LTC6103 Dual High Voltage, High Side Current Sense Amplifier FEATURES DESCRIPTION ■ The LTC®6103 is a versatile, high voltage, high side, dual current sense amplifier. The two internal amplifiers are independent except that they share the same V– terminal. Design flexibility is provided by the excellent device characteristics: 450µV maximum offset, and only 275µA of current consumption (typical at 12V) for each amplifier. The LTC6103 operates on supplies from 4V to 60V. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Two Independent Current Sense Amplifiers Wide Supply Range: 4V to 60V, 70V Absolute Maximum Low Offset Voltage: 450µV Maximum Fast Response: 1µs Response Time Gain Configurable with External Resistors Low Input Bias Current: 170nA Maximum PSRR: 110dB Minimum (6V to 60V) Output Current: 1mA Maximum Low Supply Current: 275µA per Amplifier, VS = 12V Specified for –40°C to 125°C Temperature Range Available in an 8-lead MSOP Package The LTC6103 monitors current via the voltage across an external sense resistor (shunt resistor). Internal circuitry converts input voltage to output current, allowing for a small sense signal on a high common mode voltage to be translated into a ground referenced signal. Low DC offset allows the use of a small shunt resistor and large gain-setting resistors. As a result, power loss in the shunt is minimal. APPLICATIONS ■ ■ ■ ■ ■ Current Shunt Measurement Battery Monitoring Remote Sensing Power Management High Voltage Level Translator The wide operating supply range and high accuracy make the LTC6103 ideal for an extensive variety of applications from automotive to industrial and power management. The fast response makes the LTC6103 the perfect choice for load current warnings and shutoff protection control. With very low supply current, the LTC6103 is suitable for power sensitive applications. The LTC6103 is available in an 8-lead MSOP package. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Two 16-Bit Current Sense Channels Connected Directly to the LTC2436-1 ADC VA+ VSENSE ILOAD – VB+ VSENSE + LOAD + 7 +INA – 6 –INA 2 VSB OUTA V 1 4 6 1 CH1 OUTB 2 LTC2436-1 4 ROUT 4.99k IOUT = 100µA 13 7 – 5 ROUT 4.99k 5.5V 5V 5V 1µF +INB – + VSA LTC6103 ∆VSENSE– = 100mV 5 –INB + – VSENSE– LOAD RIN 100Ω RIN 100Ω 8 Step Response ILOAD 12 TO µP 11 CH0 0.5V 0V VOUT IOUT = 0µA 500ns/DIV TA = 25°C V+ = 12V RIN = 100Ω ROUT = 5k VSENSE+ = V+ 6103 TA01b 3,8,9,10,14,15,16 6103 TA01a 6103f 1 LTC6103 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) Total Supply Voltage (+INA/+INB to V–) ....................70V Maximum Applied Output Voltage (OUTA/OUTB) ........9V Input Current........................................................±10mA Output Short-Circuit Duration (to V–)............... Indefinite Operating Temperature Range LTC6103C ............................................ –40°C to 85°C LTC6103I ............................................. –40°C to 85°C LTC6103H .......................................... –40°C to 125°C Specified Temperature Range (Note 2) LTC6103C ................................................ 0°C to 70°C LTC6103I ............................................. –40°C to 85°C LTC6103H .......................................... –40°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C TOP VIEW OUTA OUTB NC V– 1 2 3 4 8 7 6 5 +INA –INA –INB +INB MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 150°C, θJA = 300°C/W ORDER PART NUMBER MS8 PART MARKING* LTC6103CMS8 LTC6103IMS8 LTC6103HMS8 LTCMN LTCMN LTCMN Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. RIN = 100Ω, ROUT = 5k, 4V ≤ +INA/+INB ≤ 60V, V– = 0V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN ● +INA(VSA)/ +INB(VSB) Supply Voltage Range VOS Input Offset Voltage VSENSE = 5mV, LTC6103 VSENSE = 5mV, LTC6103C, LTC6103I VSENSE = 5mV, LTC6103H ● ● ΔVOS/ΔT Input Offset Voltage Drift VSENSE = 5mV ● IB Input Bias Current RIN = 1M to –INA and –INB PSRR Power Supply Rejection Ratio +INA/+INB = 6V to 60V, VSENSE = 5mV +INA/+INB = 4V to 60V, VSENSE = 5mV TYP 4 ±85 MAX 60 V ±450 ±600 ±700 µV µV µV ±1.5 100 ● UNITS µV/°C 170 245 nA nA ● 110 106 120 dB dB ● 105 98 115 dB dB 8 3 1 VOUT(MAX) Maximum Output Voltage 12V ≤ +INA/+INB ≤ 60V, VSENSE = 88mV, ROUT = 10k +INA/+INB = 6V, VSENSE = 66mV, ROUT = 5k +INA/+INB = 4V, VSENSE = 55mV, ROUT = 2k ● ● ● VOUT(O) Minimum Output Voltage (Note 3) VSENSE = 0V, LTC6103 VSENSE = 0V, LTC6103C, LTC6103I VSENSE = 0V, LTC6103H ● ● IOUT(MAX) Maximum Output Current 6V ≤ +INA/+INB ≤ 60V, VSENSE = 110mV, ROUT = 2k +INA/+INB = 4V, VSENSE = 55mV, ROUT = 2k, Gain = 20 ● ● tr Input Step Response (to 50% of Output Step) ΔVSENSE = 100mV Step, 6V ≤ +INA/+INB ≤ 60V +INA/+INB = 4V (1V Output Step), ROUT = 1k 1 1.5 µs µs BW Signal Bandwidth IOUT = 200µA, RIN = 100Ω, ROUT = 5k IOUT = 1mA, RIN = 100Ω, ROUT = 5k 120 140 kHz kHz V V V 0 1 0.5 22.5 30 35 mV mV mV mA mA 6103f 2 LTC6103 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. RIN = 100Ω, ROUT = 5k, 4V ≤ +INA/+INB ≤ 60V, V– = 0V unless otherwise noted. SYMBOL PARAMETER CONDITIONS I+INA, I+INB Supply Current per Amplifier +INA/+INB = 4V, IOUT = 0, RIN = 1M MIN ● +INA/+INB = 6V, IOUT = 0, RIN = 1M ● +INA/+INB = 12V, IOUT = 0, RIN = 1M ● +INA/+INB = 60V, IOUT = 0, RIN = 1M LTC6103I, LTC6103C LTC6103H Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC6103C is guaranteed to meet specified performance from 0°C to 70°C. The LTC6103C is designed, characterized and ● ● TYP MAX UNITS 220 450 475 µA µA 255 475 525 µA µA 275 500 590 µA µA 390 640 690 720 µA µA µA expected to meet specified performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. LTC6103I is guaranteed to meet specified performance from –40°C to 85°C. The LTC6103H is guaranteed to meet specified performance from –40°C to 125°C. Note 3: This parameter is not tested in production and is guaranteed by the VOS test. TYPICAL PERFORMANCE CHARACTERISTICS Input VOS vs Temperature Input VOS vs Supply Voltage 3 REPRESENTATIVE UNITS 50 0 –50 –100 RIN = 100Ω ROUT = 5k VIN = 5mV 0 20 40 60 80 TEMPERATURE (°C) 100 120 6103 G01 INPUT OFFSET VOLTAGE (µV) INPUT OFFSET VOLTAGE (µV) 100 –200 –40 –20 5.0 150 150 –150 Input Sense Range 200 TA = 85°C RIN = 5k 4.5 ROUT = 2.5k TA = 125°C 100 MAXIMUM VSENSE (V) 200 50 TA = 45°C 0 TA = 0°C –50 TA = –40°C –100 3.5 3.0 2.5 2.0 RIN = 100Ω ROUT = 5k VIN = 5mV –150 –200 4.0 0 10 20 40 50 30 VSUPPLY AT +INA OR +INB (V) 60 1.5 1.0 4 5 6 7 8 9 10 11 12 V+ (V) 6103 G02 6103 G03 6103f 3 LTC6103 TYPICAL PERFORMANCE CHARACTERISTICS VOUT Maximum vs Temperature MAXIMUM IOUT (mA) VS = 12V 8 6 VS = 6V 4 VS = 4V 2 TA = 25°C GAIN =10 VS = 12V 6 10 10 5 VS = 60V OUTPUT ERROR (%) VS = 60V MAXIMUM OUTPUT (V) 100 7 12 4 VS = 6V 3 VS = 4V 2 1 0.1 1 0 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 0.01 0 –40 –20 100 120 0 20 40 60 80 TEMPERATURE (°C) 100 120 6103 G04 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 INPUT VOLTAGE (V) 6103 G06 6103 G05 Gain vs Frequency Input Bias Current vs Temperature Supply Current vs Supply Voltage 450 35 140 400 120 IOUT = 1mA 25 20 VS = 4V 80 15 60 10 40 TA = 25°C 5 RIN = 100Ω ROUT = 5k 0 1k 100k 10k INPUT FREQUENCY (Hz) VS = 6V TO 100V 100 IB (nA) IOUT = 200µA SUPPLY CURRENT (µA) 40 160 30 GAIN (dB) Calculated Output Error Due to Input Offset vs Input Voltage IOUT Maximum vs Temperature 20 1M 0 20 40 60 80 TEMPERATURE (°C) 100 120 250 TA = 25°C 200 TA = –40°C TA = 0°C 150 100 VIN = 0V RIN = 1M 0 0 20 30 10 40 50 VSUPPLY AT +INA OR +INB (V) 6103 G09 Step Response 0mV to 10mV 60 6103 G10 Step Response 10mV to 20mV VSENSE– V+-10mV VSENSE– + V -20mV 0.5V 0V 350 300 50 0 –40 –20 6103 G08 V+ + V -10mV TA = 125°C TA = 85°C TA = 70°C TA = 25°C V+ = 12V RIN = 100Ω ROUT = 5k VSENSE+ = V+ 1V 0.5V VOUT TA = 25°C V+ = 12V RIN = 100Ω ROUT = 5k VSENSE+ = V+ VOUT TIME (10µs/DIV) TIME (10µs/DIV) 6103 G11 6103 G12 6103f 4 LTC6103 TYPICAL PERFORMANCE CHARACTERISTICS Step Response 0mV to 100mV VSENSE Step Response 0mV to 100mV – V+ ∆VSENSE– =100mV 5V CLOAD = 10pF VSENSE Step Response Rising Edge – VSENSE– ∆VSENSE– =100mV 5V CLOAD = 1000pF TA = 25°C V+ = 12V CLOAD = 2200pF RIN = 100Ω ROUT = 5k VSENSE+ = V+ ∆VSENSE– =100mV 5.5V 5V TA = 25°C V+ = 12V RIN = 100Ω ROUT = 5k VSENSE+ = V+ VOUT IOUT = 100µA 0V VOUT TIME (10µs/DIV) 0.5V 0V VOUT TIME (100µs/DIV) IOUT = 0µA TIME (500ns/DIV) 6103 G14 6103 G13 Step Response Falling Edge 6103 G15 PSRR vs Frequency 140 V+ 5.5V 5V ∆VSENSE– =100mV 120 VOUT 100 TA = 25°C V+ = 12V RIN = 100Ω ROUT = 5k VSENSE+ = V+ IOUT = 0µA IOUT = 100µA 0.5V 0V TIME (500ns/DIV) 6103 G16 PSRR (dB) 0V TA = 25°C V+ = 12V RIN = 100Ω ROUT = 5k VSENSE+ = V+ VS = 12V 80 VS = 4V 60 RIN = 100Ω 40 ROUT = 5k COUT = 5pF 20 GAIN = 50 IOUTDC = 100µA VINAC = 50mVP-P 0 0.1 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M 6103 G17 6103f 5 LTC6103 PIN FUNCTIONS OUTA (Pin 1): Current Output of Amplifier A. OUTA will source a current that is proportional to the sense voltage of amplifier A into an external resistor. –INB (Pin 6): The Negative Input of the Internal Sense Amplifier B. The internal sense amplifier will drive –INB to the same potential as +INB. A resistor (RIN) tied from VB+ to –INB sets the output current IOUT = VSENSE/ RIN. VSENSE is the voltage developed across the external RSENSE (Figure 1). OUTB (Pin 2): Current Output of Amplifier B. OUTB will source a current that is proportional to the sense voltage of amplifier B into an external resistor. –INA (Pin 7): The Negative Input of the Internal Sense Amplifier A. The internal sense amplifier will drive –INA to the same potential as +INA. A resistor (RIN) tied from VA+ to –INA sets the output current IOUT = VSENSE/ RIN. VSENSE is the voltage developed across the external RSENSE (Figure 1). NC (Pin 3): No Connect. V– (Pin 4): Negative Supply (or Ground for Single Supply Operation). Common to both amplifiers. +INB/VSB (Pin 5): The Positive Input of the Internal Sense Amplifier B. Must be tied to the system load end of the sense resistor. It also works as the positive supply for amplifier B. Supply current of amplifier B is drawn through this pin. The LTC6103 supply current is monitored along with the system load current. +INA/VSA (Pin 8): The Positive Input of the Internal Sense Amplifier A. Must be tied to the system load end of the sense resistor. It also works as the positive supply for amplifier A. Supply current of amplifier A is drawn through this pin. The LTC6103 supply current is monitored along with the system load current. BLOCK DIAGRAM VA+ ILOAD VSENSE VSENSE RSENSE RSENSE – LOAD VB+ + + RIN 8 6 –INA 5 –INB 5k 5k ISA LOAD RIN 7 +INA ILOAD – +INB 5k 5k + – – + VSA ISB VSB 10V 10V V– OUTA 1 4 OUTB 2 6103 F01 IOUT ROUT IOUT VOUT = VSENSE • ROUT ROUT RIN Figure 1. LTC6103 Block Diagram and Typical Connection 6103f 6 LTC6103 THEORY OF OPERATION An internal sense amplifier loop forces –IN to have the same potential as +IN. Connecting an external resistor, RIN, between –IN and V+ forces a potential across RIN that is the same as the sense voltage across RSENSE. A corresponding current, (ILOAD + IS) • RSENSE/RIN, will flow through RIN. The high impedance inputs of the sense amplifier will not conduct this input current, so the current will flow through an internal MOSFET to the OUT pin. In most application cases, IS << ILOAD, so IOUT ≈ ILOAD • RSENSE/RIN. The output current can be transformed into a voltage by adding a resistor from OUT to V–. The output voltage is then VOUT = (V–) + (IOUT • ROUT). APPLICATIONS INFORMATION In this dual current sense device, amplifiers A and B are independent except for sharing the same V– pin. So supply voltage and component values can be chosen independently for each amplifier. Selection of External Current Sense Resistor The external sense resistor, RSENSE, has a significant effect on the function of a current sensing system and must be chosen with care. First, the power dissipation in the resistor should be considered. The system load current will cause both heat and voltage loss in RSENSE. As a result, the sense resistor should be as small as possible while still providing the input dynamic range required by the measurement. Note that input dynamic range is the difference between the maximum input signal and the minimum accurately reproduced signal, and is limited primarily by input DC offset of the internal amplifier of the LTC6103. As an example, an application may require that the maximum sense voltage be 100mV. If this application is expected to draw 2A at peak load, RSENSE should be no larger than 50mΩ. V 100mV RSENSE = SENSE = = 50mΩ IPEAK 2A Once the maximum RSENSE value is determined, the minimum sense resistor value will be set by the resolution or dynamic range required. The minimum signal that can be accurately represented by this sense amp is limited by the input offset. As an example, the LTC6103 has a typical input offset of 85µV. If the minimum current is 20mA, a sense resistor of 4.25mΩ will set VSENSE to 85µV. This is the same value as the input offset. A larger sense resistor will reduce the error due to offset by increasing the sense voltage for a given load current. Choosing a 50mΩ RSENSE will maximize the dynamic range and provide a system that has 100mV across the sense resistor at peak load (2A), while input offset causes an error equivalent to only 1.7mA of load current. Peak dissipation is 200mW. If instead a 5mΩ sense resistor is employed, then the effective current error is 17mA, while the peak sense voltage is reduced to 10mV at 2A, dissipating only 20mW. The low offset and corresponding large dynamic range of the LTC6103 make it more flexible than other solutions in this respect. The 85µV typical offset gives 60dB of dynamic range for a sense voltage that is limited to 85mV max, and over 75dB of dynamic range for a maximum input of 500mV. 6103f 7 LTC6103 APPLICATIONS INFORMATION Sense Resistor Connection For example, if RIN = 100Ω, then: Kelvin connections should be used between the inputs (+IN and –IN) and the sense resistor in all but the lowest power applications. Solder connections and PC board interconnections that carry high current can cause significant error in measurement due to their relatively large resistances. One 10mm × 10mm square trace of one-ounce copper is approximately 0.5mΩ. A 1mV error can be caused by as little as 2A flowing through this small interconnect. This will cause a 1% error in a 100mV signal. A 10A load current in the same interconnect will cause a 5% error for the same 100mV signal. By isolating the sense traces from the high current paths, this error can be reduced by orders of magnitude. A sense resistor with integrated Kelvin sense terminals will give the best results. Figure 2 illustrates the recommended method. Selection of External Input Resistor, RIN The external input resistor, RIN, controls the transconductance of the current sense circuit. Since: IOUT = VSENSE 1 , transconductance gm = RIN RIN LOAD RIN +IN VSENSE 100Ω or IOUT = 1mA for VSENSE = 100mV. RIN should be chosen to allow the required resolution while limiting the output current. At low supply voltage, IOUT may be as much as 1mA. By setting RIN such that the largest expected sense voltage gives IOUT = 1mA, then the maximum output dynamic range is available. Output dynamic range is limited by both the maximum allowed output current and the maximum allowed output voltage, as well as the minimum practical output signal. If less dynamic range is required, then RIN can be increased accordingly, reducing the maximum output current and power dissipation. If low sense currents must be resolved accurately in a system that has very wide dynamic range, a smaller RIN than the maximum current specification allows may be used if the maximum current is limited in another way, such as with a Schottky diode across RSENSE (Figure 3a). This will reduce the high current measurement accuracy by limiting the result, while increasing the low current measurement resolution. This approach can be helpful in cases where occasional large burst currents may be ignored. It can also be used in a multi-range configuration where a low current circuit is added to a high current circuit (Figure 3b). Note that a comparator (LTC1540) is used to select the range, and transistor M1 limits the voltage across RSENSE(LO). V+ RSENSE ILOAD IOUT = –IN + – VS V+ 1/2 OUT LTC6103 V– DSENSE RSENSE ROUT 6103 F03a LOAD 6103 F02 Figure 2. Kelvin Input Connection Preserves Accuracy Despite Large Load Current Figure 3a. Shunt Diode Limits Maximum Input Voltage to Allow Better Low Input Resolution Without Overranging 6103f 8 LTC6103 APPLICATIONS INFORMATION CMPZ4697 10k VLOGIC (3.3V TO 5V) M1 Si4465 ILOAD 7 RSENSE(LO) 100mΩ 3 RSENSE(HI) 10mΩ 4 VIN VOUT 8 8 5 40.2k 301Ω LTC1540 + – 6 4.7k 301Ω 7 6 1.74M 5 2 LTC6103 1 2 Q1 CMPT5551 1 619k HIGH CURRENT RANGE OUT 250mV/A 4 7.5k HIGH RANGE INDICATOR (ILOAD > 1.2A) BAT54C VLOGIC R5 7.5k 6103 F03b (VLOGIC + 5V) ≤ VIN ≤ 60V 0A ≤ ILOAD ≤ 10A LOW CURRENT RANGE OUT 250mV/A Figure 3b. The LTC6103 Allows High-Low Current Ranging Care should be taken when designing the printed circuit board layout to minimize input trace resistance (to Pins 5, 6, 7 and 8), especially for small RIN values. Trace resistance to the –IN terminals will increase the effective RIN value, causing a gain error. Trace resistance on +IN terminals will have an effect on offset error. These errors are described in more detail later in this data sheet. In addition, internal device resistance will add approximately 0.3Ω to RIN. Selection of External Output Resistor, ROUT The output resistor, ROUT, determines how the output current is converted to voltage. VOUT is simply IOUT • ROUT. In choosing an output resistor, the maximum output voltage must first be considered. If the circuit following is a buffer or ADC with limited input range, then ROUT must be chosen so that IOUT(MAX) • ROUT is less than the allowed maximum input range of this circuit. In addition, the output impedance is determined by ROUT. If the circuit to be driven has high enough input impedance, then almost any useful output impedance will be acceptable. However, if the driven circuit has relatively low input impedance or draws spikes of current, as an ADC might do, then a lower ROUT value may be required in order to preserve the accuracy of the output. As an example, if the input impedance of the driven circuit is 100 times ROUT, then the accuracy of VOUT will be reduced by 1% since: VOUT = IOUT • ROUT • RIN(DRIVEN) ROUT + RIN(DRIVEN) = IOUT • ROUT • 100 = 0.99 • IOUT • ROUT 101 6103f 9 LTC6103 APPLICATIONS INFORMATION Error Sources The current sense system uses an amplifier and resistors to apply gain and level shift the result. The output is then dependent on the characteristics of the amplifier, such as bias current and input offset, as well as resistor matching. Ideally, the circuit output is: VOUT = VSENSE • ROUT RIN VSENSE = RSENSE • ISENSE supply current can cause an output error if trace resistance between RSENSE and +IN is significant (Figure 4). EOUT(RT_+IN) = (IS • RT/RIN) • ROUT Trace resistance to the –IN pin will increase the effective RIN value, causing a gain error. In addition, internal device resistance will add approximately 0.3Ω to RIN. Minimizing the trace resistance is important and care should be taken in the PCB layout. Make the trace short and wide. Kelvin connection to the shunt resistor pad should be used. In this case, the only error is due to resistor mismatch, which provides an error in gain only. However, offset voltage, bias current and finite gain in the amplifier cause additional errors. V+ ILOAD RSENSE LOAD RIN Output Error, EOUT, Due to the Amplifier DC Offset Voltage, VOS EOUT( VOS) = VOS • ROUT RIN IS Since IB(+) ≈ IB(–) = IBIAS, if RSENSE << RIN then: EOUT(IBIAS) ≈ –ROUT • IBIAS For instance, if IBIAS is 100nA and ROUT is 1k, then the output error is 0.1mV. Output Error, EOUT, Due to PCB Trace Resistance +IN –IN + – 1/2 LTC6103 OUT V– ROUT 6103 F04 Output Error, EOUT, Due to Bias Currents EOUT(IBIAS) = ROUT(IB(+) • (RSENSE/RIN) – IB(–)) RT VS The DC offset voltage of the amplifier adds directly to the value of the sense voltage, VSENSE. This is the dominant error of the system and it limits the available dynamic range. The paragraph, Selection of External Current Sense Resistor provides details. The bias current IB(+) flows into the positive input of the internal op amp. IB(–) flows into the negative input. RT Figure 4. Error Due to PCB Trace Resistance Output Error, EOUT, Due to the Finite DC Open-Loop Gain, AOL, of the LTC6103 Amplifier This error is inconsequential as the AOL of the LTC6103 is very large. Design Example: If ISENSE range = (1A to 1mA) and: VOUT ISENSE = 3V 1A The LTC6103 uses the +IN pin for both the positive amplifier input and the positive supply input for the amplifier. The 6103f 10 LTC6103 APPLICATIONS INFORMATION If the power dissipation of the sense resistor is chosen to be less than 0.5W then: RSENSE ≤ 500mW ISENSE(MAX )2 = 500mΩ VSENSE(MAX) = ISENSE(MAX) • RSENSE = 500mV Gain = VOUT(MAX ) ROUT 3V = = =6 RIN VSENSE(MAX ) 500mV If the maximum output current, IOUT, is limited to 1mA: ROUT = RIN = 3V ≈ 3.01k (1% value) and 1mA 3k ≈ 499Ω (1% value) 6 The output error due to DC offset is ±510µV (typ) and the error due to offset current: IOS is 3kΩ × 100nA = ±300µV (typical) The maximum output error can therefore reach ±810µV or 0.027% (–71dB) of the output full scale. Considering the system input 60dB dynamic range (ISENSE = 1mA to 1A), the 71dB performance of the LTC6103 makes this application feasible. In many applications the power dissipation of the sense resistor is of greater importance than the precision of the measurement. Designing for a VSENSE(MAX) of as low as 100mV is recommended in such cases. The total power dissipated is the output dissipation plus the quiescent dissipation: PTOTAL = POUTA + POUTB + PQA + PQB At maximum supply and maximum output current, the total power dissipation can exceed 100mW. This will cause significant heating of the LTC6103 die. In order to prevent damage to the LTC6103, the maximum expected dissipation in each application should be calculated. This number can be multiplied by the θJA value listed in the Package/Order Information to find the maximum expected die temperature. This must not be allowed to exceed 150°C or performance may be degraded. As an example, if an LTC6103 in the MS8 package is to be run at 55V ±5V supply with 0.5mA output current in both amplifiers at 80°C: PQ(MAX) = IS(MAX) • V+ (MAX) • 2 = 82.8mW POUT(MAX) = IOUT • V+ (MAX) • 2 = 60mW TRISE = θJA • PTOTAL(MAX) = 300°C/W • (82.8mW + 60mW) ≈ 43°C TMAX = TAMBIENT + TRISE = 80°C + 43°C = 123°C TMAX must be <150°C PTOTAL(MAX) ≈ 143mW and the maximum die temperature will be 123°C POUT = (VIN– – VOUT) • IOUT If this same circuit must run at 125°C, the maximum die temperature will exceed 150°C. (Note that supply current, and therefore PQ, is proportional to temperature. Refer to the Typical Performance Characteristics.) In this condition, the maximum output current should be reduced to avoid device damage. It is important to note that the LTC6103 has been designed to provide at least 1mA to the output when required, and can deliver more depending on the conditions. Care must be taken to limit the maximum output current by proper choice of resistors and, if input fault conditions exist, external clamps. Since VIN– ≈ VS, POUT ≈ (VS – VOUT) • IOUT Output Filtering Output Current Limitations Due to Power Dissipation The LTC6103 can deliver up to 1mA continuous current to the output pin. This current flows through RIN and enters the current sense amp via the –IN pin. The power dissipated in the LTC6103 due to the output signal is: There is also power dissipated due to the quiescent supply current: PQ = IS • VS The output voltage, VOUT, is simply IOUT • ZOUT. This makes filtering straightforward. Any circuit may be used which generates the required ZOUT to get the desired filter response. For example, a capacitor in parallel with ROUT 6103f 11 LTC6103 APPLICATIONS INFORMATION will give a lowpass response. This will reduce unwanted noise from the output, and may also be useful as a charge reservoir to keep the output steady while driving a switching circuit such as a mux or ADC. This output capacitor in parallel with an output resistor will create a pole in the output response at: f–3dB = 1 2 • π • ROUT • COUT Useful Equations Input Voltage: VSENSE = ISENSE • RSENSE Voltage Gain: Current Gain: VOUT R = OUT VSENSE RIN IOUT ISENSE Transconductance: Transimpedance: = IOUT 1 = VSENSE RIN ISENSE In addition, if the output of the LTC6103 is wired to a device that will effectively short it to high voltage (such as through an ESD protection clamp) during a reverse supply condition, the LTC6103’s output should be connected through a resistor or Schottky diode (Figure 6). Response Time RSENSE RIN VOUT external reversal of supply polarity. To prevent damage that may occur during this condition, a Schottky diode should be added in series with V– (Figure 5). This will limit the reverse current through the LTC6103. Note that this diode will limit the low voltage performance of the LTC6103 by effectively reducing the supply voltage to the part by VD. = RSENSE • ROUT RIN Reverse Supply Protection The LTC6103 is designed to exhibit fast response to inputs for the purpose of circuit protection or signal transmission. This response time will be affected by the external circuit in two ways, delay and speed. If the output current is very low and an input transient occurs, there may be an increased delay before the output voltage begins changing. This can be improved by increasing the minimum output current, either by increasing RSENSE or decreasing RIN. The effect of increased output current is illustrated in the step response curves in the Typical Performance Characteristics of this data sheet. Note that the curves are labeled with respect to the initial output currents. Some applications may be tested with reverse-polarity supplies due to an expectation of this type of fault during operation. The LTC6103 is not protected internally from V+ ILOAD LOAD V+ ILOAD RSENSE RIN RSENSE 8 7 +IN LOAD RIN –IN + – VS +IN –IN + – 1/2 OUT LTC6103 VS V– 1 4 R3 1/2 OUT LTC6103 ROUT V– D1 6103 F05 Figure 5. Schottky Prevents Damage During Supply Reversal TO mP ADC D1 ROUT 6103 F06 Figure 6. Additional Resistor, R3, Protects Output During Supply Reversal 6103f 12 LTC6103 APPLICATIONS INFORMATION the ROUT resistors so that the current generated output voltage drop is developed against a different ground reference point than the LTC6103 V–, such as at an ADC within another assembly. This method provides the elimination of ground drop errors from effecting the measurement. Ground differentials that are small enough to prevent conduction of the output protection zener (>8V positive or a couple hundred mV negative) can be rejected without affecting linearity. Voltage Translator Each amplifier of the LTC6103 can be used as a high voltage level translator circuit as shown in Figure 7. In this application, the LTC6103 translates a differential voltage signal riding on top of a high common mode voltage. VIN signals get converted to a current, through RIN, and then scaled down to a ground referenced voltage across ROUT. Since the VSUPPLY must be at least 4V and the maximum input voltage is 70V, this circuit can translate differential signals with up to 66V of variation in VTRANSLATE. In the Typical Application, “±10A Differential Output Bidirectional Monitor,” the outputs are kept separate, but are treated as a differential pair. This connection allows placing ROUT resistors local to the LTC6103, and yet ground drop errors are rejected a the destination circuit as common mode voltage shift, not signal error. This connection is also shown in the application, ±10A Bidirectional H-Bridge Monitor. With the dual LTC6103, half of the device can be used to monitor a high side referenced signal and the other amplifier can be used for current sensing. Output Connection Methods The outputs of the LTC6103 are current sources and may be connected to subsequent circuitry in several ways. As a dual current sense part, each output can be used independently and in differing ways if desired. The outputs can also be tied together to drive a single ROUT as in the Typical Application, 5A Absolute Value Bidirectional Monitor, producing an additive function. In that particular circuit the two inputs are wired oppositely form the same sense resistor, so the resulting output is an absolute value signal. For applications where the destination is local to the device, ROUT resistors may be co-located with the part to form voltage sources. It is also possible to remotely locate – VIN + RIN + – VTRANSLATE VS 1/2 LTC6103 VOUT ROUT 6103 F07 Figure 7. Operation as Voltage Translator 6103f 13 LTC6103 TYPICAL APPLICATIONS 5A Absolute Value Bidirectional Current Monitor ±10A Differential Output Bidirectional Current Monitor 20mΩ 10mΩ + + VBATT 200Ω 200Ω LOAD VBATT CHARGER 200Ω 200Ω LOAD CHARGER 4V < VBATT < 60V 8 7 +INA 6 –INA 8 5 –INB + – +INB V– OUTA 1 4 OUTB LTC6103 VSB V– OUTA 1 2 VOUT 2.5V FS 4.99k +OUTPUT MAY BE TAKEN SINGLE ENDED AS CHARGE CURRENT MONITOR * –OUTPUT MAY BE TAKEN SINGLE ENDED AS DISCHARGE CURRENT MONITOR 6103 TA02 OUTB 4 DIFFERENTIAL OUTPUT* ±2.5V FS (+ IS CHARGE CURRENT) 4.99k +INB – + 2 + – 4.99k 5 –INB VSA VSB LTC6103 6 –INA + – – + VSA 7 +INA 6103 TA03 OUTPUT SWING MAY BE LIMITED FOR VBATT BELOW 6V 48V Supply Current Monitor with Isolated Output and 70V Survivability Intelligent High Side Switch with Current Monitor 10µF 63V VLOGIC 14V 47k FAULT OFF ON 3 4 8 RS LT1910 1µF +IN 6 2 1 –IN 1/2 LTC6103 OUT VO +IN – + V– V+ 4.99k V– 5 SUB85N06-5 LOAD IL LOAD RSENSE RIN 100Ω 1% –IN ISENSE + VSENSE – VS OUT 1/2 LTC6103 VLOGIC VO = 49.9 • RS • IL FOR RS = 5mΩ, VO = 2.5V AT IL = 10A (FULL SCALE) ROUT 6103 TA06 VOUT ANY OPTOISOLATOR V– 6103 TA07 N = OPTOISOLATOR CURRENT GAIN R VOUT = VLOGIC – ISENSE • SENSE • N • ROUT RIN 6103f 14 LTC6103 PACKAGE DESCRIPTION MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 0.42 ± 0.038 (.0165 ± .0015) TYP 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.65 (.0256) BSC 8 7 6 5 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0° – 6° TYP GAUGE PLANE 1 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 2 3 4 1.10 (.043) MAX 0.86 (.034) REF 0.18 (.007) SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP 0.65 (.0256) NOTE: BSC 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.127 ± 0.076 (.005 ± .003) MSOP (MS8) 0204 6103f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LTC6103 TYPICAL APPLICATION ±10A Bidirectional H-Bridge Current Monitor V+ 4V TO 60V 10mΩ 10mΩ 200Ω 8 200Ω 7 6 –INA +INA 5 + – – + VSA LTC6103 +INB –INB VSB V– OUTA 1 4 OUTB 2 + 4.99k – DIFFERENTIAL OUTPUT ±2.5V FS (MAY BE LIMITED IF V+ < 6V) ±10A FS 4.99k – + PWM* PWM* 6103 TA04 *USE “SIGN-MAGNITUDE” PWM FOR ACCURATE LOAD CURRENT CONTROL AND MEASUREMENT RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1636 Rail-to-Rail Input/Output, Micropower Op Amp VCM Extends 44V Above VEE, 55µA Supply Current, Shutdown Function LT1637/LT1638 LT1639 Single/Dual/Quad, Rail-to-Rail, Micropower Op Amp VCM Extends 44V Above VEE, 0.4V/µs Slew Rate, >1MHz Bandwidth, <250µA Supply Current per Amplifier LT1787/LT1787HV Precision, Bidirectional, High Side Current Sense Amplifier 2.7V to 60V Operation, 75µV Offset, 60µA Current Draw LTC1921 Dual –48V Supply and Fuse Monitor ±200V Transient Protection, Drives Three Optoisolators for Status LT1990 High Voltage, Gain Selectable Difference Amplifier ±250V Common Mode, Micropower, Pin Selectable Gain = 1, 10 LT1991 Precision, Gain Selectable Difference Amplifier 2.7V to ±18V, Micropower, Pin Selectable Gain = –13 to 14 LTC2050/LTC2051 LTC2052 Single/Dual/Quad Zero-Drift Op Amp 3µV Offset, 30nV/°C Drift, Input Extends Down to V– LTC4150 Coulomb Counter/Battery Gas Gauge Indicates Charge Quantity and Polarity LT6100 Gain-Selectable High Side Current Sense Amplifier 4.1V to 48V Operation, Pin-Selectable Gain: 10, 12.5, 20, 25, 40, 50V/V LTC6101/LTC6101HV High Voltage, High Side Current Sense Amplifier High Voltage 5V to 100V Operation, SOT23 LTC6104 4V to 60V Operation, Gain Configurable with External Resistors High Side Bidirectional Current Sense Amplifier 6103f 16 Linear Technology Corporation LT 0107 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007