DFE252012PD-2R2M datasheet(22/54 Pages) TI

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fLC= 12πL ×C

(13)

Table 9-3 can be used to simplify the output filter component selection. The values in Table 9-3 are nominal

values, and the effective capacitance was considered to be +20% and –50%. Different values can work, but

care has to be taken on the loop stability which is affected. More information on the sizing of the LC filter of a

DCS-Control regulator can be found in the Optimizing the TPS62130/40/50/60 Output Filter Application Note.

Table 9-3. Recommended LC Output Filter Combinations

4.7 µF

10 µF

22 µF

47 µF

100 µF

200 µF

1 µH (3) (4)

√

√ (2)

1.5 µH

√

√ (2)

2.2 µH

√

√(1)

√

√ (2)

3.3 µH

√

4.7 µH

√

√(2)

(1)

This LC combination is the standard value and recommended for most applications.

(2)

Output capacitance must have an ESR of ≥ 10 mΩ for stable operation. See Section 9.3.1.

(3)

Not recommended for 1-MHz operation

(4)

At full load, ILpeak can exceed ILIM_HS at higher input or output voltages.

Although the TPS629211-Q1 is stable without the pole and zero being in a particular location, an external

feedforward capacitor can also be added to adjust their location based on the specific needs of the application.

This can provide better performance in power save mode, improved transient response, or both.

A more detailed discussion on the optimization for stability versus transient response can be found in

the Optimizing Transient Response of Internally Compensated DC-DC Converters Application Note and

Feedforward Capacitor to Improve Stability and Bandwidth of TPS621/821-Family Application Note.

9.2.2.3.2 Inductor Selection

The TPS629211-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.

ILMAX =IOUTMAX +∆ILMAX2

(14)

∆ILMAX =VOUT×1 − VOUT

VINMAX

LMIN × fSW

(15)

where:

• IL(max) is the maximum inductor current.

TPS629211-Q1

SLVSGD0A – MARCH 2022 – REVISED MARCH 2023

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