User's Manual

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Ordering Information
Part Number Description
OTX-***-HH-KF#-SI-xxx SI Keyfob Transmitter
MDEV-***-HH-KF#-SI SI Keyfob Development System
*** = 418 (Standard) or 433.92MHz
xxx = Color (Leave blank for standard black)
WHT = White
CRE = Red
CGY = Gray
Keyfob Electrical Specifications
Parameter Designation Min. Typ. Max. Units Notes
Power Supply
Operating Voltage V
CC
2.1 3.0 3.6 VDC
Supply Current l
CC
3.4 mA
Power-Down Current l
PDN
5.0 nA 1
Transmitter Section
Transmit Frequency Range F
C
OTX-418-HH-KF#-SI 418 MHz
OTX-433-HH-KF#-SI 433.92 MHz
OTA Modulation 2FSK
Center Frequency Accuracy –50 +50 kHz
Frequency Deviation 59.05 kHz
Data Rate 9,600 bps
Environmental
Operating Temperature Range –40 +85 °C 1
1. Characterized, but not tested
Electrical Specications
Ordering Information
Figure 3: Ordering Information
Figure 4: Electrical Specifications
Theory of Operation
The SI Series Keyfob Transmitter combines a high-performance
synthesized SoC transmitter with an on-board microcontroller input
interpretation. The transmitter’s advanced synthesized architecture delivers
superior stability and frequency accuracy while minimizing the effects of
temperature and body proximity.
The Keyfob operates in the following manner: when a button is pressed
on the Keyfob, the transmitter and microcontroller are woken from sleep
mode. The microcontroller detects the logic states of the button data
lines. The button data line logic states are sent from the microcontroller
to the transmitter as a serial data packet. The transmitter SoC generates
a 42-byte encrypted packet and transmits a three-packet burst for each
button press throught the antenna and into fre space. On the receiver
side, a Si4355 checks the preamble, the sync bytes and the CRC of the
transmitted packet. If the packet is OK the receiver responds to the button
logic state data in the manner programmed into the receiver by the end
user.
The transmitter is compatible with the Silicon Labs Si4355 receivers using
the Silicon Labs Ember One-Way Link protocol.