參數(shù)資料
型號(hào)： LP3936
廠商： National Semiconductor Corporation
英文描述： Lighting Management System for Six White LEDs and One RGB or FLASH LED
中文描述： 照明管理系統(tǒng)6個(gè)白光LED和一個(gè)RGB或閃光燈LED
文件頁(yè)數(shù)： 18/20頁(yè)
文件大小： 520K
代理商： LP3936
WLED and CLED Driver Electrical Characteristics
Symbol
I
RANGE
I
MAX
Parameter
Conditions
Min
Typ
0–25.5
25.5
Max
Units
mA
mA
mA
μA
Sink Current Range
Maximum Sink Current
V
FB
= 4.55V, Control 00h–FFh
(Note 14)
24
22
27
28
1
I
LEAKAGE
I
MATCH
Leakage Current
Sink Current Matching
(Note 15)
V
FB
= 5V
I
SINK
= 13 mA, between
WLED1 … 4 or WLED5 … 6
0.04
1.0
4
%
Note 14:
A minimum voltage, Dropout Voltage, is required on the WLED outputs for maintaining the LED current. The current reduction at lower voltages is shown
in the graph
WLED Output Current vs. Voltage
.
Note 15:
Match % = 100% * (Max – Min)/Min
WLED Current Adjustment
WLED[7:0]
WLED Current
(Typical)
0
0.1
0.2
0.3
25.3
25.4
25.5
Units
0000 0000
0000 0001
0000 0010
0000 0011
1111 1101
1111 1110
1111 1111
mA
mA
mA
mA
mA
mA
mA
WLED Output Current vs Voltage
Temperatures 40C, +25C, +85C
20081431
Recommended External
Components
OUTPUT CAPACITOR, C
OUT
The output capacitor C
directly affects the magnitude of
the output ripple voltage. In general, the higher the value of
C
, 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 V
OUT
ripple than the higher ESR tantalums of the same value. At
the higher loads, the ceramics offer a slightly lower V
OUT
ripple magnitude than the tantalums of the same value.
However, the dv/dt of the V
OUT
ripple with the ceramics is
much lower than the tantalums under all load conditions.
Capacitor voltage rating must be sufficient, 10V is recom-
mended. It should be noted that with some capacitor types
the actual capacitance depends heavily on the capacitor DC
voltage bias.
INPUT CAPACITOR, C
IN
The input capacitor C
directly affects the magnitude of the
input ripple voltage and to a lesser degree the V
ripple. A
higher value C
will give a lower V
ripple. Capacitor volt-
age rating must be sufficient, 10V is recommended.
OUTPUT DIODE, D
OUT
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 cur-
rent (1A). Schottky diodes with a low forward drop and fast
switching speeds are ideal for increasing efficiency in por-
table 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 regu-
lation to suffer.
INDUCTOR, L
The high switching frequency enables the use of the small
surface mount inductor. A 10 μH shielded inductor is sug-
gested. Values below 4.7 μH should not be used. The induc-
tor should have a saturation current rating higher than the
peak current it will experience during circuit operation (
A
1A).
Less than 300 m
ESR is suggested for high efficiency.
Open core inductors cause flux linkage with circuit compo-
nents and interfere with the normal operation of the circuit.
This should be avoided. For high efficiency, choose an in-
ductor 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 OUT pin as close to the IC as
possible. Examples of suitable inductors are TDK types
LLF4017T-100MR90C and VLF4012AT-100MR79 and Coil-
craft type DO3314T-103 (unshielded).
L
www.national.com
18
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