LM2650EVAL

Application Report SNVA001D – October 1997 – Revised April 2013 AN-1071 Information About the LM2650 Evaluation Board Rev. 1 ..................................................................................................................................................... 1 Introduction This application report contains information about the printed circuit board (PCB). 2 General Description The LM2650 evaluation board is provided as a tool for developing DC/DC converters based on the LM2650 IC. It is configured for single-output, step-down DC/DC converters. Figure 1 is a complete schematic of the board that can accommodate up to 28 components including the LM2650. Table 1 is a complete list of pads for placing components. Note: Not all applications will require the placement of all 28 components. The number of components placed depends on the requirements of the application and the use of features like programmable softstart. The LM2650 evaluation board is intended to be a reusable tool on which many different converters meeting the requirements of many different applications can be built. It is not intended to demonstrate only one application of the LM2650. For convenience, a sample of the LM2650 and eight other components have been assembled: a 0.1 µF capacitor at each of C1, C2, C6, and CB, a 0.2 µF capacitor at CVDD, a 0.01 µF capacitor at CSS, a 24.9 kΩ resistor at R2, and a 0 Ω resistor at R4. Of the eight, the first seven are common to many applications, and the last is simply a jumper grounding the SYNC input. When the synchronization feature is not being used, the SYNC input should be grounded. 3 Example Circuits The components contained in Table 2, Table 3, and Table 4 can be used to build typical application circuits. As with the design of any DC/DC converter, the design of these involved tradeoffs between efficiency, size, and cost. The converters detailed in Table 2 were designed with efficiency as the number one criteria. Those detailed in Table 4 trade slightly higher switching losses for a much smaller inductor. All trademarks are the property of their respective owners. SNVA001D – October 1997 – Revised April 2013 Submit Documentation Feedback AN-1071 Information About the LM2650 Evaluation Board Rev. 1 Copyright © 1997–2013, Texas Instruments Incorporated 1 Thermal Performance www.ti.com Figure 1. The LM2650 Evaluation Board Rev. 1 Schematic 4 Thermal Performance The 24-lead SO package is a molded plastic package with a solid copper lead frame. Most of the heat generated at the die flows through the lead frame into the 3-ounce copper planes on the board. The board then acts as a heat sink. The junction-to-ambient thermal resistance of the packaged IC mounted on the board has been measured to be 38°C/W, 37 °C/W, and 35 °C/W for the dissipation of 1.0W, 1.5W, and 2.0W respectively. These measurements were made in still air. The junction-to-ambient thermal resistance of the packaged IC alone in still air is 78°C/W. The board is 0.063" thick FR-4 material. 5 Art Figure 2 through Figure 4 show the PCB art work. Table 1. A Complete List of Pads for Placing Components 2 Label No U1 1 For placing the LM2650. Notes C1, C2, C3, and C4 4 Capacitors placed here filter high-frequency switching noise from the input power rail. C5 0 These pads should not be labeled with a C. No component is placed here. They can be used to ground the SLEEP LOGIC input. The pad connected to the SLEEP LOGIC pin can be used to pull the input up. C6 1 A capacitor placed here also filters high-frequency switching noise from the input power rail but at the VIN rail, the rail used by the signal-level circuits inside the IC. C9 1 Usually no component is placed here. A capacitor might be placed here for loop compensation purposes, but most applications don't use it. C10 1 A capacitor is placed here for loop compensation purposes. CB 1 The bootstrap capacitor is placed here. CC 1 A capacitor is placed here for loop compensation purposes. This capacitor and an internal 6.5 kΩ resistor create an integrator pole. CIN1 and CIN2 2 The bulk input capacitors are placed here. AN-1071 Information About the LM2650 Evaluation Board Rev. 1 SNVA001D – October 1997 – Revised April 2013 Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Art www.ti.com Table 1. A Complete List of Pads for Placing Components (continued) Label No COUT1, COUT2, and COUT3 3 The output filter capacitors are placed here. Notes CSS 1 A capacitor placed here programs the soft-start interval. CVDD 1 A capacitor placed here bypasses the output of the VDD regulator. L1 1 The inductor is placed here. R1 1 One of the feedback resistors is placed here. R2 1 The other feedback resistor is placed here. R3 1 A resistor is placed here for loop compensation purposes. R4 1 These pads can be used to ground the SYNC input when the synchronization feature is not being used. The pad connected to the SYNC input can be used to connect the synchronization signal. The evaluation board has a 0 Ω jumper placed here to ground the SYNC input. RC 1 A resistor is also placed here for loop compensation purposes. This resistor and the capacitor placed at CC create an integrator zero. RFA 1 A resistor placed here adjusts the switching frequency up from the nominal 90 kHz. No component is placed here for applications switching at 90 kHz. RSIA and RSIC 2 Resistors placed here program the sleep-in threshold. RSOA and RSOC 2 Resistors placed here program the sleep-out threshold. Table 2. Components for Two Typical 90 kHz Application Circuits Input Voltage 7 to 18 V IN Applicable Cell Stacks 8- to 12-Cell NiCd or NiMH, 3- to 4-Cell Li Ion, 8- to 11-Cell Alkaline, 6-Cell Lead Acid Output 5 V, 3A Out 3.3 V, 3A Out Input Filter Capacitors C1, C2, and C6 0.1 µF ceramic chip capacitor 0.1 µF ceramic chip capacitor Bootstrap Capacitor CB 0.1 µF ceramic chip capacitor 0.1 µF ceramic chip capacitor Soft-start Capacitor CSS 0.01 µF ceramic chip capacitor 0.01 µF ceramic chip capacitor VDD Bypass Capacitor CVDD 0.2 µF ceramic chip capacitor 0.2 µF ceramic chip capacitor Input Bulk Capacitors CIN1 and CIN2 22 µF, 35 V AVX TPS Series or Sprague 593D Series tantalum chip capacitor 22 µF, 35 V AVX TPS Series or Sprague 593D Series tantalum chip capacitor Inductor L1 40 µH (see Table 3) 33 µH (see Table 3) Output Capacitors COUT1, COUT2, and COUT3 220 µF, 10 V AVX TPS Series or Sprague 593D 220 µF, 10 V AVX TPS Series or Sprague 593D Series tantalum chip capacitor Series tantalum chip capacitor Feedback Resistors R1 and R2 R1 = 75 kΩ, 1%, R2 = 24.9 kΩ, 1% Compensation Components RC, CC, R3, and C10 RC = 37.4 kΩ, CC = 4.7 nF, R3= 3.57 kΩ,C10 = RC = 23.2 kΩ, CC= 8.2 nF, R3 = 2.0 kΩ, C10 = 5.6 nF 10 nF Sleep Resistors RSIA and RSOA RSIA = 33 kΩ, RSOA = 200 kΩ R1 = 41.2 kΩ, 1%, R2 = 24.9 kΩ, 1% RSIA = 39 kΩ, RSOA = 130 kΩ Table 3. Toroidal Inductors Using Cores From MICROMETALS, INC. Core No Core Material Wire Gauge No of Strands No of Turns 15 µH T38 −52 AWG #23 1 21 20 µH T38 −52 AWG #23 1 25 33 µH T50 −52 AWG #21 1 41 40 µH T50(B) −18 AWG #21 1 41 SNVA001D – October 1997 – Revised April 2013 Submit Documentation Feedback AN-1071 Information About the LM2650 Evaluation Board Rev. 1 Copyright © 1997–2013, Texas Instruments Incorporated 3 Art www.ti.com Table 4. Components for Two Typical 200 kHz Application Circuits Input Voltage 7 to 18 V IN Applicable Cell Stacks 8- to 12-Cell NiCd or NiMH, 3- to 4-Cell Li Ion, 8- to 11-Cell Alkaline, 6-Cell Lead Acid Output 5 V, 3A Out 3.3 V, 3A Out Input Filter Capacitors C1, C2, and C6 0.1 µF ceramic chip capacitor 0.1 µF ceramic chip capacitor Bootstrap Capacitor CB 0.1 µF ceramic chip capacitor 0.1 µF ceramic chip capacitor Soft-start Capacitor CSS 0.01 µF ceramic chip capacitor 0.01 µF ceramic chip capacitor VDD Bypass Capacitor CVDD 0.2 µF ceramic chip capacitor 0.2 µF ceramic chip capacitor Input Bulk Capacitors CIN1 and CIN2 22 µF, 35 V AVX TPS Series or Sprague 593D Series tantalum chip capacitor 22 µF, 35 V AVX TPS Series or Sprague 593D Series tantalum chip capacitor Inductor L1 20 µH (see Table 3) 15 µH (see Table 3) Output Capacitors COUT1, COUT2, and COUT3 220 µF, 10 V AVX TPS Series or Sprague 593D 220 µF, 10 V AVX TPS Series or Sprague 593D Series tantalum chip capacitor Series tantalum chip capacitor Feedback Resistors R1 and R2 R1 = 75 kΩ, 1%, R2 = 24.9 kΩ, 1% R1 = 41.2 kΩ, 1%, R2 = 24.9 kΩ, 1% Compensation Components RC, CC, R3, and C10 RC = 53.6 kΩ, CC = 2.7 nF, R3= 4.02 kΩ, C10 = 4.7 nF RC = 33.2 kΩ, CC= 3.9 nF, R3 = 3.01 kΩ, C10 = 6.8 nF Sleep Resistors RSIA and RSOA RSIA = 47 kΩ, RSOA = 200 kΩ RSIA = 47 kΩ, RSOA = 91 kΩ Frequency Adjusting Resistor RFA RFA = 24.9 kΩ RFA = 24.9 kΩ Figure 2. LM2650 Evaluation Board Top Silk Screen (Scale 1:1) 4 AN-1071 Information About the LM2650 Evaluation Board Rev. 1 SNVA001D – October 1997 – Revised April 2013 Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Art www.ti.com Figure 3. LM2650 Evaluation Board Bottom Silk Screen (Scale 1:1) Figure 4. LM2650 Evaluation Board Component Side (Scale 1:1) SNVA001D – October 1997 – Revised April 2013 Submit Documentation Feedback AN-1071 Information About the LM2650 Evaluation Board Rev. 1 Copyright © 1997–2013, Texas Instruments Incorporated 5 Art www.ti.com Figure 5. LM2650 Evaluation Board Solder Side (Scale 1:1) 6 AN-1071 Information About the LM2650 Evaluation Board Rev. 1 SNVA001D – October 1997 – Revised April 2013 Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. 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