8.7 Input Voltage Limitations

While a high switching frequency offers benefits such as reduced size of external passive components and improved transient response, it also introduces certain design limitations that must be considered, including:

Dropout operation
Minimum on-time

To determine the boundaries of the operating range, Equation 8-7 can be used.

Equation 8-7. Input Voltage Range

V_{I N} = \frac{V_{O U T} + I_{O U T} \times (R_{D C R} + R_{D S O N} \times D) + V_{FW} \times (1 - D)}{D}

Where:


V_OUT	=	Output voltage
I_OUT	=	Output current
L	=	Inductance value
R_DCR	=	DCR of the selected inductor
R_DSON	=	On-resistance of the internal high-side switch
D	=	Duty cycle
V_FW	=	Forward voltage drop of the diode

To determine the minimum input voltage required for proper regulation, use the maximum duty cycle in your calculations. Conversely, to determine the maximum input voltage, calculate the duty cycle to ensure it does not fall below the minimum on-time.

Figure 8-1. Input Voltage Range vs. Output Voltage