Datasheet LT6106 (Analog Devices) - 10

LT6106
APPLICATIONS INFORMATION
power dissipation is 41mW. This amount of power dis- normal operation, VSENSE should not exceed 500mV (see sipation will result in a 10°C rise in junction temperature VSENSE(MAX) under Electrical Characteristics). This ad- above the ambient temperature. ditional constraint can be stated as V+ – (+IN) ≤ 500mV. It is important to note that the LT6106 has been designed Referring to Figure 5, feedback will force the voltages at to provide at least 1mA to the output when required, and the inputs –IN and +IN to be equal to (VS – VSENSE). Con- can deliver more depending on the conditions. Care must necting V+ to the load side of the shunt results in equal be taken to limit the maximum output current by proper voltages at +IN, –IN and V+. Connecting V+ to the supply choice of sense resistor and R – end of the shunt results in the voltages at +IN and –IN to IN and, if input fault condi- tions exist, external clamps. be VSENSE below V+. If the V+ pin is connected to the supply side of the shunt
Output Filtering
resistor the supply current drawn by the LT6106 is not The output voltage, VOUT, is simply IOUT • ZOUT. This included in the monitored current. If the V+ pin is con- makes filtering straightforward. Any circuit may be used nected to the load side of the shunt resistor (Figure 5), which generates the required ZOUT to get the desired filter the supply current drawn by the LT6106 is included in response. For example, a capacitor in parallel with ROUT the monitored current. It should be noted that in either will give a lowpass response. This will reduce unwanted configuration, the output current of the LT6106 will not noise from the output, and may also be useful as a charge be monitored since it is drawn through the RIN resistor reservoir to keep the output steady while driving a switch- connected to the positive side of the shunt. Contact the ing circuit such as a MUX or ADC. This output capacitor factory for operation of the LT6106 with a V+ outside of in parallel with an output resistor will create a pole in the the recommended operating range. output response at: VS RIN f–3dB = 1 RSENSE 2 • π •ROUT •COUT +IN –IN + –
Useful Equations
LOAD V+ V– Input Voltage: VSENSE =ISENSE •RSENSE Voltage Gain: VOUT = ROUT OUT LT6106 VOUT R VSENSE RIN OUT 6106 F05 Current Gain: IOUT = RSENSE ISENSE RIN
Figure 5. LT6106 Supply Current Monitored with the Load Reverse Supply Protection
Transconductance: IOUT = 1 VSENSE RIN Some applications may be tested with reverse-polarity supplies due to an expectation of the type of fault during V R Transimpedance: OUT = R OUT operation. The LT6106 is not protected internally from SENSE • ISENSE RIN external reversal of supply polarity. To prevent damage that may occur during this condition, a Schottky diode should
Power Supply Connection
be added in series with V– (Figure 6). This will limit the For normal operation, the V+ pin should be connected to reverse current through the LT6106. Note that this diode either side of the sense resistor. Either connection will will limit the low voltage performance of the LT6106 by meet the constraint that +IN ≤ V+ and –IN ≤ V+. During effectively reducing the supply voltage to the part by VD. 6106fb 10 For more information www.linear.com/LT6106