LMZ14203H 3A SIMPLE SWITCHER® Power Module for High Output Voltage Easy to use 7 pin package Performance Benefits ■ ■ ■ ■ High efficiency reduces system heat generation Low radiated EMI (EN 55022 Class B compliant)(Note 5) No compensation required Low package thermal resistance System Performance Efficiency VOUT = 12V 30135686 Electrical Specifications ■ ■ ■ ■ Up to 3A output current Input voltage range 6V to 42V Output voltage as low as 5V Efficiency up to 97% 100 95 EFFICIENCY (%) TO-PMOD 7 Pin Package 10.16 x 13.77 x 4.57 mm (0.4 x 0.542 x 0.18 in) θJA = 16°C/W, θJC = 1.9°C/W RoHS Compliant 90 85 80 VIN = 15V VIN = 24V VIN = 30V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 OUTPUT CURRENT (A) Key Features 301356100 ■ 3.0 2.5 2.0 1.5 1.0 Intermediate bus conversions to 12V and 24V rail Time critical projects Space constrained / high thermal requirement applications Negative output voltage applications VIN = 15V VIN = 24V VIN = 42V 0.5 0.0 -20 0 20 40 60 80 100 120 140 AMBIENT TEMPERATURE (°C) 30135678 Radiated Emissions (EN 55022 Class B) 80 Applications ■ ■ ■ ■ 3.5 RADIATED EMISSIONS (dBμV/m) ■ ■ precision enable Protection against inrush currents Input UVLO and output short circuit protection – 40°C to 125°C junction temperature range Single exposed pad and standard pinout for easy mounting and manufacturing Low output voltage ripple Pin-to-pin compatible family: LMZ14203H/2H/1H (42V max 3A, 2A, 1A) LMZ14203/2/1 (42V max 3A, 2A, 1A) LMZ12003/2/1 (20V max 3A, 2A, 1A) Fully enabled for Webench® Power Designer Thermal Derating VOUT = 12V, θJA = 16°C/W OUTPUT CURRENT (A) ■ Integrated shielded inductor ■ Simple PCB layout ■ Flexible startup sequencing using external soft-start and ■ ■ ■ ■ 3.0 Emissions (Evaluation Board) EN 55022 Limit (Class B) 70 60 50 40 30 20 10 0 0 200 400 600 800 1,000 FREQUENCY (MHz) 30135691 SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation © 2011 National Semiconductor Corporation 301356 www.national.com LMZ14203H 3A SIMPLE SWITCHER® Power Module for High Output Voltage June 13, 2011 LMZ14203H Simplified Application Schematic 30135601 Connection Diagram 30135602 Top View 7-Lead TO-PMOD Ordering Information Order Number Package Type NSC Package Drawing Supplied As LMZ14203HTZ TO-PMOD-7 TZA07A 250 Units on Tape and Reel LMZ14203HTZX TO-PMOD-7 TZA07A 500 Units on Tape and Reel LMZ14203HTZE TO-PMOD-7 TZA07A 45 Units in a Rail Pin Descriptions Pin Name Description 1 VIN Supply input — Additional external input capacitance is required between this pin and the exposed pad (EP). 2 RON On time resistor — An external resistor from VIN to this pin sets the on-time and frequency of the application. Typical values range from 100k to 700k ohms. 3 EN 4 GND 5 SS Soft-Start — An internal 8 µA current source charges an external capacitor to produce the soft-start function. 6 FB Feedback — Internally connected to the regulation, over-voltage, and short-circuit comparators. The regulation reference point is 0.8V at this input pin. Connect the feedback resistor divider between the output and ground to set the output voltage. www.national.com Enable — Input to the precision enable comparator. Rising threshold is 1.18V. Ground — Reference point for all stated voltages. Must be externally connected to EP. 2 7 EP Name Description VOUT Output Voltage — Output from the internal inductor. Connect the output capacitor between this pin and the EP. EP Exposed Pad — Internally connected to pin 4. Used to dissipate heat from the package during operation. Must be electrically connected to pin 4 external to the package. 3 www.national.com LMZ14203H Pin LMZ14203H ESD Susceptibility(Note 2) For soldering specifications: see product folder at www.national.com and www.national.com/ms/MS/MS-SOLDERING.pdf Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN, RON to GND EN, FB, SS to GND Junction Temperature Storage Temperature Range Operating Ratings -0.3V to 43.5V -0.3V to 7V 150°C -65°C to 150°C ± 2 kV (Note 1) VIN EN Operation Junction Temperature 6V to 42V 0V to 6.5V −40°C to 125°C Electrical Characteristics Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the junction temperature (TJ) range 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. Unless otherwise stated the following conditions apply: VIN = 24V, VOUT = 12V, RON = 249kΩ Symbol Parameter Conditions Min (Note 3) Typ (Note 4) Max (Note 3) Units 1.10 1.18 1.25 V SYSTEM PARAMETERS Enable Control VEN VEN-HYS EN threshold trip point VEN rising EN threshold hysteresis 90 mV Soft-Start ISS ISS-DIS SS source current VSS = 0V 8 SS discharge current 10 15 -200 µA µA Current Limit ICL Current limit threshold DC average VINUVLO Input UVLO EN pin floating VIN rising 3.75 V VINUVLO-HYST Hysteresis EN pin floating VIN falling 130 mV ON timer minimum pulse width 150 ns OFF timer pulse width 260 ns 3.2 4.7 5.5 A VIN UVLO ON/OFF Timer tON-MIN tOFF Regulation and Over-Voltage Comparator VFB VFB VFB-OVP IFB www.national.com In-regulation feedback voltage In-regulation feedback voltage VIN = 24V, VOUT = 12V VSS >+ 0.8V TJ = -40°C to 125°C IOUT = 10mA to 3A 0.782 0.803 0.822 V VIN = 24V, VOUT = 12V VSS >+ 0.8V TJ = 25°C IOUT = 10mA to 3A 0.786 0.803 0.818 V VIN = 36V, VOUT = 24V VSS >+ 0.8V TJ = -40°C to 125°C IOUT = 10mA to 3A 0.780 0.803 0.826 V VIN = 36V, VOUT = 24V VSS >+ 0.8V TJ = 25°C IOUT = 10mA to 3A 0.787 0.803 0.819 V Feedback over-voltage protection threshold Feedback input bias current 4 0.92 V 5 nA Min (Note 3) Typ (Note 4) Max (Note 3) Parameter Conditions Units IQ Non Switching Input Current VFB= 0.86V 1 mA ISD Shut Down Quiescent Current VEN= 0V 25 μA Rising 165 °C 15 °C 4 layer Printed Circuit Board, 7.62cm x 7.62cm (3in x 3in) area, 1 oz Copper, No air flow 16 °C/W 4 layer Printed Circuit Board, 6.35cm x 6.35cm (2.5in x 2.5in) area, 1 oz Copper, No air flow 18.4 °C/W No air flow 1.9 °C/W 8 mV PP Thermal Characteristics TSD TSD-HYST θJA θJC Thermal Shutdown Thermal Shutdown Hysteresis Junction to Ambient Junction to Case PERFORMANCE PARAMETERS ΔVOUT Output Voltage Ripple VOUT = 5V, CO = 100µF 6.3V X7R ΔVOUT/ΔVIN Line Regulation VIN = 16V to 42V, IOUT= 3A .01 % ΔVOUT/ΔIOUT Load Regulation VIN = 24V, IOUT = 0A to 3A 1.5 mV/A η Efficiency VIN = 24V VOUT = 12V IOUT = 1A 94 % η Efficiency VIN = 24V VO = 12V IO = 3A 93 % Note 1: 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 2: The human body model is a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin. Test method is per JESD-22-114. Note 3: Min and Max limits are 100% production tested at 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 4: Typical numbers are at 25°C and represent the most likely parametric norm. Note 5: EN 55022:2006, +A1:2007, FCC Part 15 Subpart B: 2007. 5 www.national.com LMZ14203H Symbol Unless otherwise specified, the following conditions apply: VIN = 24V; Cin = 10uF X7R Ceramic; CO = 47uF; TAMB = 25°C. Efficiency VOUT = 5.0V TAMB = 25°C Power Dissipation VOUT = 5.0V TAMB = 25°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 8V VIN = 12V VIN = 24V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 4 3 2 1 0 3.0 VIN = 8V VIN = 12V VIN = 24V VIN = 36V VIN = 42V 0.0 OUTPUT CURRENT (A) 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135697 30135698 Efficiency VOUT = 12V TAMB = 25°C Power Dissipation VOUT = 12V TAMB = 25°C 100 5 95 4 POWER DISSIPATION (W) EFFICIENCY (%) LMZ14203H Typical Performance Characteristics 90 85 80 75 70 0.0 VIN = 15V VIN = 24V VIN = 30V VIN = 36V VIN = 42V 0.5 1.0 1.5 2.0 2.5 OUTPUT CURRENT (A) 3 2 1 0 3.0 VIN = 15V VIN = 24V VIN = 30V VIN = 36V VIN = 42V 0.0 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135693 301356100 www.national.com 6 Power Dissipation VOUT = 15V TAMB = 25°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 24V VIN = 30V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 4 3 2 1 0 3.0 VIN = 24V VIN = 30V VIN = 36V VIN = 42V 0.0 OUTPUT CURRENT (A) 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135699 30135660 Efficiency VOUT = 18V TAMB = 25°C Power Dissipation VOUT = 18V TAMB = 25°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 24V VIN = 30V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 4 3 2 1 0 3.0 VIN = 24V VIN = 30V VIN = 36V VIN = 42V 0.0 OUTPUT CURRENT (A) 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135661 30135662 Efficiency VOUT = 24V TAMB = 25°C Power Dissipation VOUT = 24V TAMB = 25°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 28V VIN = 30V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 LMZ14203H Efficiency VOUT = 15V TAMB = 25°C 4 3 2 1 0 3.0 OUTPUT CURRENT (A) VIN = 28V VIN = 30V VIN = 36V VIN = 42V 0.0 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135663 30135664 7 www.national.com LMZ14203H Efficiency VOUT = 30V TAMB = 25°C Power Dissipation VOUT = 30V TAMB = 25°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 34V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 4 3 2 1 0 3.0 VIN = 34V VIN = 36V VIN = 42V 0.0 OUTPUT CURRENT (A) 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135670 30135671 Efficiency VOUT = 5.0V TAMB = 85°C Power Dissipation VOUT = 5.0V TAMB = 85°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 8V VIN = 12V VIN = 24V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 4 3 2 1 0 3.0 VIN = 8V VIN = 12V VIN = 24V VIN = 36V VIN = 42V 0.0 OUTPUT CURRENT (A) 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135694 30135665 Efficiency VOUT = 12V TAMB = 85°C Power Dissipation VOUT = 12V TAMB = 85°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 15V VIN = 24V VIN = 30V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 OUTPUT CURRENT (A) 3 2 1 0.0 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135695 www.national.com 4 0 3.0 VIN = 15V VIN = 24V VIN = 30V VIN = 36V VIN = 42V 30135696 8 Power Dissipation VOUT = 15V TAMB = 85°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 24V VIN = 30V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 4 3 2 1 0 3.0 VIN = 24V VIN = 30V VIN = 36V VIN = 42V 0.0 OUTPUT CURRENT (A) 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135668 30135669 Efficiency VOUT = 18V TAMB = 85°C Power Dissipation VOUT = 18V TAMB = 85°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 24V VIN = 30V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 4 3 2 1 0 3.0 VIN = 24V VIN = 30V VIN = 36V VIN = 42V 0.0 OUTPUT CURRENT (A) 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135666 30135667 Efficiency VOUT = 24V TAMB = 85°C Power Dissipation VOUT = 24V TAMB = 85°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 28V VIN = 30V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 LMZ14203H Efficiency VOUT = 15V TAMB = 85°C 2.5 4 3 2 1 0 3.0 OUTPUT CURRENT (A) VIN = 28V VIN = 30V VIN = 36V VIN = 42V 0.0 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135672 30135673 9 www.national.com LMZ14203H Efficiency VOUT = 30V TAMB = 85°C Power Dissipation VOUT = 30V TAMB = 85°C 100 5 POWER DISSIPATION (W) EFFICIENCY (%) 95 90 85 80 VIN = 34V VIN = 36V VIN = 42V 75 70 0.0 0.5 1.0 1.5 2.0 2.5 4 3 2 1 0 3.0 VIN = 34V VIN = 36V VIN = 42V 0.0 0.5 OUTPUT CURRENT (A) 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135674 30135675 Thermal Derating VOUT = 12V, θJA = 20°C/W 3.5 3.5 3.0 3.0 OUTPUT CURRENT (A) OUTPUT CURRENT (A) Thermal Derating VOUT = 12V, θJA = 16°C/W 2.5 2.0 1.5 1.0 VIN = 15V VIN = 24V VIN = 42V 0.5 0.0 -20 0 20 40 VIN = 15V VIN = 24V VIN = 42V 2.5 2.0 1.5 1.0 0.5 60 0.0 -20 80 100 120 140 AMBIENT TEMPERATURE (°C) 0 20 40 60 80 100 120 140 AMBIENT TEMPERATURE (°C) 30135678 30135687 Thermal Derating VOUT = 24V, θJA = 20°C/W 3.5 3.5 3.0 3.0 OUTPUT CURRENT (A) OUTPUT CURRENT (A) Thermal Derating VOUT = 24V, θJA = 16°C/W 2.5 2.0 1.5 1.0 VIN = 30V VIN = 36V VIN = 42V 0.5 0.0 -20 0 20 40 2.5 2.0 1.5 1.0 0.5 60 0.0 -20 80 100 120 140 AMBIENT TEMPERATURE (°C) 0 20 40 60 80 100 120 140 AMBIENT TEMPERATURE (°C) 30135679 www.national.com VIN = 30V VIN = 36V VIN = 42V 30135688 10 3.5 3.0 3.0 OUTPUT CURRENT (A) OUTPUT CURRENT (A) Thermal Derating VOUT = 30V, θJA = 20°C/W 3.5 2.5 2.0 1.5 1.0 0.5 0.0 -20 0 VIN = 34V VIN = 36V VIN = 42V VIN = 34V VIN = 36V VIN = 42V 2.5 2.0 1.5 1.0 0.5 0.0 -20 20 40 60 80 100 120 140 AMBIENT TEMPERATURE (°C) 0 20 40 60 80 100 120 140 AMBIENT TEMPERATURE (°C) 30135653 30135654 Package Thermal Resistance θJA 4 Layer Printed Circuit Board with 1oz Copper Line and Load Regulation TAMB = 25°C 12.6 0LFM (0m/s) air 225LFM (1.14m/s) air 500LFM (2.54m/s) air Evaluation Board Area 35 30 OUTPUT VOLTAGE (V) THERMAL RESISTANCE θJA (°C/W) 40 LMZ14203H Thermal Derating VOUT = 30V, θJA = 16°C/W 25 20 15 10 VIN = 15V VIN = 24V VIN = 30V VIN = 36V VIN = 42V ±1% 12.4 12.2 12.0 11.8 5 0 0 10 20 30 40 BOARD AREA (cm2) 50 11.6 0.0 60 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135689 Output Ripple VIN = 12V, IOUT = 3A, Ceramic COUT, BW = 200 MHz 30135652 Output Ripple VIN = 24V, IOUT = 3A, Polymer Electrolytic COUT, BW = 200 MHz 30135605 30135604 11 www.national.com Load Transient Response VIN = 24V VOUT = 12V Load Step from 30% to 100% 30135606 30135603 Switching Frequency vs. Power Dissipation VOUT = 5V 6.0 6 5.5 5 POWER DISSIPATION (W) DC CURRENT LIMIT LEVEL (A) Current Limit vs. Input Voltage VOUT = 5V 5.0 4.5 4.0 Fsw = 250kHz Fsw = 400kHz Fsw = 600kHz 3.5 3.0 VIN = 12V VIN = 24V VIN = 36V VIN = 42V 4 3 2 1 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 40 45 200 300 400 500 600 700 SWITCHING FREQUENCY (kHz) 30135621 Switching Frequency vs. Power Dissipation VOUT = 12V 6 5.5 5 POWER DISSIPATION (W) 6.0 5.0 4.5 4.0 Fsw = 250kHz Fsw = 400kHz Fsw = 600kHz 3.5 3.0 VIN = 15V VIN = 24V VIN = 36V VIN = 42V 4 3 2 1 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 40 45 200 30135622 www.national.com 800 30135618 Current Limit vs. Input Voltage VOUT = 12V DC CURRENT LIMIT LEVEL (A) LMZ14203H Load Transient Response VIN = 24V VOUT = 12V Load Step from 10% to 100% 300 400 500 600 700 SWITCHING FREQUENCY (kHz) 800 30135619 12 6 5.5 5 POWER DISSIPATION (W) DC CURRENT LIMIT LEVEL (A) Switching Frequency vs. Power Dissipation VOUT = 24V 6.0 5.0 4.5 4.0 Fsw = 250kHz Fsw = 400kHz Fsw = 600kHz 3.5 LMZ14203H Current Limit vs. Input Voltage VOUT = 24V 4 3 2 VIN = 30V VIN = 36V VIN = 42V 1 3.0 0 30 33 36 39 42 INPUT VOLTAGE (V) 45 200 300 400 500 600 700 800 SWITCHING FREQUENCY (kHz) 30135623 30135620 Startup VIN = 24V IOUT = 3A Radiated EMI of Evaluation Board, VOUT = 12V RADIATED EMISSIONS (dBμV/m) 80 60 50 40 30 20 10 0 30135655 Emissions (Evaluation Board) EN 55022 Limit (Class B) 70 0 200 400 600 800 1,000 FREQUENCY (MHz) 30135691 Conducted EMI, VOUT = 12V Evaluation Board BOM and 3.3µH 2x10µF LC line filter CONDUCTED EMISSIONS (dBμV) 80 70 Emissions CISPR 22 Quasi Peak CISPR 22 Average 60 50 40 30 20 10 0 0.1 1 10 FREQUENCY (MHz) 100 30135624 13 www.national.com LMZ14203H Application Block Diagram 30135608 falling threshold of 1.09V. The maximum recommended voltage into the EN pin is 6.5V. For applications where the midpoint of the enable divider exceeds 6.5V, a small zener can be added to limit this voltage. The function of the RENT and RENB divider shown in the Application Block Diagram is to allow the designer to choose an input voltage below which the circuit will be disabled. This implements the feature of programmable under voltage lockout. This is often used in battery powered systems to prevent deep discharge of the system battery. It is also useful in system designs for sequencing of output rails or to prevent early turnon of the supply as the main input voltage rail rises at powerup. Applying the enable divider to the main input rail is often done in the case of higher input voltage systems such as 24V AC/DC systems where a lower boundary of operation should be established. In the case of sequencing supplies, the divider is connected to a rail that becomes active earlier in the powerup cycle than the LMZ14203H output rail. The two resistors should be chosen based on the following ratio: COT Control Circuit Overview Constant On Time control is based on a comparator and an on-time one shot, with the output voltage feedback compared to an internal 0.8V reference. If the feedback voltage is below the reference, the high-side MOSFET is turned on for a fixed on-time determined by a programming resistor RON. RON is connected to VIN such that on-time is reduced with increasing input supply voltage. Following this on-time, the high-side MOSFET remains off for a minimum of 260 ns. If the voltage on the feedback pin falls below the reference level again the on-time cycle is repeated. Regulation is achieved in this manner. Design Steps for the LMZ14203H Application The LMZ14203H is fully supported by Webench® which offers the following: • Component selection • Electrical simulation • Thermal simulation • Build-it prototype board for a reduction in design time RENT / RENB = (VIN-ENABLE/ 1.18V) – 1 (1) The EN pin is internally pulled up to VIN and can be left floating for always-on operation. However, it is good practice to use the enable divider and turn on the regulator when VIN is close to reaching its nominal value. This will guarantee smooth startup and will prevent overloading the input supply. The following list of steps can be used to manually design the LMZ14203H application. • Select minimum operating VIN with enable divider resistors • Program VO with divider resistor selection • Program turn-on time with soft-start capacitor selection • Select CO • Select CIN • Set operating frequency with RON • Determine module dissipation • Layout PCB for required thermal performance OUTPUT VOLTAGE SELECTION Output voltage is determined by a divider of two resistors connected between VO and ground. The midpoint of the divider is connected to the FB input. The voltage at FB is compared to a 0.8V internal reference. In normal operation an on-time cycle is initiated when the voltage on the FB pin falls below 0.8V. The high-side MOSFET on-time cycle causes the output voltage to rise and the voltage at the FB to exceed 0.8V. As long as the voltage at FB is above 0.8V, ontime cycles will not occur. The regulated output voltage determined by the external divider resistors RFBT and RFBB is: ENABLE DIVIDER, RENT AND RENB SELECTION The enable input provides a precise 1.18V reference threshold to allow direct logic drive or connection to a voltage divider from a higher enable voltage such as VIN. The enable input also incorporates 90 mV (typ) of hysteresis resulting in a www.national.com VO = 0.8V x (1 + RFBT / RFBB) (2) 14 ESR: The ESR of the output capacitor affects the output voltage ripple. High ESR will result in larger VOUT peak-to-peak ripple voltage. Furthermore, high output voltage ripple caused by excessive ESR can trigger the over-voltage protection monitored at the FB pin. The ESR should be chosen to satisfy the maximum desired VOUT peak-to-peak ripple voltage and to avoid over-voltage protection during normal operation. The following equations can be used: ESRMAX-RIPPLE ≤ VOUT-RIPPLE / ILR P-P(7) where ILR P-P is calculated using equation (19) below. RFBT / RFBB = (VO / 0.8V) - 1 (3) These resistors should be chosen from values in the range of 1 kΩ to 50 kΩ. A feed-forward capacitor is placed in parallel with RFBT to improve load step transient response. Its value is usually determined experimentally by load stepping between DCM and CCM conduction modes and adjusting for best transient response and minimum output ripple. A table of values for RFBT , RFBB , and RON is included in the simplified applications schematic. ESRMAX-OVP < (VFB-OVP - VFB) / (ILR P-P x AFB )(8) where AFB is the gain of the feedback network from VOUT to VFB at the switching frequency. SOFT-START CAPACITOR, CSS, SELECTION Programmable soft-start permits the regulator to slowly ramp to its steady state operating point after being enabled, thereby reducing current inrush from the input supply and slowing the output voltage rise-time to prevent overshoot. Upon turn-on, after all UVLO conditions have been passed, an internal 8uA current source begins charging the external soft-start capacitor. The soft-start time duration to reach steady state operation is given by the formula: As worst case, assume the gain of AFB with the CFF capacitor at the switching frequency is 1. The selected capacitor should have sufficient voltage and RMS current rating. The RMS current through the output capacitor is: I(COUT(RMS)) = ILR P-P / √12 (9) INPUT CAPACITOR, CIN, SELECTION The LMZ14203H module contains an internal 0.47 µF input ceramic capacitor. Additional input capacitance is required external to the module to handle the input ripple current of the application. This input capacitance should be located as close as possible to the module. Input capacitor selection is generally directed to satisfy the input ripple current requirements rather than by capacitance value. Worst case input ripple current rating is dictated by the equation: tSS = VREF x CSS / Iss = 0.8V x CSS / 8uA (4) This equation can be rearranged as follows: CSS = tSS x 8 μA / 0.8V Use of a 4700pF capacitor results in 0.5ms soft-start duration. This is a recommended value. Note that high values of CSS capacitance will cause more output voltage droop when a load transient goes across the DCM-CCM boundary. Use equation 18 below to find the DCM-CCM boundary load current for the specific operating condition. If a fast load transient response is desired for steps between DCM and CCM mode the softstart capacitor value should be less than 0.018µF. I(CIN(RMS)) ≊ 1 / 2 x IO x √ (D / 1-D) (10) where D ≊ VO / VIN (As a point of reference, the worst case ripple current will occur when the module is presented with full load current and when VIN = 2 x VO). Recommended minimum input capacitance is 10uF X7R ceramic with a voltage rating at least 25% higher than the maximum applied input voltage for the application. It is also recommended that attention be paid to the voltage and temperature deratings of the capacitor selected. It should be noted that ripple current rating of ceramic capacitors may be missing from the capacitor data sheet and you may have to contact the capacitor manufacturer for this rating. If the system design requires a certain maximum value of input ripple voltage ΔVIN to be maintained then the following equation may be used. Note that the following conditions will reset the soft-start capacitor by discharging the SS input to ground with an internal 200 μA current sink: • The enable input being “pulled low” • Thermal shutdown condition • Over-current fault • Internal VINUVLO OUTPUT CAPACITOR, CO, SELECTION None of the required output capacitance is contained within the module. At a minimum, the output capacitor must meet the worst case RMS current rating of 0.5 x ILR P-P, as calculated in equation (17). Beyond that, additional capacitance will reduce output ripple so long as the ESR is low enough to permit it. A minimum value of 10 μF is generally required. Experimentation will be required if attempting to operate with a minimum value. Low ESR capacitors, such as ceramic and polymer electrolytic capacitors are recommended. CIN ≥ IO x D x (1–D) / fSW-CCM x ΔVIN(11) If ΔVIN is 1% of VIN for a 24V input to 12V output application this equals 240 mV and fSW = 400 kHz. CAPACITANCE: CIN≥ 3A x 12V/24V x (1– 12V/24V) / (400000 x 0.240 V) CIN≥ 7.8μF The following equation provides a good first pass approximation of CO for load transient requirements: Additional bulk capacitance with higher ESR may be required to damp any resonant effects of the input capacitance and parasitic inductance of the incoming supply lines. CO≥ISTEP x VFB x L x VIN/ (4 x VO x (VIN — VO) x VOUT-TRAN) (6) ON TIME, RON, RESISTOR SELECTION Many designs will begin with a desired switching frequency in mind. As seen in the Typical Performance Characteristics section, the best efficiency is achieved in the 300kHz-400kHz switching frequency range. The following equation can be used to calculate the RON value. As an example, for 3A load step, VIN = 24V, VOUT = 12V, VOUT-TRAN = 50mV: CO≥ 3A x 0.8V x 10μH x 24V / (4 x 12V x ( 24V — 12V) x 50mV) CO≥ 20μF 15 www.national.com LMZ14203H Rearranging terms; the ratio of the feedback resistors for a desired output voltage is: Where VIN is the maximum input voltage and fSW is determined from equation 12. If the output current IO is determined by assuming that IO = IL, the higher and lower peak of ILR can be determined. Be aware that the lower peak of ILR must be positive if CCM operation is required. This can be rearranged as RON ≊ VO / (1.3 x 10 -10 x fSW(CCM) (13) The selection of RON and fSW(CCM) must be confined by limitations in the on-time and off-time for the COT control section. The on-time of the LMZ14203H timer is determined by the resistor RON and the input voltage VIN. It is calculated as follows: POWER DISSIPATION AND BOARD THERMAL REQUIREMENTS For a design case of VIN = 24V, VOUT = 12V, IOUT = 3A, TAMB (MAX) = 65°C , and TJUNCTION = 125°C, the device must see a maximum junction-to-ambient thermal resistance of: tON = (1.3 x 10-10 x RON) / VIN (14) The inverse relationship of tON and VIN gives a nearly constant switching frequency as VIN is varied. RON should be selected such that the on-time at maximum VIN is greater than 150 ns. The on-timer has a limiter to ensure a minimum of 150 ns for tON. This limits the maximum operating frequency, which is governed by the following equation: θJA-MAX < (TJ-MAX - TAMB(MAX)) / PD This θJA-MAX will ensure that the junction temperature of the regulator does not exceed TJ-MAX in the particular application ambient temperature. To calculate the required θJA-MAX we need to get an estimate for the power losses in the IC. The following graph is taken form the Typical Performance Characteristics section and shows the power dissipation of the LMZ14203H for VOUT = 12V at 85°C TAMB. fSW(MAX) = VO / (VIN(MAX) x 150 nsec) (15) This equation can be used to select RON if a certain operating frequency is desired so long as the minimum on-time of 150 ns is observed. The limit for RON can be calculated as follows: RON ≥ VIN(MAX) x 150 nsec / (1.3 x 10 -10) (16) Power Dissipation VOUT = 12V TAMB = 85°C If RON calculated in (13) is less than the minimum value determined in (16) a lower frequency should be selected. Alternatively, VIN(MAX) can also be limited in order to keep the frequency unchanged. Additionally, the minimum off-time of 260 ns (typ) limits the maximum duty ratio. Larger RON (lower FSW) should be selected in any application requiring large duty ratio. 5 POWER DISSIPATION (W) LMZ14203H fSW(CCM) ≊ VO / (1.3 x 10-10 x RON) (12) Discontinuous Conduction and Continuous Conduction Modes At light load the regulator will operate in discontinuous conduction mode (DCM). With load currents above the critical conduction point, it will operate in continuous conduction mode (CCM). When operating in DCM the switching cycle begins at zero amps inductor current; increases up to a peak value, and then recedes back to zero before the end of the off-time. Note that during the period of time that inductor current is zero, all load current is supplied by the output capacitor. The next on-time period starts when the voltage on the FB pin falls below the internal reference. The switching frequency is lower in DCM and varies more with load current as compared to CCM. Conversion efficiency in DCM is maintained since conduction and switching losses are reduced with the smaller load and lower switching frequency. Operating frequency in DCM can be calculated as follows: VIN = 15V VIN = 24V VIN = 30V VIN = 36V VIN = 42V 4 3 2 1 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) 30135696 Using the 85°C TAMB power dissipation data as a conservative starting point, the power dissipation PD for VIN = 24V and VOUT = 12V is estimated to be 3.5W. The necessary θJA-MAX can now be calculated. fSW(DCM)≊VO x (VIN-1) x 10μH x 1.18 x 1020 x IO / (VIN–VO) x RON2 (17) θJA-MAX < (125°C - 65°C) / 3.5W In CCM, current flows through the inductor through the entire switching cycle and never falls to zero during the off-time. The switching frequency remains relatively constant with load current and line voltage variations. The CCM operating frequency can be calculated using equation 12 above. The approximate formula for determining the DCM/CCM boundary is as follows: To achieve this thermal resistance the PCB is required to dissipate the heat effectively. The area of the PCB will have a direct effect on the overall junction-to-ambient thermal resistance. In order to estimate the necessary copper area we can refer to the following Package Thermal Resistance graph. This graph is taken from the Typical Performance Characteristics section and shows how the θJA varies with the PCB area. θJA-MAX < 17.1°C/W IDCB≊VOx (VIN–VO) / ( 2 x 10μH x fSW(CCM) x VIN) (18) The inductor internal to the module is 10μH. This value was chosen as a good balance between low and high input voltage applications. The main parameter affected by the inductor is the amplitude of the inductor ripple current (ILR). ILR can be calculated with: ILR P-P=VO x (VIN- VO) / (10µH x fSW x VIN) (19) www.national.com 16 THERMAL RESISTANCE θJA (°C/W) 40 mize 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 to the GND pin of the device. This prevents any switched or load currents from flowing in the analog ground traces. If not properly handled, 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 feed forward capacitor CFF, should be located close to the FB pin. Since the FB node is high impedance, maintain the copper area as small as possible. The traces from RFBT, RFBB, and CFF should be routed away from the body of the LMZ14203H to minimize noise pickup. 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 to 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 a plurality of copper layers, these 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 heatsinking to keep the junction temperature below 125°C. 0LFM (0m/s) air 225LFM (1.14m/s) air 500LFM (2.54m/s) air Evaluation Board Area 35 30 25 20 15 10 5 0 0 10 20 30 40 BOARD AREA (cm2) 50 60 30135689 For θJA-MAX< 17.1°C/W and only natural convection (i.e. no air flow), the PCB area will have to be at least 52cm2. This corresponds to a square board with 7.25cm x 7.25cm (2.85in x 2.85in) copper area, 4 layers, and 1oz copper thickness. Higher copper thickness will further improve the overall thermal performance. As a reference, the evaluation board has 2oz copper on the top and bottom layers, achieving θJA of 14.9°C/W for the same board area. Note that thermal vias should be placed under the IC package to easily transfer heat from the top layer of the PCB to the inner layers and the bottom layer. For more guidelines and insight on PCB copper area, thermal vias placement, and general thermal design practices please refer to Application Note AN-2020 (http://www.national.com/ an/AN/AN-2020.pdf). 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. Additional Features OUTPUT OVER-VOLTAGE COMPARATOR The voltage at FB is compared to a 0.92V internal reference. If FB rises above 0.92V the on-time is immediately terminated. This condition is known as over-voltage protection (OVP). It can occur if the input voltage is increased very suddenly or if the output load is decreased very suddenly. Once OVP is activated, the top MOSFET on-times will be inhibited until the condition clears. Additionally, the synchronous MOSFET will remain on until inductor current falls to zero. CURRENT LIMIT Current limit detection is carried out during the off-time by monitoring the current in the synchronous MOSFET. Referring to the Functional Block Diagram, when the top MOSFET is turned off, the inductor current flows through the load, the PGND pin and the internal synchronous MOSFET. If this current exceeds 4.2A (typical) the current limit comparator disables the start of the next on-time period. The next switching cycle will occur only if the FB input is less than 0.8V and the inductor current has decreased below 4.2A. Inductor current is monitored during the period of time the synchronous MOSFET is conducting. So long as inductor current exceeds 4.2A, further on-time intervals for the top MOSFET will not occur. Switching frequency is lower during current limit due to the longer off-time. It should also be noted that DC current limit varies with duty cycle, switching frequency, and temperature. 30135611 1. Minimize area of switched current loops. From an EMI reduction standpoint, it is imperative to minimize the high di/dt paths during PC board layout. The high current loops that do not overlap have high di/dt content that will cause observable high frequency noise on the output pin if the input capacitor (Cin1) is placed at a distance away from the LMZ14203H. Therefore place CIN1 as close as possible to the LMZ14203H VIN and GND exposed pad. This will mini- 17 www.national.com LMZ14203H Package Thermal Resistance θJA 4 Layer Printed Circuit Board with 1oz Copper LMZ14203H THERMAL PROTECTION The junction temperature of the LMZ14203H should not be allowed to exceed its maximum ratings. Thermal protection is implemented by an internal Thermal Shutdown circuit which activates at 165 °C (typ) causing the device to enter a low power standby state. In this state the main MOSFET remains off causing VO to fall, and additionally the CSS capacitor is discharged to ground. Thermal protection helps prevent catastrophic failures for accidental device overheating. When the junction temperature falls back below 145 °C (typ Hyst = 20 °C) the SS pin is released, VO rises smoothly, and normal operation resumes. PRE-BIASED STARTUP The LMZ14203H will properly start up into a pre-biased output. This startup situation is common in multiple rail logic applications where current paths may exist between different power rails during the startup sequence. The pre-bias level of the output voltage must be less than the input UVLO set point. This will prevent the output pre-bias from enabling the regulator through the high side MOSFET body diode. ZERO COIL CURRENT DETECTION The current of the lower (synchronous) MOSFET is monitored by a zero coil current detection circuit which inhibits the synchronous MOSFET when its current reaches zero until the next on-time. This circuit enables the DCM operating mode, which improves efficiency at light loads. www.national.com 18 LMZ14203H Physical Dimensions inches (millimeters) unless otherwise noted 7-Lead TZA Package NS Package Number TZA07A 19 www.national.com LMZ14203H 3A SIMPLE SWITCHER® Power Module for High Output Voltage Notes 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® 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® Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise® Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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