LP8556 datasheet(48/63 Pages) TI1

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LP8556

SNVS871I – JULY 2012 – REVISED MARCH 2016

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Typical Application (continued)

9.2.1 Design Requirements

Table 16. Recommended Inductance

ƒSW

MIN

TYP

MAX

UNIT

1250

3.3

µH

625

6.8

µH

312

100

µH

Table 17. Recommended Output Capacitance

ƒSW

MIN

TYP

MAX

UNIT

1250

4.7

µF

625

4.7

µF

312

µF

9.2.2 Detailed Design Procedure

9.2.2.1 Recommended Inductance for the Boost Power Stage

Assumes 20 mA as the maximum LED current per string and 3.3 V as the maximum LED forward voltage.

NUMBER OF

LED STRINGS

NUMBER OF

LEDS PER

STRING

BOOST INPUT

VOLTAGE RANGE

L1 INDUCTANCE

ƒSW = 1250 kHz

ƒSW = 625 kHz

ƒSW = 312 kHz

2.7 V - 4.4 V

3.3

μH - 6.8 μH

6.8

μH - 15 μH

μH - 33 μH

5.4 V - 8.8 V

μH - 22 μH

μH - 47 μH

μH - 100 μH

2.7 V - 4.4 V

4.7

μH - 10 μH

μH - 15 μH

μH - 33 μH

5.4 V - 8.8 V

μH - 22 μH

μH - 68 μH

μH - 100 μH

5.4 V - 8.8 V

6.8

μH - 22 μH

μH - 47 μH

μH - 100 μH

5.4 V - 8.8 V

μH - 22 μH

μH - 47 μH

μH - 100 μH

(1)

Capacitance of Multi-Layer Ceramic Capacitors (MLCC) can change significantly with the applied DC voltage. Use capacitors with good

capacitance versus DC bias characteristics. In general, MLCC in bigger packages have lower capacitance de-rating than physically

smaller capacitors.

9.2.2.2 Recommended Capacitances for the Boost and LDO Power Stages(1)

SWITCHING FREQUENCY [kHz]

CIN [μF]

COUT [μF]

CVLDO [μF]

1250

2.2

4.7

625

2.2

4.7

312

4.7

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