B404/B402 Datasheet

The B404 and B402 have been deprecated. The recommended replacement is the B404X.

See the Supply Secure FAQ for more information.

Functional description

Overview

The B Series System-on-a-Module (SoM) is a cellular device with support for BLE (Bluetooth LE). It is based on the Nordic nRF52840 micro-controller.

The B Series is designed to be integrated into your circuit board design, plugging into a M.2 NGFF connector on your board, allowing the module to be changed or upgraded easily.

Features

Features - B402, B404

  • u-blox SARA-R410M-02B or R410M-03 LTE modem (B402, B404)
    • The B402 and B404 have been deprecated, replacement is the B404X. See the Supply Secure FAQ for more information.
    • LTE Cat M1 module
    • Support for United States, Canada, and Mexico only
    • 3GPP Release 13 LTE Cat M1
    • Cat M1 bands: 2, 3, 4, 5, 8, 12, 13, 20, 28
    • Embedded Particle EtherSIM (B404)
    • Embedded Particle SIM (B402)

1 Not all bands enabled in software by default

Features - All Models

  • Nordic Semiconductor nRF52840 SoC
    • ARM Cortex-M4F 32-bit processor @ 64MHz
    • 1MB flash, 256KB RAM
    • Bluetooth 5: 2 Mbps, 1 Mbps, 500 Kbps, 125 Kbps
    • Supports DSP instructions, HW accelerated Floating Point Unit (FPU) and encryption functions
    • Up to +8 dBm TX power (down to -20 dBm in 4 dB steps)
    • NFC-A tag
  • On-module additional 4MB SPI flash
  • 24 mixed signal GPIO (8 x Analog, 8 x PWM), UART, I2C, SPI
  • USB 2.0 full speed (12 Mbps)
  • JTAG (SWD) pins
  • RGB status pins for LED
  • Reset and Mode pins for buttons
  • On-module MFF2 Particle SIM
  • Two on-module U.FL connectors for external antennas
  • M.2 interface
  • FCC and PTCRB certified
  • RoHS compliant (lead-free)

Interfaces

Block diagram

Block Diagram

Power

VCC

VCC is used to supply power to the u-blox SARA-R410M/R410S cellular module. The recommended input voltage range on this pin is between 3.6V to 4.2V DC. Make sure that the supply can handle currents of at least 2 A.

3V3

3V3 is used to supply power to nRF52840, logic ICs, memory, etc.. The 3V3 input voltage range is between 3V to 3.6V DC, but 3.3V is recommended. Make sure that the supply can handle at least 150 mA, however it may need to be larger than that if you have additional 3.3V peripherals on your base board.

We do not recommend using a single 3.6V supply for both VCC and 3V3 as the cellular modem performance may be lower below 3.7V. Use two separate regulators for best results.

VBus

VBus is connected to the USB detect pin of nRF52840 to enables the USB interface. The recommended input voltage range is between 4.35V to 5.5V DC.


Antenna

There are two radios on the B402 module. A BLE radio (nRF52840) and a cellular radio (u-blox). We have provided two u.FL connectors to plug in the cellular and BLE antenna. These are required if you wish to use the cellular and BLE. If you do not need BLE, you do not need to connect the BLE antenna.

Certified Cellular Antenna

SKU Description
ANTCW2EA Particle Cellular Flex Antenna 2G/3G/LTE [x1]
ANTCW2TY Particle Cellular Flex Antenna 2G/3G/LTE Tray of 50 [x50]
  • Type: LTE Ultra Wide Band Flex Antenna
  • Frequency/band: 698 MHz-2690 MHz
  • RoHS Compliant
  • Mechanical Specs:
    • Dimensions: 97 x 21 x 0.2 mm
    • Mounting: 3M adhesive backed for application on non-metallic surfaces
    • Connector type: FPC + IPEX connector
    • Cable length: 210 mm
    • Gain: 4.71 dBi

General Antenna Guidance

  • The antenna placement needs to follow some basic rules, as any antenna is sensitive to its environment. Mount the antenna at least 10mm from metal components or surfaces, ideally 20mm for best radiation efficiency, and try to maintain a minimum of three directions free from obstructions to be able to operate effectively.
  • Needs tuning with actual product enclosure and all components.
  • For the BLE antenna, it is recommended to use a 2.4 GHz single-frequency antenna and not a 2.4 GHz + 5 GHz antenna, so as to avoid large gain at the frequency twice of 2.4 GHz which can cause the second harmonic radiation of 2.4 GHz to exceed standards.

Peripherals and GPIO

Peripheral Type Qty Input(I) / Output(O)
Digital 24 (max) I/O
Analog (ADC) 8 (max) I
UART 1 I/O
SPI 2 I/O
I2C 2 I/O
USB 1 I/O
PWM 8 (max) O
NFC 1 O

There are some optional B402 module specific I/O:

  • u-blox USB and VBUS (for u-blox firmware upgrades)

Note: All GPIOs are only rated at 3.3VDC max.

JTAG and SWD

The B402 module has 4 pads at the bottom exposing the SWD interface of the nRF52840. This interface can be used to debug your code or reprogram your B402 bootloader, device OS, or the user firmware. We use 4 pogo-pins connecting to these pads during production for firmware flashing.

Pogo Pins

Memory map

nRF52840 Flash Layout Overview

  • Bootloader (48KB, @0xF4000)
    • User Application
    • 256KB @ 0xB4000 (Device OS 3.1 and later)
    • 128KB @ 0xD4000 (Device OS 3.0 and earlier)
  • System (656KB, @0x30000)
  • SoftDevice (192KB)

External SPI Flash Layout Overview (DFU offset: 0x80000000)

  • OTA (1500KB, @0x00289000)
  • Reserved (420KB, @0x00220000)
  • FAC (128KB, @0x00200000)
  • LittleFS (2M, @0x00000000)

Pins and button definitions

Pinout diagram

Pinout

Pins SOM0 to SOM9 will vary across various SoM modules. For example, cellular-specific pins exists in this range.

Additionally there are RESERVED3 pins, whose functions vary depending on the SoM. For example, nRF52 MCU-based modules use some of these pins for additional ADC and GPIO. They are able to be used as described on the B402, but their function may be be different on future modules.

For maximum cross-module flexibility, you should try to use only the common pins when possible.

Pin description

# Pin Common Function nRF52 Description
1 GND GND POWER System ground.
2 VCC VCC POWER System power in, connect to the +LiPo or supply a fixed 3.6-4.2v power.
3 GND GND POWER System ground.
4 VCC VCC POWER System power in, connect to the +LiPo or supply a fixed 3.6-4.2v power.
5 GND GND POWER System ground.
6 VCC VCC POWER System power in, connect to the +LiPo or supply a fixed 3.6-4.2v power.
7 GND GND POWER System ground.
8 VCC VCC POWER System power in, connect to the +LiPo or supply a fixed 3.6-4.2v power.
9 GND GND POWER System ground.
10 3V3 3V3 POWER System power in, supply a fixed 3.0-3.6v power.
11 USB D+ USB D+ IO Data+ pin of the NRF52840 USB port.
12 3V3 3V3 POWER System power in, supply a fixed 3.0-3.6v power.
13 USB D- USB D- IO Data- pin of the NRF52840 USB port.
14 NC RESERVED3 NC Leave unconnected.
15 GND GND POWER System ground.
16 VUSB VUSB POWER System power in, USB detect pin for nRF52840. 5V on this pin enables the USB interface.
17 NFC1 SOM33 NFC input P0.9 NFC antenna connection.
18 NC RESERVED3 NC Leave unconnected.
19 NFC2 SOM43 NFC input P0.10 NFC antenna connection.
20 D1 SCL IO P0.27 I2C SCL, and digital only GPIO.
21 GND GND POWER System ground.
22 D0 SDA IO P0.26 I2C SDA, and digital only GPIO.
23 A0 ADC0 IO P0.3 Analog input ADC02, and digital GPIO.
32 MODE MODE IO P0.11 Connected to the MODE button input, and digital only GPIO.
33 A1 ADC1 IO P0.4 Analog input ADC12, and digital GPIO.
34 RESET RESET I Active-low reset input.
35 A2 ADC2 IO P0.28 Analog input ADC22, and digital GPIO.
36 D9 TX IO P0.6 Primarily used as UART TX, but can also be used as a digital GPIO.
37 A3 ADC3 IO P0.29 Analog input ADC32, and digital GPIO.
38 D10 RX IO P0.08 Primarily used as UART RX, but can also be used as a digital GPIO.
39 AGND AGND POWER System analog ground.
40 D3 RESERVED3 IO P1.1 UART flow control CTS, SCL1 (Wire1), SPI1 MOSI, digital only GPIO.
41 A4 RESERVED3 IO P0.30 Analog input ADC42, and digital GPIO.
42 D2 RESERVED3 IO P1.2 UART flow control RTS, SDA1 (Wire1), SPI1 SCK, digital only GPIO.
43 A5 RESERVED3 IO P0.31 Analog input ADC52, and digital GPIO.
44 u-blox USB D+ SOM0 IO Data+ pin of the cellular modem USB port.
45 A6 RESERVED3 IO P0.5 Analog input ADC62, and digital GPIO.
46 u-blox USB D- SOM1 IO Data- pin of the cellular modem USB port.
47 A7 RESERVED3 IO P0.2 Analog input ADC72, and digital GPIO.
48 D8 CS IO P1.3 SPI interface CS, and digital only GPIO.
49 AGND AGND POWER System analog ground.
50 D11 MISO IO P1.14 SPI interface MISO, and digital only GPIO.
51 NC RESERVED3 NC Leave unconnected.
52 D12 MOSI IO P1.13 SPI interface MOSI, and digital only GPIO.
53 NC RESERVED3 NC Leave unconnected.
54 D13 SCK IO P1.15 SPI interface SCK, and digital only GPIO.
55 NC RESERVED3 NC Leave unconnected.
56 GND GND POWER System analog ground.
57 NC RESERVED3 NC Leave unconnected.
58 NC RESERVED3 NC Leave unconnected.
59 NC RESERVED3 NC Leave unconnected.
60 NC RESERVED3 NC Leave unconnected.
61 RGBR RED IO P0.13 Red pin of the RGB LED.
62 D22 GPIO0 IO P0.24 GPIO0, digital only.
63 RGBG GREEN IO P0.14 Green pin of the RGB LED.
64 D23 GPIO1 IO P1.9 GPIO1, digital only.
65 RGBB BLUE IO P0.15 Blue pin of the RGB LED.
66 D4 PWM0 IO P1.8 SPI1 MISO, Digital only GPIO, and PWM0.
67 SIM_VCC1 SOM53 POWER Leave unconnected, 1.8V/3V SIM Supply Output from cellular modem.
68 D5 PWM1 IO P1.10 Digital only GPIO, and PWM1.
69 SIM_RST1 SOM63 IO Leave unconnected, 1.8V/3V SIM Reset Output from cellular modem.
70 D6 PWM2 IO P1.11 Digital only GPIO, and PWM2.
71 SIM_CLK1 SOM73 IO Leave unconnected, 1.8V/3V SIM Clock Output from cellular modem.
72 D7 PWM3 IO P1.12 Digital only GPIO, and PWM3.
73 SIM_DATA1 SOM83 IO Leave unconnected, 1.8V/3V SIM Data I/O of cellular modem with internal 4.7 k pull-up.
74 u-blox VBUS SOM23 IO USB detect pin for cellular modem. 5V on this pin enables the u-blox USB interface.
75 NC SOM93 NC Leave unconnected.

1These pins are connected to the internal MFF2 SIM and should be left open.

2A0-A7 are 12-bit Analog-to-Digital (A/D) inputs (0-4095).

3SoM-specific and Reserved pins will vary depending on module. They are able to be used on the B402, but their function may be be different on future modules.

By default, the Tinker application firmware enables the use of the bq24195 PMIC and MAX17043 fuel gauge. This in turn uses I2C (D0 and D1) and pin A6 (PM_INT). If you are not using the PMIC and fuel gauge and with to use these pins for other purposes, be sure to disable system power configuration. This setting is persistent, so you may want to disable it with your manufacturing firmware only.

System.setPowerConfiguration(SystemPowerConfiguration());

If you are using Ethernet with the B Series SoM, the following pins are used by Ethernet:

Device OS Pin M.2 Pin Ethernet Pin
MISO 50 SPI MISO
MOSI 52 SPI MOSI
SCK 54 SPI SCK
A7 47 nRESET
D22 62 nINTERRUPT
D8 48 nCHIP SELECT

LED status

System RGB LED

Unlike the Boron, the B402 module does not have an on-module RGB system status LED. We have provided its individual control pins for you to connect an LED of your liking. This will allow greater flexibility in the end design of your products.

A detailed explanation of different color codes of the RGB system LED can be found here.

Technical specifications

Absolute maximum ratings [1]

Supply voltages

Parameter Symbol Min Typ Max Unit
Supply voltages
Supply Input Voltage VCC -0.3 +6.0 V
Supply Input Voltage 3V3 -0.3 +3.9 V
VBUS USB supply voltage VUSB -0.3 +5.8 V
I/O pin voltage
VI/O, VDD ≤ 3.6 V IO -0.3 VDD + 0.3 V
VI/O, VDD > 3.6 V IO -0.3 +3.9 V
NFC antenna pin current
INFC1/2 NFC1/NFC2 80 mA
Radio
BT RF input level (52840) 10 dBm
Environmental
Storage temperature -40 +85 °C

[1] Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

Parameter Symbol Min Typ Max Unit
Supply voltages
Supply Input Voltage VCC +3.6 +3.8 +4.2 V
Supply Input Voltage 3V3 +3.0 +3.3 +3.6 V
VBUS USB supply voltage VUSB +4.35 +5.0 +5.5 V
Environmental
Normal operating temperature1 -20 +25 +65 °C
Extended operating temperature2 -40 +85 °C
Humidity Range Non condensing, relative humidity 95 %

Notes:

1 Normal operating temperature range (fully functional and meet 3GPP specifications).

2 Extended operating temperature range (RF performance may be affected outside normal operating range, though module is fully functional)


Power consumption

Parameter Symbol Min Typ Peak Unit
Operating Current (uC on, peripherals and radio disabled) Iidle 4.48 4.71 5.17 mA
Operating Current (uC on, cellular on but not connected) Icell_idle 5.1 45.2 166 mA
Operating Current (uC on, cellular connecting to tower) Icell_conn_twr 13.7 56.0 192 mA
Operating Current (uC on, cellular connecting to cloud) Icell_conn_cloud 63.2 185 mA
Operating Current (uC on, cellular connected but idle) Icell_cloud_idle 13.4 15.5 98.3 mA
Operating Current (uC on, cellular connected and transmitting) Icell_cloud_tx 9.47 66.3 192 mA
STOP mode sleep, GPIO wake-up Istop_gpio 552 555 559 uA
STOP mode sleep, analog wake-up Istop_analog 554 557 559 uA
STOP mode sleep, RTC wake-up Istop_intrtc 553 556 558 uA
STOP mode sleep, BLE wake-up, advertising Istop_ble_adv 631 2650 uA
STOP mode sleep, BLE wake-up, connected Istop_ble_conn 47.3 630 1540 uA
STOP mode sleep, serial wake-up Istop_usart 553 556 558 uA
STOP mode sleep, cellular wake-up Istop_cell 8.87 9.65 63.6 mA
ULP mode sleep, GPIO wake-up Iulp_gpio 44.7 47.6 49.6 uA
ULP mode sleep, analog wake-up Iulp_analog 45.0 47.8 49.5 uA
ULP mode sleep, RTC wake-up Iulp_intrtc 43.4 46.4 47.9 uA
ULP mode sleep, BLE wake-up, advertising Iulp_ble_adv 130 2560 uA
ULP mode sleep, BLE wake-up, connected Iulp_ble_conn 121 1010 uA
ULP mode sleep, serial wake-up Iulp_usart 554 557 559 uA
ULP mode sleep, cellular wake-up Iulp_cell 0.37 9.47 53.7 mA
HIBERNATE mode sleep, GPIO wake-up Ihib_gpio 23.6 26.0 29.7 uA
HIBERNATE mode sleep, analog wake-up Ihib_analog 23.9 26.5 30.5 uA

1The min, and particularly peak, values may consist of very short transients. The typical (typ) values are the best indicator of overall power consumption over time. The peak values indicate the absolute minimum capacity of the power supply necessary, not overall consumption.


Radio specifications

The B Series SoM has two radio modules.

nRF52840

  • Bluetooth® 5, 2.4 GHz
    • 95 dBm sensitivity in 1 Mbps Bluetooth® low energy mode
    • 103 dBm sensitivity in 125 kbps Bluetooth® low energy mode (long range)
    • 20 to +8 dBm TX power, configurable in 4 dB steps

u-blox SARA-R410M-02B or R410M-03

Parameter Value
Protocol stack 3GPP Release 13
RAT LTE Cat M1 Half-Duplex
LTE FDD Bands Band 12 (700 MHz)
Band 28 (700 MHz)
Band 13 (750 MHz)
Band 20 (800 MHz)
Band 5 (850 MHz)
Band 8 (900 MHz)
Band 4 (1700 MHz)
Band 3 (1800 MHz)
Band 2 (1900 MHz)
Power class Class 3 (23 dBm)
  • LTE Cat M1 for United States, Canada, and Mexico.
  • Not all bands are enabled in software by default.
  • Particle LTE Cat M1 devices are not certified for use in Europe or other countries that follow EU certification requirements.

I/O Characteristics

These specifications are based on the nRF52840 datasheet.

Symbol Parameter Min Typ Max Unit
VIH Input high voltage 0.7 xVDD VDD V
VIL Input low voltage VSS 0.3 xVDD V
VOH,SD Output high voltage, standard drive, 0.5 mA, VDD ≥1.7 VDD - 0.4 VDD V
VOH,HDH Output high voltage, high drive, 5 mA, VDD >= 2.7 V VDD - 0.4 VDD V
VOH,HDL Output high voltage, high drive, 3 mA, VDD >= 1.7 V VDD - 0.4 VDD V
VOL,SD Output low voltage, standard drive, 0.5 mA, VDD ≥1.7 VSS VSS + 0.4 V
VOL,HDH Output low voltage, high drive, 5 mA, VDD >= 2.7 V VSS VSS + 0.4 V
VOL,HDL Output low voltage, high drive,3 mA, VDD >= 1.7 V VSS VSS + 0.4 V
IOL,SD Current at VSS+0.4 V, output set low, standard drive, VDD≥1.7 1 2 4 mA
IOL,HDH Current at VSS+0.4 V, output set low, high drive, VDD >= 2.7V 6 10 15 mA
IOL,HDL Current at VSS+0.4 V, output set low, high drive, VDD >= 1.7V 3 mA
IOH,SD Current at VDD-0.4 V, output set high, standard drive, VDD≥1.7 1 2 4 mA
IOH,HDH Current at VDD-0.4 V, output set high, high drive, VDD >= 2.7V 6 9 14 mA
IOH,HDL Current at VDD-0.4 V, output set high, high drive, VDD >= 1.7V 3 mA
tRF,15pF Rise/fall time, standard drivemode, 10-90%, 15 pF load1 9 ns
tRF,25pF Rise/fall time, standard drive mode, 10-90%, 25 pF load1 13 ns
tRF,50pF Rise/fall time, standard drive mode, 10-90%, 50 pF load1 25 ns
tHRF,15pF Rise/Fall time, high drive mode, 10-90%, 15 pF load1 4 ns
tHRF,25pF Rise/Fall time, high drive mode, 10-90%, 25 pF load1 5 ns
tHRF,50pF Rise/Fall time, high drive mode, 10-90%, 50 pF load1 8 ns
RPU Pull-up resistance 11 13 16
RPD Pull-down resistance 11 13 16
CPAD Pad capacitance 3 pF
CPAD_NFC Pad capacitance on NFC pads 4 pF
INFC_LEAK Leakage current between NFC pads when driven to different states 1 10 μA
  • Rise and fall times based on simulations

  • GPIO default to standard drive (2mA) but can be reconfigured to high drive (9mA) in Device OS 2.0.0 and later using the pinSetDriveStrength() function.

Mechanical specifications

Dimensions and Weight

Parameters Value Unit
Width 30 mm
Height 42 mm
Thickness 5.5 mm
Weight 6.2 grams

Mechanical drawing

Mechanical Drawing

Dimensions are in millimeters.


Mating connector and land pattern

The mating connector is a an M.2 (NGFF) type 4. Note that there are several different key configurations for the M.2, and type 4 is different than is commonly used on SSDs.

One compatible connector is the TE 2199230-4. It is widely available including at suppliers such as DigiKey.

M.2 Connector

Screw Assembly

Screw Assembly

We recommend this screw assembly to securely affix the B series SoM to your circuit board. From top to bottom:

  • M3 screw, 3mm long
  • M3 washer
  • M3 standoff, 2.45mm

Standoff

  • Mounting hole, 2.6 mm metal hole, 3.1mm metal ring diameter (picture is of the bottom side of the circuit board)

Bottom

  • An alternative design uses a JAE SM3ZS067U410-NUT1-R1200 standoff. It's reflow soldered to your base board and has a threaded hole for a M2*3 screw to hold down the SoM. This may be easier to obtain.

  • Note that a hold-down screw is required because the M.2 connector does not have integrated locks and the SoM will pop up if not attached to the base board.

Design Considerations

We strongly recommend against placing components under the SOM board because there is not enough height.

Keep-Out Area

Product Handling

ESD Precautions

The B series contains highly sensitive electronic circuitry and is an Electrostatic Sensitive Device (ESD). Handling an B series without proper ESD protection may destroy or damage it permanently. Proper ESD handling and packaging procedures must be applied throughout the processing, handling and operation of any application that incorporates the B series module. ESD precautions should be implemented on the application board where the B series is mounted. Failure to observe these precautions can result in severe damage to the B series!

Connectors

The U.FL antenna connector is not designed to be constantly plugged and unplugged. The antenna pin is static sensitive and you can destroy the radio with improper handling. A tiny dab of glue (epoxy, rubber cement, liquid tape or hot glue) on the connector can be used securely hold the plug in place.

The M.2 edge connector is static sensitive and should be handled carefully. The M.2 connector is not designed for repeated removal and insertion of the module.

Schematics

Microcontroller

Microcontroller

u-blox cellular modem

u-blox cellular modem

M.2 connector

M.2 Connector

Note: The labels for CTS and RTS are reversed in this schematic.

SIM and Flash

SIM and Flash

Buffers

Buffers

Default settings

The B series comes pre-programmed with a bootloader and a user application called Tinker. This application works with an iOS and Android app also named Tinker that allows you to very easily toggle digital pins, take analog and digital readings and drive variable PWM outputs.

The bootloader allows you to easily update the user application via several different methods, USB, OTA, Serial Y-Modem, and also internally via the Factory Reset procedure. All of these methods have multiple tools associated with them as well.


Country compatibility

Country Model Technologies Carriers
Canada B404 M1 Bell Mobility, Rogers Wireless, Telus
Mexico B404 M1 AT&T
United States B404 M1 AT&T

Ordering information

SKU Description Region Modem EtherSIM Lifecycle Replacement
B404MEA B Series LTE CAT-M1 (NorAm), [x1] NORAM R410 GA
B402MEA B Series LTE CAT-M1 (NorAm), [x1] NORAM R410 NRND B404MEA
B402MTY B Series LTE CAT-M1 (NorAm), Tray [x50] NORAM R410 Deprecated B404MTY
B404MTY B Series LTE CAT-M1 (NorAm), Tray [x50] NORAM R410 Deprecated

Revision history

Revision Date Author Comments
001 29 Apr 2019 RK Initial Release
002 03 Feb 2020 RK Fixed number of I2C, SPI, and PWM
003 18 Feb 2020 RK Keep-out diagram M.2 connector was upside-down
004 16-Sep-2020 RK Added power consumption information
005 16-Dec-2020 RK Added missing TBD power consumption values
006 04-Jan-2021 RK Fix incorrect pin number on pogo pin diagram
007 03-Feb-2021 RK Split u-blox schematics into two images
008 15-Mar-2021 RK Updated model, carrier, ordering information
009 23-Mar-2021 RK Pins 40 and 42 functions were reversed
010 26-Apr-2021 RK Added B404 model number
011 14-May-2021 RK Pins 40 and 42 were not actually reversed
012 19-May-2021 RK List Ethernet reserved pins
013 28-Jun-2021 RK Added Device OS 3.1 memory map information
014 10-Sep-2021 RK Changed wording of peak vs. max current
015 14-Mar-2022 RK Added B404X, deprecation notice
016 05-May-2022 RK Corrected number of PWM outputs (8)
017 11-Aug-2022 RK Correct typo in 3V3 explanation
018 29-Aug-2022 RK Split out B404X into separate datasheet