LINEAR TECHNOLOGY LT6106 Technical data

LT6106

36V Low Cost High Side

Current Sense in a SOT-23

FEATURES

■

Gain Conﬁ gurable with Two Resistors

■

Low Offset Voltage: 250μV 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: 65μA Typical, V+ = 12V

■

Operating Temperature Range: –40°C to 125°C

■

Low Proﬁ le (1mm) ThinSOTTM Package

APPLICATIONS

■

Current Shunt Measurement

■

Battery Monitoring

■

Power Management

■

Motor Control

■

Lamp Monitoring

■

Overcurrent and Fault Detection

DESCRIPTION

The LT®6106 is a versatile high side current sense ampliﬁ er. Design ﬂ exibility is provided by the excellent device characteristics: 250μV 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.

TYPICAL APPLICATION

3V to 36V, 5A Current Sense with AV = 10

3V TO 36V

LOAD

100Ω

–

+

–

V

LT6106

0.02Ω

–IN+IN

+

V

OUT

6106 TA01a

Measurement Accuracy vs Load Current

0.6

0.4

0.2

0

–0.2

–0.4

–0.6

–0.8

ACCURACY (% OF FULL SCALE)

–1.0

V

OUT

200mV/A

1k

–1.2

LIMIT OVER TEMPERATURE

TYPICAL PART AT TA = 25°C

LIMIT OVER TEMPERATURE

5A FULL SCALE

= 0.02Ω

R

SENSE

= 10

A

V

0

RIN = 100Ω

= 1k

R

OUT +

= 3V

V

13

2

LOAD CURRENT (A)

4

5

6106 TA01b

6106fa

1

LT6106

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS

(Note 1)

Supply Voltage (V+ to V–)..........................................44V

–

Input Voltage (+IN to V

) ............................................ V

(–IN to V–) ............................................ V

Input Current ........................................................–10mA

Output Short-Circuit Duration .......................... Indeﬁ nite

Operating Temperature Range (Note 4)

LT6106C ............................................... –40°C to 85°C

+ +

OUT 1

TOP VIEW

–

2

V

–IN 3

S5 PACKAGE

5-LEAD PLASTIC TSOT-23

T

= 150°C, θJA = 250°C/W

JMAX

5 V

4 +IN

+

LT6106H ............................................ –40°C to 125°C

Speciﬁ ed Temperature Range (Note 4)

LT6106C ................................................... 0°C to 70°C

LT6106H ............................................ –40°C to 125°C

Storage Temperature Range ................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec) ..................300°C

ORDER INFORMATION

Lead Free Finish

TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT6106CS5#TRMPBF LT6106CS5#TRPBF LTCWK 5-Lead Plastic TSOT-23 0°C to 70°C LT6106HS5#TRMPBF LT6106HS5#TRPBF LTCWK 5-Lead Plastic TSOT-23 –40°C to 125°C TRM = 500 pieces. *Temperature grades are identiﬁ ed by a label on the shipping container. Consult LTC Marketing for parts speciﬁ ed with wider operating temperature ranges.

Consult LTC Marketing for information on lead based ﬁ nish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel speciﬁ cations, go to: http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS

The ● denotes the speciﬁ cations which apply over the full speciﬁ ed operating temperature range, otherwise speciﬁ cations are at TA = 25°C. V+ = 12V, V+ = V

SENSE

+, R

= 100Ω, R

IN

= 10k, Gain = 100

OUT

unless otherwise noted. (Note 6)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

+

V

OS

/ΔT Input Offset Voltage Drift V

ΔV

OS

I

B

I

OS

I

OUT

PSRR Power Supply Rejection Ratio V

V

SENSE(MAX)

Error Gain Error (Note 3) V

A

V

OUT(HIGH)

Supply Voltage Range

Input Offset Voltage V

Input Bias Current (+IN) V+ = 12V, 36V

Input Offset Current V+ = 12V, 36V 1 nA

Maximum Output Current (Note 2)

Input Sense Voltage Full Scale RIN = 500Ω (Notes 2, 7)

Output Swing High (Referred to V

+

)

= 5mV

SENSE

= 5mV

SENSE

+

= 2.7V to 36V, V

= 500mV, RIN = 500Ω, R

SENSE

= 500mV, RIN = 500Ω, R

V

SENSE

= 120mV

V

SENSE

= 5mV

= 10k, V+ = 12.5V

OUT

= 10k, V+ = 36V

OUT

●

2.7 36 V

●

1mA

●

106 dB

●

0.5 V

●

–0.65 –0.25 0 %

●

–0.45 –0.14 0.1 %

●

150 250

350

1μV/°C

40 65

1.2

1.4

μV μV

nA nA

6106fa

2

V V

LT6106

ELECTRICAL CHARACTERISTICS

The ● denotes the speciﬁ cations which apply over the full speciﬁ ed operating temperature range, otherwise speciﬁ cations are at TA = 25°C. V+ = 12V, V+ = V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Output Voltage (Note 5)

BW Signal Bandwidth (–3dB) I

t

r

Input Step Response (to 50% of Output Step)

I

S

Supply Current V+ = 2.7V, I

= 0mV, RIN = 100Ω, R

V

SENSE

V

= 0mV, RIN = 500Ω, R

SENSE

= 1mA, RIN = 100Ω, R

OUT

ΔV

= 100mV Step, RIN = 100Ω, R

SENSE

Rising Edge

= 0μA, (V

OUT

+

= 12V, I

V

V+ = 36V, I

= 0μA, (V

OUT

= 0μA, (V

OUT

SENSE

= 10k

OUT

= 10k, V+ = 12V, 36V

OUT

= 5k 200 kHz

OUT

= 5k,

OUT

= –5mV)

SENSE

= –5mV)

SENSE

+, R

●

= 100Ω, R

IN

= 10k, Gain = 100

OUT

12 45

65

71622mV

3.5 μs

60 85

115

65 95

120

70 100

130

mV mV

mV

μA

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 150°C. 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.

characterized and expected to meet speciﬁ ed performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. The LT6106H is guaranteed to meet speciﬁ ed performance from –40°C to 125°C.

Note 5: The LT6106 output is an open collector current source. The minimum output voltage scales directly with the ratio R

Note 6: V R

Note 7: V

. See Figure 1.

SENSE

SENSE (MAX)

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.

Note 4: The LT6106C is guaranteed functional over the operating temperature range of –40°C to 85°C. The LT6106C is designed,

TYPICAL PERFORMANCE CHARACTERISTICS

Input Offset Voltage vs

VOS Distribution

V+ = 12V

16

14

12

10

8

6

PERCENT OF UNITS (%)

4

2

0

= 5mV

V

SENSE

= 100Ω

R

IN

= 10k

R

OUT

1068 UNITS

–120

–200

INPUT OFFSET VOLTAGE (μV)

–40 0

40

120

200

6106 G23

Supply Voltage

70

V

SENSE

60

= 100Ω

R

IN

50

R

OUT

40

TYPICAL UNITS

30 20 10

0 –10 –20 –30 –40 –50

CHANGE IN INPUT OFFSET VOLTAGE (μV)

–60 –70

0

= 5mV

= 10k

5

10

SUPPLY VOLTAGE (V)

20

25

15

30

/10k.

OUT

+

is the voltage at the high side of the sense resistor,

is the maximum sense voltage for which the Electrical

Input Offset Voltage vs Temperature

35

6106 G02

400

V

SENSE +

= 12V

V

300

= 100Ω

R

IN

200

100

0

–100

–200

INPUT OFFSET VOLTAGE (μV)

–300

40

–400

–55

–25 5

R

= 5mV

OUT

= 100

A

V

TYPICAL UNITS

TEMPERATURE (°C)

= 10k

35 65

125

95

6106 G03

6106fa

3

LT6106

0

TYPICAL PERFORMANCE CHARACTERISTICS

Gain Error vs Temperature

0

–0.05

–0.10

–0.15

–0.20

–0.25

–0.30

–0.35

GAIN ERROR (%)

–0.40

–0.45

V

= 1V

OUT

= 1mA

I

–0.50

OUT

= 1k

R

OUT

–0.55

TYPICAL UNIT

–0.60

–45

–25

15

–5

TEMPERATURE (°C)

Gain Error Distribution

24

V+ = 12.5V

22

20

18

16

14

12

10

8

PERCENT OF UNITS (%)

6

4

2

0 –0.60

= 500mV

V

SENSE

= 500Ω

R

IN

= 10k

R

OUT

11,072 UNITS

= 25°C

T

A

–0.48

–0.36

GAIN ERROR (%)

V+ = 36V

V+ = 12V

V+ = 5V

V+ = 2.7V

35

55 75 95 115 130

–0.24

–0.12

6106 G04

6106 G24

Power Supply Rejection Ratio vs Frequency

120

110

100

90

80

70

60

50

40

30

V

20

POWER SUPPLY REJECTION RATIO (dB)

10

0

100 10k 100k 1M

= 0.5V

OUT

V

= 1V

OUT

= 2V

V

OUT

1k

FREQUENCY (Hz)

V+ = 12.5V A R R

Gain vs Frequency

45 40 35 30 25 20 15 10

5

GAIN (dB)

0

–5 –10 –15 –20 –25 –30

V

= 10V

OUT

V

= 2.5V

OUT

1k 100k 1M 10M

10k

FREQUENCY (Hz)

V+ = 12.5V A

V

R

IN

R

OUT

= 20

V

= 100Ω

IN OUT

= 100

= 100Ω

= 10k

= 2k

6106 G08

6106 G09

Power Supply Rejection Ratio vs Frequency

120

110

100

90

80

70

60

50

40

30

V

20

POWER SUPPLY REJECTION RATIO (dB)

10

0

100 10k 100k 1M

= 2.5V

OUT

= 5V

V

OUT

= 10V

V

OUT

1k

FREQUENCY (Hz)

V+ = 12.5V A R R

Gain vs Frequency

45 40 35 30 25 20 15 10

5

GAIN (dB)

0

–5 –10 –15 –20 –25 –30

1k 100k 1M 10M

V

OUT

V

= 2.5V

OUT

10k

FREQUENCY (Hz)

= 10V

V+ = 12.5V A

V

R

IN

R

OUT

= 20

V

= 500Ω

IN OUT

= 20

= 500Ω

= 10k

6106 G06

6106 G14

Input Bias Current vs Supply Voltage

20

V

= 5mV

SENSE

19

= 100Ω

R

IN

18

17

16

15

14

13

INPUT BIAS CURRENT (nA)

12

11

10

105

0

2015

SUPPLY VOLTAGE (V)

4

30 35 45

25

TA = –40°C

= 25°C

T

A

= 70°C

T

A

= 125°C

T

A

40

6106 G05

50

V

SENSE

20mV/DIV

V

OUT

500mV/DIV

Step Response 0mV to 10mV (RIN = 100Ω)

0V

V R V

OUT OUT

+

= 12V

= 0V TO 1V = 10k

5μs/DIVAV = 100

6106 G1

V

SENSE

20mV/DIV

V

OUT

500mV/DIV

Step Response 10mV to 20mV (RIN = 100Ω)

0V

V R V

= 100

V OUT OUT

+

= 12V

= 1V TO 2V = 10k

5μs/DIVA

6106 G1

6106fa

TYPICAL PERFORMANCE CHARACTERISTICS

5

6

7

8

LT6106

V

SENSE

200mV/DIV

V

OUT

2V/DIV

V

SENSE

100mV/DIV

V

OUT

500mV/DIV

Step Response 0mV to 100mV (RIN = 100Ω)

0V

= 100

V

= 0V TO 10V

V

OUT

= 10k

R

OUT +

= 12V

V

5μs/DIVA

Step Response 0mV to 50mV (RIN = 500Ω)

0V

V R V

= 20

V OUT OUT

+

= 12V

= 0V TO 1V

= 10k

5μs/DIVA

6106 G1

V

SENSE

200mV/DIV

V

OUT

2V/DIV

V

SENSE

1V/DIV

V

OUT

2V/DIV

0V

Step Response 10mV to 100mV (RIN = 100Ω)

0V

V R V

OUT OUT

+

= 12V

= 1V TO 10V = 10k

5μs/DIVAV = 100

Step Response 50mV to 500mV (RIN = 500Ω)

V R V

= 20

V OUT

OUT

+

= 12V

= 1V TO 10V = 10k

5μs/DIVA

6106 G1

V

SENSE

100mV/DIV

V

OUT

500mV/DIV

V

SENSE

1V/DIV

V

OUT

2V/DIV

Step Response 50mV to 100mV (RIN = 500Ω)

0V

V R V

= 20

V OUT OUT

+

= 12V

= 1V TO 2V = 10k

5μs/DIVA

Step Response 0mV to 500mV (RIN = 500Ω)

0V

V R V

= 20

V OUT OUT

+

= 12V

= 0V TO 10V = 10k

5μs/DIVA

6106 G1

Output Voltage Swing vs Temperature

11.10 V+ = 12V

= 100

A

V

11.05

11.00

10.95

10.90

OUTPUT VOLTAGE (V)

10.85

10.80

–50

= 100Ω

R

IN

R

OUT

V

SENSE

–25 0

= 10k

= 120mV

TEMPERATURE (°C)

50 100 125

25 75

Output Voltage vs Input Sense Voltage (0mV ≤ V

1100

V+ = 12V

1000

= 100

A

V

= 100Ω

R

IN

900

800

700

600

(mV)

500

OUT

V

400

300

200

100

6106 G07

= 10k

R

OUT

0

2

0

3

1

4

V

SENSE

5

(mV)

≤ 10mV)

6

7

89

6106 G19

10

Output Voltage vs Input Sense Voltage (0mV ≤ V

220

V+ = 12V

200

= 20

A

V

= 500Ω

R

IN

180

160

140

120

(mV)

100

OUT

V

= 10k

R

OUT

80

60

40

20

0

1

2

SENSE

3

4

5

V

(mV)

SENSE

≤ 10mV)

6

7

89

6106 G20

6106fa

10

5

LT6106

TYPICAL PERFORMANCE CHARACTERISTICS

Output Voltage vs Input Sense Voltage (0mV ≤ V

12

V+ = 12V

= 100

A

V

10

= 100Ω

R

IN

= 10k

R

OUT

8

(V)

6

OUT

V

4

2

0

40 80 120 160

V

SENSE

(mV)

≤ 200mV)

200200 60 100 140 180

6106 G21

Output Voltage vs Input Sense Voltage (0mV ≤ V

12

V+ = 12V

= 20

A

V

10

= 500Ω

R

IN

= 10k

R

OUT

8

(V)

6

OUT

V

4

2

0

200 400 600 800

V

SENSE

PIN FUNCTIONS

OUT (Pin 1):

that is proportional to the sense voltage into an external resistor.

V– (Pin 2):

–IN (Pin 3):

the same potential as +IN. A resistor (R to –IN sets the output current I is the voltage developed across R

Current Output. OUT will source a current

Normally Connected to Ground.

The internal sense ampliﬁ er will drive –IN to

) tied from V

IN

OUT

= V

SENSE

SENSE/RIN

.

. V

SENSE

+

≤ 1V)

SENSE

(mV)

V+ (Pin 5):

10001000 300 500 700 900

6106 G22

Positive Supply Pin. The V+ pin should be con-

nected directly to either side of the sense resistor, R

Supply Current vs Supply Voltage

120

100

80

60

40

SUPPLY CURRENT (μA)

20

0

515

0

10

SUPPLY VOLTAGE (V)

25 45

20

30

TA = –40°C

= 25°C

T

A

= 70°C

T

A

= 125°C

T

A

35

40

6106 G01

SENSE

. Supply current is drawn through this pin. The circuit may be conﬁ gured 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.

+IN (Pin 4):

Must be tied to the system load end of the

sense resistor, either directly or through a resistor.

BLOCK DIAGRAM

I

LOAD

V

SENSE

+

–

R

SENSE

L

O

A

D

R

IN

–IN

3

+IN

4

14k

Figure 1. LT6106 Block Diagram and Typical Connection

6

V

BATTERY

5

+

V

–

+

I

–

V

2

OUT

6106 F01

OUT

V

1

= V

OUT

R

OUT

SENSE

R

OUT

• R

IN

6106fa

APPLICATIONS INFORMATION

LT6106

Introduction

The LT6106 high side current sense ampliﬁ er (Figure 1) provides accurate monitoring of current through a user-selected sense resistor. The sense voltage is ampliﬁ ed 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 ﬁ lter.

Theory of Operation

An internal sense ampliﬁ er loop forces –IN to have the same potential as +IN. Connecting an external resistor,

, between –IN and V+ forces a potential across RIN

R

IN

that is the same as the sense voltage across R corresponding current, V

SENSE/RIN

, will ﬂ ow through RIN.

SENSE

. A

The high impedance inputs of the sense ampliﬁ er will not conduct this current, so it will ﬂ ow through an internal PNP to the output pin as I

OUT

.

The output current can be transformed into a voltage by

–

adding a resistor from OUT to V

–

= V

+ I

then V

O

Table 1. Useful Gain Conﬁ gurations

GAIN R

20 499Ω 10k 250mV 500μA 50 200Ω 10k 100mV 500μA

100 100Ω 10k 50mV 500μA

GAIN R

20 249Ω 5k 125mV 500μA 50 100Ω 5k 50mV 500μA

100 50Ω 5k 25mV 500μA

IN

• R

OUT

R

OUTVSENSE

R

OUTVSENSE

OUT

.

at V

. The output voltage is

at V

= 5V I

OUT

= 2.5V I

OUT

at V

OUT

= 5V

= 2.5V

must be small enough that V

does not exceed the

SENSE

maximum input voltage speciﬁ ed 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, R

Once the maximum R

should be no more than 50mΩ.

SENSE

value is determined, the mini-

SENSE

mum sense resistor value will be set by the resolution or dynamic range required. The minimum signal that can be accurately represented by this sense ampliﬁ er is limited by the input offset. As an example, the LT6106 has a typical input offset of 150μV. If the minimum current is 20mA, a sense resistor of 7.5mΩ will set V

to 150μV. This is

SENSE

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 R

will maximize the dynamic range and provide a

SENSE

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 5mΩ 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 ﬂ exible than other solutions in this respect. The 150μV 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.

Selection of External Current Sense Resistor

The external sense resistor, R

, has a signiﬁ cant ef-

SENSE

fect 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 R

. As a result, the sense resistor

SENSE

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 ampliﬁ er of the LT6106. In addition, R

SENSE

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 signiﬁ cant 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 ﬂ owing 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

6106fa

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

R

LOAD

IN

–IN+IN

–

+

–

V

LT6106

V

OUT

+

6106 F02

IN

V

OUT

R

OUT

R

SENSE

Figure 2. Kelvin Input Connection Preserves Accuracy with Large Load Currents

Selection of External Input Resistor, R

RIN should be chosen to allow the required resolution while limiting the output current to 1mA. In addition, the maximum value for R the largest expected sense voltage gives I

is 500Ω. By setting RIN such that

IN

= 1mA, then

OUT

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 R

can be increased

IN

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 R

than the maximum current spec allows may

IN

be used if the maximum current is limited in another way, such as with a Schottky diode across R

SENSE

(Figure 3). 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 bursts of high currents can be ignored.

Care should be taken when designing the board layout for

, especially for small RIN values. All trace and inter-

R

IN

connect resistances will increase the effective R

value,

IN

causing a gain error.

Selection of External Output Resistor, R

The output resistor, R rent is converted to voltage. V

, determines how the output cur-

OUT

is simply I

OUT

• R

OUT

.

In choosing an output resistor, the maximum output voltage must ﬁ rst be considered. If the following circuit is a buffer or ADC with limited input range, then R chosen so that I

OUT(MAX)

• R

is less than the allowed

OUT

must be

OUT

maximum input range of this circuit.

In addition, the output impedance is determined by R

OUT

. 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 R

value may be required in order

OUT

to preserve the accuracy of the output. As an example, if the input impedance of the driven circuit is 100 times R then the accuracy of V

RR

VI

OUT OUT

=

• RR

OUT IN DRIVEN

IIR IR

•• .••

OUT OUT OUT OUT

will be reduced by 1% since:

OUT

•

OUT IN DRIVEN

()

+

()

100

099=

101

OUT

,

Error Sources

The current sense system uses an ampliﬁ er and resistors to apply gain and level shift the result. The output is then dependent on the characteristics of the ampliﬁ er, such as gain and input offset, as well as resistor matching.

+

V

R

SENSE

LOAD

Figure 3. Shunt Diode Limits Maximum Input Voltage to Allow Better Low Input Resolution Without Overranging

6106 F03

D

SENSE

8

Ideally, the circuit output is:

R

VV

==•; •

OUT SENSE

OUT

VRI

R

SENSE SENSE SENSE

IN

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.

6106fa

APPLICATIONS INFORMATION

Output Error Due to the Ampliﬁ er DC Offset Voltage, V

EV

The DC offset voltage of the ampliﬁ er adds directly to the value of the sense voltage, V error of the system and it limits the low end of the dynamic range. The paragraph “Selection of External Current Sense Resistor” provides details.

OS

OUT VOS OS

()

R

OUT

•= R

IN

. This is the dominant

SENSE

R

SENSE

V

LOAD

LT6106

+

–

R

IN

+

R

IN

+

–

V

LT6106

+

–

= R

– R

R

IN

SENSE

–IN+IN

–

+

V

OUT

6106 F04

V

OUT

R

OUT

Output Error Due to the Bias Currents, I

The bias current I internal op amp. I

E

OUT(IBIAS)

Assuming I

E

OUT(IBIAS)

+

B

+

ﬂ ows into the positive input of the

B

–

ﬂ ows into the negative input.

B

⎛

R

+

= R

≅ I

≅ –R

OUTIB

–

= I

B

OUT

⎜ ⎝

BIAS

• I

•

, and R

BIAS

SENSE

R

IN

SENSE

B

–

–I

B

<< RIN then:

+

and I

⎞ ⎟

⎠

–

B

It is convenient to refer the error to the input:

E

IN(IBIAS)

For instance if I error is 60μV. Note that in applications where R R

, I

IN

B

error due to I tions, R reduced if an external resistor R

≅ –RIN • I

BIAS

+

causes a voltage offset in R

SENSE

–

B

<< RIN, the bias current error can be similarly

BIAS

is 60nA and RIN is 1k, the input referred

that cancels the

SENSE

and E

OUT(IBIAS)

≅ 0mV. In most applica-

+

= (RIN – R

IN

SENSE

≅

) is

connected as shown in Figure 4. Under both conditions:

+

E

IN(IBIAS)

= ±RIN • IOS; where I

OS

= I

–

– I

B

If the offset current, IOS, of the LT6106 ampliﬁ er is 6nA, the 60μV error above is reduced to 6μV.

Adding R range of the circuit. For less sensitive designs, R

+

as described will maximize the dynamic

IN

+

is

not necessary.

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 V

= 0V, the output voltage will always

SENSE

be slightly positive, the result of input offset voltages and of a small amount of quiescent current (0.7μA to 1.2μA) ﬂ owing 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:

P

OUT

Since V

= (V

IN

–

≅ V+, P

– V

) • I

OUT

≅ (V+ – V

OUT

) • I

OUT

–

The power dissipated due to the quiescent supply current is:

= IS • (V+ – V–)

P

Q

The total power dissipated is the output dissipation plus the quiescent dissipation:

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 ﬁ nite gain to the PNP output transistor, which results in a small percentage of the current in R output load R

OUT

.

not appearing in the

IN

P

TOTAL

= P

OUT

+ P

Q

The junction temperature is given by:

= TA + θJA • P

T

J

TOTAL

At the maximum operating supply voltage of 36V and the maximum guaranteed output current of 1mA, the total

6106fa

9

LT6106

APPLICATIONS INFORMATION

power dissipation is 41mW. This amount of power dissipation will result in a 10°C 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 R

and, if input fault con-

IN

ditions exist, external clamps.

Output Filtering

The output voltage, V

, is simply I

OUT

• Z

OUT

. This makes ﬁ ltering straightforward. Any circuit may be used which generates the required Z sponse. For example, a capacitor in parallel with R

to get the desired ﬁ lter re-

OUT

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

dB

–

3

2=π

•• •

1

RC

OUT OUT

Useful Equations

normal operation, V V

SENSE(MAX)

under Electrical Characteristics). This ad-

ditional constraint can be stated as V

should not exceed 500mV (see

SENSE

+

– (+IN) ≤ 500mV. Referring to Figure 5, feedback will force the voltages at the inputs –IN and +IN to be equal to (V

+

Connecting V voltages at +IN, –IN and V

to the load side of the shunt results in equal

+

. Connecting V+ to the supply

S

– V

SENSE

).

end of the shunt results in the voltages at +IN and –IN to be V

If the V

below V+.

SENSE

+

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 conﬁ guration, the output current of the LT6106 will not be monitored since it is drawn through the R

resistor

IN

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.

V

S

R

IN

R

SENSE

LOAD

–

+

–

V

–IN+IN

+

V

Input Voltage: V

Voltage

GGain:

Current Gain:

Transcond

Transimpedance:

V

I

SENSE

uuctance:

= IR

SENSE

V

OUT

SENSE

OUT

SENSE SENSE

R

OUT

=

R

IN

R

SENSE

=

R

IN

I

OUT

VR

V

UUT

O

I

SENSE

=

SENSE IN

R

= •

SENSE

•

1

R

OUT

R

IN

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

OUT

6106 F05

V

OUT

R

OUT

LT6106

Figure 5. LT6106 Supply Current Monitored with the Load

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

6106fa

.

D

effectively reducing the supply voltage to the part by V

APPLICATIONS INFORMATION

LT6106

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.

L

O

A

D

Figure 6. Schottky Diode Prevents Damage During Supply Reversal

–

V

D1

LT6106

R

+

SENSE

R1 100Ω

–IN+IN

V

OUT

+

V

BATT

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 R

. The photos show that if the output cur-

IN

rent 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.

R

SENSE

R1 100Ω

–IN+IN

–

LT 6 1 0 6

+

–

L

V

O A D

D1

V

OUT

+

R3

1k

R2

4.99k

Figure 7. Additional Resistor R3 Protects Output During Supply Reversal

V

BATT

ADC

6106 F07

PACKAGE DESCRIPTION

0.62 MAX

3.85 MAX

2.62 REF

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.20 BSC

DATUM ‘A’

0.30 – 0.50 REF

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DRAWING NOT TO SCALE

3. DIMENSIONS ARE INCLUSIVE OF PLATING

S5 Package

5-Lead Plastic TSOT-23

0.95 REF

(Reference LTC DWG # 05-08-1635)

1.22 REF

1.50 – 1.75

(NOTE 3)

2.80 BSC (NOTE 4)

PIN ONE

0.95 BSC

0.80 – 0.90

1.00 MAX

1.4 MIN

0.09 – 0.20

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

2.90 BSC (NOTE 4)

1.90 BSC

0.30 – 0.45 TYP 5 PLCS (NOTE 3)

0.01 – 0.10

S5 TSOT-23 0302 REV B

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

I

SENSE

Simple 400V Current Monitor

DANGER! Lethal Potentials Present — Use Caution

V

SENSE

+–

R

SENSE

R

IN

100Ω

–IN+IN

400V

L O A D

–

V

LT6106

M1 AND M2 ARE FQD3P50

R

OUT

V

= • V

OUT

SENSE

R

IN

+

–

= 49.9 V

V

OUT

SENSE

+

V

OUT

M1

R

OUT

4.99k

6106 TA02

DANGER!!

HIGH VOLTAGE!!

12V CMPZ12L

BAT46

M2

2M

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®

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OS

12

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

●

www.linear.com

6106fa

LT 0807 REV A • PRINTED IN USA

LINEAR TECHNOLOGY LT6106 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual