BQ24266_15 Datasheet, PDF (32/41 Pages) Texas Instruments – bq24266 3A, 30V Standalone Single-Input, Single-Cell Switchmode Li-Ion Battery Charger

bq24266
SLUSBY5F – JUNE 2014 – REVISED AUGUST 2015
10 Layout
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10.1 Layout Guidelines
The following provides some guidelines:
• Place 1µF input capacitor as close to PMID pin and PGND pin as possible to make high frequency current
loop area as small as possible.
• Connect the GND of the PMID and IN caps as close as possible.
• Place 4.7µF input capacitor as close to IN pin and PGND pin as possible to make high frequency current loop
area as small as possible.
• The local bypass capacitor from SYS to GND should be connected between the SYS pin 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.
• Place all decoupling capacitors close to their respective IC pin and as close as to PGND as possible. Do not
place components such that routing interrupts power stage currents. All small control signals should be routed
away from the high current paths.
• The PCB should have a ground plane (return) connected directly to the return of all components through vias.
Two vias per capacitor for power-stage capacitors and one via per capacitor for small-signal components. It is
also recommended to put vias inside the PGND pads for the IC, if possible. 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.
• The high-current charge paths into IN, BAT, SYS 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 should be
connected to the ground plane to return current through the internal low-side FET.
• For high-current applications, the balls for the power paths should be connected to as much copper in the
board as possible. This allows better thermal performance as the board pulls heat away from the IC.
10.2 Layout Example
It is important to pay special attention to the PCB layout. Figure 30 provides a sample layout for the high current
paths of the bq24266RGE.
SW
PGND
PMID
BOOT
PMID and IN
Cap Gnds
Close together
SYS Cap
Close to
SYS Pins
IN Cap
Close to
IN Pin
BAT Cap
Close to
BAT Pins
Thermal
Vias connect
To GND
Figure 30. Recommended bq24266 PCB Layout for QFN Package
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