SP6687ER1-L/TR Ver la hoja de datos (PDF) - Signal Processing Technologies
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SP6687ER1-L/TR Datasheet PDF : 12 Pages
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APPLICATION INFORMATION
VIN
®
SP6687
CTRL2
CTRL1
CTRL0
EN
PWM
LED
LED ON
OFF
Figure 6. Typical application circuit for PWM dimming
when driving 2 LEDs.
Due to the 100µs delay time between mode transfers,
the duty cycle of the dimming frequency should not
exceed the maximum duty cycle on the CTRLx pins.
For best performance it is recommended to keep the
dimming frequency between 200Hz and 1kHz. When
the duty cycle is exceeded, the SP6687 cannot trans-
fer modes properly. The following equation shows the
relation between maximum duty of the CTRLx pins
and the PWM dimming frequency:
DMAX =(1-100 x10 -6 x FD)
Where DMAX is the Maximum Duty of CTRLX and FD is
the PWM Dimming Frequency.
Dimming using a DC voltage added to ISET
Using an analog input voltage VADJ via a resistor RADJ
that connects to the ISET pin is another method for
dimming control of LEDs. Figure 7 shows the applica-
tion circuit. For this application the LED current can be
derived from the following equation:
[ ] ILED = 440 X 1.1 x (1/RSET + 1/RADJ) - VADJ/RADJ
VADJ
®
SP6687 ISET
CTRL2
CTRL1
CTRL0
EN
RADJ
RSET
VIN
Figure 7. Typical application circuit for PWM dimming
using a DC voltage into ISET.
Dimming
Frequency (Hz)
1K
900
800
700
600
500
400
300
200
CTRLX
Maximum
Duty
0.90
0.91
0.92
0.93
0.94
0.95
0.96
0.97
0.98
ILED
Minimum Duty
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
Table 4. Dimming frequency relative to Min/Max duty.
VADJ 2.5V
1.6V
0.8V
0V
ILED
0mA
13mA 20mA
6.5mA
Figure 8. SP6687 dimming control application using a
DC voltage into ISET.
Figure 8 shows the relation between VADJ and ILED of
a typical application example, with VADJ from 0 to 2.5V,
RSET = 43kΩ and RADJ = 55kΩ.
Date: 11/15/05
SP6687 4Channel Charge Pump White LED Driver
10
© Copyright 2005 Sipex Corporation
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