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Si4438-B1C-FMR

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SILICON LABS RF Transceiver ICs, QFN-20-EP(4x4). Pinout cross-checked by two models against the datasheet, KiCad symbol/footprint/3D.

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Si4438-B1C-FMR

SILICON LABS · RF Transceiver ICs · QFN-20-EP(4x4)

Si4438-B1C-FMR from SILICON LABS, in a QFN-20-EP(4x4). Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin Name Type Function
1 SDN input Shutdown input, 0 to VDD V digital; SDN must be 0 in all modes except Shutdown, and when SDN = 1 the chip is fully shut down and register contents are lost.
2 RXp input Differential RF input pin of the LNA, to be matched per the application schematic.
3 RXn input Differential RF input pin of the LNA, to be matched per the application schematic.
4 TX output Transmit output pin; the PA output is an open-drain connection, so the L-C match must supply VDD (+3.3 VDC nominal) to this pin.
5 NC unconnected It is recommended to connect this pin to GND per the reference design schematic; it is not connected internally to any circuitry.
6 VDD power_in Supply voltage input to internal regulators, +1.8 to +3.8 V, with a recommended supply of +3.3 V.
7 TXRAMP output Programmable bias output with ramp capability for an external FET PA, as described in section 5.4.
8 VDD power_in Supply voltage input to internal regulators, +1.8 to +3.8 V, with a recommended supply of +3.3 V.
9 GPIO0 bidirectional General purpose digital I/O that can be configured for functions such as microcontroller clock output, FIFO status, POR, wake-up timer, low battery detect, TRSW and antenna diversity control.
10 GPIO1 bidirectional General purpose digital I/O; the datasheet gives no further description for this pin.
11 nIRQ output General microcontroller interrupt status output that goes low when any enabled interrupt event occurs; no external pull-up is required but one may be desirable when multiple interrupt lines are connected.
12 SCLK input Serial clock input, 0 to VDD V digital; data is clocked into the Si4438 on positive edge transitions.
13 SDO output Serial data output, 0 to VDD V digital, providing serial readback of the internal control registers.
14 SDI input Serial data input, 0 to VDD V digital, providing the serial data stream for the 4-line serial bus.
15 nSEL input Serial interface select input, 0 to VDD V digital, providing the select/enable function for the 4-line serial bus.
16 XOUT output Crystal oscillator output; connect to an external 25 to 32 MHz crystal, or leave floating when driving with an external source on XIN.
17 XIN input Crystal oscillator input; connect to an external 25 to 32 MHz crystal or to an external clock source.
18 GND power_in Ground; when using a XTAL leave floating per the reference design, and when using a TCXO connect to TCXO GND, which should be separate from the board reference ground plane.
19 GPIO2 bidirectional General purpose digital I/O that can be configured for functions such as microcontroller clock output, FIFO status, POR, wake-up timer, low battery detect, TRSW and antenna diversity control.
20 GPIO3 bidirectional General purpose digital I/O; the datasheet notes GPIO2 and GPIO3 are more susceptible to spurious synthesizer emissions than GPIO0 and GPIO1.
21 EP passive Exposed pad (from the footprint; not named in the datasheet pin table).

Key specifications

Parameter Value
Manufacturer SILICON LABS
Package QFN-20-EP(4x4)
Category RF & Radio
Pins 21

CAD (KiCad official)

  • Symbol: Si4438-B1C-FMR
  • Footprint: Package_DFN_QFN:QFN-20-1EP_4x4mm_P0.5mm_EP2.5x2.5mm
  • 3D model: QFN-20-EP(4x4) (KiCad packages3D, STEP)
  • 3D model files: si4438-b1c-fmr-etched.step / si4438-b1c-fmr-etched.glb carry the MPN laser-etched on the die in a toggleable Adom.LaserEtch group (Fusion-ready); si4438-b1c-fmr.step / si4438-b1c-fmr.glb are the bare package body.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

  • Datasheet: SILICON LABS datasheet (45 pp, sha256 dce8b8eac80fbb6e, retrieved 2026-10-27, tier: lcsc)
  • Extractor: parts-factory 2.0.0 / extract_pins 0.3, primary claude-haiku-5-5 (text), consensus claude-sonnet-5-5 (agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish.
  • CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF