LP3952 Datasheet, PDF (28/44 Pages) National Semiconductor (TI) – 6-Channel Color LED Driver with Audio Synchronization

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 ce-
ramic 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 volt-
age rating must be sufficient, 10V or greater is recommended.
Some ceramic capacitors, especially those in small pack-
ages, 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 nom-
inal capacitance. Too low output capacitance will in-
crease 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
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
C_VREF
C_VDDIO
R_RBG
R_RT
D₁
C_ASE
LEDs
C between V_REF and GND
C between V_DDIO and GND
R between I_RGB and GND
R between I_RT and GND
Rectifying Diode (Vf @ maxload)
C between Audio input and ASE
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 rec-
tifier 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 induc-
tor 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 appli-
cation VLF3010AT-4R7MR70 or Panasonic ELLVEG4R7N.
Value
100
100
100
1
10
10
4.7
100
100
5.6
82
0.3
100
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
nF Ceramic, X7R
nF Ceramic, X7R
kΩ
±1%
kΩ
±1%
V
Schottky diode
nF Ceramic, X7R / X5R
User defined
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