PAM2701 Datasheet, PDF (10/14 Pages) Power Analog Micoelectronics – 4-Channel Regulated Charge Pump White LED Driver

PAM2701
4-Channel Regulated Charge Pump White LED Driver
Application Information
Table 3: Analog Voltage for LED Current Control
V_SET(V)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
I_LED(mA)
30.0
27.7
25.3
22.9
20.5
18.1
15.7
V_SET(V)
0.7
0.8
0.9
1.0
1.1
1.2
I_LED(mA)
13.3
10.9
8.4
6.0
3.6
1.1
Figure 1: Analog Voltage for LED Current Control
Co
1.0μF
D1 D 2 D3 D4
LED1 LED2 LED3 LED4
GND
EN
CTR0
CTR1
PAM2701
C2+
C2
1.0μF
C2-
CTR2
RSET VOUT VIN
C1+
VSET
VIN
RSET
1 4 . 7k Ω
Cin
1.0μF
1.0μF
Method 3: LED Current Setting with a PWM
Signal to CTRx Pin
In circuit in Figure 2 four LEDs are turned on and
off by a PWM signal on the CTR0. A resistor R_SET
is used to set the on state current and the
average LED current is then proportional to the
percentage of on-time when the CTR0 pin is logic
low. Average LED current is approximately equal
to:
I_AVG = (t_ON*I ) _{LED_ON} / (t_ON + t_OFF)
It is recommended that PWM frequency is
between 100Hz and 1kHz. Due to start up delay
and ramp up time, frequency >1kHz will result in
error in the average value of I_LED. Frequency
<100Hz can cause the LEDs to blink visibly.
Figure 2: PWM Signal at CTR0 pin for LED Current Control
Co
1.0μF
D1 D2 D3 D4
100Hz to 1kHz
PWM
LED1 LED2 LED3 LED4
GND
EN
CTR0
C2+
PAM2701
CTR1
C2-
C2
1.0μF
CTR2
C1-
RSET VOUT VIN C1+
RSET
14.7kΩ
C1
1.0μF
Cin
1.0μF
VIN
Method 4: LED Current Setting with a PWM
Signal to EN Pin
The four LEDs are turned on and off by applying a
PWM signal to the EN pin in circuit in Figure 3.
The circuit is the same as one in method 3, using
a resistor R_SET to set the on state current and the
average LED current proportional to the
percentage of on-time when the EN pin is logic
low. Average LED current is approximately equal
to:
I_AVG = (t * _ON I_{LED_} ) _ON / (t_ON + t ) _OFF
Similarly, it is recommended that PWM frequency
is between 100Hz and 1kHz. Due to start up
delay and ramp up time, frequency >1kHz will
result in error in the average value of I . _LED
Frequency <100Hz can cause the LEDs to blink
visibly
Figure 3: PWM Signal at EN pin for LED Current Control
100Hz to 1kHz
PWM
VIN
Co
1.0μF
D1 D2 D3 D4
LED1 LED2 LED3 LED4
GND
EN
CTR0
CTR1
C2+
PAM2701
C2-
C2
1.0μF
CTR2
RSET VOUT VIN
R_SET
14.7kΩ
C1-
C1+
C1
1.0μF
Cin
1.0μF
Power Analog Microelectronics,Inc
www.poweranalog.com
10
09/2008 Rev 1.3