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LT6106 36V Low Cost High Side Current Sense in a SOT-23 FEATURES

DESCRIPTION
The LT(R)6106 is a versatile high side current sense amplifier. Design flexibility is provided by the excellent device characteristics: 250V maximum offset and 40nA maximum input bias current. Gain for each device is set by two resistors and allows for accuracy better than 1%. The LT6106 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. The low DC offset allows for monitoring very small sense voltages. As a result, a small valued shunt resistor can be used, which minimizes the power loss in the shunt. The wide 2.7V to 44V input voltage range, high accuracy and wide operating temperature range make the LT6106 ideal for automotive, industrial and power management applications. The very low power supply current of the LT6106 also makes it suitable for low power and battery operated applications.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Gain Configurable with Two Resistors Low Offset Voltage: 250V Maximum Output Current: 1mA Maximum Supply Range: 2.7V to 36V, 44V Absolute Maximum Low Input Bias Current: 40nA Maximum PSRR: 106dB Minimum Low Supply Current: 65A Typical, V+ = 12V Operating Temperature Range: -40C to 125C Low Profile (1mm) ThinSOTTM Package
APPLICATIONS

Current Shunt Measurement Battery Monitoring Power Management Motor Control Lamp Monitoring Overcurrent and Fault Detection
TYPICAL APPLICATION
3V to 36V, 5A Current Sense with AV = 10
3V TO 36V
Measurement Accuracy vs Load Current
0.6 0.4 ACCURACY (% OF FULL SCALE) LIMIT OVER TEMPERATURE
100 0.02 +IN LOAD V- -IN
0.2 0 -0.2 -0.4 -0.6 -0.8 LIMIT OVER TEMPERATURE TYPICAL PART AT TA = 25C
LT6106
-
V+ OUT 1k
6106 TA01a
+
VOUT 200mV/A
5A FULL SCALE RIN = 100 -1.0 RSENSE = 0.02 ROUT = 1k AV = 10 V+ = 3V -1.2 0 1 3 2 LOAD CURRENT (A)
4
5
6106 TA01b
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LT6106 ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V+ to V-)..........................................44V Input Voltage (+IN to V-) ............................................ V+ (-IN to V-) ............................................ V+ Input Current........................................................-10mA Output Short-Circuit Duration .......................... Indefinite Operating Temperature Range (Note 4) LT6106C............................................... -40C to 85C LT6106H ............................................ -40C to 125C Specified Temperature Range (Note 4) LT6106C................................................... 0C to 70C LT6106H ............................................ -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C
(Note 1)
PIN CONFIGURATION
TOP VIEW OUT 1 V- 2 -IN 3 4 +IN 5 V+
S5 PACKAGE 5-LEAD PLASTIC TSOT-23 TJMAX = 150C, JA = 250C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE 0C to 70C -40C to 125C LT6106CS5#TRMPBF LT6106CS5#TRPBF LTCWK 5-Lead Plastic TSOT-23 LT6106HS5#TRMPBF LT6106HS5#TRPBF LTCWK 5-Lead Plastic TSOT-23 TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL V+ VOS VOS/T IB IOS IOUT PSRR VSENSE(MAX) AV Error VOUT(HIGH) PARAMETER Supply Voltage Range Input Offset Voltage Input Offset Voltage Drift Input Bias Current (+IN) Input Offset Current Maximum Output Current Power Supply Rejection Ratio Input Sense Voltage Full Scale Gain Error (Note 3) Output Swing High (Referred to V+) CONDITIONS
The denotes the specifications which apply over the full specified operating temperature range, otherwise specifications are at TA = 25C. V+ = 12V, V+ = VSENSE+, RIN = 100, ROUT = 10k, Gain = 100 unless otherwise noted. (Note 6)
MIN
TYP 150
MAX 36 250 350 40 65
UNITS V V V V/C nA nA nA mA dB V
2.7
VSENSE = 5mV VSENSE = 5mV V+ = 12V, 36V

1
V+ = 12V, 36V (Note 2) V+ = 2.7V to 36V, V
SENSE = 5mV
1

1 106 0.5 -0.65 -0.45 -0.25 -0.14 0 0.1 1.2 1.4
RIN = 500 (Notes 2, 7) VSENSE = 500mV, RIN = 500, ROUT VSENSE = 500mV, RIN = 500, ROUT VSENSE = 120mV = 10k, V+ = 12.5V = 10k, V+ = 36V

% % V V
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LT6106 ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER Minimum Output Voltage (Note 5) CONDITIONS VSENSE = 0mV, RIN = 100, ROUT = 10k VSENSE = 0mV, RIN = 500, ROUT = 10k, V+ = 12V, 36V BW tr IS Signal Bandwidth (-3dB) Input Step Response (to 50% of Output Step) Supply Current IOUT = 1mA, RIN = 100, ROUT = 5k VSENSE = 100mV Step, RIN = 100, ROUT = 5k, Rising Edge V+ = 2.7V, IOUT = 0A, (VSENSE = -5mV) V+ = 12V, IOUT = 0A, (VSENSE = -5mV) V+ = 36V, IOUT = 0A, (VSENSE = -5mV) 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. In addition to the Absolute Maximum Ratings, the output current of the LT6106 must be limited to insure that the power dissipation in the LT6106 does not allow the die temperature to exceed 150C. See the applications information section "Power Dissipation Considerations" for further information. Note 2: Guaranteed by the gain error test. Note 3: Gain error refers to the contribution of the LT6106 internal circuitry and does not include errors in the external gain setting resistors. Note 4: The LT6106C is guaranteed functional over the operating temperature range of -40C to 85C. The LT6106C is designed,

The denotes the specifications which apply over the full specified operating temperature range, otherwise specifications are at TA = 25C. V+ = 12V, V+ = VSENSE+, RIN = 100, ROUT = 10k, Gain = 100 unless otherwise noted.
MIN TYP 12 7
MAX 45 65 16 22
UNITS mV mV mV mV kHz s
200 3.5 60 65
85 115 95 120 100 130
A A A
70
characterized and expected to meet specified performance from -40C to 85C but is not tested or QA sampled at these temperatures. The LT6106H is guaranteed to meet specified performance from -40C to 125C. Note 5: The LT6106 output is an open collector current source. The minimum output voltage scales directly with the ratio ROUT/10k. Note 6: VSENSE+ is the voltage at the high side of the sense resistor, RSENSE. See Figure 1. Note 7: VSENSE (MAX) is the maximum sense voltage for which the Electrical Characteristics will apply. Higher voltages can affect performance but will not damage the part provided that the output current of the LT6106 does not exceed the allowable power dissipation as described in Note 1.
TYPICAL PERFORMANCE CHARACTERISTICS
VOS Distribution
CHANGE IN INPUT OFFSET VOLTAGE (V) 16 14 PERCENT OF UNITS (%) 12 10 8 6 4 2 0 -200 -120 120 -40 0 40 INPUT OFFSET VOLTAGE (V) 200
6106 G23
Input Offset Voltage vs Supply Voltage
70 60 50 40 30 20 10 0 -10 -20 -30 -40 -50 -60 -70 0 VSENSE = 5mV RIN = 100 ROUT = 10k TYPICAL UNITS 400
Input Offset Voltage vs Temperature
VSENSE = 5mV ROUT = 10k + AV = 100 300 V = 12V TYPICAL UNITS RIN = 100 200 100 0 -100 -200 -300
INPUT OFFSET VOLTAGE (V) 40
V+ = 12V VSENSE = 5mV RIN = 100 ROUT = 10k 1068 UNITS
5
10 15 20 25 30 SUPPLY VOLTAGE (V)
35
-400 -55
-25
35 65 5 95 TEMPERATURE (C)
125
6106 G03
6106 G02
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LT6106 TYPICAL PERFORMANCE CHARACTERISTICS
Gain Error vs Temperature
0 -0.10 -0.15 GAIN ERROR (%) -0.20 -0.25 -0.30 -0.35 -0.40 -0.45 -0.50 -0.55 VOUT = 1V IOUT = 1mA ROUT = 1k TYPICAL UNIT 15 35 55 75 95 115 130 TEMPERATURE (C)
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Power Supply Rejection Ratio vs Frequency
120 POWER SUPPLY REJECTION RATIO (dB) POWER SUPPLY REJECTION RATIO (dB) 110 100 90 80 70 60 50 40 30 20 10 0 100 VOUT = 0.5V VOUT = 1V VOUT = 2V 1k 10k 100k FREQUENCY (Hz) 1M
6106 G08
Power Supply Rejection Ratio vs Frequency
120 110 100 90 80 70 60 50 40 30 20 10 0 100 VOUT = 2.5V VOUT = 5V VOUT = 10V 1k 10k 100k FREQUENCY (Hz) 1M
6106 G06
-0.05
V+ = 36V V+ = 12V V+ = 5V V+ = 2.7V
V+ = 12.5V AV = 20 RIN = 100 ROUT = 2k
V+ = 12.5V AV = 20 RIN = 500 ROUT = 10k
-0.60 -45 -25 -5
Gain Error Distribution
24 22 20 PERCENT OF UNITS (%) 18 16 14 12 10 8 6 4 2 0 -0.60 -0.48 -0.36 -0.24 GAIN ERROR (%) -0.12 0
6106 G24
Gain vs Frequency
45 40 35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30 1k V+ = 12.5V VOUT = 10V VOUT = 2.5V AV = 100 RIN = 100 ROUT = 10k GAIN (dB) 45 40 35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30
Gain vs Frequency
VOUT = 10V VOUT = 2.5V V+ = 12.5V AV = 20 RIN = 500 ROUT = 10k
V+ = 12.5V VSENSE = 500mV RIN = 500 ROUT = 10k 11,072 UNITS TA = 25C
GAIN (dB)
10k
100k 1M FREQUENCY (Hz)
10M
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1k
10k
100k 1M FREQUENCY (Hz)
10M
6106 G14
Input Bias Current vs Supply Voltage
20 VSENSE = 5mV 19 RIN = 100 INPUT BIAS CURRENT (nA) 18 17 16 15 14 13 12 11 10 0 5 TA = -40C TA = 25C TA = 70C TA = 125C 10 15 20 25 30 35 40 45 50 SUPPLY VOLTAGE (V)
6106 G05
Step Response 0mV to 10mV (RIN = 100)
VSENSE 20mV/DIV VSENSE 20mV/DIV
Step Response 10mV to 20mV (RIN = 100)
VOUT 500mV/DIV VOUT 500mV/DIV 0V AV = 100 VOUT = 0V TO 1V ROUT = 10k V+ = 12V 5s/DIV
6106 G1
0V AV = 100 VOUT = 1V TO 2V ROUT = 10k V+ = 12V 5s/DIV
6106 G1
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LT6106 TYPICAL PERFORMANCE CHARACTERISTICS
Step Response 0mV to 100mV (RIN = 100)
VSENSE 200mV/DIV VSENSE 200mV/DIV
Step Response 10mV to 100mV (RIN = 100)
VSENSE 100mV/DIV
Step Response 50mV to 100mV (RIN = 500)
VOUT 2V/DIV
VOUT 2V/DIV
VOUT 500mV/DIV
0V AV = 100 5s/DIV VOUT = 0V TO 10V ROUT = 10k V+ = 12V
6106 G1
0V AV = 100 5s/DIV VOUT = 1V TO 10V ROUT = 10k V+ = 12V
6106 G1
0V AV = 20 VOUT = 1V TO 2V ROUT = 10k V+ = 12V 5s/DIV
6106 G15
Step Response 0mV to 50mV (RIN = 500)
VSENSE 100mV/DIV VSENSE 1V/DIV
Step Response 50mV to 500mV (RIN = 500)
VSENSE 1V/DIV
Step Response 0mV to 500mV (RIN = 500)
VOUT 2V/DIV VOUT 500mV/DIV 0V AV = 20 VOUT = 0V TO 1V ROUT = 10k V+ = 12V 5s/DIV
6106 G16
VOUT 2V/DIV
0V AV = 20 5s/DIV VOUT = 1V TO 10V ROUT = 10k V+ = 12V
6106 G17
0V AV = 20 5s/DIV VOUT = 0V TO 10V ROUT = 10k V+ = 12V
6106 G18
Output Voltage Swing vs Temperature
11.10 11.05 OUTPUT VOLTAGE (V) 11.00 10.95 10.90 10.85 10.80 -50 -25 V+ = 12V AV = 100 RIN = 100 ROUT = 10k VSENSE = 120mV 1100 1000 900 800 VOUT (mV) 700 600 500 400 300 200 100 50 25 75 0 TEMPERATURE (C) 100 125 0
Output Voltage vs Input Sense Voltage (0mV VSENSE 10mV)
V+ = 12V AV = 100 RIN = 100 ROUT = 10k VOUT (mV) 220 200 180 160 140 120 100 80 60 40 20 0 1 2 3 4567 VSENSE (mV) 8 9 10 0
Output Voltage vs Input Sense Voltage (0mV VSENSE 10mV)
V+ = 12V AV = 20 RIN = 500 ROUT = 10k
0
1
2
3
4567 VSENSE (mV)
8
9
10
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6106 G19
6106 G20
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LT6106 TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Input Sense Voltage (0mV VSENSE 200mV)
12 10 8 VOUT (V) VOUT (V) 6 4 2 0 0 20 40 60 80 100 120 140 160 180 200 VSENSE (mV)
6106 G21
Output Voltage vs Input Sense Voltage (0mV VSENSE 1V)
12 10 8 6 4 2 0 0 100 200 300 400 500 600 700 800 900 1000 VSENSE (mV)
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Supply Current vs Supply Voltage
120 100 SUPPLY CURRENT (A) 80 60 40 20 0 0 5 10 TA = -40C TA = 25C TA = 70C TA = 125C 15 20 25 30 35 SUPPLY VOLTAGE (V) 40 45
V+ = 12V AV = 100 RIN = 100 ROUT = 10k
V+ = 12V AV = 20 RIN = 500 ROUT = 10k
6106 G01
PIN FUNCTIONS
OUT (Pin 1): Current Output. OUT will source a current that is proportional to the sense voltage into an external resistor. V- (Pin 2): Normally Connected to Ground. -IN (Pin 3): The internal sense amplifier will drive -IN to the same potential as +IN. A resistor (RIN) tied from V+ to -IN sets the output current IOUT = VSENSE/RIN. VSENSE is the voltage developed across RSENSE. +IN (Pin 4): Must be tied to the system load end of the sense resistor, either directly or through a resistor. V+ (Pin 5): Positive Supply Pin. The V+ pin should be connected directly to either side of the sense resistor, RSENSE. Supply current is drawn through this pin. The circuit may be configured so that the LT6106 supply current is or is not monitored along with the system load current. To monitor only the system load current, connect V+ to the more positive side of the sense resistor. To monitor the total current, including that of the LT6106, connect V+ to the more negative side of the sense resistor.
BLOCK DIAGRAM
ILOAD
-
VSENSE RSENSE
+
5 RIN V+
VBATTERY
L O A D
3
4
Figure 1. LT6106 Block Diagram and Typical Connection
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+
V- 2 OUT 1
6106 F01
+IN
14k
-
IOUT VOUT = VSENSE * ROUT ROUT RIN
-IN
14k
LT6106 APPLICATIONS INFORMATION
Introduction The LT6106 high side current sense amplifier (Figure 1) provides accurate monitoring of current through a user-selected sense resistor. The sense voltage is amplified by a userselected gain and level shifted from the positive power supply to a ground-referred output. The output signal is analog and may be used as is, or processed with an output filter. 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, VSENSE/RIN, will flow through RIN. The high impedance inputs of the sense amplifier will not conduct this current, so it will flow through an internal PNP to the output pin as IOUT. The output current can be transformed into a voltage by adding a resistor from OUT to V-. The output voltage is then VO = V- + IOUT * ROUT.
Table 1. Useful Gain Configurations
GAIN 20 50 100 GAIN 20 50 100 RIN 499 200 100 RIN 249 100 50 ROUT 10k 10k 10k ROUT 5k 5k 5k VSENSE at VOUT = 5V IOUT at VOUT = 5V 250mV 500A 100mV 500A 50mV 500A VSENSE at VOUT = 2.5V IOUT at VOUT = 2.5V 125mV 500A 50mV 500A 25mV 500A
must be small enough that VSENSE does not exceed the maximum input voltage specified by the LT6106, even under peak load conditions. 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 more than 50m. 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 amplifier is limited by the input offset. As an example, the LT6106 has a typical input offset of 150V. If the minimum current is 20mA, a sense resistor of 7.5m will set VSENSE to 150V. 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 50m 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 3mA of load current. Peak dissipation is 200mW. If a 5m sense resistor is employed, then the effective current error is 30mA, while the peak sense voltage is reduced to 10mV at 2A, dissipating only 20mW. The low offset and corresponding large dynamic range of the LT6106 make it more flexible than other solutions in this respect. The 150V typical offset gives 60dB of dynamic range for a sense voltage that is limited to 150mV maximum, and over 70dB of dynamic range if the rated input maximum of 0.5V is allowed. Sense Resistor Connection Kelvin connection of the -IN and +IN inputs to the sense resistor should be used 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 x 10mm square trace of one-ounce copper is approximately 0.5m. 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
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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 measured signal, and is limited primarily by input DC offset of the internal amplifier of the LT6106. In addition, RSENSE
7
LT6106 APPLICATIONS INFORMATION
magnitude. A sense resistor with integrated Kelvin sense terminals will give the best results. Figure 2 illustrates the recommended method.
V
+
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. Selection of External Output Resistor, ROUT
RSENSE
RIN +IN -IN
LOAD V-
LT6106
Figure 2. Kelvin Input Connection Preserves Accuracy with Large Load Currents
Selection of External Input Resistor, RIN RIN should be chosen to allow the required resolution while limiting the output current to 1mA. In addition, the maximum value for RIN is 500. 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 a very wide dynamic range, a smaller RIN than the maximum current spec allows may be used if the maximum current is limited in another way, such as with a Schottky diode across RSENSE (Figure 3). This will reduce the high current measurement accuracy by limiting the result, while increasing the low current measurement resolution.
V+
RSENSE
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LOAD
Figure 3. Shunt Diode Limits Maximum Input Voltage to Allow Better Low Input Resolution Without Overranging
8
-
V+ OUT ROUT
6106 F02
+
The output resistor, ROUT, determines how the output current is converted to voltage. VOUT is simply IOUT * ROUT.
VOUT
In choosing an output resistor, the maximum output voltage must first be considered. If the following circuit 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 such 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) 100 = 0.99 * IOUT * ROUT 101
= IOUT * ROUT * 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 gain and input offset, as well as resistor matching. Ideally, the circuit output is: ROUT ; VSENSE = RSENSE * ISENSE RIN
DSENSE
VOUT = VSENSE *
In this case, the only error is due to resistor mismatch, which provides an error in gain only. However, offset voltage and bias current cause additional errors.
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LT6106 APPLICATIONS INFORMATION
Output Error Due to the Amplifier DC Offset Voltage, VOS R EOUT( VOS) = VOS * OUT RIN 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 low end of the dynamic range. The paragraph "Selection of External Current Sense Resistor" provides details. Output Error Due to the Bias Currents, IB+ and IB- The bias current IB+ flows into the positive input of the internal op amp. IB- flows into the negative input. EOUT(IBIAS) R = ROUT IB + * SENSE - IB - RIN
RSENSE V+ RIN- RIN+ +IN -IN
LOAD V-
LT6106
RIN+ = RIN- - RSENSE
Figure 4. Second Input R Minimizes Error Due to Input Bias Current
Minimum Output Voltage The curves of the Output Voltage vs Input Sense Voltage show the behavior of the LT6106 with low input sense voltages. When VSENSE = 0V, the output voltage will always be slightly positive, the result of input offset voltages and of a small amount of quiescent current (0.7A to 1.2A) flowing through the output device. The minimum output voltage in the Electrical Characteristics table include both these effects. Power Dissipation Considerations The power dissipated by the LT6106 will cause a small increase in the die temperature. This rise in junction temperature can be calculated if the output current and the supply current are known. The power dissipated in the LT6106 due to the output signal is: POUT = (VIN- - VOUT) * IOUT Since VIN- V+, POUT (V+ - VOUT) * IOUT The power dissipated due to the quiescent supply current is: PQ = IS * (V+ - V-) The total power dissipated is the output dissipation plus the quiescent dissipation: PTOTAL = POUT + PQ The junction temperature is given by: TJ = TA + JA * PTOTAL At the maximum operating supply voltage of 36V and the maximum guaranteed output current of 1mA, the total
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Assuming IB+ IB- = IBIAS, and RSENSE << RIN then: EOUT(IBIAS) -ROUT * IBIAS It is convenient to refer the error to the input: EIN(IBIAS) -RIN * IBIAS For instance if IBIAS is 60nA and RIN is 1k, the input referred error is 60V. Note that in applications where RSENSE RIN, IB+ causes a voltage offset in RSENSE that cancels the error due to IB- and EOUT(IBIAS) 0mV. In most applications, RSENSE << RIN, the bias current error can be similarly reduced if an external resistor RIN+ = (RIN - RSENSE) is connected as shown in Figure 4. Under both conditions: EIN(IBIAS) = RIN * IOS; where IOS = IB+ - IB- If the offset current, IOS, of the LT6106 amplifier is 6nA, the 60V error above is reduced to 6V. Adding RIN+ as described will maximize the dynamic range of the circuit. For less sensitive designs, RIN+ is not necessary. Output Error Due to Gain Error The LT6106 exhibits a typical gain error of -0.25% at 1mA output current. The primary source of gain error is due to the finite gain to the PNP output transistor, which results in a small percentage of the current in RIN not appearing in the output load ROUT.
-
V+ OUT ROUT
6106 F04
+
VOUT
9
LT6106 APPLICATIONS INFORMATION
power dissipation is 41mW. This amount of power dissipation will result in a 10C rise in junction temperature above the ambient temperature. It is important to note that the LT6106 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 sense resistor and RIN- and, if input fault conditions exist, external clamps. Output Filtering 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 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 * * ROUT * COUT
RSENSE +IN -IN
normal operation, VSENSE should not exceed 500mV (see VSENSE(MAX) under Electrical Characteristics). This additional constraint can be stated as V+ - (+IN) 500mV. Referring to Figure 5, feedback will force the voltages at the inputs -IN and +IN to be equal to (VS - VSENSE). Connecting V+ to the load side of the shunt results in equal voltages at +IN, -IN and V+. Connecting V+ to the supply end of the shunt results in the voltages at +IN and -IN to be VSENSE below V+. If the V+ pin is connected to the supply side of the shunt resistor the supply current drawn by the LT6106 is not included in the monitored current. If the V+ pin is connected to the load side of the shunt resistor (Figure 5), the supply current drawn by the LT6106 is included in the monitored current. It should be noted that in either configuration, the output current of the LT6106 will not be monitored since it is drawn through the RIN resistor connected to the positive side of the shunt. Contract the factory for operation of the LT6106 with a V+ outside of the recommended operating range.
VS RIN
Useful Equations Input Voltage: VSENSE = ISENSE * RSENSE Voltage Gain: VOUT R = OUT VSENSE RIN IOUT ISENSE = RSENSE RIN
LOAD
V-
LT6106
Current Gain:
Figure 5. LT6106 Supply Current Monitored with the Load
Transconductance: Transimpedance:
IOUT 1 = VSENSE RIN VOUT = RSENSE * ROUT RIN
Reverse Supply Protection Some applications may be tested with reverse-polarity supplies due to an expectation of the type of fault during operation. The LT6106 is not protected internally from 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 6). This will limit the reverse current through the LT6106. Note that this diode will limit the low voltage performance of the LT6106 by effectively reducing the supply voltage to the part by VD.
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ISENSE
Power Supply Connection For normal operation, the V+ pin should be connected to either side of the sense resistor. Either connection will meet the constraint that +IN V+ and -IN V+. During
10
-
V+ OUT VOUT ROUT
6106 F05
+
LT6106 APPLICATIONS INFORMATION
In addition, if the output of the LT6106 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 LT6106's output should be connected through a resistor or Schottky diode (Figure 7). Demo Board Demo board DC1240 is available for evaluation of the LT6106.
RSENSE R1 100 L O A D VBATT D1 LT6106 OUT R2 4.99k
6106 F06
Response Time The photos in the Typical Performance Characteristics show the response of the LT6106 to a variety of input conditions and values of RIN. The photos show that if the output current is very low or zero and an input transient occurs, there will be an increased delay before the output voltage begins changing while internal nodes are being charged.
RSENSE R1 100 VBATT
+IN V-
-IN
+IN L O A D V-
-IN
+-
V+
+-
V+
LT6106 D1
OUT
R3 1k ADC R2 4.99k
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Figure 6. Schottky Diode Prevents Damage During Supply Reversal
Figure 7. Additional Resistor R3 Protects Output During Supply Reversal
PACKAGE DESCRIPTION
S5 Package 5-Lead Plastic TSOT-23
0.62 MAX 0.95 REF
(Reference LTC DWG # 05-08-1635)
2.90 BSC (NOTE 4)
1.22 REF
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4)
PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 - 0.45 TYP 5 PLCS (NOTE 3)
0.95 BSC 0.80 - 0.90
0.20 BSC 1.00 MAX DATUM `A'
0.01 - 0.10
0.30 - 0.50 REF
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING
0.09 - 0.20 (NOTE 3)
1.90 BSC
S5 TSOT-23 0302 REV B
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
6106fa
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.
11
LT6106 TYPICAL APPLICATION
Simple 400V Current Monitor
DANGER! Lethal Potentials Present -- Use Caution ISENSE
-
+IN
VSENSE
+
-IN RIN 100
400V
RSENSE
L O A D
V-
+-
V+
DANGER!! HIGH VOLTAGE!!
LT6106
OUT
12V CMPZ12L M1 BAT46
VOUT M1 AND M2 ARE FQD3P50 ROUT VOUT = * VSENSE = 49.9 VSENSE RIN
M2 ROUT 4.99k
6106 TA02
2M
RELATED PARTS
PART NUMBER LT1787 LT6100 LTC 6101/LTC6101HV LTC6103 LTC6104
(R)
DESCRIPTION Precision Bidirectional, High Side Current Sense Amplifier Gain-Selectable High Side Current Sense Amplifier High Voltage, High Side, Precision Current Sense Amplifiers Dual High Side, Precision Current Sense Amplifier Bidirectional High Side, Precision Current Sense Amplifier
COMMENTS 75V VOS, 60V, 60A Operation 4.1V to 48V, Pin-Selectable Gain: 10, 12.5, 20, 25, 40, 50V/V 4V to 60V/5V to 100V, Gain Configurable, SOT-23 4V to 60V, Gain Configurable 8-Pin MSOP 4V to 60V, Gain Configurable 8-Pin MSOP
6106fa
12 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0807 REV A * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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