LP3952 Datasheet, PDF (29/46 Pages) National Semiconductor (TI) – 6-Channel Color LED Driver with Audio Synchronization

LP3952
www.ti.com
SNVS518A – JULY 2007 – REVISED MARCH 2013
Autoincrement mode is available, with this mode it is possible to read or write bytes with autoincreasing
addresses. LP3952 has empty spaces in address register map, and it is recommended to use autoincrement
mode only for writing in pattern command registers.
Recommended External Components
OUTPUT CAPACITOR, C_OUT
The output capacitor C_OUT directly affects the magnitude of the output ripple voltage. In general, the higher the
value of C_OUT, 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 that 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, 10V or greater is recommended.
Some ceramic capacitors, especially those in small packages, exhibit a strong capacitance reduction
with the increased applied DC voltage, so called DC bias effect. The capacitance value can fall to below
half of the nominal capacitance. Too low output capacitance will increase noise and it can make the
boost converter unstable. Recommended maximum DC bias effect at 5V DC voltage is -50%.
INPUT CAPACITOR, C_IN
The input capacitor C_IN directly affects the magnitude of the input ripple voltage and to a lesser degree the V_OUT
ripple. A higher value C_IN will give a lower V_IN ripple. Capacitor voltage rating must be sufficient, 10V or greater is
recommended.
OUTPUT DIODE, D₁
A schottky diode should be used for the output diode. Peak repetitive current rating of the schottky diode should
be larger than the peak inductor current (ca. 1A). Average current rating of the schottky diode should be higher
than maximum output current used. 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.
INDUCTOR, L₁
The LP3952’s high switching frequency enables the use of the small surface mount inductor. A 4.7 μH shielded
inductor is suggested for 2 MHz operation, 10 μH should be used at 1 MHz. The inductor should have a
saturation current rating higher than the rms current it will experience during circuit operation. To get maximum
(400 mA) current from the boost, an inductor with 1A saturation current is recommended. If output current is for
example 200 mA then inductor with 600 mA saturation current can be used. Less than 300 mΩ ESR is
suggested for high efficiency. Open core inductors cause flux linkage with circuit components and interfere with
the normal operation of the circuit. This should be avoided. For high efficiency, choose an inductor with a high
frequency core material such as ferrite to reduce the core losses. The inductor should be connected to the SW
pin as close to the IC as possible. Examples of suitable inductor for 400 mA output current is TDK VLF4012AT-
4R7M1R1, and for 200mA application VLF3010AT-4R7MR70 or Panasonic ELLVEG4R7N.
LIST OF RECOMMENDED EXTERNAL COMPONENTS
Symbol
C_VDD1
C_VDD2
C_VDDIO
C_VDDA
C_OUT
C_IN
L₁
Symbol explanation
C between VDD1 and GND
C between VDD2 and GND
C between VDDIO and GND
C between VDDA and GND
C between FB and GND
C between battery voltage and GND
L between SW and V_BAT at 2 MHz
Value
100
100
100
1
10
10
4.7
Unit
Type
nF
Ceramic, X7R / X5R
nF
Ceramic, X7R / X5R
nF
Ceramic, X7R / X5R
μF
Ceramic, X7R / X5R
μF
Ceramic, X7R / X5R, 10V
μF
Ceramic, X7R / X5R
μH
Shielded, low ESR, Isat=1A for 400
mA output current, Isat=600 mA for
200 mA output current
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