LMP8640,LMP8645 Application Note 1975 LMP8640 / LMP8645 Evaluation Board User Guide Literature Number: SNOA546B National Semiconductor Application Note 1975 Domenico Granozio July 15, 2010 This evaluation board shows a bidirectional high side current sense made using LMP8640 (LMP8645) and optional differential amplifier in order to have a single output. Second case. Current flows from LOAD to IN plugs. In this case the voltage supply is connected between the LOAD and GND banana plugs, while the load between the IN and GND banana plugs. The voltage applied at LOAD pin has not to exceed the max common mode voltage allowed by the LMP8640/HV (LMP8645/HV). The max allowed common mode voltages are listed in the following table. Connectors POWER SUPPLY There are two banana plugs labeled GND and VCC to power the evaluation board. Moreover a banana plug labeled VCC_Amp is used to power an optional operational amplifier which makes the difference between the outputs of the two LMP8640 (LMP8645). SIGNAL CONNECTORS There are five connectors for signals. Input signals IN It connects the non inverting input of U1 and inverting input of U2. LOAD It connects the non inverting input of U2 and inverting input of U1. The device U1 is able to sense the current when it flows in the shunt resistor from LOAD pin to IN pin. The device U2 is able to sense the current when it flows in the shunt resistor from IN pin to LOAD pin. Output signals OUT+ Output of device U2, the voltage at this pin is related to the current which flows from IN pin to LOAD pin. OUTOutput of device U1, the voltage at this pin is related to the current which flows from LOAD pin to IN pin. OUT Optional Output of the difference amplifier which makes the difference between OUT+ and OUT- Hardware Setup POWER SUPPLY SETUP 1. High side current sense LMP8640 (LMP8645) Connect a supply voltage in the range between 2.7V and 12V to the VCC and GND turrets. 2. Optional difference amplifier Connect a supply according to the specs of the amplifier to the VCC_Amp and GND turrets. (c) 2010 National Semiconductor Corporation 300979 DEVICE MAX VCM LMP8640 42V LMP8645 42V LMP8640HV 76V LMP8645HV 76V According to the shunt resistor (Rsns), to the gain of LMP8640 (LMP8645) and to the supply voltage different ranges of currents can be sensed with this evaluation board. COMPONENTS On the evaluation board there are already the circuit and the footprint of a standard dual op amp (U3) to implement a differential Op amp (U3.B) with reference (U3.A) in order to provide a single ended output of the bidirectional current. Optional differential circuit U3 Standard Dual Op Amp 8 pin. U3.1 OUT A U3.2 -IN A U3.3 +IN A U3.4 VU3.5 +IN B U3.6 -IN B U3.7 OUT B U3.8 V+ R1, R2, R3, R4 resistors which implement the differential circuit according to the following equation: R5, R6, C5 components for voltage reference and its filter. The voltage reference is calculating according the following equation: Using the Evaluation Board INPUT AND OUTPUT SIGNALS The evaluation board allow to measure a bidirectional current, so the IN and LOAD banana connectors can act either as Source or LOAD pin. If the current flows from the IN pin to the LOAD pin, a simply way to test the performance of the LMP8640 (LMP8645) is showed in Figure 1 www.national.com AN-1975 SOURCE AND LOAD SETUP First case. Current flows from IN to LOAD plugs. A voltage supply can be connected between the IN and GND banana plugs, while a load between the LOAD and GND banana plugs. The voltage applied at IN pin has not to exceed the max common mode voltage allowed by the LMP8640/HV (LMP8645/HV). The max allowed common mode voltages are listed in the following table. Max Common Mode Voltage LMP8640 / LMP8645 Evaluation Board User Guide LMP8640 / LMP8645 Evaluation Board User Guide AN-1975 (10k, @1%) ensure a gain of 2V/V for each current sense. The Gain is evaluated according to the following formula: 30097903 The gain resistor must be chosen such that the max output voltage does not exceed the LMP8645 max output voltage rating for a given common mode voltage (further details in the Datasheet). SINGLE OUTPUT In the applications where a single measurement of a bidirectional current sense is needed is possible to populate the evaluation board with two amplifiers and some resistors (see section COMPONENTS). For instance in the following configuration: R1 = R2 = R3 = R4 = 10k, R5 = R6 =10k OUT = Vref +(OUT+ -OUT-) Vref = 0.5*Vcc_Amp. The Vref level represents the zero level; the voltages greater than Vref are related to a current which flows from IN pin to LOAD pin while the voltages less than Vref are related to a current which flows from LOAD pin to IN pin. To ensure good results in the measurements the resistors R4 and R3 and the resistors R1 and R2 need to be well matched. 30097901 FIGURE 1. LMP8640 (LMP8645) measurement setup The DMM1 is configured as a Voltmeter it measures the output of the LMP8640 (LMP8645), while the DMM2 is configured as an Ammeter; it measures the current which flows in the LOAD. The source is a voltage supply; make sure to set a voltage in the range of -2Vto +46V for LMP8640 (LMP8645) or -2V to +76V for LMP8640HV (LMP8645HV). GAIN SELECTION OF LMP8645 The evaluation board is provided with a shunt resistor Rsns (10m, @1%, 1W). While two gain resistors Rg1 and Rg2 www.national.com 2 This schematic shows the evaluation board with a LMP8645 mounted on the PCB. For the version of the PCB stuffed with LMP8640 the only difference will be the gain resistors RG1, RG2. The LMP8640 is a current sense with fixed gain, so it doesn't require any external gain resistor. 30097906 FIGURE 2. Schematic Diagram 3 www.national.com AN-1975 Schematic AN-1975 Layout 30097907 30097908 Top Layer Bottom Layer FIGURE 3. PCB Layout Bill Of Material Components marked with (*) are not soldered on the board. Components marked with (**) are soldered only on LMP8645 board. Designator Component Value Tolerance Package type C1, C3 Capacitor 0.01F 5% 0603 C2, C6* Capacitor 1F 10% 3216-18 C4 Capacitor 0.1F 10% 0805 C5*, C7 Capacitor 0.1F 10% 0603 C_Filt1*, C_Filt2* Capacitor CG1*, CG2* Capacitor R1*, R2*, R3*, R4*, R5*, R6* Resistor RG1**, RG2** Rsns** 0805 0805 min 10k 1% 0603 Resistor 10.0k 1% 0603 Resistor 0.01 1%, 1W 2010 Rsns Resistor 0.01 0.1%, 1W 2512 R_Filt_1, R_Filt2 Resistor 5% 0805 U3* Dual Op Amp www.national.com MSOP-8 4 AN-1975 Notes 5 www.national.com LMP8640 / LMP8645 Evaluation Board User Guide 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(R) 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(R) Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagicTM www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise(R) Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS, IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT NATIONAL'S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS. EXCEPT AS PROVIDED IN NATIONAL'S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE AND/OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: Life support devices or systems are devices which (a) are intended for surgical implant into the body, or (b) support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness. National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. AN-1975 Copyright(c) 2010 National Semiconductor Corporation For the most current product information visit us at www.national.com National Semiconductor Americas Technical Support Center Email: support@nsc.com Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Technical Support Center Email: europe.support@nsc.com National Semiconductor Asia Pacific Technical Support Center Email: ap.support@nsc.com National Semiconductor Japan Technical Support Center Email: jpn.feedback@nsc.com 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. All products are sold subject to TI's terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI's standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and applications using TI components. To minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right, or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI. Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in such safety-critical applications. TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are specifically designated by TI as military-grade or "enhanced plastic." Only products designated by TI as military-grade meet military specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use. TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated products in automotive applications, TI will not be responsible for any failure to meet such requirements. Following are URLs where you can obtain information on other Texas Instruments products and application solutions: Products Applications Audio www.ti.com/audio Communications and Telecom www.ti.com/communications Amplifiers amplifier.ti.com Computers and Peripherals www.ti.com/computers Data Converters dataconverter.ti.com Consumer Electronics www.ti.com/consumer-apps DLP(R) Products www.dlp.com Energy and Lighting www.ti.com/energy DSP dsp.ti.com Industrial www.ti.com/industrial Clocks and Timers www.ti.com/clocks Medical www.ti.com/medical Interface interface.ti.com Security www.ti.com/security Logic logic.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense Power Mgmt power.ti.com Transportation and Automotive www.ti.com/automotive Microcontrollers microcontroller.ti.com Video and Imaging RFID www.ti-rfid.com OMAP Mobile Processors www.ti.com/omap Wireless Connectivity www.ti.com/wirelessconnectivity TI E2E Community Home Page www.ti.com/video e2e.ti.com Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265 Copyright (c) 2011, Texas Instruments Incorporated