Power Supply Mode For The Rf Transceiver; Dc-Dc Converter Mode - Renesas RA4W1 Application Note

RA4W1 Group

2.4 Power supply mode for the RF transceiver

Note the followings for an external circuit design in two power supply modes which are the DC-DC converter
mode and the linear regulator mode in the RF transceiver. Users should select the power mode after
understanding a trade-off between an operating current and Bill Of Materials (BOM) cost of the RF
transceiver. For the lower operating current, User should select the DC-DC converter mode. On the other
hand, Users should select the linear regulator mode to reduce inductors, which saves the BOM cost and
board area.
2.4.1

DC-DC converter mode

Note the followings for an external circuit design of the DC-DC converter mode.
Figure 2-6 shows an example of the external circuits for the DC-DC converter mode, Figure 2-7 shows an
example of the pattern around power supply line for the DC-DC converter mode.
• Make the signal pattern from the "DCLOUT" pin to the "VSS_RF" through the inductor "L1" and the
capacitor "C1" shorter and wider to reduce impedance as possible. Place ground pattern in the area
which is enclosed with the line connecting the "DCLOUT" and the "DCLIN_A", as shown in Figure 2-7. In
addition, connect the capacitor "C1" and the "VSS_RF" to this ground pattern.
• Connect the line connecting the "DCLOUT" pin and the "DCLIN_A" pin on the component side of the
board without any Via.
• Reduce loop area which is enclosed with the line connecting the "DCLOUT" pin and the "DCLIN_A" pin as
possible.
• Placing the inductor "L1", "L2" and the capacitor "C1" as close as possible to the "DCLOUT" pin is
recommended.
• Do not place any SMD component except the external circuits for the DC-DC converter mode, on the loop
which is enclosed with line connecting the "DCLOUT" pin and the "DCLIN_A" pin.
• Ensure the return path in layer-2, and layer-3 if possible, from the ground in the loop to the "Exposed Die
Pad (VSS_RF)", as shown in Figure 2-7.
• Recommended electrical characteristics of the "L1" are the followings:
 Inductance
 Rated current
 DC resistance
 Self-resonate frequency ≥ 30 MHz
 Good DC superimposing characteristic
• The capacitance "C1" should be less than or equal to 2.2 μF +/– 20 %
• Do not place other analog signal, power, and ground lines than the external circuit for the DC-DC
converter mode, on and below the circuit area.
• With mounting the inductor "L2", noise caused by the DC-DC converter can be reduced. Therefore, it is
recommended to prepare a mount space of the "L2" on a board pattern.
R01AN4886EJ0100 Rev.1.00
May.07.20
Guidelines for 2.4 GHz Wireless Board Design
= 10 μH +/– 20%
≥ 90 mA
≤ 1.0 ohm
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