Design Steps

1. Calculate gain (G) for a given I_LOAD and shunt resistor.
   Equation 2. $G=\frac{I_{LOAD}\times R_{SHUNT}}{V_{IN}}=\frac{600mA\times 10\Omega }{5V}=1.2V/V$
2. Ensure V_OUT is within the voltage output swing from rails (V_{OUT_MIN}, V_{OUT_MAX}) of the op amp.
   Equation 3. $V_{OUT\_MIN}<V_{OUT}<V_{OUT\_MAX}$
   Equation 4. $V_{OUT}=\left(I_{LOAD}\times R_L\right)+V_{SHUNT}$
   Equation 5. $V_{OUT}=0+\left(600mA\times 100\Omega \right)+6V$
   Equation 6. $V_{OUT}=66V$
3. Calculate the output power of the circuit and select the MOSFET with appropriate power dissipation capabilities. The output FET power will be a function of the load, output voltage and supply voltage. For a square wave output with resistive loads, with the load ground-referenced, the average power can be found using the equation:

   The TINA-TI simulation results showing a maximum output power of approximately 22 W. Note that the output of the amplifier is significantly lower, consuming approximately 400mW of power, demonstrating the benefits of this circuit configuration. Select MOSFETs that have greater than 30W of power dissipation capability, such as FDD5N50, which has a power dissipation of at least 50 W. The maximum power dissipation at the output stage with a resistive load can be calculated using the following equation. Note that power consumption will vary with the load type (resistive vs. current). Refer to the TIPL on Power and Temperature for further details.

   Equation 7. $P_{AVG}=\frac{{V_{OUT}}^2}{R_L}\times DUTY\_CYCLE$
   Equation 8. $P_{AVG}=\frac{{\left(66V\right)}^2}{100\Omega }\times 0.5$
   Equation 9. $P_{AVG}=21.78W$
4. Select a zero-crossover resistor (R_ZCO) that provides sufficient current to drive the circuit while the MOSFET is off. Consider the trade-offs when selecting the R_ZCO. R_ZCO must be high enough to avoid current limit of the amplifier, but low enough to minimize noise and crossover distortion. A large R_ZCO, when paired with a capacitive load, can result in slower transients. However, a larger R_ZCO results in lower power dissipation.

   The value of R_ZCO can be iteratively determined through simulation. The results shown below demonstrate that resistor values below 100Ω cannot fully drive the loop. The 499 Ω resistor value drives 10.29mA of current, while the 1 kΩ drives 5.14 mA of current. The 1kΩ resistor has a thermal noise of approximately 4nV/√Hz, which is smaller than the op amp voltage noise of 13 nV/√Hz . Therefore, 1kΩ is a good choice for the R_ZCO, optimizing for both voltage noise and low power dissipation.

5. Calculate the voltage divider resistor values based on the V_TH of the selected MOSFET or BJT. To minimize power dissipation from VCC and VEE, use relatively large resistance for R₅.

Given: R₅ = 60.4 kΩ.

From the FDD5N50 datasheet, 3 V < V_GS(th) < 5 V.

Optimize the resistor divider network by selecting R₆ such that V_GS(th) = 3 V.

Set V_GS to nominal value 3 V to optimize for crossover distortion without cross conduction.

Choose conservative standard resistor value such that $R_6=R_7 = 2k\Omega$.

R₆ and R₇ can be further optimized for crossover distortion empirically, as individual V_GS(th) values for the chosen MOSFET varies due to process variation.