BQ25700A Datasheet, PDF (73/82 Pages) Texas Instruments – SMBus Multi-Chemistry Battery Buck-Boost Charge Controller With System Power Monitor and Processor Hot Monitor

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11 Layout
bq25700A
SLUSCQ8 – MAY 2017
11.1 Layout Guidelines
The switching node rise and fall times should be minimized for minimum switching loss. Proper layout of the
components to minimize high frequency current path loop (see Layout Example section) is important to prevent
electrical and magnetic field radiation and high frequency resonant problems. Here is a PCB layout priority list for
proper layout. Layout PCB according to this specific order is essential.
1. Place the input capacitor as close as possible to the supply of the switching MOSFET and ground
connections. Use a short copper trace connection. These parts must be placed on the same layer of PCB
using vias to make this connection.
2. The device must be placed close to the gate pins of the switching MOSFET. Keep the gate drive signal
traces short for a clean MOSFET drive. The device can be placed on the other side of the PCB of switching
MOSFETs.
3. Place an inductor input pin as close as possible to the output pin of the switching MOSFET. 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.
4. The charging current sensing resistor should be placed right next to the inductor output. Route the sense
leads connected across the sensing resistor back to the device in same layer, close to each other (minimize
loop area) and do not route the sense leads through a high-current path (see Figure 61 for Kelvin connection
for best current accuracy). Place a decoupling capacitor on these traces next to the device.
5. Place an output capacitor next to the sensing resistor output and ground.
6. Output capacitor ground connections must be tied to the same copper that connects to the input capacitor
ground before connecting to system ground.
7. Use a single ground connection to tie the charger power ground to the charger analog ground. Just beneath
the device, use analog ground copper pour but avoid power pins to reduce inductive and capacitive noise
coupling.
8. 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 using a 0-Ω resistor to tie analog ground to power ground (power pad should tie to
analog ground in this case if possible).
9. Decoupling capacitors must be placed next to the device pins. Make trace connection as short as possible.
10. It is critical that the exposed power pad on the backside of the device package be soldered to the PCB
ground.
11. The via size and number should be enough for a given current path. See the EVM design (SLUUBG6) for
the recommended component placement with trace and via locations. For WQFN information, see SLUA271.
11.2 Layout Example
11.2.1 Layout Consideration of Current Path
PHASE
L1 R1
V
BAT
High
V_IN
Frequency
Current
BAT
C1
Path
GND
C2
Figure 60. High Frequency Current Path
Copyright © 2017, Texas Instruments Incorporated
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