SBOS836C March 2020 – March 2021 TLV9041 , TLV9042 , TLV9044
PRODUCTION DATA
The transfer function of the circuit in Figure 9-1 is given in Equation 1.
The load current (I_{LOAD}) produces a voltage drop across the shunt resistor (R_{SHUNT}). 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 shown using Equation 2.
Using Equation 2, R_{SHUNT} is calculated to be 100 mΩ. The voltage drop produced by I_{LOAD} and R_{SHUNT} is amplified by the TLV904x to produce an output voltage of approximately 0 V to 4.9 V. The gain needed by the TLV904x 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 R_{F} and R_{G}. Equation 4 sizes the resistors R_{F} and R_{G}, to set the gain of the TLV904x to 49 V/V.
Selecting R_{F} as 57.6 kΩ and R_{G} as 1.2 kΩ provides a combination that equals 49 V/V. Figure 9-2 shows the measured transfer function of the circuit shown in Figure 9-1. Notice that the gain is only a function of the feedback and gain resistors. This gain is adjusted by varying the ratio of the resistors and the actual resistors values are determined by the impedance levels that the designer wants to establish. The impedance level determines the current drain, the effect that stray capacitance has, and a few other behaviors. There is no optimal impedance selection that works for every system; you must choose an impedance that is ideal for your system parameters.