LMP8645/LMP8645HV Precision High Voltage Current Sense Amplifier General Description Features The LMP8645 and the LMP8645HV 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 LMP8645 accepts input signals with common mode voltage range from -2V to 42V, while the LMP8645HV accepts input signal with common mode voltage range from -2V to 76V. The LMP8645 and LMP8645HV have adjustable gain for applications where supply current and high common mode voltage are the determining factors. The gain is configured with a single resistor, providing a high level of flexibility, the accuracy could be as low as 2% (max) including the gain setting resistor. 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 LMP8645 is an 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 — LMP8645 -2V to 76V — LMP8645HV 2.7V to 12V ■ Supply voltage range ■ Gain configurable with a single resistor ■ Max variable gain accuracy (with external resistor) 2.0% 200 μA/V ■ Transconductance 1 mV ■ Low offset voltage 12 μA ■ Input bias 90 dB ■ PSRR 95 dB ■ CMRR −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 30071632 LMP™ is a trademark of National Semiconductor Corporation. © 2010 National Semiconductor Corporation 300716 www.national.com LMP8645/LMP8645HV Precision High Voltage Current Sense Amplifier July 1, 2010 LMP8645/LMP8645HV LMP8645 -6V to 60V Voltage at RG pin 13.2V Voltage at OUT 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 LMP8645HV ±5000V ±2000V 200V 1250V 13.2V 6V Operating Ratings V+ Supply Voltage (VS = Temperature Range (Note 3) Package Thermal Resistance(Note 3) TSOT-6 -6V to 80V 2.7V Electrical Characteristics (Note 1) V−) 2.7V to 12V -40°C to 125°C 96°C/W (Note 4) Unless otherwise specified, all limits guaranteed for at TA = 25°C, VS=V+ – V-, V+ = 2.7V, V− = 0V, −2V < VCM < 76V, RG= 25kΩ, RL = 10 MΩ. Boldface limits apply at the temperature extremes. Symbol Parameter Condition Min Typ Max (Note 6) (Note 5) (Note 6) VOS Input Offset Voltage VCM = 2.1V -1 -1.7 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, RG = 5 kΩ 120 VSENSE(MAX) Max Input Sense Voltage (Note 9) VCM = 12V, RG = 5 kΩ 600 Gain AV Adjustable Gain Setting (Note 9) VCM = 12V Gm Transconductance VCM = 2.1V Accuracy VCM = 2.1V Gm drift(Note 9) −40°C to 125°C, VCM=2.1V 1 Power Supply Rejection Ratio VCM = 2.1V, 2.7V < CMRR Common Mode Rejection Ratio LMP8645HV 2.1V < VCM < 76V LMP8645 2.1V < VCM< 42V 95 -2V <VCM < 2V 60 −3 dB Bandwidth (Note 9) μV/°C 20 μA nV/ mV 200 V+ < 12V mV 7 100 -2 -3.4 PSRR BW 1 1.7 Units V/V µA/V 2 3.4 % 140 ppm /°C 90 dB dB 990 RG = 10 kΩ,, CG = 4 pF VSENSE = 400 mV, CL = 30 pF ,RL= 1MΩ 260 RG = 25 kΩ, CG = 4 pF, VSENSE = 200 mV, kHz CL = 30 pF, RL = 1MΩ 135 Rg = 50kΩ, CG = 4 pF, VSENSE = 100 mV, CL = 30 pF, RL = 1MΩ SR Slew Rate(Note 8, Note 9) VCM =5V, CG = 4 pF, VSENSE from 25 mV 0.5 V/µs IS Supply Current VCM = 2.1V 380 525 710 VCM = −2V 2000 2500 2700 to 175 mV, CL = 30 pF, RL = 1MΩ VOUT www.national.com Maximum Output Voltage VCM = 2.1V, Rg= 500 kΩ Minimum Output Voltage VCM = 2.1V 1.2 V 20 2 uA mV IOUT CLOAD Parameter Output current (Note 9) Condition Min Typ Max (Note 6) (Note 5) (Note 6) Sourcing, VOUT= 600mV, Rg = 150kΩ 5 Sinking, VOUT= 600mV, Rg = 150kΩ 5 Max Output Capacitance Load (Note 9) mA 30 5V Electrical Characteristics Units pF (Note 4) Unless otherwise specified, all limits guaranteed for at TA = 25°C, VS=V+-V-, V+ = 5V, V− = 0V, −2V < VCM < 76V, Rg= 25kΩ, RL = 10 MΩ. Boldface limits apply at the temperature extremes. Symbol Parameter Condition Min Typ Max (Note 6) (Note 5) (Note 6) VOS Input Offset Voltage VCM = 2.1V -1 -1.7 TCVOS Input Offset Voltage Drift(Note 7, Note 9) VCM = 2.1V IB Input Bias Current(Note 10) VCM = 2.1V 12.5 eni Input Voltage Noise (Note 9) f > 10 kHz, RG = 5 kΩ 120 VSENSE(MAX) Max Input Sense Voltage (Note 9) VCM = 12V, RG = 5 kΩ Gain AV Adjustable Gain Setting (Note 9) VCM = 12V Gm Transconductance VCM = 2.1V Accuracy VCM = 2.1V 22 μA nV/ mV 200 Gm drift (Note 9) −40°C to 125°C, VCM= 2.1V Power Supply Rejection Ratio VCM = 2.1V, , 2.7V < V+ < 12V 90 CMRR Common Mode Rejection Ratio LMP8645HV 2.1V <VCM < 76V LMP8645 2.1V <VCM< 42V 95 -2V < VCM < 2V 60 −3 dB Bandwidth (Note 9) μV/°C 100 -2 -3.4 mV 7 600 1 PSRR BW 1 1.7 Units V/V µA/V 2 3.4 % 140 ppm /°C dB dB 850 RG= 10 kΩ, CG = 4 pF VSENSE = 400 mV, CL = 30 pF, RL = 1MΩ 260 RG= 25 kΩ, CG = 4 pF, VSENSE = 300 mV, kHz CL = 30 pF, RL = 1MΩ 140 RG= 50 kΩ, CG = 4 pF, VSENSE = 300mV, CL = 30 pF, RL = 1MΩ SR Slew Rate(Note 8, Note 9) VCM = 5V, CG = 4 pF, VSENSE from 100 mV 0.5 V/µs to 500 mV, CL = 30 pF, RL= 1MΩ IS VOUT IOUT CLOAD Supply Current VCM = 2.1V 450 610 780 VCM = −2V 2100 2800 3030 Maximum Output Voltage VCM =5V, Rg= 500 kΩ 3.3 Minimum Output Voltage VCM =2.1V Output current (Note 9) Sourcing, VOUT= 1.65V, Rg= 150kΩ 5 Sinking, VOUT= 1.65V, Rg= 150kΩ 5 V 22 Max Output Capacitance Load (Note 9) 30 3 uA mV mA pF www.national.com LMP8645/LMP8645HV Symbol LMP8645/LMP8645HV 12V Electrical Characteristics (Note 4) Unless otherwise specified, all limits guaranteed for at TA = 25°C, VS=V+-V-, V+ = 12V, V− = 0V, −2V < VCM < 76V, Rg= 25kΩ, RL = 10 MΩ. Boldface limits apply at the temperature extremes. Symbol Parameter Condition Min Typ Max (Note 6) (Note 5) (Note 6) 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 13 eni Input Voltage Noise (Note 9) f > 10 kHz, RG = 5 kΩ 120 VSENSE(MAX) Max Input Sense Voltage(Note 9) VCM =12V, RG = 5 kΩ Gain AV Adjustable Gain Setting (Note 9) VCM = 12V Gm Transconductance VCM = 2.1V Accuracy VCM = 2.1V Gm drift (Note 9) −40°C to 125°C, VCM =2.1V PSRR Power Supply Rejection Ratio VCM =2.1V, 2.7V <V+ < 12V 90 CMRR Common Mode Rejection Ratio LMP8645HV 2.1V <VCM < 76V LMP8645 2.1V <VCM< 42V 95 –2V <VCM < 2V 60 BW −3 dB Bandwidth (Note 9) -1 -1.7 1 1.7 μV/°C 23 μA nV/ mV 100 200 -2 -3.4 mV 7 600 1 Units V/V µA/V 2 3.4 % 140 ppm /°C dB dB 860 RG = 10 kΩ, CG = 4 pF VSENSE = 400 mV, CL = 30 pF, RL= 1MΩ 260 RG = 25 kΩ, CG = 4 pF, VSENSE = 400 mV, kHz CL = 30 pF, RL= 1MΩ 140 RG = 50 kΩ, CG = 4 pF, VSENSE =400 mV, CL = 30 pF, RL= 1MΩ SR Slew Rate(Note 8, Note 9) VCM = 5V, CG = 4 pF, VSENSE from 100 mV 0.6 V/µs to 500 mV, CL = 30 pF, RL=1MΩ IS Supply Current VOUT VCM = 2.1V 555 765 920 VCM = −2V 2200 2900 3110 Maximum Output Voltage VCM = 12V, RG= 500kΩ Minimum Output Voltage VCM = 2.1V IOUT Output current (Note 9) Sourcing, VOUT= 5.25V, Rg= 150kΩ CLOAD Max Output Capacitance Load (Note 9) 10.2 V 24 Sinking, VOUT= 5.25V, Rg= 150kΩ uA 5 mV mA 5 30 pF Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics Tables. Note 2: Human Body Model, applicable std. MIL-STD-883, Method 3015.7. Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC) FieldInduced Charge-Device Model, applicable std. JESD22-C101-C (ESD FICDM std. of JEDEC). 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: Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of the device such that TJ = TA. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ > TA. 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: All limits are guaranteed by testing, design, or statistical analysis. Note 7: Offset voltage temperature drift is determined by dividing the change in VOS at the temperature extremes by the total temperature change. www.national.com 4 LMP8645/LMP8645HV 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 LMP8645/LMP8645HV Block Diagram 30071630 Connection Diagram 6-Pin TSOT 30071602 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 RG External Gain Resistor 6 V+ Positive Supply Voltage www.national.com 6 Package Part Number Package Marking LMP8645MK LMP8645MKE 6-Pin TSOT Transport Media AJ6A 250 Units Tape and Reel LMP8645MKX 3k Units Tape and Reel LMP8645HVMK 1k Units Tape and Reel LMP8645HVMKE NSC Drawing 1k Units Tape and Reel AK6A MK06A 250 Units Tape and Reel LMP8645HVMKX 3k Units Tape and Reel 7 www.national.com LMP8645/LMP8645HV Ordering Information LMP8645/LMP8645HV 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 30071625 30071626 AC PSRR vs. Frequency AC CMRR vs. Frequency 30071613 30071612 Gain vs. Frequency CMRR vs. VCM 30071624 30071614 www.national.com 8 Output voltage vs. VSENSE (ZOOM close to 0V) 30071617 30071616 Large Step response Small Step response 30071618 30071619 Settling time (rise) Settling time (fall) 30071621 30071620 9 www.national.com LMP8645/LMP8645HV Output voltage vs. VSENSE LMP8645/LMP8645HV Common mode step response (rise) Common mode step response (fall) 30071622 www.national.com 30071615 10 value that provides a full-scale shunt voltage range of 100 mV to 200 mV. GENERAL The LMP8645 and LMP8645HV are single supply high side current sense amplifiers with variable gain selected through an external resistor and a common mode voltage range of -2V to 42V or -2V to 76V depending on the grade. The sense voltage is amplified by a user-selected gain and level shifted from the positive power supply to a ground-referred output. SELECTION OF THE GAIN RESISTOR In the LMP8645 and LMP8645HV the gain is selected through an external resistor connected to the RG pin. Moreover the gain resistor RGAIN determines the voltage of the output buffer which is related to the supply voltage and to the common mode voltage of the input signal. The gain resistor must be chosen such that the max output voltage does not exceed the LMP8645 max output voltage rating for a given common mode voltage. The following equations explain how to select the gain resistor for various range of the input common mode voltage. 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: Case 1 −2V < VCM ≤ 1.8V The max voltage at the RG pin is given by the following inequality VRG=Vsense*RGAIN *Gm ≤ min(1.3V; Vout_max) where Vout_max is the maximum allowable output voltage according to the Electrical Tables.All the gain resistors (RGAIN) which respect the previous inequality are allowed. The graphical representation in Figure 2 helps in the selection; all the combinations (VSENSE, RGAIN) below the curve are allowed. IS′ = VSENSE/RIN = RS*IS/RIN , where RIN = 1/Gm flows entirely in the external gain resistor developing a voltage drop equal to VG = IS′ *RGAIN = (VSENSE/RIN) *RGAIN = ((RS*IS)/RIN)*RGAIN This voltage is buffered and showed at the output with a very low impedance allowing a very easy interface of the LMP8645 with other ICs (ADC, μC…). VOUT = (RS*IS)*G, where G = RGAIN/RIN 30071604 FIGURE 2. Allowed Gains for CASE 1 As a consequence once selected the gain (RGAIN) the VSENSE range is fixed too. For example if an application required a Gain of 10, RG will be 50 kΩ and VSENSE will be in the range 10 mV to 100 mV. Case 2 1.8V < VCM ≤ VS In this case the max voltage at the RG pin is related to the common mode voltage and VSENSE. So all the RGAIN resistors which respect the following inequalities are allowed: 30071603 FIGURE 1. Current monitor VRG ≤ min (Vout_max; (VCM - Vsense-250mV)) where VRG = VSENSE*RGAIN*Gm and Vout_max is the maximum allowable output voltage according to the Electrical Tables. SELECTION OF THE SHUNT RESISTOR The accuracy of the current measurement strictly depends on the value of the shunt resistor RS. Its value depends on the application and it is a compromise between small-signal accuracy and maximum permissible voltage loss in the measurement section. High values of RS provide better accuracy at lower currents by minimizing the effects of offset, while low values of RS minimize voltage loss in the supply section. For most applications, best performance is obtained with an RS The graphical representation in Figure 3 helps in the selection; all the combinations (VSENSE, RGAIN) below the curves for given VCM and supply voltage are allowed. 11 www.national.com LMP8645/LMP8645HV Application Information LMP8645/LMP8645HV 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 LMP8645 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 LMP8645 to reduce the noise and the bandwidth of the current sense. Any other filter solution which implies a capacitance connected to the RG pin is not suggested due to the high impedance of that pin. 30071605 FIGURE 3. Allowed Gains for CASE 2 Also in this case once selected the RGAIN (Gain) the VSENSE range is fixed too. Case 3 VCM ≥ VS The max voltage at the RG pin is Vout_max, it means that VOUT = VSENSE * RGAIN/RIN ≤ Vout_max where Vout_max is the maximum allowable output voltage according to the Electrical Tables.So all the RGAIN resistors which respect the previous inequality are allowed. The graphical representation in helps in the selection; all the combinations (VSENSE, RGAIN) below the curves are allowed. 30071631 FIGURE 5. LMP8645 to ADC interface SENSING CURRENT IN LED DRIVER APPLICATIONS The LMP8645 is the right choice in the applications which requires high side current sense, such as High Brightness LED for automotive where the LED's cathode has to be connected to the case (ground) of the car. In this case the classical low side current sense with a shunt resistor connected between the LED's cathode and the case doesn't guarantee the ground connection. In Figure 6, the LMP8645 monitors the current for the LM3406 a constant current buck regulator. The LMP8645 is supplied by the internal LDO of the LM3406 thorough the pin VCC, the current which flows in the LED is programmed according the following formula: IF= VCS/(RS*Gain), where Gain = RGAIN*Gm and VCS=200 mV. In this application the current which flows in the HB LED is in the range between 350 mA and 1A, so in order to reduce the power dissipation on the shunt resistor and have a good accuracy, the RS should be in the range between 50 mΩ and 200 mΩ. In the table below two examples are analyzed. 30071606 FIGURE 4. Allowed Gains for CASE 3 Also in this case once selected the RGAIN (Gain) the VSENSE range is fixed too. From the cases showed above a good way to maximize the output voltage swing of the LMP8645 is to select the max allowable Rgain according to the previous equations. For a fixed supply voltage and Vsense as the common mode voltage increases, the max allowable Rgain increases too. IF=1A RGAIN 40kΩ 36kΩ RS 77mΩ 27mΩ Dissipated Power 9.5mW Total Accuracy DRIVING ADC The input stage of an Analog to Digital converter can be modeled with a resistor and a capacitance versus ground. So if www.national.com IF=350mA 12 ≊5% 27mW ≊5% LMP8645/LMP8645HV 30071608 FIGURE 6. High Side Current Sensing in Driving HP/HB LED 13 www.national.com LMP8645/LMP8645HV Physical Dimensions inches (millimeters) unless otherwise noted TSOT-6 NS Package Number MK06A www.national.com 14 LMP8645/LMP8645HV Notes 15 www.national.com LMP8645/LMP8645HV Precision High Voltage Current Sense 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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