Inductor Selection (Buck-Boost Converter)

Rectifier Diode Selection (Buck-Boost Converter)

Output Capacitor Selection (Buck-Boost Converter)

TPS65166

The buck-boost converter is able to operate with 10

µH to 47µH inductors, a 22µH inductor is typical. The main

parameter for inductor selection is the saturation current of the inductor which should be higher than the peak

switch current as calculated in the Design Procedure section with additional margin to cover for heavy load

transients. The alternative more conservative approach is to choose an inductor with saturation current at least

as high as the minimum switch current limit of 1.1A. Another important parameter is the inductor dc resistance.

Usually the lower the dc resistance the higher the efficiency. The type and core material of the inductor

influences the efficiency as well. The efficiency difference among inductors can vary up to 5%. Possible inductors

are listed in Table 10.

Table 10. Inductor Selection Buck-Boost Converter

INDUCTOR VALUE

COMPONENT SUPPLIER

SIZE (LxWxH mm)

Isat/DCR

22

µH

Sumida CDRH3D23/HP

4.0 × 4.0 × 2.5

0.8A/306m

Ω

22

µH

Sumida CDRH4D22/HP

5.0 × 5.0 × 2.4

1.1A/214m

Ω

22

µH

Sumida CDH3D13D/SHP

3.2 × 3.2 × 1.5

0.6A/753m

Ω

To achieve high efficiency, a Schottky diode should be used. The reverse voltage rating should be higher than

(33)

Usually a Schottky diode with a 500mA maximum average rectified forward current rating is sufficient for most

applications. The Schottky rectifier can be selected with lower forward current capability depending on the output

current times the diode forward voltage. The efficiency rises with lower forward voltage.

(34)

Table 11. Rectifier Diode Selection (Buck-Boost Converter)

SIZE

COMPONENT SUPPLIER

40V/0.5A

0.43V at 0.5A

206°C/W

SOD-123

MBR0540, Vishay Semiconductor

40V/1A

0.42V at 0.5A

88°C/W

SMA

SS14, Fairchild Semiconductor

For the best output voltage filtering, low ESR ceramic capacitors are recommended. One 22

µF or two 10µF

output capacitors with sufficient voltage ratings in parallel are adequate for most applications. Additional

capacitors can be added to improve load transient regulation. See Table 12 for output capacitor selection.

Table 12. Output Capacitor Selection (Buck-Boost Converter)

CAPACITOR

COMPONENT SUPPLIER

22

µF/25V

Murata, GRM32ER61E226KE15

10

µF/25V

Murata, GRM31CR61E106KA12

10

µF/50V

Taiyo Yuden, UMK325BJ106MM

This output rail is required to power the scan driver and is generated with a charge pump doubler stage running

voltage to the programmed voltage set by the feedback resistor divider. Power dissipation and average collector

current of the transistor must be taken into consideration when choosing a suitable transistor. Also the power

dissipation of the resistor R12 must be considered.

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