PAM2846 Datasheet, PDF (12/14 Pages) Power Analog Micoelectronics – Integrated 6 String LED Boost Type Driver

PAM2846
Integrated 6 String LED Boost Type Driver
PCB Layout Guidelines
Careful PCB layout is important for proper
operation. Use the following guidelines for good
PCB layout:
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, to 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
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
PAM2846 Evaluation Board
noise spikes. Create an analog ground island
(GND) consisting of the output voltage
detection-divider ground connection, the I_SET
resistor connections, VCC-5V and VCC-driver
capacitor connections, and the device's exposed
backside pad. Connect the GND and PGND
islands by connecting the GND pins directly to
the exposed backside pad. Make sure no other
connections between these separate ground
planes.
4) Place the output voltage setting-divider
resistors as close to the OVP 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 and ground. If
possible, avoid running the SW node from one
side of the PCB to the other.
7) Refer to the PAM2846 Evaluation board for an
example of proper board layout.
Power Analog Microelectronics,Inc
www.poweranalog.com
12
07/2008 Rev 1.2