LP8550TLESLASHNOPB datasheet(38/49 Pages) TI1

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LP8550

SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014

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9.2.1.2.4

Output Diode

A Schottky diode should be used for the output diode. Peak repetitive current should be greater than inductor

peak current (2.5 A) to ensure reliable operation. Average current rating should be greater than the maximum

output current. Schottky diodes with a low forward drop and fast switching speeds are ideal for increasing

efficiency in portable applications. Choose a reverse breakdown voltage of the Schottky diode significantly larger

(approximately 60 V) than the output voltage. Do not use ordinary rectifier diodes, since slow switching speeds

and long recovery times cause the efficiency and the load regulation to suffer.

9.2.1.2.5

Resistors for Setting the LED Current and PWM Frequency

See EEPROM Bit Explanations on how to select values for these resistors.

9.2.1.2.6

Filter Component Values

Optimal components for 60-Hz VSYNC frequency and 4-Hz cut-off frequency of the low-pass filter are shown in

Figure 27, Figure 28, and Figure 31. If a 2-Hz cut-off frequency, that is, slower response time is desired, filter

components are: C1 = 1 μF, C2 = 10 μF and R = 47 kΩ. If different VSYNC frequency or response time is desired,

please contact a TI representative for guidance.

Figure 28. Filter Components

9.2.1.3 Application Curves

Typical Boost and LED Current Waveforms with fLED = 9.6 kHz.

fLED = 9.6 kHz

Figure 30. Typical Waveforms

Figure 29. Typical Waveforms

9.2.2 Typical Application for Low Input Voltage

In Single Li-Ion cell powered application the internal circuitry of LP8550 can be powered from external 5-V rail.

Boost is powered directly from Li-Ion battery and VLDO and VIN pins are connected to external 5-V rail. Current

draw from the 5-V rail is maximum 10 mA. A separate 5-V rail to VIN/VLDO can be used also in higher input

voltage application to improve efficiency or add increase input voltage range above 22 V in some cases. There

are no power sequencing requirement for VIN/VLDO and VBATT other than VBATT must be available when enabling

backlight to prevent a false overcurrent fault.

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