Datasheet LT6107 (Analog Devices) - 10

LT6107 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 addi- above the ambient temperature. tional constraint can be stated as V+ – (+IN) ≤ 500mV. It is important to note that the LT6107 has been designed Referring to Figure 5, feedback will force the voltages to provide at least 1mA to the output when required, and at the inputs –IN and +IN to be equal to (VS – VSENSE). can deliver more depending on the conditions. Care must Connecting 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 con- ditions 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 LT6107 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 LT6107 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 LT6107 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 LT6107 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 1 f–3dB RSENSE +IN –IN 2 • • ROUT • COUT + – LOAD
Useful Equations
V+ V– Input Voltage: VSENSE ISENSE • RSENSE V R OUT LT6107 VOUT Voltage Gain: OUT OUT ROUT VSENSE RIN 6107 F05 I R Current Gain: OUT SENSE
Figure 5. LT6107 Supply Current Monitored with the Load
ISENSE RIN I 1
Reverse Supply Protection
Transconductance: OUT V Some applications may be tested with reverse-polarity SENSE RIN V R supplies due to an expectation of the type of fault during Transimpedance: OUT R OUT operation. The LT6107 is not protected internally from I SENSE • R SENSE IN external reversal of supply polarity. To prevent damage that may occur during this condition, a Schottky diode
Power Supply Connection
should be added in series with V– (Figure 6). This will For normal operation, the V+ pin should be connected to limit the reverse current through the LT6107. Note that either side of the sense resistor. Either connection will this diode will limit the low voltage performance of the meet the constraint that +IN ≤ V+ and –IN ≤ V+. During LT6107 by effectively reducing the supply voltage to the part by VD. 6107fc 10 For more information www.linear.com/LT6107