BQ25895_16 Datasheet, PDF (55/67 Pages) Texas Instruments – Adjustable Voltage 3.1-A Boost Operation

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bq25895
SLUSC88A – MARCH 2015 – REVISED MAY 2016
10 Power Supply Recommendations
In order to provide an output voltage on SYS, the device requires a power supply between 3.9 V and 14 V input
with at least 100-mA current rating connected to VBUS or a single-cell Li-Ion battery with voltage > V_BATUVLO
connected to BAT. The source current rating needs to be at least 3 A in order for the buck converter of the
charger to provide maximum output power to SYS.
11 Layout
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 Figure 60) 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 input capacitor as close as possible to PMID pin and GND pin connections and use shortest copper
trace connection or GND plane.
2. Place inductor input terminal to SW pin as close 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 output capacitor near to the inductor and the IC. Ground connections need to be tied 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 using a 0Ω resistor to tie analog ground to power ground.
5. Use single ground connection to tie charger power ground to charger analog ground. Just beneath the IC.
Use ground copper pour but avoid power pins to reduce inductive and capacitive noise coupling.
6. Decoupling capacitors should be placed next to the IC pins and make 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 VQFN
information, refer to SCBA017 and SLUA271.
11.2 Layout Example
Figure 60. High Frequency Current Path
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