otherwise noted TO-PMOD-7 Pin Package NS Package Number TZA07A 21 www.national.com LMZ10505 5A SIMPLE SWITCHER(R) Power Module with 5.5V Maximum Input Voltage For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Design Support Amplifiers www.national.com/amplifiers WEBENCH(R) Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise(R) Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagicTM www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise(R) Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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