LMP8601/LMP8601Q 60V Common Mode, Bidirectional Precision Current Sensing Amplifier General Description Features 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. 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 60V Common Mode, Bidirectional Precision Current Sensing Amplifier July 16, 2009 LMP8601/LMP8601Q 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) 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 (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 6) (Note 5) (Note 6) 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 Supply Current 0.6 1 1.3 mA AV Total Gain 19.9 20 20.1 V/V −2.7 ±20 ppm/°C Gain Drift (Note 14) −40°C ≤ TA ≤ 125°C SR Slew Rate (Note 7) VIN = ±0.165V BW Bandwidth VOS Input Offset Voltage VCM = VS / 2 TCVOS Input Offset Voltage Drift (Note 8) −40°C ≤ TA ≤ 125°C en Input Referred Voltage Noise 0.1 Hz − 10 Hz, 6 Sigma 16.4 μVP-P Spectral Density, 1 kHz 830 nV/√Hz PSRR Power Supply Rejection Ratio DC, 3.0V ≤ VS ≤ 3.6V, VCM = VS/2 0.4 0.7 V/μs 50 60 kHz 70 Mid−scale Offset Scaling Accuracy 0.15 ±1 mV 2 ±10 μV/°C 86 ±0.15 Input Referred dB ±0.5 % ±0.413 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 CMRR AC Common Mode Rejection Ratio (Note 9) f = 1 kHz 80 94 f = 10 kHz CMVR Input Common Mode Voltage Range for 80 dB CMRR A1V Gain (Note 14) RF-INT Output Impedance Filter Resistor TCRF-INT Output Impedance Filter Resistor Drift A1 VOUT A1 Output Voltage Swing dB 85 −4 V V/V 10.0 99 100 101 ±5 ±50 2 10 3.2 2 27 10.05 9.95 RL = ∞ VOL VOH www.national.com dB 3.25 kΩ ppm/°C mV V Parameter Conditions Min Typ Max (Note 6) (Note 5) (Note 6) Units Output Buffer (From A2 (pin 4) to OUT( pin 5 )) 0V ≤ VCM ≤ VS VOS Input Offset Voltage −2 −2.5 A2V Gain (Note 14) IB Input Bias Current of A2 (Note 10), A2 VOUT A2 Output Voltage Swing (Note 11, Note 12) VOL VOH 3.28 3.29 ISC Output Short-Circuit Current (Note 13) Sourcing, VIN = VS, VOUT = GND -25 -38 -60 Sinking, VIN = GND, VOUT = VS 30 46 65 1.99 5V Electrical Characteristics ±0.5 2 2.5 mV 2 2.01 V/V −40 4 RL = 100 kΩ fA ±20 nA 20 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 6) (Note 5) (Note 6) 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 Supply Current 0.7 AV Total Gain (Note 14) 19.9 1.1 1.5 mA 20 20.1 V/V −2.8 ±20 ppm/°C Gain Drift −40°C ≤ TA ≤ 125°C SR Slew Rate (Note 7) VIN = ±0.25V BW Bandwidth VOS Input Offset Voltage TCVOS Input Offset Voltage Drift (Note 8) −40°C ≤ TA ≤ 125°C eN Input Referred Voltage Noise 0.1 Hz − 10 Hz, 6 Sigma 17.5 μVP-P Spectral Density, 1 kHz 890 nV/√Hz 90 dB PSRR Power Supply Rejection Ratio 0.6 50 DC 4.5V ≤ VS ≤ 5.5V 70 Mid−scale Offset Scaling Accuracy 0.83 V/μs 60 kHz 0.15 ±1 mV 2 ±10 μV/°C ±0.15 Input Referred ±0.5 % ±0.625 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 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 DC CMRR DC Common Mode Rejection Ratio −20V ≤ VCM ≤ 60V 90 105 AC CMRR AC Common Mode Rejection Ratio (Note 9) f = 1 kHz 80 96 CMVR Input Common Mode Voltage Range for 80 dB CMRR A1V Gain (Note 14) RF-INT Output Impedance Filter Resistor TCRF-INT Output Impedance Filter Resistor Drift A1 VOUT A1 Ouput Voltage Swing f = 10 kHz dB dB 83 −22 VOH 10 10.05 V/V 99 100 101 kΩ ±5 ±50 ppm/°C 2 10 mV 4.95 3 V 9.95 RL = ∞ VOL 60 4.985 V www.national.com LMP8601/LMP8601Q Symbol LMP8601/LMP8601Q Symbol Parameter Conditions Min Typ Max (Note 6) (Note 5) (Note 6) Units Output Buffer (From A2 (pin 4) to OUT( pin 5 )) VOS Input Offset Voltage A2V Gain (Note 14) IB Input Bias Current of A2 (Note 10) A2 VOUT A2 Ouput Voltage Swing (Note 11, Note 12) ISC Output Short-Circuit Current (Note 13) 0V ≤ VCM ≤ VS −2 −2.5 ±0.5 2 2.5 mV 2 2.01 V/V 1.99 −40 VOL 4 RL = 100 kΩ fA ±20 nA 20 mV VOH 4.98 4.99 Sourcing, VIN = VS, VOUT = GND –25 –42 –60 Sinking, VIN = GND, VOUT = VS 30 48 65 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 Power Supply 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 Inputs Filter Network 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 NSC Drawing 95 Units/Rail 2.5K Units Tape and Reel 95 Units/Rail M08A 2.5K 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, −22 ≤ 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 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 Typical Performance Characteristics 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 20157112 20157111 CMRR vs. Frequency at VS = 3.3V CMRR vs. Frequency at VS = 5V 20157128 www.national.com 20157129 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 20157121 20157120 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 www.national.com 20157135 10 LMP8601/LMP8601Q TCVOS Distribution Gain Drift Distribution 20157137 20157136 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 20157133 20157132 11 www.national.com LMP8601/LMP8601Q 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. 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. 20157105 K2 = 2 FIGURE 1. Theory of Operation www.national.com 12 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: 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: 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: 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 and the quality factor of the filter is given by: 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: 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: 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: Given a desired value of the reduced gain Gr, using this equation the required value for Rr can be calculated with: www.national.com 14 From this equation, for a desired value of the gain, the required value of Ri can be calculated with: 20157157 K2 = 2 FIGURE 4. Increase Gain some cases an additional 10 µF bypass capacitor may further reduce the supply noise. 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. DRIVING SWITCHED CAPACITIVE LOADS Some ADCs load their signal source with a sample and hold capacitor. The capacitor may be discharged prior to being connected to the signal source. If the LMP8601/LMP8601Q 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. 20157160 FIGURE 5. Driving Switched Capacitive Load This circuit simulates the switched connection of a discharged capacitor to the LMP8601/LMP8601Q output. The resulting VOUT disturbance signals are shown in Figure 6 and Figure 7. Note: 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 LMP8601/LMP8601Q 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 15 www.national.com LMP8601/LMP8601Q 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. LMP8601/LMP8601Q minimize the error signal introduced by the sampling that occurs on the ADC input, an additional RC filter can be placed in between the LMP8601/LMP8601Q and the ADC as illustrated in Figure 8. 20157161 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. 20157130 FIGURE 6. Capacitive Load Response at 3.3V LOW SIDE CURRENT SENSING APPLICATION Figure 9 illustrates a low side current sensing application with a low side driver. The power transistor is pulse width modulated 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 LMP8601/LMP8601Q and because of the high AC common mode rejection ratio, the LMP8601/LMP8601Q is very well suited for this application. 20157131 FIGURE 7. Capacitive Load Response at 5.0V These figures can be used to estimate the disturbance that will be caused when driving a switched capacitive load. To www.national.com 16 LMP8601/LMP8601Q 20157152 RSENSE = 0.01Ω, K2 = 2, VOUT = 0.2 V/A FIGURE 9. Low Side Current Sensing Application on the shunt drops below ground when the driver is switched off. Because the common mode voltage range of the LMP8601/LMP8601Q extends below the negative rail, the LMP8601/LMP8601Q is also very well suited for this application. HIGH SIDE CURRENT SENSING APPLICATION Figure 10 illustrates the application of the LMP8601/LMP8601Q in a high side sensing application. This application is similar to the low side sensing discussed above, except in this application the common mode voltage 20157153 K2 = 2 FIGURE 10. High Side Current Sensing Application 17 www.national.com LMP8601/LMP8601Q for such applications. If the load current of the battery is higher then the charging current, the output voltage of the LMP8601/ LMP8601Q 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 LMP8601/LMP8601Q can be used to monitor the current flowing in and out a battery pack. The fact that the LMP8601/LMP8601Q can measure small voltages at a high offset voltage outside the parts own supply range makes this part a very good choice 20157154 K2 = 2 FIGURE 11. Battery Current Monitor Application A/D converter and used as an input for the charge controller. The Charge controller can me 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 LMP8601/LMP8601Q is digitized with the www.national.com 18 LMP8601/LMP8601Q 20157103 K2 = 2 FIGURE 12. Advanced Battery Charger Application LMP8601/LMP8601Q can be used as a current loop receiver as shown in Figure 13. CURRENT LOOP RECEIVER APPLICATION Many industrial applications use 4 to 20 mA transmitters to send a sensor’s analog value to a central control room. The 20157151 K2 = 2 FIGURE 13. Current Loop Receiver Application 19 www.national.com LMP8601/LMP8601Q Physical Dimensions inches (millimeters) unless otherwise noted 8Pin SOIC NS Package Number M08A www.national.com 20 LMP8601/LMP8601Q Notes 21 www.national.com LMP8601/LMP8601Q 60V Common Mode, Bidirectional Precision Current Sensing Amplifier Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: 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 Reference www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Solutions 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 Wireless (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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