LMP8640MKE-F

National Semiconductor is now part of Texas Instruments. Search http://www.ti.com/ for the latest technical information and details on our current products and services. LMP8640/LMP8640HV Precision High Voltage Current Sense Amplifier General Description Features The LMP8640 and the LMP8640HV are precision current sense amplifiers that detect small differential voltages across a sense resistor in the presence of high input common mode voltages with a supply voltage range from 2.7V to 12V. The LMP8640 accepts input signals with common mode voltage range from -2V to 42V, while the LMP8640HV accepts input signal with common mode voltage range from -2V to 76V. The LMP8640 and LMP8640HV have fixed gain for applications that demand accuracy over temperature. The LMP8640 and LMP8640HV come out with three different fixed gains 20V/V, 50V/V, 100V/V ensuring a gain accuracy as low as 0.25%. The output is buffered in order to provide low output impedance. This high side current sense amplifier is ideal for sensing and monitoring currents in DC or battery powered systems, excellent AC and DC specifications over temperature, and keeps errors in the current sense loop to a minimum. The LMP8640 and LMP8640HV are ideal choice for industrial, automotive and consumer applications, and it is available in TSOT-6 package. Typical values, TA = 25°C ■ High common-mode voltage range -2V to 42V — LMP8640 -2V to 76V — LMP8640HV 2.7V to 12V ■ Supply voltage range 20V/V; 50V/V; 100V/V ■ Gain options 0.25% ■ Max gain error 900µV ■ Low offset voltage 13 μA ■ Input bias current 85 dB ■ PSRR 103 dB ■ CMRR (2.1V to 42V) -40°C to 125°C ■ Temperature range ■ 6-Pin TSOT Package Applications ■ ■ ■ ■ ■ ■ High-side current sense Vehicle current measurement Motor controls Battery monitoring Remote sensing Power management Typical Application 30071462 LMP™ is a trademark of National Semiconductor Corporation. © 2010 National Semiconductor Corporation 300714 www.national.com LMP8640/LMP8640HV Precision High Voltage Current Sense Amplifier September 7, 2010 LMP8640/LMP8640HV LMP8640 -6V to 60V Voltage at VOUT pin V- to V+ Storage Temperature Range -65°C to 150°C Junction Temperature (Note 3) 150°C For soldering specifications, see product folder at www.national.com and www.national.com/ms/MS/MS-SOLDERING.pdf Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. ESD Tolerance (Note 2) Human Body Model For input pins +IN, -IN For all other pins Machine Model Charge device model Supply Voltage (VS = V+ - V−) Differential Voltage +IN- (-IN) Voltage at pins +IN, -IN LMP8640HV 5000V 2000V 200V 1250V 13.2V 6V Operating Ratings (Note 1) Supply Voltage (VS = V+ - V−) Temperature Range (Note 3) Package Thermal Resistance(Note 3) TSOT-6 2.7V to 12V -40°C to 125°C 96°C/W -6V to 80V 2.7V Electrical Characteristics (Note 4) Unless otherwise specified, all limits guaranteed for at TA = 25°C, VS=V+ – V-, VSENSE= +IN-(-IN), V+ = 2.7V, V− = 0V, −2V < VCM < 76V, RL = 10MΩ. Boldface limits apply at the temperature extremes. Symbol Parameter Condition Min Typ Max (Note 6) (Note 5) (Note 6) -900 -1160 VOS Input Offset Voltage VCM = 2.1V TCVOS Input Offset Voltage Drift (Note 7, Note 9) VCM = 2.1V IB Input Bias Current (Note 10) VCM = 2.1V 12 eni Input Voltage Noise (Note 9) f > 10 kHz 117 Gain AV Fixed Gain LMP8640-T LMP8640HV-T 20 V/V Fixed Gain LMP8640-F LMP8640HV-F 50 V/V Fixed Gain LMP8640-H LMP8640HV-H 100 V/V Gain error VCM = 2.1V Accuracy over temperature (Note 9) −40°C to 125°C, VCM=2.1V PSRR Power Supply Rejection Ratio VCM = 2.1V, 2.7V < V+ < 12V, 85 CMRR Common Mode Rejection Ratio LMP8640HV 2.1V < VCM < 42V LMP8640 2.1V < VCM< 42V 103 LMP8640HV 2.1V < VCM < 76V 95 -2V 10 kHz 117 Gain AV Fixed Gain LMP8640-T LMP8640HV-T 20 V/V Fixed Gain LMP8640-F LMP8640HV-F 50 V/V Fixed Gain LMP8640-H LMP8640HV-H 100 V/V Gain error VCM = 2.1V Accuracy over temperature (Note 9) −40°C to 125°C, VCM=2.1V PSRR Power Supply Rejection Ratio VCM = 2.1V, 2.7V < V+ < 12V, 85 CMRR Common Mode Rejection Ratio LMP8640HV 2.1V < VCM < 42V LMP8640 2.1V < VCM< 42V 103 LMP8640HV 2.1V < VCM < 76V 95 -2V 10 kHz 117 Gain AV Fixed Gain LMP8640-T LMP8640HV-T 20 V/V Fixed Gain LMP8640-F LMP8640HV-F 50 V/V Fixed Gain LMP8640-H LMP8640HV-H 100 V/V Gain error VCM = 2.1V Accuracy over temperature (Note 9) −40°C to 125°C, VCM=2.1V PSRR Power Supply Rejection Ratio VCM = 2.1V, 2.7V < V+ < 12V, 85 CMRR Common Mode Rejection Ratio LMP8640HV 2.1V < VCM < 42V LMP8640 2.1V < VCM< 42V 103 LMP8640HV 2.1V < VCM < 76V 95 -2V TA. Absolute Maximum Ratings indicate junction temperature limits beyond which the device may be permanently degraded, either mechanically or electrically. Note 5: Typical values represent the most likely parametric norm at the time of characterization. Actual typical values may vary over time and will also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material. Note 6: Limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlations using statistical quality control (SQC) method. Note 7: Offset voltage temperature drift is determined by dividing the change in VOS at the temperature extremes by the total temperature change. Note 8: The number specified is the average of rising and falling slew rates and measured at 90% to 10%. Note 9: This parameter is guaranteed by design and/or characterization and is not tested in production. Note 10: Positive Bias Current corresponds to current flowing into the device. 5 www.national.com LMP8640/LMP8640HV Symbol LMP8640/LMP8640HV Block Diagram 30071430 Connection Diagram 6-Pin TSOT 30071402 Top View Pin Descriptions Pin Name Description 1 VOUT Single Ended Output 2 V- Negative Supply Voltage 3 +IN Positive Input 4 -IN Negative Input 5 NC Not Connected 6 V+ Positive Supply Voltage www.national.com 6 Package Gain Part Number Package Marking LMP8640MK-T LMP8640MKE-T 6-Pin TSOT 20V/V AA6A LMP8640MKX-T 3k Units Tape and Reel 1k Units Tape and Reel AB6A LMP8640HVMKX-T 50V/V 1k Units Tape and Reel AC6A LMP8640HVMK-F 1k Units Tape and Reel AD6A 250 Units Tape and Reel 1k Units Tape and Reel AE6A 250 Units Tape and Reel LMP8640MKX-H 3k Units Tape and Reel LMP8640HVMK-H 1k Units Tape and Reel LMP8640HVMKE-H MK06A 3k Units Tape and Reel LMP8640MK-H LMP8640MKE-H 100V/V 250 Units Tape and Reel 3k Units Tape and Reel LMP8640HVMKX-F 6-Pin TSOT 250 Units Tape and Reel LMP8640MKX-F LMP8640HVMKE-F MK06A 3k Units Tape and Reel LMP8640MK-F LMP8640MKE-F NSC Drawing 250 Units Tape and Reel LMP8640HVMK-T LMP8640HVMKE-T 6-Pin TSOT Transport Media 1k Units Tape and Reel AF6A LMP8640HVMKX-H MK06A 250 Units Tape and Reel 3k Units Tape and Reel 7 www.national.com LMP8640/LMP8640HV Ordering Information LMP8640/LMP8640HV Typical Performance Characteristics Unless otherwise specified: TA = 25°C, VS=V+-V-, VSENSE= +IN - (-IN), RL = 10 MΩ. Supply Curent vs. Supply Voltage Supply Current vs. VCM 30071425 30071426 Supply Current vs. VCM Supply Current vs. VCM 30071427 30071428 CMRR vs. VCM (Gain 20V/V) CMRR vs. VCM (Gain 50V/V) 30071423 30071422 www.national.com 8 LMP8640/LMP8640HV CMRR vs. VCM (Gain 100V/V) Gain vs. Frequency 30071424 30071414 Output voltage vs. VSENSE Output voltage vs. VSENSE (ZOOM close to 0V) 30071416 30071417 Large Step response Small Step response 30071418 30071419 9 www.national.com LMP8640/LMP8640HV Settling time (fall) Settling time (rise) 30071420 30071421 Common mode step response (rise) Common mode step response (fall) 30071411 30071410 Load regulation (Sinking) Load regulation (Sourcing) 30071432 www.national.com 30071431 10 LMP8640/LMP8640HV AC PSRR vs. Frequency AC CMRR vs. Frequency 30071412 30071413 11 www.national.com LMP8640/LMP8640HV gested. In this condition is required to take in account also the power rating of RS resistor. The low input offset of the LMP8640 allows the use of small sense resistors to reduce power dissipation still providing a good input dynamic range. The input dynamic range is the ratio expressed in dB between the maximum signal that can be measured and the minimum signal that can be detected, usually the input offset is the principal limiting factor. Application Information GENERAL The LMP8640 and LMP8640HV are single supply high side current sense amplifiers with a fixed gain of 20V/V, 50V/V, 100V/V and a common mode voltage range of -2V to 42V or -2V to 76V depending on the grade. THEORY OF OPERATION As seen from the picture below, the current flowing through RS develops a voltage drop equal to VSENSE across RS. The high impedance inputs of the amplifier doesn’t conduct this current and the high open loop gain of the sense amplifier forces its non-inverting input to the same voltage as the inverting input. In this way the voltage drop across RIN matches VSENSE. A current proportional to IS according to the following relation: DRIVING ADC The input stage of an Analog to Digital converter can be modelled with a resistor and a capacitance versus ground. So if the voltage source doesn't have a low impedance an error in the amplitude's measurement will occur. In this case a buffer is needed to drive the ADC. The LMP8640 has an internal output buffer able to drive a capacitance load up to 30 pF or the input stage of an ADC. If required an external low pass RC filter can be added at the output of the LMP8640 to reduce the noise and the bandwidth of the current sense. IG = VSENSE/RIN = RS*IS/RIN , flows entirely in the internal gain resistor RG developing a voltage drop equal to VRG = IG *RG = (VSENSE/RIN) *RG = ((RS*IS)/RIN)*RG This voltage is buffered and showed at the output with a very low impedance allowing a very easy interface of the LMP8640 with other ICs (ADC, μC…). VOUT = 2*(RS*IS)*G, where G=RG/RIN = 10V/V, 25V/V, 50V/V, according to the gain options. 30071461 FIGURE 2. LMP8640 to ADC interface DESIGN EXAMPLE For example in a current monitor application is required to measure the current sunk by a load (peak current 10A) with a resolution of 10mA and 0.5% of accuracy. The 10bit analog to digital converter accepts a max input voltage of 4.1V. Moreover in order to not burn much power on the shunt resistor it needs to be less than 10mΩ. In the table below are summarized the other working condition. Working Condition 30071403 FIGURE 1. Current monitor SELECTION OF THE SHUNT RESISTOR The value chosen for the shunt resistor, RS, depends on the application. It plays a big role in a current sensing system and must be chosen with care. The selection of the shunt resistor needs to take in account the small-signal accuracy, the power dissipated and the voltage loss across the shunt itself. In applications where a small current is sensed, a bigger value of RS is selected to minimize the error in the proportional output voltage. Higher resistor value improves the SNR at the input of the current sense amplifier and hence gives an accurate output. Similarly when high current is sensed, the power losses in RS can be significant so a smaller value of RS is sugwww.national.com Value Min Max Supply Voltage 5V 5.5V Common mode Voltage 48V 70V Temperature 0°C 70°C Signal BW 50kHz First step – LMP8640 / LMP8640HV selection The required common mode voltage of the application implies that the right choice is the LMP8640HV (High common mode voltage up tp 76V). Second step – Gain option selection We can choose between three gain option (20V/V, 50V/V, 100V/V). considering the max input voltage of the ADC 12 Accuracy Calculation ERROR SOURCE Rs=4.1mΩ Rs=8.1mΩ Tc Vos 182µV 182µV Nosie 216µV 216µV Gain drift 75.2µV 151µV Total error (squared sum of contribution) 293µV 320µV Accuracy 100*(Max_VSENSE / Total Error) 0.7% 0.4% From the tables above is clear that the 8.2mΩ shunt resistor allows the respect of the project's constraints. The power burned on the Shunt is 820mW at 10A. Resolution Calculation ERROR SOURCE Rs=4.1mΩ Rs=8.1mΩ CMRR calibrated ad mid VCM range 77.9µV 77.9µV PSRR calibrated at 5V 8.9µV 8.9µV Total error (squared sum of contribution) 78µV 78µV Resolution (Total error / RS) 19.2mA 9.6mA 13 www.national.com LMP8640/LMP8640HV (4.1V) , the max Sense voltage across the shunt resistor is evaluated according the following formula: VSENSE= (MAX Vin ADC) / Gain; hence the max VSENSE will be 205mV, 82mV, 41mV respectively. The shunt resistor are then evaluated considering the maximum monitored current : RS = (max VSENSE) / I_MAX For each gain option the max shunt resistors are the following : 20.5mΩ, 8.2mΩ, 4.1mΩ respectively. One of the project constraints requires RS