PIFE32251B-R47MS datasheet(75/96 Pages) TI1

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OUT

L(MAX)

OUT(MAX)

)

OUT

OUT(MAX)

IND

)

TPS65094

www.ti.com

SWCS133C – SEPTEMBER 2015 – REVISED FEBRUARY 2019

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Application and Implementation

7.2.2.1.1 Selecting the Output Capacitors

TI recommends using ceramic capacitors with low ESR values to provide the lowest output voltage ripple.

The output capacitor requires either an X7R or an X5R dielectric. Capacitors with Y5V or Z5U dielectrics

display a wide variation in capacitance over temperature and become resistive at high frequencies.

At light load currents, the controller operates in PFM mode, and the output voltage ripple is dependent on

the output-capacitor value and the PFM peak inductor current. Higher output-capacitor values minimize

the voltage ripple in PFM mode. To achieve specified regulation performance and low output voltage

ripple, the DC-bias characteristic of ceramic capacitors must be considered. The effective capacitance of

ceramic capacitors drops with increasing DC bias voltage.

For the output capacitors of the BUCK controllers, TI recommends placing small ceramic capacitors

between the inductor and load with many vias to the PGND plane. This solution typically provides the

smallest and lowest cost solution available for DCAP2 controllers.

To meet the transient specifications, the output capacitance must equal or exceed the minimum

capacitance listed in the electrical characteristics table for BUCK1, BUCK2, and BUCK6 (assuming quality

layout techniques are followed). See Section 5.7, Electrical Characteristics: Buck Controllers.

7.2.2.1.2 Selecting the Inductor

An inductor must be placed between the external FETs and the output capacitors. Together, the inductor

and output capacitors make the double-pole that contributes to stability. In addition, the inductor is

responsible for the output ripple, efficiency, and transient performance. When the inductance increases,

the ripple current decreases, which typically results in an increased efficiency. However, with an increase

in inductance, the transient performance decreases. Finally, the inductor selected must be rated for

appropriate saturation current, core losses, and DC resistance (DCR).

Equation 3 shows the calculation for the recommended inductance for the controller.

where

•

VOUT is the typical output voltage.

•

VIN is the typical input voltage.

•

fSW is the typical switching frequency.

•

IOUT(MAX) is the maximum load current.

•

KIND is the ratio of ILripple to the IOUT(MAX). For this application, TI recommends that KIND is set to a value

from 0.2 to 0.4.

(3)

With the chosen inductance value and the peak current for the inductor in steady state operation, IL(max)

can be calculated using Equation 4. The rated saturation current of the inductor must be higher than the

IL(MAX) current.

(4)

Following the previous equations, Table 7-1 lists the preferred inductor selected for the controllers..

Table 7-1. Recommended Inductors

MANUFACTURER

PART NUMBER

VALUE

SIZE

HEIGHT

Cyntec

PIMB061H

0.47 µH

6.8 mm × 7.3 mm

1.8 mm

Cyntec

PIMB062D

0.22 µH

6.8 mm × 7.3 mm

2.4 mm

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