The CV circuit shown in Figure 2-3 is mainly composed of the upper and lower feedback resistors (designated as R_FB1 and R_FB2, respectively), a follower and a diode. The circuit adjusts the output voltage by adjusting the resistance value of R_FB1 and R_FB2 by Equation 5.

Figure 2-3 External CV Circuit

For example, assume that V_out = 5 V. When we use this circuit on TPSM63610EVM or LM61495EVM, according to Equation 5, we can get R_FB1 = 100 kΩ, R_FB2 = 24.9 kΩ.

For the selection of the resistance values ​​of R_FB1 and R_FB2, please refer to the data sheet of the buck products. In addition, the resistor R_loop in Figure 2-3 is used for frequency response measurements, and a typical value of 49.9 Ω is used. Diode D₁ is mainly used to make sure that only one loop (current loop or voltage loop) is working at a time. In this application note, the voltage loop is the main loop, and the current loop is the secondary loop. Generally speaking, the current loop can be slowed down as much as possible to avoid interference with the voltage loop. Finally, the negative feedback look of the buffer is wrapped aroind diode D1 to ensure that the diodes voltage drop and temperature variations are nullfied and will not effect the voltage set point accuracy.