PCB Layout Guideline
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PCB Layout Guideline
1. To obtain optimal performance, the power input capacitors, connected from input to PGND, must be
placed as close as possible to the integrated circuit (IC).
2. The output inductor must be placed close to the IC and the output capacitor connected between the
inductor and PGND of the IC. The intent is to minimize the current path loop area from the SW pin
through the LC filter and back to the PGND pin. To prevent high-frequency oscillation problems, proper
layout to minimize high-frequency current path loop is critical.
3. The sense resistor must be adjacent to the junction of the inductor and output capacitor. Route the
sense leads connected across the RSNS back to the IC, close to each other (minimize loop area) or
on top of each other on adjacent layers. (Do not route the sense leads through a high-current path.)
4. Place all decoupling capacitors close to their respective IC pin and as close as possible to PGND. (Do
not place components such that routing interrupts power stage currents.) All small control signals must
be routed away from the high-current paths.
5. The printed-circuit board must have a ground plane (return) connected directly to the return of all
components through vias (two vias per capacitor for power-stage capacitors, two vias for the IC PGND,
one via per capacitor for small-signal components). A star ground design approach is typically used to
keep circuit block currents isolated (high-power/low-power small-signal) which reduces noise-coupling
and ground-bounce issues. A single ground plane for this design gives good results. With this small
layout and a single ground plane, no ground-bounce issue occurs, and having the components
segregated minimizes coupling between signals.
6. The high-current charge paths into VBUS, PMID, and from the SW pins must be sized appropriately for
the maximum charge current in order to avoid voltage drops in these traces. The PGND pins must be
connected to the ground plane to return current through the internal low-side FET.
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bq2415x RGY EVM (HPA255)
SLUU366A – March 2010 – Revised April 2010
Copyright © 2010, Texas Instruments Incorporated
