LMP8601QMA

LMP8601/LMP8601Q 60V Common Mode, Bidirectional Precision Current Sensing Amplifier July 16, 2009 LMP8601/LMP8601Q 60V Common Mode, Bidirectional Precision Current Sensing Amplifier General Description The LMP8601 and LMP8601Q are fixed 20x gain precision amplifiers. The part will amplify and filter small differential signals in the presence of high common mode voltages. The input common mode voltage range is –22V to +60V when operating from a single 5V supply. With 3.3V supply, the input common mode voltage range is from –4V to +27V. The LMP8601 and LMP8601Q are members of the Linear Monolithic Precision (LMP®) family and are ideal parts for unidirectional and bidirectional current sensing applications. All parameter values of the part that are shown in the tables are 100% tested and all bold values are also 100% tested over temperature. The part has a precise gain of 20x which is adequate in most targeted applications to drive an ADC to its full scale value. The fixed gain is achieved in two separate stages, a preamplifier with a gain of 10x and an output stage buffer amplifier with a gain of 2x. The connection between the two stages of the signal path is brought out on two pins to enable the possibility to create an additional filter network around the output buffer amplifier. These pins can also be used for alternative configurations with different gain as described in the applications section . The mid-rail offset adjustment pin enables the user to use these devices for bidirectional single supply voltage current sensing. The output signal is bidirectional and mid-rail referenced when this pin is connected to the positive supply rail. With the offset pin connected to ground, the output signal is unidirectional and ground-referenced . The LMP8601Q incorporates enhanced manufacturing and support processes for the automotive market, including defect detection methodologies. Reliability qualification is compliant with the requirements and temperature grades defined in the AEC Q100 standard. Features Unless otherwise noted, typical values at TA = 25°C, VS = 5.0V, Gain = 20x 10μV/°C max ■ TCVOS 90 dB min ■ CMRR 1 mV max ■ Input offset voltage −4V to 27V ■ CMVR at VS = 3.3V −22V to 60V ■ CMVR at VS = 5.0V ■ Operating ambient temperature range −40°C to 125°C ■ LMP8601Q available in Automotive AEC-Q100 Grade 1 qualified version ■ Single supply bidirectional operation ■ All Min / Max limits 100% tested Applications ■ ■ ■ ■ ■ ■ ■ High side and low side driver configuration current sensing Bidirectional current measurement Current loop to voltage conversion Automotive fuel injection control Transmission control Power steering Battery management systems Typical Applications 20157101 LMP™ is a trademark of National Semiconductor Corporation. © 2009 National Semiconductor Corporation 201571 www.national.com LMP8601/LMP8601Q 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 4) Human Body For input pins only For all other pins Machine Model Charge Device Model Supply Voltage (VS - GND) Continuous Input Voltage ((−IN and +IN) Transient (400 ms) Maximum Voltage at A1, A2, OFFSET and OUT Pins Storage Temperature Range Junction Temperature (Note 3) Mounting Temperature Infrared or Convection (20 sec) Wave Soldering Lead (10 sec) −65°C to 150°C 150°C 235°C 260°C ±4000V ±2000V 200V 1000V 6.0V −22V to 60V −25V to 65V VS +0.3V and GND -0.3V (Note 2) Operating Ratings (Note 1) Supply Voltage (VS – GND) 3.0V to 5.5V Offset Voltage (Pin 7 ) 0 to VS Temperature Range (Note 3) Packaged devices −40°C to +125°C Package Thermal Resistance (Note 3) 8-Pin SOIC (θJA) 190°C/W 3.3V Electrical Characteristics Unless otherwise specified, all limits guaranteed at TA = 25°C, VS = 3.3V, GND = 0V, −4V ≤ VCM ≤ 27V, and RL = ∞, Offset (Pin 7) is grounded, 10nF between VS and GND. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min Typ Max (Note 6) (Note 5) (Note 6) 0.6 19.9 −40°C ≤ TA ≤ 125°C VIN = ±0.165V VCM = VS / 2 −40°C ≤ TA ≤ 125°C 0.1 Hz − 10 Hz, 6 Sigma Spectral Density, 1 kHz PSRR Power Supply Rejection Ratio Mid−scale Offset Scaling Accuracy Input Referred Preamplifier (From input pins -IN (pin 1) and +IN (pin 8) to A1 (pin 3)) RCM RDM VOS Input Impedance Common Mode Input Impedance Differential Mode Input Offset Voltage −4V ≤ VCM ≤ 27V −4V ≤ VCM ≤ 27V VCM = VS / 2 −2V ≤ VCM ≤ 24V f = 1 kHz f = 10 kHz for 80 dB CMRR −4 9.95 99 VOL VOH RL = ∞ 3.2 10.0 100 ±5 2 3.25 86 80 250 500 295 590 ±0.15 96 94 85 27 10.05 101 ±50 10 350 700 ±1 kΩ kΩ mV dB dB V V/V kΩ ppm/°C mV V DC, 3.0V ≤ VS ≤ 3.6V, VCM = VS/2 70 0.4 50 1 20 −2.7 0.7 60 0.15 2 16.4 830 86 ±0.15 ±0.5 ±0.413 ±1 ±10 1.3 20.1 ±20 Units Overall Performance (From -IN (pin 1) and +IN (pin 8) to OUT (pin 5) with pins A1 (pin 3) and A2 (pin 4) connected) IS AV SR BW VOS TCVOS en Supply Current Total Gain Gain Drift (Note 14) Slew Rate (Note 7) Bandwidth Input Offset Voltage Input Offset Voltage Drift (Note 8) Input Referred Voltage Noise mA V/V ppm/°C V/μs kHz mV μV/°C μVP-P nV/√Hz dB % mV DC CMRR DC Common Mode Rejection Ratio AC CMRR AC Common Mode Rejection Ratio (Note 9) CMVR A1V RF-INT TCRF-INT A1 VOUT Input Common Mode Voltage Range Gain (Note 14) Output Impedance Filter Resistor Output Impedance Filter Resistor Drift A1 Output Voltage Swing www.national.com 2 LMP8601/LMP8601Q Symbol Parameter Conditions Min Typ Max (Note 6) (Note 5) (Note 6) −2 −2.5 1.99 2 2.5 2.01 ±20 Units Output Buffer (From A2 (pin 4) to OUT( pin 5 )) VOS A2V IB A2 VOUT ISC Input Offset Voltage Gain (Note 14) Input Bias Current of A2 (Note 10), A2 Output Voltage Swing (Note 11, Note 12) Output Short-Circuit Current (Note 13) VOL VOH Sourcing, VIN = VS, VOUT = GND Sinking, VIN = GND, VOUT = VS RL = 100 kΩ 3.28 -25 30 0V ≤ VCM ≤ VS ±0.5 2 −40 4 3.29 -38 46 -60 65 20 mV V/V fA nA mV V mA 5V Electrical Characteristics (Note 2) Unless otherwise specified, all limits guaranteed for at TA = 25°C, VS = 5V, GND = 0V, −22V ≤ VCM ≤ 60V, and RL = ∞, Offset (Pin 7) is grounded, 10nF between VS and GND. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min Typ Max (Note 6) (Note 5) (Note 6) 0.7 19.9 −40°C ≤ TA ≤ 125°C VIN = ±0.25V 0.6 50 −40°C ≤ TA ≤ 125°C 0.1 Hz − 10 Hz, 6 Sigma Spectral Density, 1 kHz PSRR Power Supply Rejection Ratio Mid−scale Offset Scaling Accuracy Input Referred Preamplifier (From input pins -IN (pin 1) and +IN (pin 8) to A1 (pin 3)) RCM Input Impedance Common Mode 0V ≤ VCM ≤ 60V −20V ≤ VCM ≤ 0V RDM Input Impedance Differential Mode 0V ≤ VCM ≤ 60V −20V ≤ VCM ≤ 0V VOS Input Offset Voltage VCM = VS / 2 −20V ≤ VCM ≤ 60V f = 1 kHz f = 10 kHz for 80 dB CMRR −22 9.95 99 VOL VOH RL = ∞ 4.95 10 100 ±5 2 4.985 90 80 DC CMRR DC Common Mode Rejection Ratio AC CMRR AC Common Mode Rejection Ratio (Note 9) CMVR A1V RF-INT TCRF-INT A1 VOUT Input Common Mode Voltage Range Gain (Note 14) Output Impedance Filter Resistor Output Impedance Filter Resistor Drift A1 Ouput Voltage Swing 250 165 500 300 295 193 590 386 ±0.15 105 96 83 60 10.05 101 ±50 10 350 250 700 500 ±1 kΩ kΩ kΩ kΩ mV dB dB V V/V kΩ ppm/°C mV V DC 4.5V ≤ VS ≤ 5.5V 70 1.1 20 −2.8 0.83 60 0.15 2 17.5 890 90 ±0.15 ±0.5 ±0.625 ±1 ±10 1.5 20.1 ±20 Units Overall Performance (From -IN (pin 1) and +IN (pin 8) to OUT (pin 5) with pins A1 (pin 3) and A2 (pin 4) connected) IS AV SR BW VOS TCVOS eN Supply Current Total Gain (Note 14) Gain Drift Slew Rate (Note 7) Bandwidth Input Offset Voltage Input Offset Voltage Drift (Note 8) Input Referred Voltage Noise mA V/V ppm/°C V/μs kHz mV μV/°C μVP-P nV/√Hz dB % mV 3 www.national.com LMP8601/LMP8601Q Symbol Parameter Conditions Min Typ Max (Note 6) (Note 5) (Note 6) −2 −2.5 1.99 2 2.5 2.01 ±20 Units Output Buffer (From A2 (pin 4) to OUT( pin 5 )) VOS A2V IB A2 VOUT ISC Input Offset Voltage Gain (Note 14) Input Bias Current of A2 (Note 10) A2 Ouput Voltage Swing (Note 11, Note 12) Output Short-Circuit Current (Note 13) VOL VOH Sourcing, VIN = VS, VOUT = GND Sinking, VIN = GND, VOUT = VS RL = 100 kΩ 4.98 –25 30 0V ≤ VCM ≤ VS ±0.5 2 −40 4 4.99 –42 48 –60 65 20 mV V/V fA nA mV V mA Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of the device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and the device should not be beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: The electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed. Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJ(MAX), θJA, and the ambient temperature, TA. The maximum allowable power dissipation PDMAX = (TJ(MAX) - TA)/ θJA or the number given in Absolute Maximum Ratings, whichever is lower. Note 4: Human Body Model per MIL-STD-883, Method 3015.7. Machine Model, per JESD22-A115-A. Field-Induced Charge-Device Model, per JESD22-C101C. Note 5: Typical values represent the most likely parameter norms at TA = +25°C, and at the Recommended Operation Conditions at the time of product characterization and are not guaranteed. Note 6: Datasheet min/max specification limits are guaranteed by test. Note 7: Slew rate is the average of the rising and falling slew rates. Note 8: Offset voltage drift determined by dividing the change in VOS at temperature extremes into the total temperature change. Note 9: AC Common Mode Signal is a 5VPP sine-wave (0V to 5V) at the given frequency. Note 10: Positive current corresponds to current flowing into the device Note 11: For this test input is driven from A1 stage. Note 12: For VOL, RL is connected to VS and for VOH, RL is connected to GND. Note 13: Short-Circuit test is a momentary test. Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature of 150°C Note 14: Both the gain of the preamplifier A1V and the gain of the buffer amplifier A2V are measured individually. The over all gain of both amplifiers AV is also measured to assure the gain of all parts is always within the AV limits www.national.com 4 LMP8601/LMP8601Q Block Diagram 20157105 K2 = 2 Connection Diagram 8-Pin SOIC 20157102 Top View 5 www.national.com LMP8601/LMP8601Q Pin Descriptions Pin Power Supply Inputs Filter Network Offset Output 2 6 1 8 3 4 7 5 Name GND VS −IN +IN A1 A2 OFFSET OUT Description Power Ground Positive Supply Voltage Negative Input Positive Input Preamplifier output Input from the external filter network and / or A1 DC Offset for bidirectional signals Single ended output Ordering Information Package Part Number LMP8601MA 8-Pin SOIC LMP8601MAX LMP8601QMA LMP8601QMAX Package Marking LMP8601MA LMP8601QMA Transport Media 95 Units/Rail 2.5K Units Tape and Reel 95 Units/Rail 2.5K Units Tape and Reel M08A NSC Drawing Automotive Grade (Q) product incorporates enhanced manufacturing and support processes for the automotive market, including defect detection methodologies. Reliability qualification is compliant with the requirements and temperature grades defined in the AEC Q100 standard. Automotive Grade products are identified with the letter Q. Fully compliant PPAP documentation is available. For more information go to http://www.national.com/automotive. www.national.com 6 LMP8601/LMP8601Q Typical Performance Characteristics VOS vs. VCM at VS = 3.3V Unless otherwise specified, all limits guaranteed for at TA = 25°C, VS = 5V, GND = 0V, −22 ≤ VCM ≤ 60V, and RL = ∞, Offset (Pin 7) connected to VS, 10nF between VS and GND. VOS vs. VCM at VS = 5V 20157124 20157125 Input Bias Current Over Temperature (+IN and −IN pins) at VS = 3.3V Input Bias Current Over Temperature (+IN and −IN pins) at VS = 5V 20157141 20157142 Input Bias Current Over Temperature (A2 pin) at VS = 5V Input Bias Current Over Temperature (A2 pin) at VS = 5V 20157127 20157126 7 www.national.com LMP8601/LMP8601Q Input Referred Voltage Noise vs. Frequency PSRR vs. Frequency 20157110 20157117 Gain vs. Frequency at VS = 3.3V Gain vs. Frequency at VS = 5V 20157111 20157112 CMRR vs. Frequency at VS = 3.3V CMRR vs. Frequency at VS = 5V 20157128 20157129 www.national.com 8 LMP8601/LMP8601Q Step Response at VS = 3.3V Step Response at VS = 5V 20157118 20157119 Settling Time (Falling Edge) at VS = 3.3V Settling Time (Falling Edge) at VS = 5V 20157120 20157121 Settling Time (Rising Edge) at VS = 3.3V Settling Time (Rising Edge) at VS = 5V 20157122 20157123 9 www.national.com LMP8601/LMP8601Q Positive Swing vs. RLOAD at VS = 3.3V Negative Swing vs. RLOAD at VS = 3.3V 20157113 20157114 Positive Swing vs. RLOAD VS = 5V Negative Swing vs. RLOAD at VS = 5V 20157115 20157116 VOS Distribution at VS = 3.3V VOS Distribution at VS = 5V 20157134 20157135 www.national.com 10 LMP8601/LMP8601Q TCVOS Distribution Gain Drift Distribution 20157136 20157137 Gain error Distribution at VS = 3.3V Gain error Distribution at VS = 5V 20157138 20157139 CMRR Distribution at VS = 3.3V CMRR Distribution at VS = 5V 20157132 20157133 11 www.national.com LMP8601/LMP8601Q Application Information GENERAL The LMP8601 and LMP8601Q are fixed gain differential voltage precision amplifiers with a gain of 20x and a -22V to +60V input common mode voltage range when operating from a single 5V supply or a -4V to +27V input common mode voltage range when operating from a single 3.3V supply. The LMP8601 and LMP8601Q are members of the LMP family and are ideal parts for unidirectional and bidirectional current sensing applications. Because of the proprietary chopping level-shift input stage the LMP8601/LMP8601Q achieve very low offset, very low thermal offset drift, and very high CMRR. The LMP8601 and LMP8601Q will amplify and filter small differential signals in the presence of high common mode voltages. The LMP8601/LMP8601Q use level shift resistors at the inputs. Because of these resistors, the LMP8601/LMP8601Q can easily withstand very large differential input voltages that may exist in fault conditions where some other less protected high-performance current sense amplifiers might sustain permanent damage. PERFORMANCE GUARANTIES To guaranty the high performance of the LMP8601/ LMP8601Q, all minimum and maximum values shown in the parameter tables of this data sheet are 100% tested where all bold limits are also 100% tested over temperature. THEORY OF OPERATION The schematic shown in Figure 1 gives a schematic representation of the internal operation of the LMP8601/LMP8601Q. The signal on the input pins is typically a small differential voltage across a current sensing shunt resistor. The input signal may appear at a high common mode voltage. The input signals are accessed through two input resistors. The proprietary chopping level-shift current circuit pulls or pushes current through the input resistors to bring the common mode voltage behind these resistors within the supply rails. Subsequently, the signal is gained up by a factor of 10 and brought out on the A1 pin through a trimmed 100 kΩ resistor. In the application, additional gain adjustment or filtering components can be added between the A1 and A2 pins as will be explained in subsequent sections. The signal on the A2 pin is further amplified by a factor of 2 and brought out on the OUT pin. The OFFSET pin allows the output signal to be levelshifted to enable bidirectional current sensing as will be explained below. 20157105 K2 = 2 FIGURE 1. Theory of Operation www.national.com 12 LMP8601/LMP8601Q ADDITIONAL SECOND ORDER LOW PASS FILTER The LMP8601/LMP8601Q has a third order Butterworth lowpass characteristic with a typical bandwidth of 60 kHz integrated in the preamplifier stage of the part. The bandwidth of the output buffer can be reduced by adding a capacitor on the A1 pin to create a first order low pass filter with a time constant determined by the 100 kΩ internal resistor and the external filter capacitor. It is also possible to create an additional second order SallenKey low pass filter by adding external components R2, C1 and C2. Together with the internal 100 kΩ resistor R1 as illustrated in Figure 2, this circuit creates a second order low-pass filter characteristic. When the corner frequency of the additional filter is much lower than 60 kHz, the transfer function of the described amplifier van be written as: and the quality factor of the filter is given by: With K2 = 2x, the above equation transforms results in: With this filter gain K2= 2x, the design procedure can be very simple if the two capacitors are chosen to be equal, C1=C2=C. In this case, given the predetermined value of R1 = 100kΩ ( the internal resistor), the quality factor is set solely by the value of the resistor R2. R2 can be calculated based on the desired value of Q as the first step of the design procedure with the following equation: Where K1 equals the gain of the preamplifier and K2 that of the buffer amplifier. The above equation can be written in the normalized frequency response for a 2nd order low pass filter: For instance, the value of Q can be set to 0.5√2 to create a Butterworth response, to 1/√3 to create a Bessel response, or a 0.5 to create a critically damped response. Once the value of R2 has been found, the second and last step of the design procedure is to calculate the required value of C to give the desired low-pass cut-off frequency using: The cutt-off frequency ωo in rad/sec (divide by 2π to get the cut-off frequency in Hz) is given by: Note that the frequency response achieved using this procedure will only be accurate if the cut-off frequency of the second order filter is much smaller than the intrinsic 60 kHz low-pass filter. In other words, to have the frequency response of the LMP8601/LMP8601Q circuit chosen such that the internal poles do not affect the external second order filter. 13 www.national.com LMP8601/LMP8601Q 20157155 K1 = 10, K2 = 2 FIGURE 2. Second Order Low Pass Filter GAIN ADJUSTMENT The gain of the LMP8601/LMP8601Q is 20; however, this gain can be adjusted as the signal path in between the two internal amplifiers is available on the external pins. Reduce Gain Figure 3 shows the configuration that can be used to reduce the gain of the LMP8601/LMP8601Q. 20157156 K2 = 2 FIGURE 3. Reduce Gain Rr creates a resistive divider together with the internal 100 kΩ resistor such that the reduced gain Gr becomes: Given a desired value of the reduced gain Gr, using this equation the required value for Rr can be calculated with: Increase Gain Figure 4 shows the configuration that can be used to increase the gain of the LMP8601/LMP8601Q. Ri creates positive feedback from the output pin to the input of the buffer amplifier. The positive feedback increases the gain. The increased gain Gi becomes: www.national.com 14 LMP8601/LMP8601Q From this equation, for a desired value of the gain, the required value of Ri can be calculated with: It should be noted from the equation for the gain Gi that for large gains Ri approaches 100 kΩ. In this case, the denominator in the equation becomes close to zero. In practice, for large gains the denominator will be determined by tolerances in the value of the external resistor Ri and the internal 100 kΩ resistor. In this case, the gain becomes very inaccurate. If the denominator becomes equal to zero, the system will even become instable. It is recommended to limit the application of this technique to gain values of 50 or smaller. 20157157 K2 = 2 FIGURE 4. Increase Gain BIDIRECTIONAL CURRENT SENSING The signal on the A1 and OUT pins is ground-referenced when the OFFSET pin is connected to ground. This means that the output signal can only represent positive values of the current through the shunt resistor, so only currents flowing in one direction can be measured. When the offset pin is tied to the positive supply rail, the signal on the A1 and OUT pins is referenced to a mid-rail voltage which allows bidirectional current sensing. When the offset pin is connected to a voltage source, the output signal will be level shifted to that voltage divided by two. In principle, the output signal can be shifted to any voltage between 0 and VS/2 by applying twice that voltage to the OFFSET pin. With the offset pin connected to the supply pin (VS) the operation of the amplifier will be fully bidirectional and symmetrical around 0V differential at the input pins. The signal at the output will follow this voltage difference multiplied by the gain and at an offset voltage at the output of half VS. Example: With 5V supply and a gain of 20x, a differential input signal of +10mV will result in 2.7V at the output pin. similarly -10mV at the input will result in 2.3V at the output pin. Note: The OFFSET pin has to be driven from a very low-impedance source (