The inductor selection is affected by several effects like inductor ripple current, output ripple voltage, PWM-to-PSM transition point and efficiency. In addition, the inductor selected has to be rated for appropriate saturation current and DC resistance (DCR). Equation 7 and Equation 8 calculate the maximum inductor current under static load conditions.
IL(max) is the maximum inductor current,
ΔIL is the Peak to Peak Inductor Ripple Current,
L(min) is the minimum effective inductor value and
fSW is the actual PWM Switching Frequency.
Calculating the maximum inductor current using the actual operating conditions gives the minimum saturation current of the inductor needed. A margin of about 20% is recommended to add. A larger inductor value is also useful to get lower ripple current, but increases the transient response time and solution size as well. The following inductors have been used with the TPS6215xA-Q1 and are recommended for use:
|Type||Inductance [µH]||Current [A](2)||Dimensions [LxBxH] mm||MANUFACTURER|
|XFL4020-102ME_||1.0 µH, ±20%||4.7||4 x 4 x 2.1||Coilcraft|
|XFL4020-152ME_||1.5 µH, ±20%||4.2||4 x 4 x 2.1||Coilcraft|
|XFL4020-222ME_||2.2 µH, ±20%||3.8||4 x 4 x 2.1||Coilcraft|
|IHLP1212BZ-11||1.0 µH, ±20%||4.5||3 x 3.6 x 2||Vishay|
|IHLP1212BZ-11||2.2 µH, ±20%||3.0||3 x 3.6 x 2||Vishay|
|SRP4020-3R3M||3.3µH, ±20%||3.3||4.8 x 4 x 2||Bourns|
|VLC5045T-3R3N||3.3µH, ±30%||4.0||5 x 5 x 4.5||TDK|
The inductor value also determines the load current at which Power Save Mode is entered:
Using Equation 8, this current level can be adjusted by changing the inductor value.