PAM2842 Datasheet, PDF (14/17 Pages) Power Analog Micoelectronics – High Power LED Driver

PAM2842
High Power LED Driver
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°C.
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.
PCB Layout Guidelines
Careful PCB layout is important for normal
operation. Use the following guidelines for good
PCB layout: (BOOST)
1) Minimize the area of the high current
switching loop of the rectifier diode and output
capacitor to avoid excessive switching noise.
2) 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.
3) Create a ground island (PGND) consisting of
TSSOP-20 BOOST
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 separate
ground planes.
4) 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.
5) 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.
6) 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.
7) 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.
8) Refer to the example of a PAM2842
Evaluation board layout below.
QFN6x6-40 BOOST
PCB Layout Example
Power Analog Microelectronics,Inc
www.poweranalog.com
14
09/2008 Rev 1.1