PAM2842 datasheet(14/17 Pages) PAM

14 / 17 page

Above description does not consider the IC

control power, so the total power will be more than

calculated value.

PAM2842 has over-temperature protection. When

junction temperature is over 150°C, it will shut

down and auto restart when junction temperature

decrease below 120

In high temperature circumstance application,

one must pay attention to heat dissipation, or it

will shut down and restart. It is recommended to

use external heat-sink and placed near to the IC

surface.

Careful PCB layout is important for normal

operation. Use the following guidelines for good

PCB layout: (BOOST)

Minimize the area of the high current

switching loop of the rectifier diode and output

capacitor to avoid excessive switching noise.

Connect high-current input and output

components with short and wide connections. The

high-current input loop goes from the positive

terminal of the input capacitor to the inductor and

the SW pin. The high-current output loop is from

the positive terminal of the input capacitor

through the inductor, rectifier diode, and positive

terminal of the output capacitors, reconnecting

between the output capacitor and input capacitor

ground terminals. Avoid using vias in the high-

current paths. If vias are unavoidable, use

multiple vias in parallel to reduce resistance and

inductance.

Create a ground island (PGND) consisting of

the input and output capacitor ground and PGND

pin. Connect all these together with short, wide

traces or a small ground plane. Maximizing the

width of the power ground traces improves

efficiency and reduces output-voltage ripple and

noise spikes. Create an analog ground island

(AGND) consisting of the output voltage

detection-divider ground connection, the Sense-

pin connection, VCC-5V and VCC-driver

capacitor connections. Connect the device's

exposed backside pad to PGND. Make sure no

other connections between these s eparate

ground planes.

Place the output voltage setting-divider

resistors as close to the OV pin as possible. The

divider's center trace should be kept short. Avoid

running the sensing traces near SW Pin.

Place the VIN pin bypass capacitor as close

to the device as possible. The ground connection

of the VIN bypass capacitor should be connected

directly to GND pins with a wide trace.

Minimize the size of the SW node while

keeping it wide and short. Keep the SW node

away from the feedback node. If possible, avoid

running the SW node from one side of the PCB to

the other.

For the good thermal dissipation, PAM2842

has a heat dissipate pad in the bottom side, it

should be soldered to PCB surface. As the copper

area cannot be large in the component side, we

can use multiple vias connecting to other side of

the PCB.

Refer to the e xample of a PAM2842

Evaluation board layout below.

°C

PCB Layout Guidelines

PAM2842

High Power LED Driver

Power Analog Microelectronics Inc

www.poweranalog.com

09/2008 Rev 1.1

PCB Layout Example

TSSOP-20 BOOST

QFN6x6-40 BOOST

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