PAM2842 Datasheet, PDF (13/17 Pages) Power Analog Micoelectronics – High Power LED Driver

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PAM2842
Application Information (cont.)
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-cur rent 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 highcurrent 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
noise spikes. Create an analog ground island (AGND) consisting of the output voltage detection-divider ground connection, the Sense-pin
connection, V_CC-5V and V_CC-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.
TSSOP-20 Boost
QFN6x6-40 Boost
PCB Layout Example
PAM2842
Document number: DSxxxxx Rev. 1 - 2
13 of 17
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October 2012
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