THS3115/25 EVM User’s Guide May 2002 HPL SLOU126
IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.
EVM IMPORTANT NOTICE Texas Instruments (TI) provides the enclosed product(s) under the following conditions: This evaluation kit being sold by TI is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY and is not considered by TI to be fit for commercial use.
EVM WARNINGS AND RESTRICTIONS It is important to operate this EVM within the specified input and output ranges described in the EVM User’s Guide. Exceeding the specified input range may cause unexpected operation and/or irreversible damage to the EVM. If there are questions concerning the input range, please contact a TI field representative prior to connecting the input power.
Information About Cautions and Warnings Preface Read This First About This Manual This manual provides information about the evaluation module of the current feedback amplifier under test. Additionally, this document provides a good example of PCB design for high-speed applications. The user should keep in mind the following points. - The design of the high-speed amplifier PCB is a delicate process. - The user must approach the PCB design with care and awareness.
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Contents Contents 1 Introduction and Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Evaluation Module Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 THS3115/25 EVM Operating Conditions . . . . . . . . . . . . . . . . . . . . . .
Contents Figures 1--1 2--1 2--2 2--3 2--4 2--5 2--6 2--7 3--1 3--2 5--1 5--2 5--3 Schematic of the Populated Circuit on the EVM (Default Configuration) . . . . . . . . . . . . . . Power Supply Connection for ±15 Vdc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Signal Connections for Channel 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oscilloscope Output for Channel 1 . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1 Introduction and Description The Texas Instruments THS3115/25 evaluation module (EVM) helps designers evaluate the performance of the THS3115/25 current feedback operational amplifier (CFA). This EVM is also a good example of high-speed PCB design. This document details the THS3115/25 EVM.
Description 1.1 Description The THS3115/25 EVM provides a platform for developing high-speed CFA application circuits. It contains the THS3115/25 high-speed CFA, a number of passive components, and various features and footprints that enable the user to experiment, test, and verify various operational amplifier circuit implementations. The PC board measures 3.52 by 2.81 inches. 1.
EVM Default Configuration The default configuration assumes a 50-W signal source, and contains a termination resistor R2 or R8 (49.9 W) for the source. Some components such as C1, C2, C3, C4, J1, J2, and J3 are omitted on the application schematics of chapter 4 for clarity. In addition, only the components associated with the section of the IC being used (A or B) are shown. Figure 1--1.
Chapter 2 Using the THS3115/25 EVM It is recommended that the user perform the following exercises to learn the function of the EVM. This practice helps the user learn about the various terminals on the EVM and their function. In addition, it lists the components and equipment needed to operate the EVM. Topic Page 2.1 Required Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2.2 Power Supply Setup for ±15 Vdc . . . . . . . . . . . . . . . . . . . . . .
Required Equipment 2.1 Required Equipment - One double-output dc power supply (±15 V, 1-A output minimum) - One single-output dc power supply (+5V, 100-mA output minimum) – referred to in this document as a shutdown supply - Two dc current meters with resolution to 1 mA and capable of the maximum current from the dc power supply. If available, set the current limit on the dc power supply to 100 mA. NOTE: Some power supplies incorporate current meters which may be applicable to this test.
Input and Output Setup for Channel 1 Figure 2--1. Power Supply Connection for ±15 Vdc 2.3 Input and Output Setup for Channel 1 1) Set the function generator to generate a 1-MHz, ±0.5 V (1-VPP) sine wave with no dc offset. 2) Turn off the function generator before proceeding to the next step. 3) Connect a BNC T connector to the output of the function generator. 4) Using a BNC-to-SMA cable, connect the function generator to J5 (--IN1) on the EVM.
Operating the EVM on Channel 1 Figure 2--2. Signal Connections for Channel 1 2.4 Operating the EVM on Channel 1 1) Turn on the dc power supply. 2) Verify that both the +15 V (current meter 1) and the –15 V (current meter 2) currents are below 25 mA. Currents above the limits stated above indicate a possible short or a wrong resistor value on the PCB. Do not proceed until this situation is correct. 3) Turn on the function generator.
Operating the EVM on Channel 1 Figure 2--3. Oscilloscope Output for Channel 1 600 m 400 m INPUT Voltage -- V 200 m 0 --200 m OUTPUT --400 m --600 m 0 500 n 1 ms t -- Time -- s 5) Set the shutdown supply to 0 V, but leave it off. 6) Turn on the shutdown supply and verify that the output is unchanged from step 4. Turn off the supply. 7) Disconnect the shutdown supply from the EVM. 8) Set the shutdown supply to 5 V, but turn it off during the next step. 9) Reconnect the shutdown supply to the EVM.
Input and Output Setup for Channel 2 2.5 Input and Output Setup for Channel 2 1) Verify that the function generator is still set to generate a 1-MHz, ±0.5 V (1-VPP) sine wave with no dc offset. 2) Turn off the function generator before proceeding to the next step. 3) Connect a BNC T connector to the output of the function generator. 4) Using a BNC-to-SMA cable, connect the function generator to J7 (+IN2) on the EVM.
Operating the EVM on Channel 2 2.6 Operating the EVM on Channel 2 1) Turn on the dc power supply. 2) Verify that both the +15 V (current meter 1) and the –15 V (current meter 2) currents are below 25 mA. Currents above the limits stated above indicate a possible short or a wrong resistor value on the PCB. Do not proceed until this situation is correct. 3) Turn on the function generator. 4) Verify the oscilloscope is showing two 1-MHz sine waves as shown in Figure 2--6. Both should have amplitude of ±0.
Operating the EVM on Channel 2 Figure 2--7.
Chapter 3 Circuit Design Examples Several example applications are presented in this chapter. These applications demonstrate the most popular circuits to the user, but many other circuits can be constructed. The user is encouraged to experiment with different circuits, exploring new and creative design techniques. That, after all, is the function of an evaluation board. Topic Page 3.1 Inverting Stage (Channel 1) Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3.
Inverting Stage (Channel 1) Operation 3.1 Inverting Stage (Channel 1) Operation Inverting stage operation was shown in Chapter 2 of this manual. The default configuration is a 50-W terminated input (R2), a 50-W matching resistor output (R5B), and a 100-W load (R6B). The terminating and matching values can be changed if the user requires different termination and matching—for example, 75-W video applications.
Inverting Stage (Channel 1) Operation R termination R g R termination)R g 49.9 750 49.9)750 V output + + + 0.483 peak 49.9 750 R termination R g 50 ) R source ) 49.9)750 R )R termination g This can also be viewed as the Thevenin equivalent voltage looking into the source at J4 of the EVM. - From the EVM side. The Thevenin equivalent resistance of the EVM plus the source—looking towards the source from the inverting input of the op amp is: R th + R g ) R source R termination + 750 ) 50 49.9 + 774.
Noninverting Stage (Channel 2) Operation 3.2 Noninverting Stage (Channel 2) Operation Noninverting stage operation was shown in Chapter 2 of this manual. The default configuration is a 50-W terminated input (R8), a 50-W matching resistor output (R11B), and a 100-W load (R12B). The terminating and matching values can be changed if the user requires different termination and matching—for example, 75-W video applications.
Chapter 4 General High-Speed Amplifier Design Considerations The THS3115/25 EVM layout has been designed for use with high-speed signals and can be used as an example when designing PCBs incorporating the THS3115/25. Careful attention has been given to component selection, grounding, power supply bypassing, and signal path layout. Disregarding these basic design considerations could result in less than optimum performance of the THS3115/25 high-speed operational amplifier.
In general, it is best to keep signal lines as short and as straight as possible. Incorporation of microstrip or stripline techniques is also recommended when signal lines are greater than 1 inch in length. These traces must be designed with a characteristic impedance of either 50 W or 75 W, as required by the application. Such a signal line must also be properly terminated with an appropriate resistor. Finally, proper termination of all inputs and outputs must be incorporated into the layout.
Chapter 5 EVM Hardware Description This chapter describes the EVM hardware. It includes the EVM parts list, the printed-circuit board layout, and the schematic. Topic Page 5.1 Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 5.2 Circuit Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4 5.3 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bill of Materials 5.1 Bill of Materials Table 5--1. THS3115 EVM Bill of Materials ITEM DESCRIPTION CAP, 6.8 mF, tantalum, 35 V, 10% 2 REF DESIGNATOR PCB QTY MANUFACTURER’S PART NUMBER DISTRIBUTOR’S PART NUMBER D C1, C2 2 (AVX) TAJD685K035R (Garrett) TAJD685K035R CAP, 0.
Bill of Materials Table 5--2. THS3125 EVM Bill of Materials ITEM DESCRIPTION SMD SIZE REF DESIGNATOR PCB QTY MANUFACTURER’S PART NUMBER DISTRIBUTOR’S PART NUMBER 1 CAP, 6.8 mF, tantalum, 35 V, 10% D C1, C2 2 (AVX) TAJD685K035R (Garrett) TAJD685K035R 2 CAP, 0.
Circuit Board Layout 5.2 Circuit Board Layout Figure 5--1.
Circuit Board Layout Figure 5--2.
Schematic 5.3 Schematic The full schematic for the THS3115/25 EVM appears below Figure 5--3. Full Schematic of the EVM R13 0 J10 SHUTDOWN R3 750 W J5 --IN1 R4 750 W R2 49.9W +VS 14 2 -- J4 +IN1 R5B 49.9W 9 U1A THS31x5PWP SD 1 3 + R1 0 4 R5A * R6A * 6 J6 OUT1 R6B 100 W --VS R9 909 W J8 --IN2 R10 909 W R11B 49.9W R7 0 12 -- J7 +IN2 11 + R8 49.9W U1B THS31x5PWP R11A * 13 R12A * R12B 100 W +VS J1 +VS Note: 5-6 + C1 6.8 mF J9 OUT2 --VS C3 0.1 mF J2 GND J3 --VS + C2 6.
