NEO-D9S - Integration manual
bias supply due to power dissipation. Take the current limit capability of the antenna bias
supply into consideration. In the case where the module supplies the voltage via VCC_RF, a
higher value resistor will be needed to ensure the module supply inductor is protected. The
current should be limited to below 150 mA at the module supply voltage under short-circuit
conditions. In this case a value of 17 Ω or more is required at a module supply of 3 V to limit
short circuit current to 150 mA. The DC resistance of the bias-t inductor is assumed to be
1-2 Ω and the module internal feed inductor is assumed to be 1.2 Ω.
If the VCC_RF voltage does not match with the supply voltage of the active antenna, use a filtered
external supply.
The power dissipation in the resistor and inductor needs to be taken into account based on
the supply voltage and short circuit current. The bias-t inductor current capability and the
bias resistor value need to be calculated as shown above. The supply voltage for the bias-t
and its current capability is part of the calculation.
Figure 18: NEO-D9S external voltage antenna bias
4.3 Power supply
The u-blox NEO-D9S module has two power supply pins: VCC and V_USB.
4.3.1 VCC: Main supply voltage
The
VCC
pin is connected to the main supply voltage. During operation, the current drawn by the
module can vary by some orders of magnitude. For this reason, it is important that the supply
circuitry be able to support the peak power for a short time (see the applicable data sheet [
] for
specification).
To reduce peak current during power on, users can employ an LDO that has an in-built
current limiter.
Do not add any series resistance greater than 0.2
Ω
to the VCC supply as it will generate
input voltage noise due to dynamic current conditions.
For the NEO-D9S module the equipment must be supplied by an external limited power
source in compliance with the clause 2.5 of the standard IEC 60950-1.
4.3.2 NEO-D9S power supply
The NEO-D9S requires a low-noise, low-dropout voltage, and a very low source impedance power
supply of 3.3 V typically. No inductors or ferrite beads should be used from LDO to the module
VCC pin. The peak currents need to be taken into account for the source supplying the LDO for the
module.
UBX-19026111 - R07
4 Design
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