LT6108-1/LT6108-2 High Side Current Sense Amplifier with Reference and Comparator FEATURES n n n n n n n n DESCRIPTION Current Sense Amplifier – Fast Step Response: 500ns – Low Offset Voltage: 125µV Maximum – Low Gain Error: 0.2% Maximum Internal 400mV Precision Reference Internal Comparator – Fast Response Time: 500ns – Total Threshold Error: ±1.25% Maximum – Latching or Non-Latching Comparator Option Wide Supply Range: 2.
LT6108-1/LT6108-2 ABSOLUTE MAXIMUM RATINGS (Note 1) Total Supply Voltage (V+ to V–)..................................60V Maximum Voltage (SENSELO, SENSEHI, OUTA)................................ V+ + 1V Maximum V+ – (SENSELO or SENSEHI).....................33V Maximum EN, EN/RST Voltage..................................60V Maximum Comparator Input Voltage.........................60V Maximum Comparator Output Voltage......................60V Input Current (Note 2)...........................................
LT6108-1/LT6108-2 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LT6108AIMS8-1#PBF LT6108AIMS8-1#TRPBF LTFND 8-Lead Plastic MSOP –40°C to 85°C LT6108IMS8-1#PBF LT6108IMS8-1#TRPBF LTFND 8-Lead Plastic MSOP –40°C to 85°C LT6108AHMS8-1#PBF LT6108AHMS8-1#TRPBF LTFND 8-Lead Plastic MSOP –40°C to 125°C LT6108HMS8-1#PBF LT6108HMS8-1#TRPBF LTFND 8-Lead Plastic MSOP –40°C to 125°C LT6108AIMS8-2#PBF LT6108AIMS8-2#TRPBF LTFNG 8
LT6108-1/LT6108-2 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 12V, VPULLUP = V+, VEN = VEN/RST = 2.7V, RIN = 100Ω, ROUT = R1 + R2 = 10k, gain = 100, RC = 25.5k, CL = CLC = 2pF, unless otherwise noted. (See Figure 3) SYMBOL PARAMETER V+ Supply Voltage Range IS Supply Current (Note 4) CONDITIONS MIN l TYP 2.7 V+ = 2.
LT6108-1/LT6108-2 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 12V, VPULLUP = V+, VEN = VEN/RST = 2.7V, RIN = 100Ω, ROUT = R1 + R2 = 10k, gain = 100, RC = 25.5k, CL = CLC = 2pF, unless otherwise noted.
LT6108-1/LT6108-2 TYPICAL PERFORMANCE CHARACTERISTICS Performance characteristics taken at TA = 25°C, + + V = 12V, VPULLUP = V , VEN = VEN/RST = 2.7V, RIN = 100Ω, ROUT = R1 + R2 = 10k, gain = 100, RC = 25.5k, CL = CLC = 2pF, unless otherwise noted.
LT6108-1/LT6108-2 TYPICAL PERFORMANCE CHARACTERISTICS Performance characteristics taken at TA = 25°C, + + V = 12V, VPULLUP = V , VEN = VEN/RST = 2.7V, RIN = 100Ω, ROUT = R1 + R2 = 10k, gain = 100, RC = 25.5k, CL = CLC = 2pF, unless otherwise noted.
LT6108-1/LT6108-2 TYPICAL PERFORMANCE CHARACTERISTICS Performance characteristics taken at TA = 25°C, + + V = 12V, VPULLUP = V , VEN = VEN/RST = 2.7V, RIN = 100Ω, ROUT = R1 + R2 = 10k, gain = 100, RC = 25.5k, CL = CLC = 2pF, unless otherwise noted.
LT6108-1/LT6108-2 TYPICAL PERFORMANCE CHARACTERISTICS Performance characteristics taken at TA = 25°C, + + V = 12V, VPULLUP = V , VEN = VEN/RST = 2.7V, RIN = 100Ω, ROUT = R1 + R2 = 10k, gain = 100, RC = 25.5k, CL = CLC = 2pF, unless otherwise noted. (See Figure 3) Comparator Input Bias Current vs Input Voltage Comparator Input Bias Current vs Input Voltage 10 5 0 –5 –10 125°C 25°C –40°C –15 0 20 40 COMPARATOR INPUT VOLTAGE (V) 0.75 0 –5 –10 0 0.2 0.4 0.6 0.
LT6108-1/LT6108-2 TYPICAL PERFORMANCE CHARACTERISTICS Performance characteristics taken at TA = 25°C, + + V = 12V, VPULLUP = V , VEN = VEN/RST = 2.7V, RIN = 100Ω, ROUT = R1 + R2 = 10k, gain = 100, RC = 25.5k, CL = CLC = 2pF, unless otherwise noted. (See Figure 3) LT6108-2 Comparator Step Response (5mV INC Overdrive) VINC 0.5V/DIV 0V V+ = 5V LT6108-2 Comparator Step Response (100mV INC Overdrive) VINC 0.
LT6108-1/LT6108-2 BLOCK DIAGRAMS 7 V+ LT6108-1 100Ω 8 1 SENSEHI 3k SENSELO 3k 34V – + OUTA V– 6 V– V+ V– 6V 200nA 2 EN/RST ENABLE AND RESET TIMING RESET V+ INC – 3 OVERCURRENT FLAG OUTC + V– 5 400mV REFERENCE V– 4 610812 F01 Figure 1. LT6108-1 Block Diagram (Latching Comparator) 7 V+ LT6108-2 100Ω 8 1 SENSEHI 3k SENSELO 3k 34V – + OUTA V– V– 6V 6 V– V+ 100nA OVERCURRENT FLAG OUTC + 3 V+ V– 4 INC – 2 EN 5 400mV REFERENCE V– 610812 F02 Figure 2.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION The LT6108 high side current sense amplifier provides accurate monitoring of currents through an external sense resistor. The input sense voltage is level-shifted from the sensed power supply to a ground referenced output and is amplified by a user-selected gain to the output. The output voltage is directly proportional to the current flowing through the sense resistor.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION The low offset and corresponding large dynamic range of the LT6108 make it more flexible than other solutions in this respect. The 125µV maximum offset gives 72dB of dynamic range for a sense voltage that is limited to 500mV max. Selection of External Input Gain Resistor, RIN RIN should be chosen to allow the required speed and resolution while limiting the output current to 1mA. The maximum value for RIN is 1k to maintain good loop stability.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION This approach can be helpful in cases where occasional bursts of high currents can be ignored. Care should be taken when designing the board layout for RIN, especially for small RIN values. All trace and interconnect resistances will increase the effective RIN value, causing a gain error.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION be reduced if an external resistor, RIN+, is connected as shown in Figure 5, the error is then reduced to: VOUT(IBIAS) = ±ROUT • IOS; IOS = IB+ – IB– Minimizing low current errors will maximize the dynamic range of the circuit. V+ V+ LT6108 RIN RSENSE 8 SENSEHI – 1 SENSELO + RIN+ PS = IS • V+ VOUT ROUT – 4 610812 F05 Figure 5.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION such as a MUX or ADC. This output capacitor in parallel with ROUT will create an output pole at: 1 2 • π •ROUT • CL SENSELO, SENSEHI Range The difference between VBATT (see Figure 7) and V+, as well as the maximum value of VSENSE, must be considered to ensure that the SENSELO pin doesn’t exceed the range listed in the Electrical Characteristics table. The SENSELO and SENSEHI pins of the LT6108 can function from 0.2V above the positive supply to 33V below it.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION sense voltage produces an output voltage. With a positive offset voltage, the output voltage is zero until the input sense voltage exceeds the input offset voltage. Neglecting VOS, the output circuit is not limited by saturation of pull-down circuitry and can reach 0V. Response Time The LT6108 amplifier is designed to exhibit fast response to inputs for the purpose of circuit protection or current monitoring.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION Setting Comparator Threshold The comparator has an internal 400mV precision reference. In order to set the trip point of the LT6108 comparator as configured in Figure 11, the input sense voltage at which the comparator will trip, VSENSE(TRIP) must be calculated: VSENSE(TRIP) = ISENSE(TRIP) • RSENSE The selection of RIN is discussed in the Selection of External Input Gain Resistor RIN section.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION VSUPPLY RSENSE + VSENSE RIN – LT6108-1 1 SENSELO + LOAD V ISENSE = SENSE RSENSE – V– V+ V+ C1 7 2 EN/RST VRESET OUTA 6 VPULLUP V+ 3 OUTC CLC VOUT IOUTA R2 INC 5 – RC OVERCURRENT FLAG SENSEHI 8 CL R1 400mV REFERENCE + V– 610812 F12 4 Figure 12: Comparator Configuration with Increased AV VSUPPLY VSENSE RIN – + LOAD V ISENSE = SENSE RSENSE VRESET RC SENSEHI 8 – V– V+ V+ 7 C1 2 EN/RST OUTA 6 V+ VPULLUP OVERCURRENT
LT6108-1/LT6108-2 APPLICATIONS INFORMATION This gain equation can be easily solved for R1: circuitry will have an effect on both the rising and falling input thresholds, VTH (the actual internal threshold remains unaffected). R1 = AV • RIN The value of R2 can be calculated: R2 = Figure 15 shows how to add additional hysteresis to the comparator.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION The approximate total hysteresis is: V – 390mV VHYS = 10mV +R1• DD R2 For example, to achieve IOVER = 900µA with 50mV of total hysteresis, R5 = 442Ω. Choosing R1 = 4.42k, R3 = 10k and VDD = 5V results in R2 = 513k. The analog output voltage will also be affected when the comparator trips due to the current injected into R5 by the positive feedback. Because of this, it is desirable to have (R1 + R2) >> R5.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION Power Up current. Figure 17 shows this behavior and the impact it has on VOUTA. Circuitry connected to OUTA can be protected from these transients by using an external diode to clamp VOUTA, or a capacitor to filter VOUTA. After powering on the LT6108-1, the comparator must be reset in order to guarantee a valid state at its output. Fast supply ramps may cause a supply current transient during start-up as shown in the Typical Performance Characteristics.
LT6108-1/LT6108-2 APPLICATIONS INFORMATION differentially across R1 and R2. The comparator output low voltage will also be shifted up by VD. The EN/RST pin threshold is referenced to the V– pin. In order to provide valid input levels to the LT6108 and avoid driving EN/RST below V– the negative supply of the driving circuit should be tied to V– of the LT6108. TYPICAL APPLICATIONS Overcurrent Battery Fault Protection 12 LITHIUM 40V CELL STACK IRF9640 0.
LT6108-1/LT6108-2 TYPICAL APPLICATIONS Simplified DC Motor Torque Control VMOTOR 100µF 1k 8 7 SENSEHI SENSELO V+ OUTA 6 LT6108-1 RESET 2 3 EN/RST INC 0.1Ω 1 5 CURRENT SET POINT (0V TO 5V) VOUT 0.47µF 100k 9k 5V 2 1k OUTC BRUSHED DC MOTOR (0A TO 5A) MABUCHI RS-540SH 1µF 3 V– – + 4 7 4 6 1 LTC6246 78.7k 5 V+ 6 MOD OUT LTC6992-1 3 1N5818 4 SET DIV GND 2 IRF640 100k 1M 280k 5V 610812 TA04 The figure above shows a simplified DC motor control circuit.
LT6108-1/LT6108-2 TYPICAL APPLICATIONS LT6108-2 with External Latch and Power-On Reset or Disconnect 5V 7 V+ LT6108-2 RIN 100Ω 8 R3 10k RSENSE 1 SENSEHI – SENSELO + V+ OUTA 6 ILOAD V– V+ 3 INC 5 – OUTC + R1 24.9k VTH R7 9.53k R8 499Ω 400mV REFERENCE V– R9* 30k Q1* 2N2222 C1 0.1µF VDD R4* 3.4k R5* 100k R2 200k 4 610812 TA06 R6 1M An external latch is implemented with positive feedback. R6 and C1 provide a reset pulse on power-up.
LT6108-1/LT6108-2 TYPICAL APPLICATIONS Precision Power-On Reset Using TimerBlox Circuit 5V 7 V+ LT6108-1 RIN 100Ω 8 R3 10k RSENSE 1 SENSEHI – SENSELO + ILOAD V+ OUTA 6 V– R1 9.53k V+ R8 100k C1 0.1µF 3 1 SECOND DELAY ON START-UP 10µs RESET PULSE GENERATOR TRIG OUT LTC6994-1 V+ GND TRIG OUT LTC6993-1 GND V+ SET R7 191k DIV R6 1M R5 681k SET DIV 2 C2 0.
LT6108-1/LT6108-2 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660 Rev F) 0.889 ±0.127 (.035 ±.005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 ±0.102 (.118 ±.004) (NOTE 3) 0.65 (.0256) BSC 0.42 ± 0.038 (.0165 ±.0015) TYP 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 ±.
LT6108-1/LT6108-2 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DCB Package 8-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1718 Rev A) 0.70 ±0.05 1.35 ±0.05 3.50 ±0.05 1.65 ±0.05 2.10 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.45 BSC 1.35 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.115 TYP R = 0.05 5 TYP 2.00 ±0.10 (2 SIDES) 0.40 ±0.10 8 1.35 ±0.10 1.65 ±0.10 3.
LT6108-1/LT6108-2 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 12/12 Addition of A-grade Performance and Electrical Characteristics Addition of A-grade Order Information Clarification to Absolute Maximum Short Circuit Duration Clarification to nomenclature used in Typical Performance Characteristics 1, 3, 4, 5, 12, 13, 16 (Fig10), 28 2 2 6, 7, 9 Clarification to Description of EN/RST Pin Function 10 Internal Reference Block redrawn for consistency 11, 13, 18, 19 Additional information pro
LT6108-1/LT6108-2 TYPICAL APPLICATION ADC Driving Application IN SENSE HIGH SENSE LOW 0.1Ω OUT 0.1µF VCC VREF 100Ω 8 SENSEHI SENSELO 7 VCC 10k V+ RESET 2 OUTA LT6108-1 6 OUTC IN+ 8.66k EN/RST 3 COMP 1 V– INC LTC2470 TO MCU 0.1µF 5 4 1.33k OVERCURRENT 6108 TA05 The low sampling current of the LTC2470 16-bit delta sigma ADC is ideal for the LT6108. RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1787 Bidirectional High Side Current Sense Amplifier 2.