The TPS629203-Q1 is designed for a nominal 2.2-μH inductor. Larger values can be used to achieve a lower inductor current ripple but they can have a negative impact on efficiency and transient response. Smaller values than 2.2 μH cause larger inductor current ripple, which cause larger negative inductor currents in forced PWM mode and higher peak currents at full load. Therefore, they are not recommended at larger voltages across the inductor as it is the case for high input voltages and low output voltages. With low output current in forced PWM mode, this causes a larger negative inductor current peak that can exceed the negative current limit. At low or no output current and small inductor values, the output voltage can therefore not be regulated any more. More detailed information on further LC combinations can be found in the Optimizing the TPS62130/40/50/60 Output Filter Application Note.

The inductor selection is affected by several effects like the following:

• Inductor ripple current
• Output ripple voltage
• PWM-to-PFM transition point
• Efficiency

In addition, the inductor selected has to be rated for appropriate saturation current and DC resistance (DCR). Equation 14 calculates the maximum inductor current.

Equation 14.

Equation 15.

where:

• I_L(max) is the maximum inductor current.
• ΔI_L is the peak-to-peak inductor ripple current.
• L(min) is the minimum effective inductor value.

Calculating the maximum inductor current using the actual operating conditions gives the minimum saturation current of the inductor needed. It is recommended to add a margin of about 20%. A larger inductor value is also useful to get lower ripple current, but increases the transient response time and size as well. The following inductors have been used with the TPS629203-Q1 and are recommended for use:

The inductor value also determines the load current at which power save mode is entered:

Equation 16.