LT6105 datasheet(13/20 Pages) LINER

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LT6105

6105fa

a 20m

Ω sense resistor to give a 100mV full-scale input

to the LT6105. Input offset voltage will limit resolution to

5mA. Neglecting contact resistance at solder joints, even

one square of PC board copper at each resistor end will

cause an error of 5%. This error will grow proportionately

higher as monitored current levels rise.

Gain Setting

The gain is set with three external resistors, RIN1, RIN2,

ROUT. The gain, ROUT/RIN, can be selected from 1V/V to

100V/V as long as the maximum current does not exceed

1mA. Select Gain = ROUT/RIN2 for sense input voltage op-

eration greater than 1.6V. Select gain = ROUT/RIN1 for sense

input voltage operation less than 1.6V. The overall system

error will depend on the resistor tolerance chosen for the

application. Set RIN1= RIN2 for best accuracy across the

entire input range. The total error will be gain error of the

resistors plus the gain error of the LT6105 device.

Output Signal Range

The LT6105’s output signal is developed by current

through RIN2 (44V > V–IN > 1.6V) or RIN1 (0V < V–IN <

1.6V) conducted to the output resistor, ROUT. This current

is VSENSE/RIN2 or VSENSE/RIN1. The sense ampliﬁer’s maxi-

mum output current before gain error begins to increase

APPLICATIONS INFORMATION

is 1mA. This allows low value output resistors to be used

which helps preserve signal accuracy when the output pin

is connected to other systems.

For zero VSENSE, the internal circuitry gain will force VOUT

to VO(MIN) referred to V –. Depending on output currents,

VOUT may swing positive to within VO(MAX) referred to V+

or a maximum of 36V, a limit set by internal junction break-

down. Within these constraints, an ampliﬁed, level shifted

representation of RSENSE voltage is developed at VOUT. The

output is well behaved driving capacitive loads.

CM Input Signal Range

The LT6105 has high CMRR over the full input voltage

range. The minimum operation voltage of the sense ampli-

ﬁer inputs is 0V whether V+ is at 2.7V or 36V. The output

remains accurate even when the sense inputs are driven

to 44V. The graph in Figure 2 shows that VOS changes very

slightly over a wide input range. Furthermore, either sense

inputs VS+ and VS– can collapse to 0V without incurring any

damage to the device. The LT6105 can handle differential

sense voltages up to 44V. For example, VS+ = 44V and VS– =

0V can be a valid condition in a current monitoring applica-

tion (Figure 3) when an overload protection fuse is blown

and VS– voltage collapses to ground. Under this condition,

the output of the LT6105 goes to the positive rail, VO(MAX).

Figure 2. Input Offset Voltage vs VS+ Input Voltage

Figure 3. Current Monitoring of a Fuse Protected Circuit

OUTPUT

OUT

6105 F03

RSENSE

FUSE

LT6105

–

V–

V+

0.1 F

DC SOURCE

(≤ 44V)

TO LOAD

–IN

+IN

RIN2

ROUT

RIN1

+ INPUT VOLTAGE (V)

0.20

0.40

0.60

–0.20

–0.80

–1.00

–0.40

0.80

–0.60

6105 F02

TA = – 40°C

TA = 25°C

TA = 85°C

TA = 125°C

V+ = 12V

VSENSE = 5mV

AV = 50V/V

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