6TPE330MIL

LMZ10503 3A SIMPLE SWITCHER® Power Module with 5.5V Maximum Input Voltage June 10, 2010 LMZ10503 3A SIMPLE SWITCHER® 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) ■ Low output voltage ripple of 10 mV allows for powering noise-sensitive transceiver and signaling ICs ■ Fast transient response for powering FPGAs and ASICs System Performance 301118a4 TO-PMOD 7 Pin Package 10.16 x 13.77 x 4.57 mm (0.4 x 0.39 x 0.18 in) θJA = 20°C/W, θJC = 1.9°C/W (Note 3) RoHS Compliant Current Derating (VOUT = 3.3V) Electrical Specifications ■ ■ ■ ■ ■ ■ 15W maximum total output power Up to 3A 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% 301118a5 Key Features ■ Integrated shielded inductor ■ Flexible startup sequencing using external soft-start, tracking, and precision enable UVLO and output short-circuit Efficiency (VOUT = 3.3V) ■ Protection against in-rush currents and faults such as input ■ -40°C to +125°C junction temperature operating range ■ Single exposed pad and standard pinout for easy mounting and manufacturing ■ Pin-to-pin compatible with LMZ10504 (4A/20W max) LMZ10505 (5A/25W max) ■ Fully enabled for WEBENCH® and Power Designer 30111871 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) Radiated Emissions (EN 55022, Class B) Note 1: Note 1: θ 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: Note 2: EN 55022:2006, +A1:2007, FCC Part 15 Subpart B: 2007. See Figure 5 and layout for information on device under test. 301118a6 © 2010 National Semiconductor Corporation 301118 www.national.com LMZ10503 Typical Application Circuit 30111801 Connection Diagram 30111872 Top View 7-Lead TO-PMOD Ordering Information Order Number LMZ10503TZE-ADJ LMZ10503TZ-ADJ LMZ10503TZX-ADJ Supplied As 45 Units in a Rail 250 Units in Tape and Reel 500 Units in Tape and Reel TO-PMOD-7 TZA07A LMZ10503TZ-ADJ Package Type NSC Package Drawing Package Marking Pin Descriptions Pin Number 1 2 3 Name VIN EN SS Description Power supply input. A low ESR input capacitance should be located as close as possible to the VIN pin and exposed pad (EP). Active high enable input for the device. Soft-start control pin. An internal 2 µA 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. 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. 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. 4 5 GND FB www.national.com 2 LMZ10503 Pin Number 6, 7 EP Name VOUT Exposed Pad Description The output terminal of the internal inductor. Connect the output filter capacitor between VOUT pin and EP. 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 LMZ10503 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 -0.3V to 6.0V ±2 kV Internally Limited 150°C Storage Temperature Range -65°C to 150°C For Soldering Specs see: www.national.com/ms/MS/MS-SOLDERING.pdf Operating Ratings VIN to GND Junction Temperature (TJ) (Note 5) 2.95V to 5.5V -40°C to 125°C Electrical Characteristics Specifications with standard typeface are for TJ = 25°C only; limits in bold face type apply over the operating junction temperature range TJ of -40°C to 125°C. Minimum and maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. VIN = VEN = 3.3V, unless otherwise indicated in the conditions column. Symbol Parameter Conditions Min (Note 7) 0.78 Typ (Note 8) 0.8 Max (Note 7) 0.82 Units SYSTEM PARAMETERS V FB Total Feedback Voltage Variation Including Line and Load Regulation Feedback Voltage Variation Feedback Voltage Variation VIN = 2.95V to 5.5V VOUT = 2.5V IOUT = 0A to 3A VIN = 3.3V, VOUT = 2.5V IOUT = 0A VIN = 3.3V, VOUT = 2.5V IOUT = 3A V V FB V FB VIN(UVLO) ISS IQ ISD IOCL fFB PWM SECTION fSW Drange ENABLE CONTROL VEN-IH VEN-IF TSD TSD-HYS θJA θJC 0.787 0.785 0.8 0.798 2.6 0.812 0.81 2.95 V V V µA Input UVLO Threshold (Measured at VIN Rising pin) Falling Soft-Start Current Non-Switching Input Current Shut Down Quiescent Current Output Current Limit (Average Current) Frequency Fold-back Switching Frequency PWM Duty Cycle Range EN Pin Rising Threshold EN Pin Falling Threshold TJ for Thermal Shutdown Hysteresis for Thermal Shutdown Junction to Ambient Junction to Case (Note 3) No air flow Charging Current VFB = 1V VIN = 5.5V, VEN = 0V VOUT = 2.5V In current limit 1.95 2.4 2 1.7 260 3 500 6.7 mA µA A kHz 1160 100 1.23 1.8 kHz % V V °C °C °C/W °C/W 3.8 5.2 250 750 0 1000 0.8 1.06 145 10 20 1.9 THERMAL CONTROL THERMAL RESISTANCE www.national.com 4 LMZ10503 Electrical Characteristics Specifications with standard typeface are for TJ = 25°C only; limits in bold face type apply over the operating junction temperature range TJ of -40°C to 125°C. Minimum and maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C, 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) 7 Max (Note 7) Units PERFORMANCE PARAMETERS ΔVOUT Output Voltage Ripple Refer to Table 3 VOUT = 2.5V Bandwidth Limit = 2 MHz Refer to Table 5 Bandwidth Limit = 20 MHz ΔVIN = 2.95V to 5.5V IOUT = 0A ΔVOUT / VOUT ΔVFB / VFB ΔVOUT / VOUT Efficiency VOUT = 3.3V VOUT = 2.5V η Peak Efficiency (1A) VIN = 5V VOUT = 1.8V VOUT = 1.5V VOUT = 1.2V VOUT = 0.8V VOUT = 2.5V VOUT = 1.8V η Peak Efficiency (1A) VIN = 3.3V VOUT = 1.5V VOUT = 1.2V VOUT = 0.8V VOUT = 3.3V VOUT = 2.5V η Full Load Efficiency (3A) VIN = 5V VOUT = 1.8V VOUT = 1.5V VOUT = 1.2V VOUT = 0.8V VOUT = 2.5V VOUT = 1.8V η Full Load Efficiency (3A) VIN = 3.3V VOUT = 1.5V VOUT = 1.2V VOUT = 0.8V 96.3 94.9 93.3 92.2 90.5 86.9 95.7 94.0 92.9 91.3 87.9 94.8 93 90.8 89.3 87.1 82.3 92.4 89.8 88.2 85.9 80.8 % % % % Output Voltage Line Regulation Feedback Voltage Load Regulation Output Voltage Load Regulation ΔVIN = 2.95V to 5.5V IOUT = 0A, VOUT = 2.5V IOUT = 0A to 3A IOUT = 0A to 3A VOUT = 2.5V mVpk-pk ΔVOUT ΔVFB / VFB Output Voltage Ripple Feedback Voltage Line Regulation 5 mVpk-pk 0.04 0.04 0.25 0.25 % % % % Note 3: θ 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 kΩ 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 25°C. 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 25°C and represent the most likely parametric norm. 5 www.national.com LMZ10503 Typical Performance Characteristics Unless otherwise specified, the following conditions apply: VIN = VEN = 5.0V, CIN is 47 µF 10V X5R ceramic capacitor; TAMBIENT = 25°C for efficiency curves and waveforms. Load Transient Response VIN = 3.3V, VOUT = 2.5V, IOUT = 0.3A to 2.7A to 0.3A step 20 MHz Bandwidth Limited Refer to Table 5 for BOM, includes optional components Load Transient Response VIN = 5.0V, VOUT = 2.5V, IOUT = 0.3A to 2.7A to 0.3A step 20 MHz Bandwidth Limited Refer to Table 5 for BOM, includes optional components 30111862 30111863 Output Voltage Ripple VIN = 3.3V, VOUT = 2.5V, IOUT = 3A, 20 mV/DIV Refer to Table 5 for BOM Output Voltage Ripple VIN = 5.0V, VOUT = 2.5V, IOUT = 3A, 20 mV/DIV Refer to Table 5 for BOM 30111864 30111865 www.national.com 6 LMZ10503 Efficiency VOUT = 3.3V Efficiency VOUT = 2.5V 30111871 30111870 Efficiency VOUT = 1.8V Efficiency VOUT = 1.5V 30111869 301118a0 Efficiency VOUT = 1.2V Efficiency VOUT = 0.8V 30111868 30111867 7 www.national.com LMZ10503 Current Derating VIN = 5V, θJA = 20°C / W Current Derating VIN = 3.3V, θJA = 20°C / W 301118b3 301118b4 Radiated Emissions (EN55022, Class B) VIN = 5V, VOUT = 2.5V, IOUT = 3A Evaluation board Startup VOUT = 2.5V, IOUT = 0A 30111856 301118a6 Pre-biased Startup VOUT = 2.5V, IOUT = 0A 30111855 www.national.com 8 LMZ10503 Block Diagram 30111836 General Description The LMZ10503 SIMPLE SWITCHER® power module is a complete, easy-to-use DC-DC solution capable of driving up to a 3A load with exceptional power conversion efficiency, output voltage accuracy, line and load regulation. The LMZ10503 is available in an innovative package that enhances thermal performance and allows for hand or machine soldering. The LMZ10503 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 LMZ10503 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. 6. Follow the PCB design guideline. 7. Learn about the LMZ10503 features such as enable, input UVLO, soft-start, tracking, pre-biased startup, current limit, and thermal shutdown. Design Example For this example the following application parameters exist. • VIN = 5V • VOUT = 2.5V • IOUT = 3A • ΔVOUT = 20 mVpk-pk • ΔVo_tran = ±20 mVpk-pk Input Capacitor Selection A 22 µF or 47 µF 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 (ΔVIN) of VIN is specified as follows: Design Guideline And Operating Description Design Steps LMZ10503 is fully supported by Webench® 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. 9 where the PWM duty cycle, D, is given by: If ΔVIN is 1% of VIN, this equals to 50 mV and fSW = 1 MHz www.national.com LMZ10503 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 RESR is the total output capacitor ESR, L is the inductance value of the internal power inductor, where L = 2.2 µH, and fSW = 1 MHz. Therefore, per the design example: 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 µF to 100 µF 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 (ΔVOUT) requirement, is determined by the following equation: Where Istep is the peak to peak load step (for this example Istep = 10% to 90% of the maximum load), VFB = 0.8V, and ΔVo_tran is the maximum output voltage deviation, which is ±20 mV. Therefore the capacitance requirement for the given design parameters is: Where the peak to peak inductor current ripple (ΔiL) is equal to: 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 LMZ10503. www.national.com 10 LMZ10503 TABLE 1. Recommended Output Filter Capacitors CO (µF) 22 47 47 47 100 100 100 150 330 470 Voltage (V), RESR (mΩ) 6.3, < 5 6.3, < 5 6.3, < 5 10.0, < 5 6.3, < 5 6.3, 50 6.3, 25 6.3, 18 6.3, 18 6.3, 23 Make Ceramic, X5R Ceramic, X5R Ceramic, X5R Ceramic, X5R Ceramic, X5R Tantalum Organic Polymer Organic Polymer Organic Polymer Niobium Oxide Manufacturer TDK TDK TDK TDK TDK AVX Sanyo Sanyo Sanyo AVX Part Number C3216X5R0J226M C3216X5R0J476M C3225X5R0J476M C3225X5R1A476M C3225X5R0J107M TPSD157M006#0050 6TPE100MPB2 6TPE150MIC2 6TPE330MIL NOME37M006#0023 Case Size 1206 1206 1210 1210 1210 D, 7.5 x 4.3 x 2.9 mm B2, 3.5 x 2.8 x 1.9 mm C2, 6.0 x 3.2 x 1.8 mm D3L, 7.3 x 4.3 x 2.8 mm E, 7.3 x 4.3 x 4.1 mm Output Voltage Setting A resistor divider network from VOUT to the FB pin determines the desired output voltage as follows: operation is 30° to 60° of phase margin, with a bandwidth of 100 kHz ±20 kHz. 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 LMZ10503 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. 30111848 TABLE 2. LMZ10503 Compensation Component Values VIN CO (µF) (V) 22 47 100 5.0 150 150 150 220 220 22 47 100 3.3 150 150 150 220 220 ESR (mΩ) Min 2 2 1 1 10 26 15 31 2 2 1 1 10 26 15 31 Max 20 20 10 5 25 50 30 60 20 20 10 5 25 50 30 60 Rfbt (kΩ) 143 100 71.5 56.2 59 66.5 53.6 59 100 66.5 45.3 40.2 40.2 43.2 40.2 40.2 Ccomp (pF) 39 100 180 270 270 270 360 360 56.2 150 270 360 360 360 470 470 Rcomp (kΩ) 8.06 8.25 4.32 2.1 10.8 23.7 14 30.1 5.62 5.49 2.8 1.5 7.32 15.4 10.5 20.5 Loop Compensation The LMZ10503 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 11 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. www.national.com LMZ10503 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 = 3A, TA(MAX) = 85°C , and TJ(MAX) = 125°C, the device must see a thermal resistance from case to ambient (θCA) of less than: 301118b5 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 LMZ10503 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 μm) thermal vias spaced 59mils (1.5 mm). Ensure enough copper area is used for heat-sinking to keep the junction temperature below 125°C. Given the typical thermal resistance from junction to case (θJC) to be 1.9°C/W (typ.). Continuously operating at a TJ greater than 125°C will have a shorten life span. To reach θCA = 69.5°C/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 7.2 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 μm) 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 θJA of 20°C/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 LMZ10503 Additional Features Enable The LMZ10503 features an enable (EN) pin and associated comparator to allow the user to easily sequence the LMZ10503 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 LMZ10503 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. during startup and allows the user more control and flexibility when sequencing the LMZ10503 with other power supplies. 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 µA (typ.) current sink to ground. Soft-Start Capacitor Determine the soft-start capacitance with the following relationship 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 where VFB is the internal reference voltage (nominally 0.8V), ISS is the soft-start charging current (nominally 2 µA) and CSS is the external soft-start capacitance. Thus, the required soft-start capacitor per unit output voltage startup time is given by 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. For example, suppose that the required input UVLO level is 3.69V. Choosing Renb = 10 kΩ, then we calculate Rent = 20 kΩ. Tracking The LMZ10503 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 LMZ10503 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. 30111844 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 LMZ10503 that is sequenced to start based on the voltage level of a master system rail (VOUT1). 30111857 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 LMZ10503 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 30111845 Soft-Start The LMZ10503 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 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 LMZ10503. This offset will cause the LMZ10503 output voltage to reach regulation slightly before 13 www.national.com LMZ10503 the master supply. A value of 33 kΩ 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 µA soft-start current source. For example, if the master supply voltage VOUT1 is 3.3V and the LMZ10503 output voltage was 1.8V, then the value of Rtrkb needed to give the two supplies identical soft-start times would be 14.3 kΩ. A timing diagram for this example, the equal soft-start time case, is shown below. Pre-Bias Startup Capability At startup, the LMZ10503 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 LMZ10503 is a synchronous converter, it will not pull the output low when a pre-bias condition exists. The LMZ10503 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 µA. 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. 30111859 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 LMZ10503 senses a junction temperature greater than 145°C (typ.), both switching MOSFETs are turned off and the part enters a standby state. Upon sensing a junction temperature below 135°C (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 kΩ as before, Rtrkb is calculated from the above equation to be 15.5 kΩ. A timing diagram for the case of equal slew rates is shown below. 30111861 www.national.com 14 LMZ10503 LMZ10503 Application Circuit Schematic and BOMs 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. 30111854 FIGURE 2. TABLE 3. Bill of Materials, VIN = 3.3V to 5V, VOUT = 2.5V, IOUT (MAX) = 3A, Optimized for Electrolytic Input and Output Capacitance Designator U1 Cin1 CO1 Rfbt Rfbb Rcomp Ccomp CSS Description SIMPLE SWITCHER ® 150 µF, 6.3V, 18 mΩ 330 µF, 6.3V, 18 mΩ 100 kΩ 47.5 kΩ 15 kΩ 330 pF, ±5%, C0G, 50V 10 nF, ±10%, X7R, 16V Case Size TO-PMOD-7 C2, 6.0 x 3.2 x 1.8 mm D3L, 7.3 x 4.3 x 2.8 mm 0603 0603 0603 0603 0603 Manufacturer National Semiconductor Sanyo Sanyo Vishay Dale Vishay Dale Vishay Dale TDK Murata Manufacturer P/N LMZ10503TZ-ADJ 6TPE150MIC2 6TPE330MIL CRCW0603100KFKEA CRCW060347K5FKEA CRCW060315K0FKEA C1608C0G1H331J GRM188R71C103KA01 Quantity 1 1 1 1 1 1 1 1 TABLE 4. Bill of Materials, VIN = 3.3V, VOUT = 0.8V, IOUT (MAX) = 3A, Optimized for Solution Size and Transient Response Designator U1 Cin1, CO1 Rfbt Rcomp Ccomp CSS Description SIMPLE SWITCHER ® 47 µF, X5R, 6.3V 110 kΩ 1.0 kΩ 27 pF, ±5%, C0G, 50V 10 nF, ±10%, X7R, 16V Case Size TO-PMOD-7 1206 0402 0402 0402 0402 Manufacturer National Semiconductor TDK Vishay Dale Vishay Dale Murata Murata Manufacturer P/N LMZ10503TZ-ADJ C3216X5R0J476M CRCW0402100KFKED CRCW04021K00FKED GRM1555C1H270JZ01 GRM155R71C103KA01 Quantity 1 2 1 1 1 1 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 LMZ10503 30111881 FIGURE 3. TABLE 5. Bill of Materials, VIN = 3.3V to 5V, VOUT = 2.5V, IOUT (MAX) = 3A, Optimized for Low Input and Output Ripple Voltage and Fast Transient Response Designator U1 Cin1 Cin2 CO1 CO2 CO3 Rfbt Rfbb Rcomp Ccomp CSS Description SIMPLE SWITCHER® 22 µF, X5R, 10V 220 µF, 10V, AL-Elec 4.7 µF, X5R, 10V 22 µF, X5R, 6.3V 100 µF, X5R, 6.3V 75 kΩ 34.8 kΩ 1.0 kΩ 220 pF, ±5%, C0G, 50V 10 nF, ±10%, X7R, 16V Case Size TO-PMOD-7 1210 E 0805 1206 1812 0402 0402 0402 0402 0402 Manufacturer National Semiconductor AVX Panasonic AVX AVX AVX Vishay Dale Vishay Dale Vishay Dale Murata Murata Manufacturer P/N LMZ10503TZ-ADJ 1210ZD226MAT EEE1AA221AP 0805ZD475MAT 12066D226MAT 18126D107MAT CRCW040275K0FKED CRCW040234K8FKED CRCW04021K00FKED GRM1555C1H221JA01D GRM155R71C103KA01 Quantity 1 2 1* 1* 1* 1 1 1 1 1 1 * Optional components, include for low input and output voltage ripple. TABLE 6. Output Voltage Setting (Rfbt = 75 kΩ) VOUT 3.3V 2.5 V 1.8 V 1.5 V 1.2 V 0.9 V Rfbb 23.7 kΩ 34.8 kΩ 59 kΩ 84.5 kΩ 150 kΩ 590 kΩ www.national.com 16 LMZ10503 30111880 FIGURE 4. TABLE 7. Bill of Materials for Evaluation Board, VIN = 3.3V to 5V, VOUT = 2.5V, IOUT (MAX) = 3A Designator U1 Cin1 Cin2, CO1 Cin3, CO2 Cin4 Cin5 CO3 Rfbt Rfbb Rcomp Ccomp Ren1 CSS Description SIMPLE SWITCHER® 1 µF, X7R, 16V 4.7 µF, X5R, 6.3V 22 µF, X5R, 16V 47 µF, X5R, 6.3V 220 µF, 10V, AL-Elec 100 µF, X5R, 6.3V 75 kΩ 34.8 kΩ 1.1 kΩ 180 pF, ±5%, C0G, 50V 100 kΩ 10 nF, ±5%, C0G, 50V Case Size TO-PMOD-7 0805 0805 1210 1210 E 1812 0805 0805 0805 0603 0805 0805 Manufacturer National Semiconductor TDK TDK TDK TDK Panasonic TDK Vishay Dale Vishay Dale Vishay Dale TDK Vishay Dale TDK Manufacturer P/N LMZ10503TZ-ADJ C2012X7R1C105K C2012X5R0J475K C3225X5R1C226M C3225X5R0J476M EEE1AA221AP C4532X5R0J107M CRCW080575K0FKEA CRCW080534K8FKEA CRCW08051K10FKEA C1608C0G1H181J CRCW0805100KFKEA C2012C0G1H103J Quantity 1 1 2 2 1 1 1 1 1 1 1 1 1 TABLE 8. Output Voltage Setting (Rfbt = 75 kΩ) VOUT 3.3V 2.5 V 1.8 V 1.5 V 1.2 V 0.9 V Rfbb 23.7 kΩ 34.8 kΩ 59 kΩ 84.5 kΩ 150 kΩ 590 kΩ 17 www.national.com LMZ10503 301118b1 FIGURE 5. TABLE 9. Bill of Materials, VIN = 5V, VOUT = 2.5V, IOUT (MAX) = 3A, Complies with EN55022 Class B Radiated Emissions Designator U1 Cin1 Cin2 Cin3 CO1 Rfbt Rfbb Rcomp Ccomp CSS Description SIMPLE SWITCHER® 1 µF, X7R, 16V 4.7 µF, X5R, 6.3V 47 µF, X5R, 6.3V 100 µF, X5R, 6.3V 75 kΩ 34.8 kΩ 1.1 kΩ 180 pF, ±5%, C0G, 50V 10 nF, ±5%, C0G, 50V Case Size TO-PMOD-7 0805 0805 1210 1812 0805 0805 0805 0603 0805 Manufacturer National Semiconductor TDK TDK TDK TDK Vishay Dale Vishay Dale Vishay Dale TDK TDK Manufacturer P/N LMZ10503TZ-ADJ C2012X7R1C105K C2012X5R0J475K C3225X5R0J476M C4532X5R0J107M CRCW080575K0FKEA CRCW080534K8FKEA CRCW08051K10FKEA C1608C0G1H181J C2012C0G1H103J Quantity 1 1 1 1 1 1 1 1 1 1 TABLE 10. Output Voltage Setting (Rfbt = 75 kΩ) VOUT 3.3 V 2.5 V 1.8 V 1.5 V 1.2 V 0.9 V Rfbb 23.7 kΩ 34.8 kΩ 59 kΩ 84.5 kΩ 150 kΩ 590 kΩ www.national.com 18 LMZ10503 PCB Layout Diagrams The PCB design is available in the LMZ10503 product folder at www.national.com. 30111876 FIGURE 6. Top Copper 30111877 FIGURE 7. Internal Layer 1 (Ground) 19 www.national.com LMZ10503 30111878 FIGURE 8. Internal Layer 2 (Ground and Signal Traces) 30111879 FIGURE 9. Bottom Copper www.national.com 20 LMZ10503 Physical Dimensions inches (millimeters) unless otherwise noted TO-PMOD-7 Pin Package NS Package Number TZA07A 21 www.national.com LMZ10503 3A SIMPLE SWITCHER® 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 Amplifiers Audio Clock and Timing Data Converters Interface LVDS Power Management Switching Regulators LDOs LED Lighting Voltage References PowerWise® Solutions Temperature Sensors PLL/VCO www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/vref www.national.com/powerwise WEBENCH® Tools App Notes Reference Designs Samples Eval Boards Packaging Green Compliance Distributors Quality and Reliability Feedback/Support Design Made Easy Design Support www.national.com/webench www.national.com/appnotes www.national.com/refdesigns www.national.com/samples www.national.com/evalboards www.national.com/packaging www.national.com/quality/green www.national.com/contacts www.national.com/quality www.national.com/feedback www.national.com/easy www.national.com/solutions www.national.com/milaero www.national.com/solarmagic www.national.com/training Applications & Markets Mil/Aero PowerWise® Design University Serial Digital Interface (SDI) www.national.com/sdi www.national.com/wireless www.national.com/tempsensors SolarMagic™ THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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