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SE3362 Datasheet(HTML) 7 Page - Seaward Electronics Inc.

Part No. SE3362
Description  4-Channel Regulated Charge Pump White LED Driver
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Maker  SEAWARD [Seaward Electronics Inc.]
Homepage  http://www.seawardinc.com
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SE3362 Datasheet(HTML) 7 Page - Seaward Electronics Inc.

   
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Revision 12/4/2008
Preliminary and all contents are subject to change without prior notice
© Seaward Electronics, Inc., 2007. • www.seawardinc.com.cn • Page 7
The following equation shows the relation between
maximum duty of CTRLX pin and PWM dimming
frequency. Table 4 is shown the common dimming
frequency and its corresponding maximum duty. For
better performance consideration, the maximum PWM
dimming frequency is recommended below 1kHz.
D(MAX) = (1-100×10
-6×FD)
Table 4. The common dimming frequency and its
corresponding maximum duty.
Dimming
Frequency (Hz)
CTRLX
Maximum Duty
RLED
Minimum Duty
1000
0.90
0.10
900
0.91
0.09
800
0.92
0.08
700
0.93
0.07
600
0.94
0.06
500
0.95
0.05
400
0.96
0.04
300
0.97
0.03
200
0.98
0.02
(2). The PWM dimming by GPIO
The PWM dimming by GPIO is shown as Figure 6. DZ
shall be a Schottky diode with forward voltage less
than 0.3V at IF = 1mA. C3 is a capacitor to keep the
enable pin voltage is higher than the threshold voltage.
R1 is discharge resister and it should be not too high to
prevent the off time too long while turned-off. The
recommended conditions are shown as following.
1. The recommended value for R1 and C3 are
200k
Ω (±5%) and 0.22μF (X7R, ±10%).
2. The forward voltage of the Schottky diode shall be
less than 0.3V at 1mA.
3. The output voltage of GPIO should be greater than
2.8V and keep the voltage on EN pin is higher than
1.5V.
4. The PWM frequency should be in the range of
500Hz~1.5kHz or 20kHz~30kHz for audio noise
consideration.
5. The PWM duty cycle shall be in the range of 30% to
95%.
6. The driving capability of the GPIO should be greater
than 2mA @ 2.8V.
7. The LED current can be obtained by the equation,
ILED = 400×
)
1
(
PWM
SET
RSET
D
R
V
×
(The typical value of VRSET is 1.25V)
Figure 6. The GPIO PWM dimming application
circuit


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