•
The PCB traces connecting the FN990 and bypass capacitor must be wide
enough to avoid voltage drops even when 4A current absorption peaks
occur. These traces should be kept as short as possible.
•
The PCB traces connecting the switching output to the inductor and the
switching diode must be kept as short as possible by placing the inductor
and the diode as close as possible to the power switching IC (only for the
switching power supplies). This is done to reduce the radiated field (noise)
at the switching frequency (usually 100-500 kHz).
•
Use a good common ground plane.
•
Place the power supply on the board to ensure that the high current return
paths in the ground plane do not overlap any noise-sensitive circuitry, such
as microphone amplifier/buffer or earphone amplifier.
•
The power supply input cables must be kept separate from noise-sensitive
lines, such as microphone/earphone cables.
5.4 RTC
The RTC within the FN990 Family module does not have a dedicated RTC supply pin. The
RTC block is supplied by the VPH_PWR supply.
If the VPH_PWR power is removed, RTC is not maintained so if it is necessary to maintain
an internal RTC, VPH_PWR must be supplied continuously.
5.5 Reference Voltage
The 1.8V regulated power supply output is supplied as the reference voltage to a host
board. This output is active when the module is turned ON and turns OFF when the
module is shut down.
The table below lists the reference voltage of the FN990 Family modules.
Table 17: FN990 Family Reference Voltage
5.6 Internal LDO for GNSS Bias
The LDO for GNSS bias is applied inside the FN990 Family model.
The voltage supply is generated internally by the FN990 (LDO) and is fed to GNSS active
antenna.
The table below lists the LDO for GNSS bias of FN990 Family modules.
Table 18: LDO for GNSS bias of FN990 Family
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