Bidirectional, ZeroDrift, - PDF document

Bidirectional, ZeroDrift, Current Sense Amplifier Data Sheet AD8418 FEATURESTypical 0.1/°C offset driftMaximumvoltageoffset over full temperature range2.7 V to 5.5 V ower upply operating AD8205Current sense mplifier, ain = 50 AD8206Current sense mplifier, ain = 20 AD8207 AD8210High speed current senseamplifier, gain = 20 FUNCTIONAL BLOCK DIAGRAM + SHUNT G = 20 = –2V TO +70V = 2.7V TO 5.5V REFREFOUT 0VVSVS/2 OUT SHUNT FILTERFILTER VCM AD8418 +IN–INGNDSHUNT 1546-001 Figure �� Rev.Document FeedbackInformation furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.One Technology Way, P.O. Box 9106,Norwood, MA 020629106, U.S.A.Tel: 781.329.47002013Analog Devices, Inc. All rights reserved.Technical Supportwww.analog.com Data Sheet TABLE OF CONTENTSFeaturesApplicationsGeneral DescriptionFunctional Block DiagramRevision HistorySpecificationsAbsolute Maximum RatingsESD CautionPin Configuration and Function DescriptionsTypical Performance CharacteristicsTheory of OperationOutput Offset AdjustmentUnidirectional OperationBidirectional OperationExternal Referenced OutputSplitting the SupplySplitting an External ReferenceApplications InformationMotor ControlSolenoid ControlOutline DimensionsOrdering Guideutomotive ProductsREVISION HISTORY/13Revision 0: Initial Version��Rev. | Page of Data Sheet SPECIFICATIONS40°Cto +125°Coperating temperature range= 5 V, unless otherwise noted.Table ParameterTest Conditions/CommentsMinTypMaxUnit GAIN InitialV/V ErrorOver TemperatureSpecified temperature range in vs. Temperatureppm/°C VOLTAGE OFFSET Offset VoltageReferred to the Input (RTI25°C±200 Over Temperature (RTI)Specified temperature range±400 Offset DriftV/°C INPUT Input Bias Current Input Voltage RangeCommon mode, continuous CommonMode Rejection Ratio (CMRR)Specified temperature range, f = dc f = dc to 0 kHz OUTPUT Output Voltage Range= 25 k0.00.0 Output Resistance DYNAMIC RESPONSE Small Signal 3 dB BandwidthkHz Slew RateV/µs NOISE 0.1 Hz to 10 Hz RTI2.3µV p Spectral Density, 1 kHz RTI OFFSET ADJUSTMENT Ratiometric AccuracyDivider to supplies0.490.50V/V Accuracyferred to the OutputRTOVoltage applied to VREF1 and VREFin parallelmV/V Output Offset Adjustment Range= 5 V0.00.0 POWER SUPPLY Operating Range2.75.5 Quiescent Current Over Temperture= 0.1 V dc2.6 ower Supply Rejection Ratio Temperature Range For Specified PerformanceOperating temperature range40+125 The offset adjustment isratiometric to the power supply when VREF1 and VREF2 are used as a divider between the supplies.��Rev. | Page of Data Sheet ABSOLUTE MAXIMUM RATINGSTable ParameterRating Supply Voltage Input Voltage Range Continuous to +70 Survival 4 V to +85 V Differential Input Survival 5.5 Reverse Supply Voltage0.3 V ESD Human Body Model(HBM)±2000 V Operating Temperature Range 40°C to +125°C Storage Temperature Range65°C to +150°C Output ShortCircuit DurationIndefinite Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.ESD CAUTION ��Rev. | Page of Data Sheet PIN CONFIGURATION AND FUNCTION DESCRIPTI NC = NO CONNECT. DO NOTCONNECT TO THIS PIN. –IN GND REF NC4 +IN REF VS6 OUTAD8418TOP VIEW(Not to Scale) 1546-002 Figure . Pin ConfigurationTable . Pin Function DescriptionsPin No.MnemonicDescription INNegative Input GNDGround REFReference Input 4 NC No Connect . Do not connect to this pin. OUTOutput Supply REFReference Input +INPositive Input ��Rev. | Page of Data Sheet TYPICAL PERFORMANCE CHARACTERITICS OFFSET VOAGE (TEMPERTURE (°C) 1546-003 Figure . Typical Offset Drift vs. Temperature CMRR (dB)FREQUENC (Hz)1546-004 Figure . Typical CMRR vs. Frequency GAIN ERROR (µV/V)TEMPERTURE (°C)1546-005 NORMALIZED AT 25°C Figure . Typical Gain Error vs. Temperature GAIN (dB)FREQUENC (Hz)1546-006 Figure . Typical Small Signal Bandwidth (VOUT= 200 mV p OUTPUT ERROR (%)DIFFERENTIA INPUT VOAGE (mV)1546-007 Figure . Total Output Error vs. Differential Input Voltage 0.50.40.30.20.1–0.1–0.2–0.3–0.4–0.5BIAS CURRENT PER INPUT PIN (mA) = 5V+IN –IN1546-008 Figure . Bias Current per Input Pin vs. CommonMode Voltage��Rev. | Page of Data Sheet 2.01.91.81.71.61.51.41.31.21.11.0SUPP CURRENT (mA)INPUT COMMON-MODE VOLTAGE (V) = 5V = 2.7V 1546-009 Figure . Supply Current vs. Input CommonMode Voltage TIME (1µs/DIV) INPUT 25mV/DIV 500mV/DIV = 2.7V OUTPUT1546-010 Figure 10. Rise Time = 2.7 V) TIME (1µs/DIV) INPUT 25mV/DIV 500mV/DIV = 5V OUTPUT1546-0 Figure 11. Rise Time (V= 5 V) TIME (1µs/DIV) 25mV/DIV 500mV/DIV = 2.7V INPUTOUTPUT1546-012 Figure 12. Fall Time (V2.7 TIME (1µs/DIV) 25mV/DIV 500mV/DIV = 5VOUTPUTINPUT1546-013 Figure 13. Fall Time (V= 5 V) TIME (1µs/DIV) OUTPUT INPUT 100mV/DIV 1V/DIV = 2.7V 1546-014 Figure 14. Differential Overload Recovery, Rising = 2.7 V)��Rev. | Page of Data Sheet TIME (1µs/DIV) OUTPUT INPUT 200mV/DIV 2V/DIV = 5V 1546-015 Figu15. Differential Overload Recovery, Rising (V= 5 V) TIME (1µs/DIV) 100mV/DIV 1V/DIV = 2.7V OUTPUT INPUT 1546-016 Figure 16. Differential Overload Recovery, Falling (V= 2.7 V) TIME (1µs/DIV) OUTPUT INPUT 200mV/DIV 2V/DIV = 5V 1546-017 Figure 17. Differential Overload Recovery, Falling= 5 V) TIME (4µs/DIV) INPUT COMMON MODE OUTPUT100mV/DIV 40V/DIV1546-018 Figure 18. Input CommonMode Step Response (V= 5 V, Inputs Shorted) MAXIMUM OUTPUT SINK CURRENT (mA)TEMPERATURE (°C)2.7V 1546-019 Figure 19. Maximum Output Sink Current vs. Temperature MAXIMUM OUTPUT SOURCE CURRENT (mA)TEMPERTURE (°C)2.7V 1546-020 Figure 20. Maximum Output Source Current vs. Temperature��Rev. | Page of Data Sheet AGE FROM POSITIVE RAI (mV)OUTPUT SOURCE CURRENT (mA)1546-021 Figure 21. Output Voltage Range from Positive Rail vs. Output Source Current AGE FROM GROUND (mV)OUTPUT SINK CURRENT (mA) 1546-022 Figure 22. Output Voltage Range from Groundvs. Output Sink Current VOS (µ = 5V –300 –200 –100 0 100 2003004000 300 600 900 1200 1500 HITS 1546-024 +125°C+25°C–40°C Figure 23. Offset VoltageDistribution –0.4–0.3–0.2–0.10.10.20.30.4CMRR (µV/V)TEMPERTURE (°C) 1546-023 Figure 24CMRR vs. Temperatur –8 –6 –4 –2 0 2 4 680 300 600 900 1200 1500 GAIN ERROR DRIFT (PPM/°C) 1546-125HITS Figure 25Gain Drift Distribution��Rev. | Page of Data Sheet THEORY OF OPERATIONThe AD8418is a singlesupply, zero drift, difference amplifier that uses a unique architecture to accurately amplify small differential current shunt voltages in the presence of rapidly changing comonmode voltageIn typical applications, the AD8418is used to measure current by amplifying the voltage across a shunt resistor connected to its inputs by a gain of 20V/Vsee Figure The AD8418is designed to provide excellent commonmode rejection, even with PWM commonmode inputs that can change at very fast rates, for example, 1 V/nsThe AD8418contains patentedtechnology to eliminate the negative effects of such fastchanging external commonmode variations. The AD8418features an input offset drift of less than 500nV/°CThis performance is achieved through a novel zerodrift architecture that does not compromise bandwidth, which is typically rated at 50 kHz. The reference inputs, VREF1 and VREF2, are tied through 100k resistors to the positive input of the main amplifier, which allows the output offset to be adjusted anywhere in the output operating range. The gain is 1V/V from the reference pins to the output when the reference pins are used in parallel. When the pins are used to divide the supply, the gain is 0.5 V/V.The AD8418offers breakthrough performance without compromising any of the robust application needs typical of solenoid or motor control. The ability to reject PWM input commonmode voltages and the zero drift architectureprovidinglow offset and offset driftallowthe AD8418to deliver total accuracy forthese demanding applications. + SHUNT G = 20 = –2V TO +70V = 2.7V TO 5.5V REFREFOUT 0VVSVS/2 OUT SHUNT FILTERFILTER VCM AD8418 +IN–INGNDSHUNT 1546-225 Figure 26Typical Application��Rev. | Page of Data Sheet OUTPUT OFFSET ADJUSTMENTThe output of the AD8418can be adjusted for unidirectional or bidirectional operation. UNIDIRECTIONAL OPERATIONUnidirectional operation allows the AD8418to measure curents through a resistive shunt in one direction. The basic modes for unidirectional operation are ground referenceput mode and referenced output mode.Forunidirectional operation, the outputbe set at the negativerail (near ground) or at the positive rail (near ) when the differential input is 0 V. The output moves to the opposite rail when a correct polarity differential input voltage is applied. The quired polarity of the differential input depends on the output voltage setting. If the output is set at the positive rail, the input polarity needs to be negative to move the output down. If the output is set at ground, the polarity must bepositive to move the ouput up. Ground Referenced OutputWhen using the AD8418in this mode, both referenceinputs are tied to ground, which causes the output to sit at the negative rail when there are zero differential volts at the input (see Figure –+ OUTGNDREFREFAD8418 –IN+IN 1546-025 Figure 27. Ground Referenced OutputReferenced Output This mode is set when both referencepins are tied to the positivesupply. It is typically used when the diagnostic scheme rquires detection of the amplifier and the wiring before power is appliedto the load (see Figure –+ OUTGNDREFREFAD8418 –IN+IN 1546-026 Figure 28Referenced OutputBIDIRECTIONAL OPERATIONBidirectional operation allows the AD8418to measure currents through a resistive shunt in two directions.In this case, the output is set anywhere within the output range. Typically, it is set at halfscale for equal range in both directions. In some cases, however, it is set at a voltage other than half scale when the bidirectional current is nonsymmetrical.Adjusting the output is accomplished by applying voltage(s) to the referenceinputs.REF1 and VREF2 are tied to internal resistors that connect to an internal offset node. There is no operational difference between the pins. ��Rev. | Page of Data Sheet EXTERNAL REFERENCEOUTPUTTying both pins together and to a reference produces an output equal to thereference voltage when there is no differential input (see Figure ). The output moves down from the reference volage when the input is negativerelative to the IN pinand up when the input is positiverelative to the IN pin. –+ OUTGNDREFREFAD8418 –IN+IN 2.5V1546-027 Figure 29. External ReferenceOutputSPLITTING THE SUPPLYBy tying one reference pin tand the other to the ground pin, the output is set at half of the supply when there is no diferentialinput (see Figure ). The benefit is that external reference not required to offset the output for bidirectional current measurement. ying one reference pin to Vand the other to the ground pincreates a midscale offset that is ratometric to thesupply, which means that if the supply increases or decreasesthe output remains at half the supply. For exaple, if the supply is 5.0 V, the output is at half scale or 2.5 V. Ifthe suply increasesby 10% (to 5.5 V), the output goes to 2.75 V. –+ OUTGNDREFREFAD8418 –IN+IN 1546-028 Figure 30. Split SupplySPLITTING AN EXTERNAL REFERENCETheinternal reference resistors can be used to divide an externalreference by 2 with an acuracy of approximately 0.5%Splitting an external referencecan be doneby connecting one VREFpin toground and the other VREFpin to the reference (see Figure –+ OUTGNDREFREFAD8418 –IN+IN 1546-029 Figure 31. Split External Reference��Rev. | Page of Data Sheet APPLICATIONSINFORMATIONMOTOR CONTROLPhase Motor ControlThe AD8418is ideally suited for monitoring current in 3phase motor applications. The 250 kHz typical bandwidth of the AD8418allows instantaneous current monitoring. Additionally, the typical lowoffset drift of 0.1 µV/°Cmeans that the measurement error between the two motor phases at a minimum over temperatureThe AD8418rejects PWM input commonmode voltages in the V to +V (witha 5V supply) range. Monitoring the currenton the motor phase allows sampling of the current at any point and provis diagnostic information such as a short to GND and battery. Refer to Figurefor thetypical phase current measurement setup withthe AD8418Bridge Motor ControlAnother typical application for the AD8418is as part of the control loop in Hbridge motor control. In this case, the shunt resistor is placed in the middle of the Hbridge so that it can accurately measure current in both directions by using the shunt available at the motor(see Figure ). Using an amplifier and shunt in this location is a better soltion than a ground referenced op amp because groundis not typically a stable reference voltage in this type of appliction. The instability of the ground reference causes inaccuracies in the measurments that cbe made with a simple ground referenced op amp. The AD8418measures current in both directions as the Hbridge switches and the motor changes direction. The output of the AD8418is configured in an external referenced bidireonal mode (see the Bidirectional Operationsection). AD8418+INSHUNTREFOUT–INGNDCONTROLLERREF 5V 2.5V 1546-030 Figure 32Bridge Motor Control AD8418BIDIRECTIONA CURRENT MEASUREMENTREJECTION OF HIGH PWM COMMON-MODE VOAGE (–2VO +70V)AMPLIFICHIGH OUTPUT DRIVEAD8214INTERCIRCUITOPTIONAART FOROVERCURRENTPROTECTIONAST (DIRECT)SHUTDOWN OFPOWER SAGE AD8418 CONTROLLER 1546-031 Figure33Phase Motor Control��Rev. | Page of Data Sheet SOLENOID ONTROLHighSide Current Sense with a LowSide SwitchIn thcaseof a highside current sense with a lowside switchthe PWM control switch is ground referenced. An inductive load (solenoid) is tied to a power supply. A resistive shunt is placed between the switch and the load (see Figure ). An advantage of placing the shunt on the high side is that the entire current, including the recirculation current, can be measured becausethe shunt remains in the loop when the switch is off. In addition, diagnostics can be enhanced because shorts to ground can be detected with the shunt on the high sideIn this circuit configuration, when the switch is closed, the commonmode voltage moves down to near the negative rail. When the switch is open, the voltage reversal across the iductive load causes the commonmode voltage to be held one diode drop above the battery by the clamp diode. –IN GND REF NC4 +IN REF VS6 OUTOUTPUTINDUCTIVELOADCLAMPDIODEBATTERYSWITCHSHUNTNC = NO CONNECT.AD8418 1546-032 Figure 34. LowSide SwitchHighSide Current Sense with a HighSide Switche highside current sense with a highside switch configurationminimizes the possibility of unexpected solenoid activation and excessive corrosion (see Figure ). In this case, both the switch and the shunt are on the high side. When the switch is off, the battery is removefrom the load, which prevents damage from potential shorts to ground while still allowing the recirculating current to be measured and to viddiagnostics. Removingthe power supply from the load for the majority of the time minimizesthe corrosive effects that cbe caused by the differential voltage between the load and ground.When using a highside switch, the battery voltage is connected to the load when the switch is closed, causing the commonmodevoltage to increase to the battery voltage. In this case, when the switch is open, the voltage reversal across the iductive load causes the commonmode voltage to be held one diode drop below ground by the clamp diode. –IN GND REF NC4 +IN REF VS6 OUTOUTPUTINDUCTIVELOADSHUNTCLAMPDIODEBATTERYSWITCHNC = NO CONNECT.AD8418 1546-033 Figure 35. HighSide SwitchHigh Rail CurrenensingIn the high rail, current sensing configuration, the shunt resistoris referenced to the battery. High voltage is present at the inputs of the current sense amplifier. When the shunt is battery referencedthe AD8418produces a linear groundreferenced analog output. Additionally, the AD8214can be used to provide an overcurrent detection signal in as little as 100ns (see Figure ). This feature is useful in high current systems where fast shutdown in overcurrent conditions is essential. VS1 +IN REG NC4 –IN NC7 GND OUTOUTPUTOVERCURRENTDETECTION (100ns)SHUNTINDUCTIVELOADSWITCHCLAMPDIODEBATTERYAD8214 NC = NO CONNECT. –IN GND REF NC4 +IN REF VS6 OUTAD8418TOP VIEW(Not to Scale) 1546-034 Figure 36High Rail Current Sensing��Rev. | Page of Data Sheet OUTLINE DIMENSIONS CONTROLLINGDIMENSIONSAREINMILLIMETERS;INCHDIMENSIONS(INPARENTHESES)AREROUNDED-OFFMILLIMETEREQUIVALENTSFORREFERENCEONLYANDARENOTAPPROPRIATEFORUSEINDESIGN.COMPLIANTTOJEDECSTANDARDSMS-012-AA012407-A 0.25(0.0098)0.17(0.0067) 1.27(0.0500)0.40(0.0157) 0.50(0.0196)0.25(0.0099) 45° 8°0° 1.75(0.0688)1.35(0.0532) SEATINGPLANE 0.25(0.0098)0.10(0.0040) 41855.00(0.1968)4.80(0.1890) 4.00(0.1574)3.80(0.1497) 1.27(0.0500)BSC 6.20(0.2441)5.80(0.2284)0.51(0.0201)0.31(0.0122) COPLANARITY0.10 Figure 37Lead Standard Small Outline Package [SOIC_NNarrow Body8)Dimensions shown in millimeters and (inches) CTJSM60000 4815 0B 00 1M 332C000 332 544 P1I 1M 000 0 1 Figure 38Lead Mini Small Outline Package [MSOP] (RM8)Dimensions shown in millimet��Rev. | Page of Data Sheet ORDERING GUIDE Model 1, 2 Temperature Range Package Description Package Option Branding AD8418BRMZ40°C to +125°CLead MSOPY4N AD8418BRMZ40°C to +125°CLead MSOP, 13” Tape and ReelY4N AD8418WBRMZ40°C to +125°CLead MSOPY4M AD8418WBRMZ40°C to +125°CLead MSOP, 13” Tape and ReelY4M AD8418WBRZ40°C to +125°CLead SOIC_N AD8418WBRZ40°C to +125°CLead SOIC_N, 13” Tape and Reel Z = RoHS Compliant Part.W = Qualified for Automotive Applications.AUTOMOTIVE PRODUCTSThe AD8418W models are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. Note that these automotive models may have specifications that differ from the commercial models; therefore, designers should review the Specificationssection of this data sheet carefully. Only the automotive grade products shown are available for use in automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for these models. © 2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.D115469/13(0) ��Rev. | Page of