LP55281 datasheet(32/42 Pages) TI2

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LP55281

SNVS458D – JUNE 2007 – REVISED OCTOBER 2016

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Typical Application (continued)

8.2.1 Design Requirements

For typical LED-driver applications, use the parameters listed in Table 10.

Table 10. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Input voltage

3 V

Output voltage

5 V

SW pin current limit

550 mA (minimum)

Efficiency

75%

8.2.2 Detailed Design Procedure

The output current can be approximated by using this formula: IOUT = (VIN × ISW_MAX × efficiency) / VOUT.

Example: 3 V × 550 mA × 0.75 / 5 V = 248 mA

8.2.2.1 Recommended External Components

8.2.2.1.1

Output Capacitor, COUT

The output capacitor COUT directly affects the magnitude of the output ripple voltage. In general, the higher the

value of COUT, the lower the output ripple magnitude. Multilayer ceramic capacitors with low ESR are the best

choice. At the lighter loads, the low ESR ceramics offer a much lower VOUT ripple than the higher ESR tantalums

of the same value. At the higher loads, the ceramics offer a slightly lower VOUT ripple magnitude than the

tantalums of the same value. However, the dv/dt of the VOUT ripple with the ceramics is much lower than the

tantalums under all load conditions. Capacitor voltage rating must be sufficient, TI recommends 10 V or greater.

Some ceramic capacitors, especially those in small packages, exhibit a strong capacitance reduction with the

increased applied voltage. The capacitance value can fall to below half of the nominal capacitance. Output

capacitance that is too low increase the noise, and it can make the boost converter unstable.

8.2.2.1.2

List Of Recommended External Components

PARAMETER

VALUE

UNIT

TYPE

CVDD1

C between VDD1 and GND

100

Ceramic, X7R/X5R

CVDD2

C between VDD2 and GND

100

Ceramic, X7R/X5R

CVDDIO

C between VDDIO and GND

100

Ceramic, X7R/X5R

CVDDA

C between VDDA and GND

µF

Ceramic, X7R/X5R

COUT

C between FB and GND

µF

Ceramic, X7R/X5R

CIN

C between battery voltage and GND

µF

Ceramic, X7R/X5R

LBOOST

L between SW and VBAT at 2 MHz

4.7

µH

Shielded, low ESR, ISAT 1A

CVREF

C between VREF and GND

100

Ceramic, X7R

CVDDIO

C between VDDIO and GND

100

Ceramic, X7R

RRGB

R between IRGB and GND

8.2

Ω

±1%

RRT

R between IRT and GND

Ω

±1%

Rectifying Diode (Vf at maxload)

0.3

Schottky diode

CASE

C between Audio input and ASEx

100

Ceramic, X7R/X5R

LEDs

User defined

8.2.2.1.3

Input Capacitor, CIN

The input capacitor CIN directly affects the magnitude of the input ripple voltage and to a lesser degree the VOUT

ripple. A higher value CIN gives a lower VIN ripple. Capacitor voltage rating must be sufficient, TI recommends 10

V or greater.

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