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Datasheet of BQ25892EVM-664 - EVAL MOD BQ25892 COMPLETE CHARGR
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PCB Layout Guideline
11
SLUUBA2B – March 2015 – Revised November 2015
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Copyright © 2015, Texas Instruments Incorporated
bq25890EVM, bq25892EVM, bq25895EVM, bq25896EVM and
bq25895MEVM(PWR664)
in series with the battery or battery simulator should not be set to auto-range and may need be
removed entirely. An alternate method for measuring charge current is to either use an oscilloscope
with hall effect current probe or place a 1% or better, thermally capable (for example, 0.010
Ω
in 1210
or larger footprint) resistor in series between the BAT pin and battery and measure the voltage across
that resistor.
3
PCB Layout Guideline
Minimize the switching node rise and fall times for minimum switching loss. Proper layout of the
components minimizing high-frequency current path loop is important to prevent electrical and magnetic
field radiation and high-frequency resonant problems. This PCB layout priority list must be followed in the
order presented for proper layout:
1. Place the input capacitor as close as possible to the PMID and GND pin connections and use the
shortest possible copper trace connection or GND plane.
2. Place the inductor input terminal as close to the SW pin as possible. Minimize the copper area of this
trace to lower electrical and magnetic field radiation but make the trace wide enough to carry the
charging current. Do not use multiple layers in parallel for this connection. Minimize parasitic
capacitance from this area to any other trace or plane.
3. Put an output capacitor near to the inductor and the IC. Tie ground connections to the IC ground with a
short copper trace connection or GND plane.
4. Route analog ground separately from power ground. Connect analog ground and connect power
ground separately. Connect analog ground and power ground together using power pad as the single
ground connection point or use a 0-
Ω
resistor to tie analog ground to power ground.
5. Use a single ground connection to tie the charger power ground to the charger analog ground just
beneath the IC. Use ground copper pour but avoid power pins to reduce inductive and capacitive noise
coupling.
6. Place decoupling capacitors next to the IC pins and make the trace connection as short as possible.
7. It is critical that the exposed power pad on the backside of the IC package be soldered to the PCB
ground. Ensure that there are sufficient thermal vias directly under the IC, connecting to the ground
plane on the other layers.
8. The via size and number should be enough for a given current path.
See the EVM design for the recommended component placement with trace and via locations. For the
QFN information, refer to
Quad Flatpack No-Lead Logic Packages
(
SCBA017
) and
QFN/SON PCB
Attachment
(
SLUA271
).
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