* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Integrating a Current Sense Resistor With a
Power engineering wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Stepper motor wikipedia , lookup
Thermal runaway wikipedia , lookup
History of electric power transmission wikipedia , lookup
Voltage optimisation wikipedia , lookup
Ground loop (electricity) wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Ground (electricity) wikipedia , lookup
Stray voltage wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Power electronics wikipedia , lookup
Mains electricity wikipedia , lookup
Power MOSFET wikipedia , lookup
Earthing system wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Surge protector wikipedia , lookup
Buck converter wikipedia , lookup
Electrical ballast wikipedia , lookup
Rectiverter wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Current source wikipedia , lookup
Network analysis (electrical circuits) wikipedia , lookup
Alternating current wikipedia , lookup
____________________________________________________ Integrating the Current Sensing Resistor Scott Hill, Current Sensing Products Current is one of the most common signals used for evaluating and diagnosing the operational effectiveness of an electronic system. However, measuring this signal directly is very challenging. Instead, many types of sensors are used to measure the proportional effects that occur due to current flowing throughout the system. The most common sensing element used for detecting current flowing in a system is a resistor. Placing a resistor, called a shunt, in series with the current path develops a differential voltage across the resistor as current passes through it. One common signal chain configuration for monitoring a current signal involves an analog front-end (AFE), an analog to digital converter (ADC), and a system controller as shown in Figure 1. An AFE, such as an operational amplifier or dedicated current sense amplifier, converts the small differetial voltage developed across the shunt resistor to a larger output voltage that the ADC can digitize before sending the information to a controller. The system controller uses the current information to optimize the system's operational performance or reduce functionality in the event of an out-of-range condition to prevent potential damaging conditions from occurring. + ADC CONTROLLER Figure 1. Current Sensing Signal Chain The proper resistance value selection is critical in optimizing the signal chain path. The resistance value and corresponding voltage developed across the shunt results in a system power loss. To limit the power loss, it is preferred to minimize the shunt resistance. The resistor value is directly proportional to the signal developed and sent to the current sensing amplifier. SBOA170A – October 2016 – Revised December 2016 Submit Documentation Feedback Amplifiers have fixed inherent errors associated with them, input offset voltage for example, that impact the measurement accuracy. As the input signal increases, the influence of these internal errors on the total measurement accuracy decreases. When the input signal decreases the corresponding measurement error is a higher . This relationship between the signal level and the acceptable measurement accuracy provides general lower limits for the current sensing resistor selection. The upper limit value for the current sensing resistor should be limited based on an application’s acceptable power loss for this component. One benefit of using resistors for current measurement is the availability of accurate components that provide both high precision and temperature stable measurements. Precision current sensing amplifiers are available featuring measurement capabilities optimized for interfacing with very small signals to accommodate small value resistors and low power losses. There are two trends for resistors as the ohmic value decreases into the single digit milliohm level and below. One trend for this segment of resistors is the reduced package availability and resistor value combinations. The other trend is the increased cost for precision and low temperature coefficient components. Pairing a low ohmic, low temperature coefficient current sensing resistors with precision tolerance levels (~0.1%) result in solution costs in the several dollar range without including the cost associated with the precision amplifier. A component such as the INA250, shown in Figure 2, helps reduce the challenges of selecting these increased accuracy, higher cost resistors for applications needing precise and temperature stable measurements. This device pairs a precision, zerodrift, voltage output current sense amplifier with a 2mΩ integrated current sensing resistor with a 0.1% maximum tolerance and a temperature drift of 15ppm/ºC over the device's entire tempeature range of -40ºC to +125ºC. This device can accommodate continuous currents flowing through the on-board resistor of up to 15A. Integrating the Current Sensing Resistor Scott Hill, Current Sensing Products Copyright © 2016, Texas Instruments Incorporated 1 www.ti.com 0V to 36V Supply Supply Voltage 0V to 36V Supply VS IN+ INA250 IN- IN+ VBUS Load INA260 SDA V SCL ADC I2C Interface Alert - + A0 A1 I ADC Reference Voltage IN- REF OUT ADC GPIO Controller Load GND Controller Figure 2. Integrating The Current Sensing Resistor In addition to the integrated precision resistor inside this device, the INA250 also addresses one of the most common issues associated with implementing a current sensing solution. A low-ohmic shunt resistor is used to reduce the current sensing power dissipation. A challenge in accommodating this low resistance value is the potential impact of parasitic resistance on the PCB. Parasitic resistance in series with the shunt resistor can cause additional measurement errors as current flows through the resistance to create the shunt voltage. The most common source for these measurement errors is poor layout techniques. A Kelvin connection, also known as a four terminal connection or a force-sense, is required to ensure that minimal additional resistance is present to alter the differential voltage developed between the amplifier's input pins. There are PCB layout techniques to reduce the effect of parasitic resistance, however, this concern is removed with the INA250. As previously described, the typical current sensing signal chain path includes the current sensing resistor, the analog front-end, ADC and system controller. The INA250 combines the shunt resistor and the current sensing amplifier. The INA260 combines the current sensing resistor, measurement front-end and the ADC into one single device. Figure 3 shows the INA260 featuring the same precision, integrated sensing resistor, pairing it with a 16-bit, precision ADC optimized for current sensing applications. This combination provides an even higher performance measurement capability than the INA250 resulting in a maximum measurement gain error of 0.5% over the entire temperature range and a maximum input offset current of 5mA. 2 GND SDA SCL Integrating the Current Sensing Resistor Scott Hill, Current Sensing Products Figure 3. Integrated Signal Path Pairing the precision, low-drift current sensing with these precision current sensing devices provides measurement solutions that are challenging to accomplish using discrete amplifier and resistor combinations. There are few catalog current sensing resistors available that are capable of enabling the combination of precision and temperature stable measurements but achieving this level of accuracy in a solution size comparable to TSSOP-16 packaged integrated solutions doesn't exist. Alternate Device Recommendations For additional design flexibility, many stand-alone current sensing amplifiers and digital power monitors are also available. For lower performance applications with higher current requirements than the integrated solutions support, use the INA210 stand-alone current sensing amplifier. For applications requring a standalone digital power monitor, use the INA226. For applications implementing over-current detection, the INA301 features an integrated comparator for on-chip over-current detection as fast as 1μs. Table 1. Alternative Device Recommendations Device Optimized Parameter Performance TradeOff INA210 35μV VOS, Package: SC706, QFN-10 No on-boad current sensing resistor INA226 10μV VOS, Package: MSOP-10 No on-boad current sensing resistor INA301 Signal Bandwidth, OnBoard Comparator No on-boad current sensing resistor Table 2. Related TI TechNotes SBOA162 Measuring Current To Detect Out-of-Range Conditions SBOA165 Precision Current Measurements on HighVoltage Power Supply Rails SBOA167 Integrating the Current Sensing Signal Path SBOA169 Precision, Low-Side Current Measurement SBOA170A – October 2016 – Revised December 2016 Submit Documentation Feedback Copyright © 2016, 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. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily performed. TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information published by TI regarding third-party products or services does not constitute a license 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 significant portions 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. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components in safety-critical applications. In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and requirements. Nonetheless, such components are subject to these terms. No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties have executed a special agreement specifically governing such use. Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and regulatory requirements in connection with such use. TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of non-designated products, TI will not be responsible for any failure to meet ISO/TS16949. Products Applications Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers DLP® Products www.dlp.com Consumer Electronics www.ti.com/consumer-apps DSP dsp.ti.com Energy and Lighting www.ti.com/energy Clocks and Timers www.ti.com/clocks Industrial www.ti.com/industrial Interface interface.ti.com Medical www.ti.com/medical Logic logic.ti.com Security www.ti.com/security Power Mgmt power.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video RFID www.ti-rfid.com OMAP Applications Processors www.ti.com/omap TI E2E Community e2e.ti.com Wireless Connectivity www.ti.com/wirelessconnectivity Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265 Copyright © 2016, Texas Instruments Incorporated