RAK4630 PCB Power & Antenna Layout Questions

WisBlock
1

Hi RAK Team / Community,

I’m designing a PCB with a RAK4630 module powered by a coin cell through a TPS61094 regulator. I want to make sure my power and RF layout is correct before I proceed. Here’s my current plan and the questions I have:

:one: Power Setup

Coin cell → TPS61094 regulator → 3.3 V rail
VDD_NRF connected to 3.3 V
VBAT pins: VBAT_NRF, VBAT_SX, VBAT_IO_SX all tied to VDD_NRF (single-rail design)

Decoupling capacitors (all 0402):

Pin Capacitors
VDD_NRF 0.1 µF + 10 µF + 3×22 µF
VBAT_NRF 0.1 µF
VBAT_SX 0.1 µF + 10 µF
VBAT_IO-SX 0.1 µF

Questions:

  1. Is it correct to tie all VBAT pins to VDD_NRF in a single-rail coin-cell setup?
  2. Are the decoupling caps sufficient for LoRa TX bursts (~100–150 mA)?
  3. Any concern about additional caps affecting coin-cell current draw or module operation?
    :two: RF Pins

RF-LORA and RF-BT pins **left as they are on the module
Plan to use an external antenna via the onboard U.FL port

Questions:
4. Can I leave the RF pins as is, since the module already has internal matching and routing?
5. Any recommendations for connecting the external antenna to maintain proper RF performance?

image
image1296×732 22.1 KB

2

Welcome to RAK forum @fab .

  1. The RAK4630 works in high voltage mode. You need to use a higher VBAT than your VDD.
  2. This is something to be tested. You are using a switching regulator and this are prone to stability issues.
  3. Something to be tested too. Most of WisBlock modules are run by Li-Ion batteries. We have limited info with regards to coin cell and its specific characteristics. There are coincells that has low current drawn specs.
  4. Yes. You can leave it floating.
  5. Any properly tuned antenna for the frequency you need will work fine. Antenna characteristics are different so you need to take not on those - propagation profile, gain, etc.
3
  1. VBAT pins: VBAT_NRF, VBAT_SX, VBAT_IO_SX all tied to VDD_NRF (single-rail design) they are all tied to 3.3V is this okey ?
  2. The regulator is a boost up from 3v coin cell to 3.3v
  3. So you will recommend lipo battery than the coin cell ?
4
  1. The default RAK4630 will work on this configuration but it is not how nRF52 state it on its specifications. Since RAK4630 is in high voltage mode by default, VBAT must be higher. Please check the link I shared.
  2. I understand.
  3. I am not saying you use Li-Po. What I am saying is that we have more use case that uses Li-Ion batteries than Coin cell. We cannot provide expert advise on coin cell operation.
5

  1. Well thanks as i can see we are not actually working on higher voltage we are working on 3.3V based on this Image i can see all VBAT_NRF, VBAT_SX, VBAT_IO_SX and VDD_NRF they are all tied to 3.3V so i think this configuration is the same with mine

    image
    image827×673 93.6 KB

  2. Is there any affordable outdoor gateway you can recommand ? which have the simcard slot working on europe ? should also be economic

6

  1. We will update the docs and put note that this configuration requires a special RAK4630 variant.

  2. Low cost outdoor gateway is this - RAK7267 WisGate Soho Pro - LoRaWAN, LTE, Wi-Fi, GPS - Indoor & outdoor LoRaWAN Gateway