PAM2701 datasheet(10/14 Pages) PAM

10 / 14 page

CTR0

PAM2701

CTR1

LED1

CTR2

LED2

RSET

LED3

VOUT

LED4

VIN

GND

C1+

C2+

C1-

C2-

SET

14.7kΩ

VIN

Cin

1.0 F

PWM

100Hz to 1kHz

Table 3: Analog Voltage for LED Current Control

In circuit in Figure 2 four LEDs are turned on and

off by a PWM signal on the CTR0. A resistor R

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= (t *I

)/ (t

+ t

)

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

Frequency

<100Hz can cause the LEDs to blink visibly.

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

to set the on state current and the

average LED c urrent proportional to the

percentage of on-time when the EN pin is logic

low. Average LED current is approximately equal

to:

I= (t *I

)/ (t

+ t

)

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

Frequency <100Hz can cause the LEDs to blink

visibly

Figure 1: Analog Voltage for LED Current Control

Figure 2: PWM Signal at CTR0 pin for LED Current Control

Figure 3: PWM Signal at EN pin for LED Current Control

Method 3:

LED Current Setting with a PWM

Signal to CTRx Pin

Method 4: LED Current Setting with a PWM

Signal to EN Pin

SET

AVG

LED_ON

OFF

LED.

SET

AVG

LED_ON

OFF

LED

Application Information

VSET(V)

ILED(mA)

VSET(V)

ILED(mA)

0.0

30.0

0.7

13.3

0.1

27.7

0.8

10.9

0.2

25.3

0.9

8.4

0.3

22.9

1.0

6.0

0.4

20.5

1.1

3.6

0.5

18.1

1.2

1.1

0.6

15.7

Power Analog Microelectronics Inc

www.poweranalog.com

09/2008 Rev 1.3

PAM2701

4-Channel Regulated Charge Pump White LED Driver

CTR0

PAM2701

CTR1

LED1

CTR2

LED2

RSET

LED3

VOUT

LED4

VIN

GND

C1+

C2+

C2-

RSET

14.7kΩ

VSET

VIN

Cin

1.0μF

CTR0

CTR1

LED1

CTR2

LED2

RSET

LED3

VOUT

LED4

VIN

GND

C1+

C2+

C2-

SET

14.7kΩ

VIN

Cin

1.0 F

PWM

100Hz to 1kHz

PAM2701

PAM2701 Datasheet(PDF) 10 Page - Power Analog Micoelectronics

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