SC4505MLTRT Ver la hoja de datos (PDF) - Semtech Corporation
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SC4505MLTRT Datasheet PDF : 15 Pages
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SC4505
POWER MANAGEMENT
Applications Information
VENDOR
KEMET
Murata
Taiyo Yuden
PHONE
WEBSITE
408-986-0424 www.kemet.com
814-237-1431 www.murada.com
408-573-4150 www.t-yuden.com
Table 5. Recommended Ceramic Capacitor
Manufacturers
Output Rectifying Diode Selection
Schottky diodes are the ideal choice for SC4505 due to
their low forward voltage drop and fast switching speed.
Table 6 shows several different Schottky diodes that
work well with the SC4505. Make sure that the diode
has a voltage rating greater that the possible maximum
ouput voltage. The diode conducts current only when
the power switch is turned off. So a 1A diode will be
sufficient for most designs.
PART
SS13
SS14
10BQ015
VENDOR
Vishay
www.vishay.com
International Rectifier
www.irf.com
Table 6. Recommended Rectifying Diodes
IO1SET Resistor Selection Chart
160
140
120
100
80
60
40
20
0
0
20
40
60
80
100
IO1 Current (mA)
Figure 2. IO1SET Resistor Selection Chart
160
140
120
100
80
60
40
20
0
0
IO2SET Resistor Selection Chart
20 40 60 80 100 120 140
IO2 Current (mA)
Output Current Programming
The SC4505 features two independent LED current
regulators. The LED current setpoints are chosen using
external resistors. The relationships between the
programming resistors and the two channel output
current setpoints are shown as in the Figure 2 and Figure
3 below.
The relationships between the programming resistor
value and the output current setpoint can be described
as follows:
RO1SET = (140 V) / IO1
RO2SET = (154 V) / IO2
Where RO1SET and RO2SET are in Ohms. IO1 and IO2 are in
Amperes.
Figure 3. IO2SET Resistor Selection Chart
PWM Dimming
Either of the enable pins can be toggled by external
circuitry to allow PWM dimming. In a typical application,
a microcontroller sets a register or counter that varies
the pulsewidth on a GPIO pin. The SC4505 allows
dimming over two decades in frequency (50Hz-50 kHz)
in order to allow compatibility with a wide range of
devices, including newest dimming strategies that avoid
the audio band by using high frequency PWM dimming.
In this manner, a wide range of illumination can be
generated while keeping the instantaneous LED current
at its peak value for luminescent efficiency and color
purity. Furthermore, advanced lighting effects such as
backlight “dim-on” or photographic red-eye reduction can
be implemented as the SC4505 can resolve PWM from
12% to 90% duty at 32kHz.
2007 Semtech Corp.
9
www.semtech.com
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