lp5527tlx National Semiconductor Corporation, lp5527tlx Datasheet - Page 19

• Manufacturer Part Number: lp5527tlx
• Description: Tiny Led Driver For Camera Flash And 4 Leds With I2c Programmability, Connectivity Test And Audio Synchronization
• Manufacturer: National Semiconductor Corporation

Recommended External
Components
OUTPUT CAPACITOR, C
The output capacitors C
nitude of the output ripple voltage. In general, the higher the
value of C
layer ceramic capacitors with low ESR are the best choice.
At the lighter loads, the low ESR ceramics offer a much
lower V
value. At the higher loads, the ceramics offer a slightly lower
V
However, the dv/dt of the V
much lower that the tantalums under all load conditions.
Capacitor voltage rating must be sufficient, 10V is recom-
mended
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, C
The input capacitor C
input ripple voltage and to a lesser degree the V
higher value C
age rating must be sufficient, 10V or greater is recom-
mended.
OUTPUT DIODE, D
The output diode for a boost converter must be chosen
correctly depending on the output voltage and the output
current. The diode must be rated for a reverse voltage
Table List of Recommended External Components
Symbol
C
C
C
C
C
C
C
RT
RF
C
L
D
OUT
1
VDD1
VDD2
OUT1,2
IN
VDDIO
VDDA
1,2
VREF
1
ripple magnitude than the tantalums of the same value.
OUT
OUT
ripple that the higher ESR tantalums of the same
, the lower the output ripple magnitude. Multi-
IN
will give a lower V
Symbol Explanation
V
V
Output Capacitors from FB to GND
Input Capacitor from Battery Voltage to GND
V
V
Audio Input Capacitors
Oscillator Frequency Bias Resistor
Flash Current Set Resistor for 400 mA Sink
Current
Reference Voltage Capacitor, between V
and GND
Boost Converter Inductor
Rectifying Diode, V
Flash LED
LED1 to LED4
DD1
DD2
DD_IO
DDA
1
IN
Bypass Capacitor
Bypass Capacitor
Bypass Capacitor
IN
OUT1
directly affects the magnitude of the
Bypass Capacitor
OUT1
OUT
, C
, C
OUT2
ripple with the ceramics is
OUT2
IN
directly affect the mag-
F
ripple. Capacitor volt-
@
maxload
OUT
ripple. A
REF
19
Value
100
100
2 x 10 µF
10
100
4.7
47
82
1200
100
4.7
0.35
User defined
greater than the output voltage used. The average current
rating must be greater than the maximum load current ex-
pected, and the peak current rating must be greater than the
peak inductor current ( ~ 1.6A at maximum load). A Schottky
diode should be used for the output diode. Schottky diodes
with a low forward voltage drop (V
speeds are ideal for increasing efficiency in portable appli-
cations. Do not use ordinary rectifier diodes, since slow
switching speeds and long recovery times cause the effi-
ciency and the load regulation to suffer. In Schottky barrier
diodes reverse leakage current increases quickly with the
junction temperature. Therefore, reverse power dissipation
and the possibility of thermal runaway has to be considered
when operating under high temperature conditions. Ex-
amples of suitable diodes are Diodes Incorporated type
DFLS220L, ON Semiconductor type MBRA210LT3 and Phil-
ips type PMEG1020.
INDUCTOR, L
The LP5527 high switching frequency enables the use of the
small surface mount inductor. A 4.7 µH shielded inductor is
suggested for 2 MHz switching frequency. The inductor
should have a saturation current rating higher than the peak
current it will experience during circuit operation ( ~ 1.7A at
maximum load). 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. To minimize radiated
noise, use a toroid, pot core or shielded core inductor. The
inductor should be connected to the SW1 and SW2 pins as
close to the I
TDK type VLCF5020T-4R7N1R7-1.
±
10%
±
10%
C
1
as possible. Example of a suitable inductor is
Unit
nF
nF
µF
µF
nF
µF
nF
kΩ
Ω
nF
µH
V
Type
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R, 10V
Ceramic, X5R, 10V
Ceramic, X5R
Ceramic, X5R, 6.3V
Ceramic, X5R
1%
1%
Ceramic, X5R
Shielded, low ESR,
I
Schottky diode
SAT
F
) and fast switching
~ 1.7A
www.national.com