• ΔIL is the peak-peak inductor current ripple

• VIN is the input voltage

• D is the duty cycle

• L is the inductor

• ƒSW is the switching frequency

• Ripple% is the ripple ration versus the DC current

• VOUT is the output voltage

• IOUT is the output current

• η is the efficiency

The current flowing through the inductor is the inductor ripple current plus the average input current. During

power up, load faults, or transient load conditions, the inductor current can increase above the peak inductor

current calculated.

Inductor values can have ±20% or even ±30% tolerance with no current bias. When the inductor current

approaches the saturation level, the inductance can decrease 20% to 35% from the value at 0A bias current

depending on how the inductor vendor defines saturation. When selecting an inductor, make sure the rated

current, especially the saturation current, is larger than the peak current during the operation.

The inductor peak current varies as a function of the load, the switching frequency, and the input and output

voltages and can be calculated by Equation 5 and Equation 6.

IPEAK=IIN+12×∆IL

(5)

where

• IPEAK is the peak current of the inductor

• IIN is the input average current

• ΔIL is the ripple current of the inductor

The input DC current is determined by the output voltage, the output current, and efficiency can be calculated by:

IIN=VOUT×IOUT

VIN×η

(6)

where

• IIN is the input current of the inductor

• VOUT is the output voltage

• VIN is the input voltage

• η is the efficiency

While the inductor ripple current depends on the inductance, the frequency, the input voltage, and duty cycle

calculated by Equation 2, replace Equation 2, Equation 6 into Equation 5 to calculate the inductor peak current:

IPEAK= IOUT

1−D ×η+12×VIN×D

L×fSW

(7)

where

• IPEAK is the peak current of the inductor

• IOUT is the output current

• D is the duty cycle

• η is the efficiency

• VIN is the input voltage

• L is the inductor

• ƒSW is the switching frequency

The heat rating current (RMS) is calculated by Equation 8:

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TPS61371

SLVSI31 – APRIL 2026

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