SI4431-A0-FM Silicon Laboratories Inc, SI4431-A0-FM Datasheet - Page 27

• Manufacturer Part Number: SI4431-A0-FM
• Description: IC TXRX ISM 930MHZ 3.6V 20-QFN
• Manufacturer: Silicon Laboratories Inc

Specifications of SI4431-A0-FM

• Package / Case: 20-QFN
• Mfg Application Notes: Transitioning SI4430/31 to Rev B
• Frequency: 240MHz ~ 930MHz
• Data Rate - Maximum: 128kbps
• Modulation Or Protocol: FSK, GFSK, OOK
• Power - Output: 13dBm
• Sensitivity: -118dBm
• Voltage - Supply: 1.8 V ~ 3.6 V
• Current - Receiving: 18.5mA
• Current - Transmitting: 28mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Operating Temperature: -40°C ~ 85°C
• Number Of Receivers: 2
• Number Of Transmitters: 1
• Wireless Frequency: 240 MHz to 930 MHz
• Output Power: 13 dBm
• Operating Supply Voltage: 1.8 V to 3.6 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Maximum Supply Current: 28 mA
• Minimum Operating Temperature: - 40 C
• Modulation: FSK, GFSK, OOK
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Applications: -
• Memory Size: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: 336-1633-5

3.6. Frequency Control
For calculating the necessary frequency register settings it is recommended to use the easy control window in
Silicon Labs’ Wireless Design Suite (WDS) or the Excel Calculator available on the product website. These
methods offer a simple method to quickly determine the correct settings based on the application requirements.
The following information can be used to calculated these values manually.
3.6.1. Frequency Programming
In order to receive or transmit an RF signal, the desired channel frequency, fcarrier, must be programmed into the
Si4431. Note that this frequency is the center frequency of the desired channel and not an LO frequency. The
carrier frequency is generated by a Fractional-N Synthesizer, using 10 MHz both as the reference frequency and
the clock of the (3
to obtain the desired frequency resolution of the synthesizer. The overall division ratio of the feedback loop consist
of an integer part (N) and a fractional part (F).In a generic sense, the output frequency of the synthesizer is:
The fractional part (F) is determined by three different values, Carrier Frequency (fc[15:0]), Frequency Offset
(fo[8:0]), and Frequency Modulation (fd[7:0]). Due to the fine resolution and high loop bandwidth of the synthesizer,
FSK modulation is applied inside the loop and is done by varying F according to the incoming data; this is
discussed further in "3.6.4. Frequency Deviation" on page 29. Also, a fixed offset can be added to fine-tune the
carrier frequency and counteract crystal tolerance errors. For simplicity assume that only the fc[15:0] register will
determine the fractional component. The equation for selection of the carrier frequency is shown below:
The integer part (N) is determined by fb[4:0]. Additionally, the output frequency can be halved by connecting a ÷2
divider to the output. This divider is not inside the loop and is controlled by the hbsel bit in "Register 75h.
Frequency Band Select". This effectively partitions the entire 240–930 MHz frequency range into two separate
bands: High Band (HB) for hbsel = 1, and Low Band (LB) for hbsel = 0. The valid range of fb[4:0] is from 0 to 23. If
a higher value is written into the register, it will default to a value of 23. The integer part has a fixed offset of 24
added to it as shown in the formula above. Table 12 demonstrates the selection of fb[4:0] for the corresponding
frequency band.
After selection of the fb (N) the fractional component may be solved with the following equation:
fb and fc are the actual numbers stored in the corresponding registers.
Add R/W Function/Description
73
74
75
76
77
R/W
R/W
R/W Frequency Band Select
R/W
R/W
Frequency Offset 1
Frequency Offset 2
Nominal Carrier
Nominal Carrier
Frequency 1
Frequency 0
rd
order) ΔΣ modulator. This modulator uses modulo 64000 accumulators. This design was made
fc
f
[
15
TX
:

] 0
10
fc[15]

fo[7]
fc[7]
MHz
f
D7
carrier

 

10
MHz
( *

f
OUT
10
hbsel
sbsel
fc[14]
fo[6]
fc[6]
Preliminary Rev. 0.4
D6
( *
MHz
f

TX
hbsel
10

) 1
MHz

(
( *
fc[13]
hbsel
fo[5]
fc[5]
hbsel

D5
) 1
fb

[
(

: 4
N

fb
) 1
] 0

fc[12]
[
fo[4]
fb[4]
fc[4]
D4
: 4
F


(
)
24
] 0
N



24
F
fc
fc[11]
fo[3]
fb[3]
64000
fc[3]
)
D3
[

 

15
*
64000
:
] 0
)
fc[10]
fo[2]
fb[2]
fc[2]
D2
fo[1] fo[0]
fo[9] fo[8]
fb[1] fb[0]
fc[9] fc[8]
fc[1] fc[0]
D1
Si4431
D0 POR Def.
BBh
00h
00h
35h
80h
27