SC4505 Semtech Corporation, SC4505 Datasheet - Page 9

• Manufacturer Part Number: SC4505
• Description: High Efficiency Boost Converter
• Manufacturer: Semtech Corporation

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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.
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:
Where R
Amperes.
POWER MANAGEMENT
Applications Information
2006 Semtech Corp.
Taiyo Yuden
VENDOR
Table 5. Recommended Ceramic Capacitor
KEMET
Table 6. Recommended Rectifying Diodes
Murata
1
O1SET
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S
S
B
A
S
S
Q
R
1
1
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T
3
4
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1
5
R
R
O2SET
O1SET
O2SET
408-986-0424
408-573-4150
814-237-1431
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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
10% to 90% duty at its highest frequency.
160
140
120
100
160
140
120
100
80
60
40
20
Figure 2. I
Figure 3. I
80
60
40
20
0
0
0
0
20
I
O2SET
I
O1SET
20
O1SET
O2SET
Resistor Selection Chart
40
Resistor Selection Chart
Resistor Selection Chart
Resistor Selection Chart
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O2
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O1
40
Current (mA)
60
Current (mA)
80
60
100
www.semtech.com
80
120
SC4505
140
100