JAJSDJ1A June 2017 – January 2018 LMV722-Q1
PRODUCTION DATA.
The transfer function of the circuit in Figure 26 is given in Equation 1
The load current (ILOAD) produces a voltage drop across the shunt resistor (RSHUNT). The load current is set from 0 A to 1 A. To keep the shunt voltage below 100 mV at maximum load current, the largest shunt resistor is defined using Equation 2.
Using Equation 2, RSHUNT is calculated to be 100 mΩ. The voltage drop produced by ILOAD and RSHUNT is amplified by the LMV722-Q1 to produce an output voltage of roughly 0 V to 4.9 V. The gain needed by the LMV722-Q1 to produce the necessary output voltage is calculated using Equation 3:
Using Equation 3, the required gain is calculated to be 49 V/V, which is set with resistors RF and RG. Equation 4 is used to size the resistors, RF and RG, to set the gain of the LMV722-Q1 to 49 V/V.
Choosing RF as 57.6 kΩ and RG as 1.2 kΩ provides a combination that equals roughly 49 V/V. Figure 27 shows the measured transfer function of the circuit shown in Figure 26.