Rainbow Electronics MAX1554 - Manual (Page 9)

MAX1553/MAX1554
High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
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Ensure the diode’s average and peak current ratings
exceed the average output current and peak inductor
current. In addition, the diode’s reverse breakdown
voltage must exceed V
OUT .
Applications Information
Low Input-Voltage Applications
The MAX1553/MAX1554 have minimum input voltages
of 2.7V (MAX1553) and 3.15V (MAX1554). However,
lower battery voltages can still be boosted for LED
drive as long as V
CC remains within the operating
range. Since most systems have a 3.3V system supply
active when the display is active and backlit, that logic
supply can be used to supply V
CC , while the battery
power connects directly to the boost inductor. No bat-
tery current is drawn when EN is low (Figure 4).
PC Board Layout
Due to fast-switching waveforms and high-current
paths, careful PC board layout is required. An evalua-
tion kit (MAX1553EVKIT) is available as an example of
a proper layout.
When laying out a board, minimize trace lengths
between the IC and the inductor, diode, input capaci-
tor, output capacitor, and R1. Keep traces short, direct,
and wide. Keep noisy traces, such as the LX node
trace, away from FB. Place the V
CC bypass capacitor
(C1) as close to the IC as possible. The ground con-
nections of C1 and C2 should be as close together as
possible. Star connect the grounds for R1, R3, C3, and
the BRT voltage supply as close to the IC as possible.
The traces from V
CC to C1, from C2 to the LEDs, and
from the LEDs to R1 can be longer if required.
Chip Information
TRANSISTOR COUNT: 740
PROCESS: BiCMOS
SUPPLIER PHONE WEBSITE
Central
Semiconductor
631-435-1110 www.centralsemi.com
Kamaya 260-489-1533 www.kamaya.com
Murata 814-237-1431 www.murata.com
Nichia 248-352-6575 www.nichia.com
Panasonic 714-373-7939 www.panasonic.com
Sumida 847-956-0666 www.sumida.com
Taiyo Yuden 408-573-4150 www.t-yuden.com
TDK 847-803-6100 www.component.tdk.com
TOKO 847-297-0070 www.toko.com
Table 1. Component Suppliers
Figure 4. The MAX1553/MAX1554 can drive LEDs from battery
voltages that are lower than the device operating voltage
range by powering V
CC from a logic supply and connecting
the boost inductor to the battery.
LX
SS
V CC
FB
ON
OFF
BRT
GND
BATTERY
INPUT
C1
4.7 µF
C3
0.1 µF
C2
0.47 µF
OV EN
WHITE
LEDs
C4
0.1 µF
3.3V
LOGIC
MAX1553
MAX1554
L1 D1
R2
R3
R1