SBOSAG6 November 2023 OPA2994-Q1
ADVANCE INFORMATION
Refer to the PDF data sheet for device specific package drawings
The transfer function of the circuit in Figure 7-1 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 OPA994-Q1 to produce an output voltage of 0 V to 4.9 V. The gain needed by the OPA994-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 OPA994-Q1 to 49 V/V.
Choosing RF as 5.76 kΩ, RG is calculated to be 120 Ω. RF and RG were chosen as 5.76 kΩ and 120 Ω because they are standard value resistors that create a 49:1 ratio. Other resistors that create a 49:1 ratio can also be used. However, excessively large resistors will generate thermal noise that exceeds the intrinsic noise of the op amp. Figure 7-2 shows the measured transfer function of the circuit shown in Figure 7-1.