LT6106

10

Rev. C

For more information www.analog.com

APPLICATIONS INFORMATION

power dissipation is 41mW. This amount of power dis-

sipation 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 RIN– and, if input fault condi-

tions 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 switch-

ing 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: VOUT

VSENSE

=

ROUT

RIN

Current Gain: IOUT

ISENSE

=

RSENSE

RIN

Transconductance: IOUT

VSENSE

=

1

RIN

Transimpedance:

VOUT

ISENSE

= RSENSE •

ROUT

RIN

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

normal operation, VSENSE should not exceed 500mV (see

VSENSE(MAX) under Electrical Characteristics). This ad-

ditional 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). Con-

necting 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 con-

nected 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. Contact the

factory for operation of the LT6106 with a V+ outside of

the recommended operating range.

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

externalreversalofsupplypolarity.Topreventdamagethat

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.

LT6106

ROUT

VOUT

6106 F05

RIN

VS

LOAD

RSENSE

V+

V–

OUT

–IN

+IN