PAM2810ENG datasheet(7/10 Pages) PAM

7 / 10 page

LED1

LED2

LED3

LED4

VIN

GND

ISET

Cin

01 F

. μ

Rset

Figure 2

One Parallel Connected LED

LED1

LED2

LED3

LED4

VIN

GND

ISET

Cin

01 F

. μ

Rset

Figure 1

Two Parallel Connected LEDs

Power Analog Microelectronics Inc

www.poweranalog.com

Parallel LEDx Outputs for Increased Current

Drive

Power Dissipation

Input Capacitor Selection

Output pins LED1 to LED4 may be connected

together in any combination to sink higher current

through fewer LEDs. For example in Figure 1,

outputs LED1 and LED2 are connected together

to drive one LED while LED3 and LED4 are

connected together to drive a second LED.

With this configuration, two parallel current sinks

of equal value both provide current to each LED.

If the current sink provides 10mA each, every LED

can be drived with 20mA and gets double

brightness. Other combinations of parallel

outputs can be implemented similarly, such as in

Figure 2.

Connecting outputs in parallel does not affect

internal operation of the PAM2810 and has no

impact on the electrical characteristics.

If less than four LEDs connected, the left pin can

be floating or connected to GND, as shown in

Typical Application Circuit on page 2.Connecting

to GND is recommended. The current calculating

method is the same as the RSET equation

mentioned.

The maximum allowable power dissipation that

the package is capable of handling can be

determined as follows:

P= (T

- T ) /

Where T

is the maximum junction temperature,

is the ambient temperature, and

is the

junction-to-ambient thermal resistance of the

specified package. The DFN 2x2 package has a

of 80°C/W and the SOT23-8 250°C/W. This

value of

is highly dependant upon the layout of

the PCB. The actual power dissipated by the

PAM2810 follows the equation:

=(V *I )-N(V

)

Where N equals the number of active outputs,

is the LED forward voltage, and I

is the

current supplied to the LEDx.

The PAM2810 is designed to work under a stable

input voltage. To ensure the stability of input, it

may be necessary to add a small input capacitor

to help filter out any noise that probably appears

on the line. Surface-mount multi-layer ceramic

capacitors are recommended, which are small

and inexpensive. A capacitance of 0.1 F is

typically sufficient.

DMAX

JMAX

DISS

DIODE

LEDX

DIODE

LEDX

PAM2810

4-Channel Programmable LED Current Sink

07/2008 Rev 1.1

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