March 18, 2010 60V Common Mode, Fixed Gain, Bidirectional Precision Current Sensing Amplifier General Description Features The LMP8602 and LMP8603 are fixed gain precision amplifiers. The parts 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 a 3.3V supply, the input common mode voltage range is from –4V to +27V. The LMP8602 and LMP8603 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 parts that are shown in the tables are 100% tested and all bold values are also 100% tested over temperature. The parts have a precise gain of 50x for the LMP8602 and 100x for the LMP8603, which are 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 5x for the LMP8602 and 10x for the LMP8603. 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 LMP8602 and LMP8603 are available in a 8–Pin SOIC package and in a 8–Pin MSOP package. The LMP8602Q and LMP8603Q incorporate 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. Unless otherwise noted, typical values at TA = 25°C, VS = 5.0V, Gain = 50x (LMP8602), Gain = 100x (LMP8603) 10μV/°C max ■ TCVos 90 dB min ■ CMRR Input offset voltage 1 mV max ■ −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 ■ Single supply bidirectional operation ■ All Min / Max limits 100% tested ■ LMP8602Q and LMP8603Q available in Automotive AECQ100 Grade 1 qualified version 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 30083401 LMP™ is a trademark of National Semiconductor Corporation. © 2010 National Semiconductor Corporation 300834 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q 60V Common Mode, Fixed Gain, Bidirectional Precision Current Sensing Amplifier LMP8602/LMP8602Q/ LMP8603/LMP8603Q LMP8602/LMP8602Q/LMP8603/LMP8603Q Storage Temperature Range Junction Temperature (Note 3) Mounting Temperature Infrared or Convection (20 sec) Wave Soldering Lead (10 sec) 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) (Note 6) Transient (400 ms) Maximum Voltage at A1, A2, OFFSET and OUT Pins Operating Ratings ±4000V ±2000V 200V 1000V 6.0V 235°C 260°C (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) −22V to 60V −25V to 65V VS +0.3V and GND -0.3V 3.3V Electrical Characteristics −65°C to 150°C 150°C 8-Pin SOIC (θJA) 190°C/W 8-Pin MSOP (θJA) 203°C/W (Note 2) 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 7) (Note 5) (Note 7) 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 Supply Current Total Gain 1 1.3 LMP8602 49.75 50 50.25 LMP8603 99.5 100 100.5 −2.7 ±20 Gain Drift (Note 15) −40°C ≤ TA ≤ 125°C SR Slew Rate (Note 8) VIN = ±0.165V BW Bandwidth VOS Input Offset Voltage VCM = VS / 2 TCVOS Input Offset Voltage Drift (Note 9) −40°C ≤ TA ≤ 125°C en Input Referred Voltage Noise PSRR Power Supply Rejection Ratio V/V ppm/°C 0.4 0.7 V/μs 50 60 kHz 0.15 ±1 mV 2 ±10 μV/°C 0.1 Hz − 10 Hz, 6 Sigma 16.4 μVP-P Spectral Density, 1 kHz 830 nV/√Hz DC, 3.0V ≤ VS ≤ 3.6V, VCM = VS/2 70 LMP8602 Mid−scale Offset Scaling Accuracy mA 86 ±0.25 Input Referred LMP8603 ±0.45 Input Referred dB ±1 % ±0.33 mV ±1.5 % ±0.248 mV Preamplifier (From input pins -IN (pin 1) and +IN (pin 8) to A1 (pin 3)) RCM Input Impedance Common Mode −4V ≤ VCM ≤ 27V 250 295 350 kΩ RDM Input Impedance Differential Mode −4V ≤ VCM ≤ 27V 500 590 700 kΩ VOS Input Offset Voltage VCM = VS / 2 ±0.15 ±1 mV DC CMRR DC Common Mode Rejection Ratio −2V ≤ VCM ≤ 24V 86 96 AC Common Mode Rejection Ratio AC CMRR (Note 10) f = 1 kHz 80 94 f = 10 kHz CMVR Input Common Mode Voltage Range for 80 dB CMRR K1 Gain (Note 15) RF-INT Output Impedance Filter Resistor TCRF-INT Output Impedance Filter Resistor Drift A1 VOUT A1 Output Voltage Swing www.national.com dB dB 85 27 V 9.95 10.0 10.05 V/V 99 100 101 ±5 ±50 2 10 −4 RL = ∞ VOL VOH 3.2 2 3.25 kΩ ppm/°C mV V Parameter Conditions Min Typ Max (Note 7) (Note 5) (Note 7) Units Output Buffer (From A2 (pin 4) to OUT ( pin 5 ) VOS Input Offset Voltage K2 Gain (Note 15) IB Input Bias Current of A2 (Note 11) A2 VOUT A2 Output Voltage Swing (Note 12, Note 13) 0V ≤ VCM ≤ VS −2 −2.5 LMP8602 LMP8603 Output Short-Circuit Current (Note 14) 5V Electrical Characteristics 2 2.5 4.975 5 5.025 9.95 10 10.05 −40 VOL, LMP8602 10 40 RL = 100 kΩ LMP8603 10 80 VOH, mV V/V fA ±20 3.28 3.29 Sourcing, VIN = VS, VOUT = GND -25 -38 -60 Sinking, VIN = GND, VOUT = VS 30 46 65 RL = 100 kΩ ISC ±0.5 nA mV V mA (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 7) (Note 5) (Note 7) 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 Supply Current Total Gain (Note 15) 1.1 1.5 LMP8602 49.75 50 50.25 LMP8603 99.5 100 100.5 −2.8 ±20 Gain Drift −40°C ≤ TA ≤ 125°C SR Slew Rate (Note 8) VIN = ±0.25V BW Bandwidth VOS Input Offset Voltage TCVOS Input Offset Voltage Drift (Note 9) eN Input Referred Voltage Noise PSRR Power Supply Rejection Ratio V/V ppm/°C 0.6 0.83 V/μs 50 60 kHz −40°C ≤ TA ≤ 125°C 0.15 ±1 mV 2 ±10 μV/°C 0.1 Hz − 10 Hz, 6 Sigma 17.5 μVP-P Spectral Density, 1 kHz 890 nV/√Hz 90 dB DC 4.5V ≤ VS ≤ 5.5V 70 LMP8602 Mid−scale Offset Scaling Accuracy mA ±0.25 Input Referred LMP8603 ±0.45 Input Referred ±1 % ±0.50 mV ±1.5 % ±0.375 mV Preamplifier (From input pins -IN (pin 1) and +IN (pin 8) to A1 (pin 3)) RCM Input Impedance Common Mode RDM Input Impedance Differential Mode VOS Input Offset Voltage DC CMRR DC Common Mode Rejection Ratio 0V ≤ VCM ≤ 60V 250 295 350 kΩ −20V ≤ VCM< 0V 165 193 250 kΩ 0V ≤ VCM ≤ 60V 500 590 700 kΩ −20V ≤ VCM < 0V 300 386 500 kΩ ±0.15 ±1 mV VCM = VS / 2 −20V ≤ VCM ≤ 60V 90 105 80 96 AC CMRR AC Common Mode Rejection Ratio (Note 10) f = 1 kHz CMVR Input Common Mode Voltage Range for 80 dB CMRR K1 Gain (Note 15) RF-INT Output Impedance Filter Resistor f = 10 kHz dB dB 83 3 60 V 9.95 10 10.05 V/V 99 100 101 kΩ −22 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q Symbol LMP8602/LMP8602Q/LMP8603/LMP8603Q Symbol TCRF-INT A1 VOUT Parameter Conditions Min Typ Max (Note 7) (Note 5) (Note 7) Units ±5 ±50 ppm/°C 2 10 mV Output Impedance Filter Resistor Drift A1 Ouput Voltage Swing RL = ∞ VOL VOH 4.95 4.985 0V ≤ VCM ≤ VS −2 −2.5 ±0.5 2 2.5 LMP8602 4.975 5 5.025 LMP8603 9.95 10 10.05 V Output Buffer (From A2 (pin 4) to OUT ( pin 5 ) VOS Input Offset Voltage K2 Gain (Note 15) IB Input Bias Current of A2 (Note 11) A2 VOUT A2 Ouput Voltage Swing (Note 12, Note 13) −40 VOL, LMP8602 10 40 RL = 100 kΩ LMP8603 10 80 4.98 4.99 Sourcing, VIN = VS, VOUT = GND –25 –42 –60 Sinking, VIN = GND, VOUT = VS 30 48 65 RL = 100 kΩ ISC Output Short-Circuit Current (Note 14) V/V fA ±20 VOH, mV 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: For the MSOP package, the bare board spacing at the solder pads of the package will be to small for reliable use at higher voltages (VCM >25V) Therefore it is strongly advised to add a conformal coating on the PCB assembled with the LMP8602 and LMP8603. Note 7: Datasheet min/max specification limits are guaranteed by test. Note 8: Slew rate is the average of the rising and falling slew rates. Note 9: Offset voltage drift determined by dividing the change in VOS at temperature extremes into the total temperature change. Note 10: AC Common Mode Signal is a 5VPP sine-wave (0V to 5V) at the given frequency. Note 11: Positive current corresponds to current flowing into the device. Note 12: For this test input is driven from A1 stage in uni-directional mode (Offset pin connected to GND). Note 13: For VOL, RL is connected to VS and for VOH, RL is connected to GND. Note 14: 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 15: 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 LMP8602/LMP8602Q/LMP8603/LMP8603Q Block Diagram 30083405 K2 = 5 for LMP8602, K2 = 10 for LMP8603 Connection Diagram 8-Pin SOIC / MSOP 30083402 Top View Pin Descriptions Pin Name Description 2 GND Power Ground 6 VS Positive Supply Voltage 1 −IN Negative Input 8 +IN Positive Input 3 A1 Preamplifier output 4 A2 Input from the external filter network and / or A1 Offset 7 OFFSET Output 5 OUT Power Supply Inputs Filter Network DC Offset for bidirectional signals Single ended output 5 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q Ordering Information Package Part Number LMP8602MA 8-Pin SOIC LMP8602MAX LMP8602QMA LMP8602QMAX LMP8602MM 8–Pin MSOP LMP8602MMX LMP8602QMM LMP8602QMMX Package Part Number LMP8603MA 8-Pin SOIC LMP8603MAX LMP8603QMA LMP8603QMAX LMP8603MM 8–Pin MSOP LMP8603MMX LMP8603QMM LMP8603QMMX Package Marking LMP8602MA LMP8602QMA Transport Media NSC Drawing 95 Units/Rail 2.5K Units Tape and Reel 95 Units/Rail M08A 2.5K Units Tape and Reel 1k Units Tape and Reel AN3A 3.5K Units Tape and Reel 1k Units Tape and Reel AF7A MUA08A 3.5K Units Tape and Reel Package Marking LMP8603MA LMP8603QMA Transport Media NSC Drawing 95 Units/Rail 2.5K Units Tape and Reel 95 Units/Rail M08A 2.5K Units Tape and Reel 1k Units Tape and Reel AP3A 3.5K Units Tape and Reel 1k Units Tape and Reel AH7A MUA08A 3.5K Units Tape and Reel 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 Unless otherwise specified, all limits guaranteed for at TA = 25°C, VS = 5V, GND = 0V, −22V ≤ VCM ≤ 60V, and RL = ∞, Offset (Pin 7) connected to VS, 10nF between VS and GND. VOS vs. VCM at VS = 3.3V VOS vs. VCM at VS = 5V 30083424 30083425 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 30083441 30083442 Input Bias Current Over Temperature (A2 pin) at VS = 5V Input Bias Current Over Temperature (A2 pin) at VS = 5V 30083427 30083426 7 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q Typical Performance Characteristics LMP8602/LMP8602Q/LMP8603/LMP8603Q Input Referred Voltage Noise vs. Frequency PSRR vs. Frequency 30083410 30083417 Gain vs. Frequency LMP8602 Gain vs. Frequency LMP8603 30083411 30083412 CMRR vs. Frequency at VS = 3.3V CMRR vs. Frequency at VS = 5V 30083428 www.national.com 30083429 8 Step Response at VS = 5V RL = 10kΩ LMP8602 30083418 30083419 Settling Time (Falling Edge) at VS = 3.3V LMP8602 Settling Time (Falling Edge) at VS = 5V LMP8602 30083420 30083421 Settling Time (Rising Edge) at VS = 3.3V LMP8602 Settling Time (Rising Edge) at VS = 5V LMP8602 30083422 30083423 9 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q Step Response at VS = 3.3V RL = 10kΩ LMP8602 LMP8602/LMP8602Q/LMP8603/LMP8603Q Step Response at VS = 3.3V RL = 10kΩ LMP8603 Step Response at VS = 5V RL = 10kΩ LMP8603 30083443 30083444 Settling Time (Falling Edge) at VS = 3.3V LMP8603 Settling Time (Falling Edge) at VS = 5V LMP8603 30083445 30083446 Settling Time (Rising Edge) at VS = 3.3V LMP8603 Settling Time (Rising Edge) at VS = 5V LMP8603 30083447 www.national.com 30083448 10 Positive Swing vs. RLOAD VS = 5V 30083413 30083415 Negative Swing vs. RLOAD at VS = 3.3V Negative Swing vs. RLOAD at VS = 5V 30083414 30083416 Gain Drift Distribution LMP8602 5000 parts Gain Drift Distribution LMP8603 5000 parts 30083483 30083437 11 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q Positive Swing vs. RLOAD at VS = 3.3V LMP8602/LMP8602Q/LMP8603/LMP8603Q Gain error Distribution at VS = 3.3V LMP8602 5000 parts Gain error Distribution at VS = 3.3V LMP8603 5000 parts 30083484 30083438 Gain error Distribution at VS = 5V LMP8602 5000 parts Gain error Distribution at VS = 5V LMP8603 5000 parts 30083485 30083439 CMRR Distribution at VS = 3.3V 5000 parts CMRR Distribution at VS = 5V 5000 parts 30083433 30083432 www.national.com 12 LMP8602/LMP8602Q/LMP8603/LMP8603Q VOS Distribution at VS = 3.3V 5000 parts VOS Distribution at VS = 5V 5000 parts 30083434 30083435 TCVOS Distribution 5000 parts 30083436 13 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q THEORY OF OPERATION The schematic shown in Figure 1 gives a schematic representation of the internal operation of the LMP8602/ LMP8603. 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 (K1) 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 (K2) which equals a factor of 5 for the LMP8602 and a factor of 10 for the LMP8603. The output signal of the final gain stage is provided on the OUT pin. The OFFSET pin allows the output signal to be level-shifted to enable bidirectional current sensing as will be explained below. Application Information GENERAL The LMP8602 and LMP8603 are fixed gain differential voltage precision amplifiers with a gain of 50x for the LMP8602, and 100x for the LMP8603. The input common mode voltage range is -22V to +60V when operating from a single 5V supply or -4V to +27V input common mode voltage range when operating from a single 3.3V supply. The LMP8602 and LMP8603 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 LMP8602 and LMP8603 achieve very low offset, very low thermal offset drift, and very high CMRR. The LMP8602 and LMP8603 will amplify and filter small differential signals in the presence of high common mode voltages. The LMP8602/LMP8602Q/LMP8603/LMP8603Q use level shift resistors at the inputs. Because of these resistors, the LMP8602/LMP8602Q/LMP8603/LMP8603Q 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 LMP8602/LMP8602Q/LMP8603/LMP8603Q, 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. 30083405 K2 = 5 for LMP8602, K2 = 10 for LMP8603 FIGURE 1. Theory of Operation www.national.com 14 30083455 K1 = 10, K2 = 5 for LMP8602, K2 = 10 for LMP8603 FIGURE 2. Second Order Low Pass Filter 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: For any filter gain K > 1x, the design procedure can be very simple if the two capacitors are chosen to in a certain ratio. Inserting this in the above equation for Q results in: 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: Which results in: The Cutt-off frequency ωo in rad/sec (divide by 2π to get the cut-off frequency in Hz) is given by: In this case, given the predetermined value of R1 = 100 kΩ ( the internal resistor), the quality factor is set solely by the value of the resistor R2. and the quality factor of the filter is given by: 15 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q It is also possible to create an additional second order SallenKey low pass filter as shown in Figure 2 by adding external components R2, C1 and C2. Together with the internal 100 kΩ resistor R1, this circuit creates a second order lowpass filter characteristic. ADDITIONAL SECOND ORDER LOW PASS FILTER The LMP8602/LMP8602Q/LMP8603/LMP8603Q has a third order Butterworth low-pass 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. LMP8602/LMP8602Q/LMP8603/LMP8603Q For C2 the value is calculated with: R2 can be calculated based on the desired value of Q as the first step of the design procedure with the following equation: Or for a gain = 5: For the gain of 5 for the LMP8602 this results in: and for a gain = 10: For the gain of 10 for the LMP8603 this is: 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 LMP8602/LMP8602Q/LMP8603/LMP8603Q circuit chosen such that the internal poles do not affect the external second order filter. For a desired Q = 0.707 and a cut off frequency = 3 kHz, this will result for the LMP8602 in rounded values for R2 = 51 kΩ, C1 = 1.5 nF and C2 = 3.9 nF And for the LMP8603 this will result in rounded values for R2 = 22 kΩ, C1 = 3.3 nF and C2 = 0.39 nF 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: Which for the gain = 5 will give: GAIN ADJUSTMENT The gain of the LMP8602 is 50 and the gain of the LMP8603 is 100, 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 LMP8602 and the LMP8603. and for the gain = 10: 30083456 FIGURE 3. Reduce Gain www.national.com 16 and for the LMP8603: For the LMP8603: From this equation, for a desired value of the gain, the required value of Ri can be calculated for the LMP8602 with: Given a desired value of the reduced gain Gr, using this equation the required value for Rr can be calculated for the LMP8602 with: and for the LMP8603 with: and for the LMP8603 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 increases of a factor 2.5 or smaller. Increase Gain Figure 4 shows the configuration that can be used to increase the gain of the LMP8602/LMP8602Q/LMP8603/LMP8603Q. 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 for the LMP8602 becomes: 30083457 FIGURE 4. Increase Gain 17 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q Rr creates a resistive divider together with the internal 100 kΩ resistor such that, for the LMP8602, the reduced gain Gr becomes: LMP8602/LMP8602Q/LMP8603/LMP8603Q connected to the signal source. If the LMP8602/LMP8602Q/ LMP8603/LMP8603Q is driving such ADCs the sudden current that should be delivered when the sampling occurs may disturb the output signal. This effect was simulated with the circuit shown in Figure 5 where the output is to a capacitor that is driven by a rail to rail square wave. 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 from a low impedance source (Note 16) 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 50x for the LMP8602, a differential input signal of +10 mV will result in 3.0V at the output pin. similarly -10 mV at the input will result in 2.0V at the output pin. With 5V supply and a gain of 100x for the LMP8603, a differential input signal of +10 mV will result in 3.5V at the output pin. similarly -10 mV at the input will result in 1.5V at the output pin. 30083460 FIGURE 5. Driving Switched Capacitive Load This circuit simulates the switched connection of a discharged capacitor to the LMP8602/LMP8602Q/LMP8603/LMP8603Q output. The resulting VOUT disturbance signals are shown in Figure 6 and Figure 7. Note 16: The OFFSET pin has to be driven from a very low-impedance source (<10Ω). This is because the OFFSET pin internally connects directly to the resistive feedback networks of the two gain stages. When the OFFSET pin is driven from a relatively large impedance (e.g. a resistive divider between the supply rails) accuracy will decrease. POWER SUPPLY DECOUPLING In order to decouple the LMP8602/LMP8602Q/LMP8603/LMP8603Q from AC noise on the power supply, it is recommended to use a 0.1 µF bypass capacitor between the VS and GND pins. This capacitor should be placed as close as possible to the supply pins. In some cases an additional 10 µF bypass capacitor may further reduce the supply noise. 30083430 FIGURE 6. Capacitive Load Response at 3.3V LAYOUT CONSIDERATIONS The two input signals of the LMP8602/LMP8602Q/LMP8603/ LMP8603Q are differential signals and should be handled as a differential pair. For optimum performance these signals should be closely together and of equal length. Keep all impedances in both traces equal and do not allow any other signal or ground in between the traces of this signals. The connection between the preamplifier and the output buffer amplifier is a high impedance signal due to the 100 kΩ series resistor at the output of the preamplifier. Keep the traces at this point as short as possible and away from interfering signals. The LMP8602/LMP8602Q/LMP8603/LMP8603Q is available in a 8–Pin SOIC package and in a 8–Pin MSOP package. For the MSOP package, the bare board spacing at the solder pads of the package will be too small for reliable use at higher voltages (VCM > 25V) In this situation it is strongly advised to add a conformal coating on the PCB assembled with the LMP8602/LMP8602Q/LMP8603/LMP8603Q in MSOP package. 30083431 FIGURE 7. Capacitive Load Response at 5.0V DRIVING SWITCHED CAPACITIVE LOADS Some ADCs load their signal source with a sample and hold capacitor. The capacitor may be discharged prior to being www.national.com 18 lated to control the average current flowing through the inductive load which is connected to a relatively high battery voltage. The current through the load is measured across a shunt resistor RSENSE in series with the load. When the power transistor is on, current flows from the battery through the inductive load, the shunt resistor and the power transistor to ground. In this case, the common mode voltage on the shunt is close to ground. When the power transistor is off, current flows through the inductive load, through the shunt resistor and through the freewheeling diode. In this case the common mode voltage on the shunt is at least one diode voltage drop above the battery voltage. Therefore, in this application the common mode voltage on the shunt is varying between a large positive voltage and a relatively low voltage. Because the large common mode voltage range of the LMP8602/ LMP8603 and because of the high AC common mode rejection ratio, the LMP8602/LMP8603 is very well suited for this application. For this application the following example can be used for the calculation of the output signal: When using a sense resistor, RSENSE, of 0.01 Ω and a current of 1A, then the output voltage at the input pins of the LMP8602 is: RSENSE * ILOAD = 0.01 Ω * 1A = 0.01V With the gain of 50 for the LMP8602 this will give an output of 0.5V. Or in other words, VOUT = 0.5V/A. For the LMP8603 the calculation is similar, but with a gain of 100, giving an output of 1 V/A. 30083461 FIGURE 8. Reduce Error When Driving ADCs The external capacitor absorbs the charge that flows when the ADC sampling capacitor is connected. The external capacitor should be much larger than the sample and hold capacitor at the input of the ADC and the RC time constant of the external filter should be such that the speed of the system is not affected. LOW SIDE CURRENT SENSING APPLICATION WITH LARGE COMMON MODE TRANSIENTS Figure 9 illustrates a low side current sensing application with a low side driver. The power transistor is pulse width modu- 30083452 FIGURE 9. Low Side Current Sensing Application with Large Common Mode Transients 19 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q These figures can be used to estimate the disturbance that will be caused when driving a switched capacitive load. To minimize the error signal introduced by the sampling that occurs on the ADC input, an additional RC filter can be placed in between the LMP8602/LMP8602Q/LMP8603/LMP8603Q and the ADC as illustrated in Figure 8. LMP8602/LMP8602Q/LMP8603/LMP8603Q this application the common mode voltage on the shunt drops below ground when the driver is switched off. Because the common mode voltage range of the LMP8602/LMP8603 extends below the negative rail, the LMP8602/LMP8603 is also very well suited for this application. LOW SIDE CURRENT SENSING APPLICATION WITH NEGATIVE COMMON MODE TRANSIENTS Figure 10 illustrates the application of the LMP8602/ LMP8603 in a high side sensing application. This application is similar to the low side sensing discussed above, except in 30083453 FIGURE 10. High Side Current Sensing Application with Negative Common Mode Transients www.national.com 20 30083454 FIGURE 11. Battery Current Monitor Application 21 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q for such applications. If the load current of the battery is higher then the charging current, the output voltage of the LMP8602/LMP8603 will be above the “half offset voltage” for a net current flowing out of the battery. When the charging current is higher then the load current the output will be below this “half offset voltage”. BATTERY CURRENT MONITOR APPLICATION This application example shows how the LMP8602/ LMP8603 can be used to monitor the current flowing in and out a battery pack. The fact that the LMP8602/LMP8603 can measure small voltages at a high offset voltage outside the parts own supply range makes this part a very good choice LMP8602/LMP8602Q/LMP8603/LMP8603Q P8603Q is digitized with the A/D converter and used as an input for the charge controller. The charge controller can be used to regulate the charger circuit to deliver exactly the current that is required by the load, avoiding overcharging a fully loaded battery. ADVANCED BATTERY CHARGER APPLICATION The above circuit can be used to realize an advanced battery charger that has the capability to monitor the exact net current that flows in and out the battery as show in Figure 12. The output signal of the LMP8602/LMP8602Q/LMP8603/LM- 30083403 K2 = 5 for LMP8602 K2 = 10 for LMP8603 FIGURE 12. Advanced Battery Charger Application www.national.com 22 LMP8602/LMP8602Q/LMP8603/LMP8603Q Physical Dimensions inches (millimeters) unless otherwise noted 8Pin SOIC NS Package Number M08A 8Pin MSOP NS Package Number MUA08A 23 www.national.com LMP8602/LMP8602Q/LMP8603/LMP8603Q 60V Common Mode, Fixed Gain, Bidirectional Precision Current Sensing Amplifier 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® 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® Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise® Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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