
N720 OpenLinux
Hardware User Guide
Copyright © Neoway Technology Co., Ltd
19
TVS diodes work in the same way as those in Figure 3-2 and they should meet the same
requirements.
Add surge protection to the front end of the power supply circuit if automotive battery supplies
power. The withstand voltage of the component should be larger than 42V.
Electronics used in vehicles must meet strict test standards and requirements for power supply, for
example, transient Pulse1/2a/5a. To meet these requirements, developers need to design a dedicated
protection circuit based on application scenarios. Figure 3-5 shows a simple reference circuit, which
might not pass the test for in-vehicle power supply. Texas Instruments launched a series of power supply
solutions to in-vehicle electronics. For more information, contact them.
PCB Design Guidelines
PCB layout and routing is also important for the performance of applications. Comply with the following
guidelines:
If the power supply circuits are laid on the outer layer of the PCB board, apply one complete
piece of copper foil to all VBAT pins.
If the power supply circuits are laid on the inner layer of the PCB board, apply one complete
piece of copper foil under all VBAT pins and connect the pins to the power supply through via
holes.
Place TVS diodes as close to the power input interface as possible to ensure that the surge
voltage can be clamped before the pulse is coupled to the neighbor traces.
Place C1 and C2 close to the module to respond transient peak currents.
Place bypass capacitors (C3, C4, and C5) close to the power pin of the module to filter out the
high-frequency signal from the power supply.
Ensure that the trace width of VBAT allows 2A current and ensure no obvious decrease of loop
voltages. Trace width of VBAT should be at least 2 mm and the ground plane should be as
complete as possible. The traces of power supply circuit should be as short and wide as
possible.
Noise-sensitive circuits such as audio and RF, should be placed far away from power supply
circuits, especially when DC-DC is adopted in the design.
Ensure that the loop is minimum in design with DC-DC since the frequency is high at SW pin.
Place sensitive components far away from SW pin in case of noise coupling. Place feeding
components as close to FB pin and COMP pin as possible.
Connect GND pins and bottom pads to ground to optimize heat sink and separate noise.
3.1.2 VDD_1P8
N720 OpenLinux provides one VDD_1P8 output, load current lower than 50 mA.
It is recommended that VDD_1P8 is used only for level shift and digital IO power supply. An ESD