LN920 HW Design Guide
1VV0301730 Rev. 1
Page 32 of 81
2021-08-11
Not Subject to NDA
Note: For best RF performance, thermal dissipation and mechanical
stability, the LN920 must be connected to the ground and metal
chassis of the host board.
The module shield and host device main board or metal chassis
should be connected by means of conductive materials.
4.3.3.
Power Supply PCB Layout Guidelines
As mentioned in the electrical design guidelines, the power supply shall have a low ESR
capacitor on the output to absorb current peaks on the input and protect the supply from
voltage spikes. Placement of this component is crucial for the correct working of the
circuitry. A misplaced component can be useless or can even decrease the power supply
performances.
•
The Bypass low ESR capacitor must be placed closed to the LN920 power input
pins or. In the case the power supply is a switching type, it can be placed close to
the inductor to reduce ripple, provided the PCB trace from the capacitor to the
LN920 is wide enough to ensure a voltage dropless connection even during an
TBD(A) current peaks.
•
The protection diode must be placed close to the input connector where the power
source is drained.
•
PCB traces from the input connector to the power regulator IC must be wide
enough to ensure no voltage drops occurs when an TBD A current peak is
absorbed.
•
The PCB traces to the LN920 and the Bypass capacitor must be wide enough to
ensure no significant voltage drops occurs. This is for the same reason as previous
point. Try to keep this trace as short as possible.
•
To reduce EMI due to switching, it is important to keep the mesh involved very
small; therefore the input capacitor, the output diode (if not embodied in the IC)
and the regulator, shall form a very small loop. This is done in order to reduce the
radiated field (noise) at the switching frequency (100-500 kHz usually).
•
Power supply placement on the board should be designed to guarantee that the
high current return paths on the ground plane are not overlapping to any noise
sensitive circuitry, such as audio amplifiers etc.
