XH2596-5.0

XH2596 TO-263 3.3 5.0 12 ADJ FEATURES DESCRIPTION • The XH2596 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving a 3A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, 12V, and an adjustable output version. 1 23 • • • • • • • • • • • 3.3V,5V,12V,ADJ and Adjustable Output Versions Adjustable Version Output Voltage Range, 1.2V to 37V ±4% Max Over Line and Load Conditions Ensured 3A Output Load Current Input Voltage Range Up to 40V Requires Only 4 External Components Excellent Line and Load Regulation Specifications 150 kHz Fixed Frequency Internal Oscillator TTL Shutdown Capability Low Power Standby Mode, IQ Typically 80 μA High Efficiency Uses Readily Available Standard Inductors Thermal Shutdown and Current Limit Protection Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation , and a fixed-frequency oscillator. The XH2596 series operates at a switching frequency of 150 kHz thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. Available in a different lead bend options, and a 5-lead TO-263 surface mount package. A standard series of inductors are available from several different manufacturers optimized for use with the XH2596 series. This feature greatly simplifies the design of switch-mode power supplies. APPLICATIONS • • • Other features include a ensured ±4% tolerance on output voltage under specified input voltage and output load conditions, and ±15% on the oscillator frequency. External shutdown is included, featuring typically 80 μA standby current. Self protection features include a two stage frequency reducing current limit for the output switch and an over temperature shutdown for complete protection under fault conditions. (1) Simple High-Efficiency Step-Down (Buck) Regulator On-Card Switching Regulators Positive to Negative Converter Typical Application (Fixed Output Voltage Versions) XH2596 5.0 1 XH2596 TO-263 3.3 5.0 12 ADJ Connection Diagrams Figure 2. 5-Lead TO-263 (S) Package See Package Number KTT0005B Absolute Maximum Ratings (1) (2) Maximum Supply Voltage 45V ON /OFF Pin Input Voltage −0.3 ≤ V ≤ +25V Feedback Pin Voltage −0.3 ≤ V ≤+25V −1V Output Voltage to Ground (Steady State) Power Dissipation Internally limited −65°C to +150°C Storage Temperature Range ESD Susceptibility Human Body Model (3) 2 kV Lead Temperature DDPAK/TO-263 Package Vapor Phase (60 sec.) +215°C Infrared (10 sec.) +245°C Maximum Junction Temperature (1) (2) +150°C Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not ensure specific performance limits. For ensured specifications and test conditions, see the Electrical Characteristics. The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin. Operating Conditions −40°C ≤ TJ ≤ +125°C Temperature Range Supply Voltage 4.5V to 40V 2 XH2596 TO-263 3.3 5.0 12 ADJ XH2596-3.3 Electrical Characteristics Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range XH2596-3.3 Symbol Parameter Conditions Typ (1) SYSTEM PARAMETERS VOUT η (1) (2) (3) (3) Limit (2) Units (Limits) 3.168/3.135 V(min) 3.432/3.465 V(max) Test Circuit Figure 20 Output Voltage Efficiency 4.75V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 3A VIN = 12V, ILOAD = 3A 3.3 V 73 % Typical numbers are at 25°C and represent the most likely norm. All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. When the XH2596 is used as shown in the Figure 20 test circuit, system performance will be as shown in system parameters of Electrical Characteristics section. XH2596-5.0 Electrical Characteristics Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range XH2596-5.0 Symbol Parameter Conditions Typ (1) SYSTEM PARAMETERS VOUT η (1) (2) (3) (3) Limit (2) Units (Limits) Test Circuit Figure 20 Output Voltage Efficiency 7V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 3A VIN = 12V, ILOAD = 3A 5.0 V 4.800/4.750 V(min) 5.200/5.250 V(max) 80 % Typical numbers are at 25°C and represent the most likely norm. All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. When the XH2596 is used as shown in the Figure 20 test circuit, system performance will be as shown in system parameters of Electrical Characteristics section. XH2596-12 Electrical Characteristics Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range XH2596-12 Symbol Parameter Conditions Typ (1) SYSTEM PARAMETERS VOUT η (1) (2) (3) (3) (2) Units (Limits) Test Circuit Figure 20 Output Voltage Efficiency Limit 15V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 3A VIN = 25V, ILOAD = 3A 12.0 90 V 11.52/11.40 V(min) 12.48/12.60 V(max) % Typical numbers are at 25°C and represent the most likely norm. All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. When the XH2596 is used as shown in the Figure 20 test circuit, system performance will be as shown in system parameters of Electrical Characteristics section. 3 XH2596 TO-263 3.3 5.0 12 ADJ XH2596-ADJ Electrical Characteristics Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range XH2596-ADJ Symbol Parameter Conditions Typ (1) SYSTEM PARAMETERS VFB (3) 4.5V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 3A Efficiency (3) Units (Limits) 1.193/1.180 V(min) 1.267/1.280 V(max) 1.230 V VOUT programmed for 3V. Circuit of Figure 20 (1) (2) (2) Test Circuit Figure 20 Feedback Voltage η Limit VIN = 12V, VOUT = 3V, ILOAD = 3A 73 % Typical numbers are at 25°C and represent the most likely norm. All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. When the XH2596 is used as shown in the Figure 20 test circuit, system performance will be as shown in system parameters of Electrical Characteristics section. All Output Voltage Versions Electrical Characteristics Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version and VIN = 24V for the 12V version. ILOAD = 500 mA XH2596-XX Symbol Parameter Conditions Typ (1) Limit (2) Units (Limits) 50/100 nA (max) 127/110 kHz(min) 173/173 kHz(max) 1.4/1.5 V(max) DEVICE PARAMETERS Ib Feedback Bias Current fO Oscillator Frequency VSAT DC ICL IL Saturation Voltage Adjustable Version Only, VFB = 1.3V See (3) IOUT = 3A (4) (5) See (5) 100 Min Duty Cycle (OFF) See (6) 0 Current Limit Peak Current Output = 0V (1) (2) (3) (4) (5) (6) (7) Quiescent Current See kHz 1.16 Max Duty Cycle (ON) Output Leakage Current nA 150 (4) (5) V % 4.5 (4) (6) Output = −1V IQ 10 (7) A 3.6/3.4 A(min) 6.9/7.5 A(max) 50 μA(max) 30 mA(max) 10 mA(max) 2 (6) mA 5 mA Typical numbers are at 25°C and represent the most likely norm. All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). The switching frequency is reduced when the second stage current limit is activated. No diode, inductor or capacitor connected to output pin. Feedback pin removed from output and connected to 0V to force the output transistor switch ON. Feedback pin removed from output and connected to 12V for the 3.3V, 5V, and the ADJ. version, and 15V for the 12V version, to force the output transistor switch OFF. VIN = 40V. 4 XH2596 TO-263 3.3 5.0 12 ADJ All Output Voltage Versions Electrical Characteristics (continued) Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version and VIN = 24V for the 12V version. ILOAD = 500 mA XH2596-XX Symbol Parameter Conditions Typ (1) ISTBY θJC Standby Quiescent Current ON/OFF pin = 5V (OFF) (7) Limit (2) Units (Limits) 200/250 μA(max) μA 80 Thermal Resistance 2 °C/W TO-263 Package, Junction to Ambient (9) 50 °C/W θJA TO-263 Package, Junction to Ambient (10) 50 °C/W θJA TO-263 Package, Junction to Ambient (11) 30 °C/W 20 °C/W θJA θJA ON/OFF CONTROL Test Circuit Figure 20 ON /OFF Pin Logic Input VIH Threshold Voltage VIL IH IL 1.3 Low (Regulator ON) High (Regulator OFF) ON /OFF Pin Input Current VLOGIC = 2.5V (Regulator OFF) VLOGIC = 0.5V (Regulator ON) V 0.6 V(max) 2.0 V(min) 15 μA(max) μA 5 μA 0.02 μA(max) 5 2 (9) Junction to ambient thermal resistance with the TO-263 package tab soldered to a single printed circuit board with 0.5 in of (1 oz.) copper area. (10) Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in2 of (1 oz.) copper area. (11) Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in2 of (1 oz.) copper area on the XH2596S side of the board, and approximately 16 in2 of copper on the other side of the p-c board. See Application Information in this data sheet and the thermal model in Switchers Made Simple™ version 4.3 software. 5 XH2596 TO-263 3.3 5.0 12 ADJ Typical Performance Characteristics (Circuit of Figure 20) Normalized Output Voltage Line Regulation Figure 3. Figure 4. Efficiency Switch Saturation Voltage Figure 5. Figure 6. Switch Current Limit Dropout Voltage Figure 7. Figure 8. 6 XH2596 TO-263 3.3 5.0 12 ADJ Typical Performance Characteristics (continued) (Circuit of Figure 20) Operating Quiescent Current Shutdown Quiescent Current Figure 9. Figure 10. Minimum Operating Supply Voltage ON /OFF Threshold Voltage Figure 11. Figure 12. ON /OFF Pin Current (Sinking) Switching Frequency Figure 13. Figure 14. 7 XH2596 TO-263 3.3 5.0 12 ADJ Typical Performance Characteristics (continued) (Circuit of Figure 20) Continuous Mode Switching Waveforms VIN = 20V, VOUT = 5V, ILOAD = 2A L = 32 μH, COUT = 220 μF, COUT ESR = 50 mΩ Feedback Pin Bias Current A: Output Pin Voltage, 10V/div. B: Inductor Current 1A/div. C: Output Ripple Voltage, 50 mV/div. Figure 16. Horizontal Time Base: 2 μs/div. Figure 15. Discontinuous Mode Switching Waveforms VIN = 20V, VOUT = 5V, ILOAD = 500 mA L = 10 μH, COUT = 330 μF, COUT ESR = 45 mΩ Load Transient Response for Continuous Mode VIN = 20V, VOUT = 5V, ILOAD = 500 mA to 2A L = 32 μH, COUT = 220 μF, COUT ESR = 50 mΩ A: Output Voltage, 100 mV/div. (AC) B: 500 mA to 2A Load Pulse A: Output Pin Voltage, 10V/div. B: Inductor Current 0.5A/div. C: Output Ripple Voltage, 100 mV/div. Figure 17. Horizontal Time Base: 2 μs/div. Figure 18. Horizontal Time Base: 100 μs/div. Load Transient Response for Discontinuous Mode VIN = 20V, VOUT = 5V, ILOAD = 500 mA to 2A L = 10 μH, COUT = 330 μF, COUT ESR = 45 mΩ A: Output Voltage, 100 mV/div. (AC) B: 500 mA to 2A Load Pulse Figure 19. Horizontal Time Base: 200 μs/div. 8 XH2596 TO-263 3.3 5.0 12 ADJ Test Circuit and Layout Guidelines Fixed Output Voltage Versions XH2596 CIN —470 μF, 50V, Aluminum Electrolytic Nichicon “PL Series” COUT —220 μF, 25V Aluminum Electrolytic, Nichicon “PL Series” D1 —5A, 40V Schottky Rectifier, 1N5825 L1 —68 μH, L38 Adjustable Output Voltage Versions XH2596 where VREF = 1.23V Select R1 to be approximately 1 kΩ, use a 1% resistor for best stability. CIN —470 μF, 50V, Aluminum Electrolytic Nichicon “PL Series” COUT —220 μF, 35V Aluminum Electrolytic, Nichicon “PL Series” D1 —5A, 40V Schottky Rectifier, 1N5825 L1 —68 μH, L38 R1 —1 kΩ, 1% CFF —See Application Information Section Figure 20. Standard Test Circuits and Layout Guides As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by heavy lines should be wide printed circuit traces and should be kept as short as possible. For best results, external components should be located as close to the switcher lC as possible using ground plane construction or single point grounding. If open core inductors are used, special care must be taken as to the location and positioning of this type of inductor. Allowing the inductor flux to intersect sensitive feedback, lC groundpath and COUT wiring can cause problems. When using the adjustable version, special care must be taken as to the location of the feedback resistors and the associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor. (See Application Information section for more information.) 9 XH2596 TO-263 3.3 5.0 12 ADJ XH2596 Series Buck Regulator Design Procedure (Fixed Output) PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version) Given: VOUT = Regulated Output Voltage (3.3V, 5V or 12V) VIN(max) = Maximum DC Input Voltage ILOAD(max) = Maximum Load Current Given: VOUT = 5V VIN(max) = 12V ILOAD(max) = 3A 1. Inductor Selection (L1) A. Select the correct inductor value selection guide from Figures Figure 21, Figure 22, or Figure 23. (Output voltages of 3.3V, 5V, or 12V respectively.) For all other voltages, see the Design Procedure for the adjustable version. B. From the inductor value selection guide, identify the inductance region intersected by the Maximum Input Voltage line and the Maximum Load Current line. Each region is identified by an inductance value and an inductor code (LXX). C. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 3. 1. Inductor Selection (L1) A. Use the inductor selection guide for the 5V version shown in Figure 22. B. From the inductor value selection guide shown in Figure 22, the inductance region intersected by the 12V horizontal line and the 3A vertical line is 33 μH, and the inductor code is L40. C. The inductance value required is 33 μH. From the table in Table 3, go to the L40 line and choose an inductor part number from any of the four manufacturers shown. (In most instance, both through hole and surface mount inductors are available.) 2. Output Capacitor Selection (COUT) A. In the majority of applications, low ESR (Equivalent Series Resistance) electrolytic capacitors between 82 μF and 820 μF and low ESR solid tantalum capacitors between 10 μF and 470 μF provide the best results. This capacitor should be located close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 μF . For additional information, see section on output capacitors in Application Information section. B. To simplify the capacitor selection procedure, refer to the quick design component selection table shown in Table 1. This table contains different input voltages, output voltages, and load currents, and lists various inductors and output capacitors that will provide the best design solutions. C. The capacitor voltage rating for electrolytic capacitors should be at least 1.5 times greater than the output voltage, and often much higher voltage ratings are needed to satisfy the low ESR requirements for low output ripple voltage. D. For computer aided design software, see Switchers Made Simple™ version 4.3 or later. 2. Output Capacitor Selection (COUT) A. See section on output capacitors in Application Information section. B. From the quick design component selection table shown in Table 1, locate the 5V output voltage section. In the load current column, choose the load current line that is closest to the current needed in your application, for this example, use the 3A line. In the maximum input voltage column, select the line that covers the input voltage needed in your application, in this example, use the 15V line. Continuing on this line are recommended inductors and capacitors that will provide the best overall performance. The capacitor list contains both through hole electrolytic and surface mount tantalum capacitors from four different capacitor manufacturers. It is recommended that both the manufacturers and the manufacturer's series that are listed in the table be used. In this example aluminum electrolytic capacitors from several different manufacturers are available with the range of ESR numbers needed. 330 μF 35V Panasonic HFQ Series 330 μF 35V Nichicon PL Series C. For a 5V output, a capacitor voltage rating at least 7.5V or more is needed. But even a low ESR, switching grade, 220 μF 10V aluminum electrolytic capacitor would exhibit approximately 225 mΩ of ESR (see the curve in Figure 26 for the ESR vs voltage rating). This amount of ESR would result in relatively high output ripple voltage. To reduce the ripple to 1% of the output voltage, or less, a capacitor with a higher value or with a higher voltage rating (lower ESR) should be selected. A 16V or 25V capacitor will reduce the ripple voltage by approximately half. 10 XH2596 TO-263 3.3 5.0 12 ADJ PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version) 3. Catch Diode Selection (D1) A. The catch diode current rating must be at least 1.3 times greater than the maximum load current. Also, if the power supply design must withstand a continuous output short, the diode should have a current rating equal to the maximum current limit of the XH2596. The most stressful condition for this diode is an overload or shorted output condition. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. C. This diode must be fast (short reverse recovery time) and must be located close to the XH2596 using short leads and short printed circuit traces. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency, and should be the first choice, especially in low output voltage applications. Ultra-fast recovery, or High-Efficiency rectifiers also provide good results. Ultra-fast recovery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such as the 1N5400 series are much too slow and should not be used. 3. Catch Diode Selection (D1) A. Refer to the table shown in Table 6. In this example, a 5A, 20V, 1N5823 Schottky diode will provide the best performance, and will not be overstressed even for a shorted output. 4. Input Capacitor (CIN) A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin to prevent large voltage transients from appearing at the input. This capacitor should be located close to the IC using short leads. In addition, the RMS current rating of the input capacitor should be selected to be at least ½ the DC load current. The capacitor manufacturers data sheet must be checked to assure that this current rating is not exceeded. The curve shown in Figure 25 shows typical RMS current ratings for several different aluminum electrolytic capacitor values. For an aluminum electrolytic, the capacitor voltage rating should be approximately 1.5 times the maximum input voltage. Caution must be exercised if solid tantalum capacitors are used (see Application Information on input capacitor). The tantalum capacitor voltage rating should be 2 times the maximum input voltage and it is recommended that they be surge current tested by the manufacturer. Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN pin. For additional information, see section on input capacitors in Application Information section. 4. Input Capacitor (CIN) The important parameters for the Input capacitor are the input voltage rating and the RMS current rating. With a nominal input voltage of 12V, an aluminum electrolytic capacitor with a voltage rating greater than 18V (1.5 × VIN) would be needed. The next higher capacitor voltage rating is 25V. The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load current. In this example, with a 3A load, a capacitor with a RMS current rating of at least 1.5A is needed. The curves shown in Figure 25 can be used to select an appropriate input capacitor. From the curves, locate the 35V line and note which capacitor values have RMS current ratings greater than 1.5A. A 680 μF/35V capacitor could be used. For a through hole design, a 680 μF/35V electrolytic capacitor (Panasonic HFQ series or Nichicon PL series or equivalent) would be adequate. other types or other manufacturers capacitors can be used provided the RMS ripple current ratings are adequate. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating (see Application Information on input capacitors in this data sheet). The TPS series available from AVX, and the 593D series from Sprague are both surge current tested. Table 1. XH2596 Fixed Voltage Quick Design Component Selection Table Conditions Inductor Output Capacitor Through Hole Electrolytic Output Voltage (V) Load Current (A) 3.3 3 2 Max Input Voltage (V) Inductance (μH) Inductor (#) Surface Mount Tantalum Panasonic HFQ Series (μF/V) Nichicon PL Series (μF/V) AVX TPS Series (μF/V) Sprague 595D Series (μF/V) 5 22 L41 470/25 560/16 330/6.3 390/6.3 7 22 L41 560/35 560/35 330/6.3 390/6.3 10 22 L41 680/35 680/35 330/6.3 390/6.3 40 33 L40 560/35 470/35 330/6.3 390/6.3 6 22 L33 470/25 470/35 330/6.3 390/6.3 10 33 L32 330/35 330/35 330/6.3 390/6.3 40 47 L39 330/35 270/50 220/10 330/10 11 XH2596 TO-263 3.3 5.0 12 ADJ Table 1. XH2596 Fixed Voltage Quick Design Component Selection Table (continued) Conditions Inductor Output Capacitor Through Hole Electrolytic Output Voltage (V) Load Current (A) 5 3 2 12 3 2 Max Input Voltage (V) Inductance (μH) Inductor (#) Surface Mount Tantalum Panasonic HFQ Series (μF/V) Nichicon PL Series (μF/V) AVX TPS Series (μF/V) Sprague 595D Series (μF/V) 8 22 L41 470/25 560/16 220/10 330/10 10 22 L41 560/25 560/25 220/10 330/10 15 33 L40 330/35 330/35 220/10 330/10 40 47 L39 330/35 270/35 220/10 330/10 9 22 L33 470/25 560/16 220/10 330/10 20 68 L38 180/35 180/35 100/10 270/10 40 68 L38 180/35 180/35 100/10 270/10 15 22 L41 470/25 470/25 100/16 180/16 18 33 L40 330/25 330/25 100/16 180/16 30 68 L44 180/25 180/25 100/16 120/20 40 68 L44 180/35 180/35 100/16 120/20 15 33 L32 330/25 330/25 100/16 180/16 20 68 L38 180/25 180/25 100/16 120/20 40 150 L42 82/25 82/25 68/20 68/25 XH2596 Series Buck Regulator Design Procedure (Adjustable Output) PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version) Given: VOUT = Regulated Output Voltage VIN(max) = Maximum Input Voltage ILOAD(max) = Maximum Load Current F = Switching Frequency (Fixed at a nominal 150 kHz). Given: VOUT = 20V VIN(max) = 28V ILOAD(max) = 3A F = Switching Frequency (Fixed at a nominal 150 kHz). 1. Programming Output Voltage (Selecting R1 and R2, as shown in 1. Programming Output Voltage (Selecting R1 and R2, as shown in Figure 20 ) Figure 20 ) Use the following formula to select the appropriate resistor values. Select R1 to be 1 kΩ, 1%. Solve for R2. (1) Select a value for R1 between 240Ω and 1.5 kΩ. The lower resistor R2 = 1k (16.26 − 1) = 15.26k, closest 1% value is 15.4 kΩ. values minimize noise pickup in the sensitive feedback pin. (For the R = 15.4 kΩ. 2 lowest temperature coefficient and the best stability with time, use 1% metal film resistors.) (2) 12 (3) XH2596 TO-263 3.3 5.0 12 ADJ PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version) 2. Inductor Selection (L1) 2. Inductor Selection (L1) A. Calculate the inductor Volt • microsecond constant E • T (V • μs), A. Calculate the inductor Volt • microsecond constant from the following formula: (E • T), where • • VSAT = internal switch saturation voltage = B. E • T = 34.2 (V • μs) 1.16V C. ILOAD(max) = 3A VD = diode forward voltage drop = 0.5V (4) (5) D. From the inductor value selection guide shown in Figure 24, the inductance region intersected by the 34 (V • μs) horizontal line and B. Use the E • T value from the previous formula and match it with the 3A vertical line is 47 μH, and the inductor code is L39. the E • T number on the vertical axis of the Inductor Value Selection E. From the table in Table 3, locate line L39, and select an inductor Guide shown in Figure 24. part number from the list of manufacturers part numbers. C. on the horizontal axis, select the maximum load current. D. Identify the inductance region intersected by the E • T value and the Maximum Load Current value. Each region is identified by an inductance value and an inductor code (LXX). E. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 3. 3. Output Capacitor Selection (COUT) A. In the majority of applications, low ESR electrolytic or solid tantalum capacitors between 82 μF and 820 μF provide the best results. This capacitor should be located close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 μF. For additional information, see section on output capacitors in Application Information section. B. To simplify the capacitor selection procedure, refer to the quick design table shown in Table 2. This table contains different output voltages, and lists various output capacitors that will provide the best design solutions. C. The capacitor voltage rating should be at least 1.5 times greater than the output voltage, and often much higher voltage ratings are needed to satisfy the low ESR requirements needed for low output ripple voltage. 3. Output Capacitor SeIection (COUT) A. See section on COUT in Application Information section. B. From the quick design table shown in Table 2, locate the output voltage column. From that column, locate the output voltage closest to the output voltage in your application. In this example, select the 24V line. Under the OUTPUT CAPACITOR section, select a capacitor from the list of through hole electrolytic or surface mount tantalum types from four different capacitor manufacturers. It is recommended that both the manufacturers and the manufacturers series that are listed in the table be used. In this example, through hole aluminum electrolytic capacitors from several different manufacturers are available. 220 μF/35V Panasonic HFQ Series 150 μF/35V Nichicon PL Series C. For a 20V output, a capacitor rating of at least 30V or more is needed. In this example, either a 35V or 50V capacitor would work. A 35V rating was chosen, although a 50V rating could also be used if a lower output ripple voltage is needed. Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications (especially the 100 kHz ESR) closely match the types listed in the table. Refer to the capacitor manufacturers data sheet for this information. 4. Feedforward Capacitor (CFF) (See Figure 20) For output voltages greater than approximately 10V, an additional capacitor is required. The compensation capacitor is typically between 100 pF and 33 nF, and is wired in parallel with the output voltage setting resistor, R2. It provides additional stability for high output voltages, low input-output voltages, and/or very low ESR output capacitors, such as solid tantalum capacitors. 4. Feedforward Capacitor (CFF) The table shown in Table 2 contains feed forward capacitor values for various output voltages. In this example, a 560 pF capacitor is needed. (6) This capacitor type can be ceramic, plastic, silver mica, etc. (Because of the unstable characteristics of ceramic capacitors made with Z5U material, they are not recommended.) 13 XH2596 TO-263 3.3 5.0 12 ADJ PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version) 5. Catch Diode Selection (D1) A. The catch diode current rating must be at least 1.3 times greater than the maximum load current. Also, if the power supply design must withstand a continuous output short, the diode should have a current rating equal to the maximum current limit of the XH2596. The most stressful condition for this diode is an overload or shorted output condition. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. C. This diode must be fast (short reverse recovery time) and must be located close to the XH2596 using short leads and short printed circuit traces. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency, and should be the first choice, especially in low output voltage applications. Ultra-fast recovery, or High-Efficiency rectifiers are also a good choice, but some types with an abrupt turn-off characteristic may cause instability or EMl problems. Ultra-fast recovery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such as the 1N4001 series are much too slow and should not be used. 5. Catch Diode Selection (D1) A. Refer to the table shown in Table 6. Schottky diodes provide the best performance, and in this example a 5A, 40V, 1N5825 Schottky diode would be a good choice. The 5A diode rating is more than adequate and will not be overstressed even for a shorted output. 6. Input Capacitor (CIN) A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground to prevent large voltage transients from appearing at the input. In addition, the RMS current rating of the input capacitor should be selected to be at least ½ the DC load current. The capacitor manufacturers data sheet must be checked to assure that this current rating is not exceeded. The curve shown in Figure 25 shows typical RMS current ratings for several different aluminum electrolytic capacitor values. This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5 times the maximum input voltage. If solid tantalum input capacitors are used, it is recomended that they be surge current tested by the manufacturer. Use caution when using a high dielectric constant ceramic capacitor for input bypassing, because it may cause severe ringing at the VIN pin. For additional information, see section on input capacitors in Application Information section. 6. Input Capacitor (CIN) The important parameters for the Input capacitor are the input voltage rating and the RMS current rating. With a nominal input voltage of 28V, an aluminum electrolytic aluminum electrolytic capacitor with a voltage rating greater than 42V (1.5 × VIN) would be needed. Since the the next higher capacitor voltage rating is 50V, a 50V capacitor should be used. The capacitor voltage rating of (1.5 × VIN) is a conservative guideline, and can be modified somewhat if desired. The RMS current rating requirement for the input capacitor of a buck regulator is approximately ½ the DC load current. In this example, with a 3A load, a capacitor with a RMS current rating of at least 1.5A is needed. The curves shown in Figure 25 can be used to select an appropriate input capacitor. From the curves, locate the 50V line and note which capacitor values have RMS current ratings greater than 1.5A. Either a 470 μF or 680 μF, 50V capacitor could be used. For a through hole design, a 680 μF/50V electrolytic capacitor (Panasonic HFQ series or Nichicon PL series or equivalent) would be adequate. Other types or other manufacturers capacitors can be used provided the RMS ripple current ratings are adequate. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rting (see Application Information or input capacitors in this data sheet). The TPS series available from AVX, and the 593D series from Sprague are both surge current tested. To further simplify the buck regulator design procedure, Texas Instruments is making available computer design software to be used with the Simple Switcher line ot switching regulators. Switchers Made Simple (version 4.3 or later) is available on a 3½″ diskette for IBM compatible computers. XH2596 Series Buck Regulator Design Procedure (Adjustable Output) Table 2. Output Capacitor and Feedforward Capacitor Selection Table Output Voltage (V) Through Hole Output Capacitor Panasonic HFQ Series (μF/V) Nichicon PL Series (μF/V) 2 820/35 820/35 4 560/35 6 470/25 Surface Mount Output Capacitor Feedforward Capacitor AVX TPS Series (μF/V) Sprague 595D Series (μF/V) Feedforward Capacitor 33 nF 330/6.3 470/4 33 nF 470/35 10 nF 330/6.3 390/6.3 10 nF 470/25 3.3 nF 220/10 330/10 3.3 nF 14 XH2596 TO-263 3.3 5.0 12 ADJ Table 2. Output Capacitor and Feedforward Capacitor Selection Table (continued) Output Voltage (V) Through Hole Output Capacitor Panasonic HFQ Series (μF/V) Nichicon PL Series (μF/V) 9 330/25 330/25 12 330/25 15 220/35 24 28 Surface Mount Output Capacitor Feedforward Capacitor AVX TPS Series (μF/V) Sprague 595D Series (μF/V) Feedforward Capacitor 1.5 nF 100/16 180/16 1.5 nF 330/25 1 nF 100/16 180/16 1 nF 220/35 680 pF 68/20 120/20 680 pF 220/35 150/35 560 pF 33/25 33/25 220 pF 100/50 100/50 390 pF 10/35 15/50 220 pF XH2596 Series Buck Regulator Design Procedure INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) Figure 21. XH2596-3.3 Figure 22. XH2596-5.0 Figure 23. XH2596-12 XHure 24. XH2596-ADJ 15 XH2596 TO-263 3.3 5.0 12 ADJ 16 15 XH2596 TO-263 3.3 5.0 12 ADJ 17 15