LP3950SLSLASHNOPB datasheet(27/38 Pages) TI1

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LP3950

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SNVS331C – NOVEMBER 2004 – REVISED APRIL 2013

MODE CONTROL IN THE DEFAULT MODE

One of the main benefits of LP3950 is the default mode, which enables user to build applications without I2C or

SPI control. The LP3950 is set to the default mode when DME pin is high. DME pin high –state forces registers

NSTBY and EN_SYNC to the high [1] state so that the start-up sequence get started (see start-up sequence on

Modes of Operation). Function of LP3950 in the default mode of operation is controlled by AMODE pin. If

AMODE is pulled low the LP3950 is in the amplitude synchronization mode. If the AMODE pin is pulled high the

LP3950 is in the frequency synchronization mode. In the default mode default control register values are used,

see Table 8. Please refer to Figure 32 in Typical Applications for wiring.

RGB OUTPUT SELECTOR

The usage of RGB outputs (RGB1 and RGB2) can be selected with RGB_SEL[1:0] control bits. Audio

synchronization and RGB pattern generator output can be connected to RGB ports as shown in the following

table.

Table 6. RGB Output Control

RGB_SEL[0]

RGB_SEL[1]

RGB1 Output Control

RGB2 Output Control

Pattern Generator

Audio Sync

Pattern Generator

Audio Sync

Recommended External Components

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 (Equivalent

Series Resistance) 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 that the tantalums under all load conditions. Capacitor voltage rating must be sufficient, 10V is

recommended.

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. Too low output capacitance can make the boost converter unstable.

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 will give a lower VIN ripple. Capacitor voltage rating must be sufficient, 10V is

recommended.

OUTPUT DIODE, D1

A Schottky diode should be used for the output diode. To maintain high efficiency the average current rating of

the schottky diode should be larger than the peak inductor current (1.0A). Schottky diodes with a low forward

drop and fast switching speeds are ideal for increasing efficiency in portable applications. Choose a reverse

breakdown of the schottky diode larger 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.

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