Si4021 Universal ISM
Si4021
Band FSK Transmitter
PIN ASSIGNMENT
DESCRIPTION
Silicon Labs’ Si4021 is a single chip, low power, multi-channel FSK
transmitter designed for use in applications requiring FCC or ETSI
conformance for unlicensed use in the 433, 868, and 915 MHz bands.
Used in conjunction with Si4020, Silicon Labs’ FSK receiver, the Si4021
TM
transmitter features EZRadio
technology, which produces a flexible, low
cost, and highly integrated solution that does not require production
alignments. All required RF functions are integrated. Only an external
crystal and bypass filtering are needed for operation. The Si4021 builds on
the features presented by the Si4020 by offering a higher output power
and an improved phase noise characteristic. The Si4021 shares the same
pinout and control command set as the Si4020. The Si4021 offers all of
the frequencies as the Si4020, with the exception of the 315 MHz band.
Microcontroller Mode
EEPROM Mode
This document refers to Si4021-IC Rev A1.
See www.silabs.com/integration for any applicable
errata. See back page for ordering information.
The Si4021 features a completely integrated PLL for easy RF design, and
its rapid settling time allows for fast frequency hopping, bypassing
multipath fading and interference to achieve robust wireless links. In
addition, highly stable and accurate FSK modulation is accomplished by
direct closed-loop modulation with bit rates up to 115.2 kbps. The PLL’s
high resolution allows the use of multiple channels in any of the bands.
FEATURES
Fully integrated (low BOM, easy design-in)
No alignment required in production
Fast settling, programmable, high-resolution PLL
Fast frequency hopping capability
Stable and accurate FSK modulation with programmable
deviation
Programmable PLL loop bandwidth
Direct loop antenna drive
Automatic antenna tuning circuit
Programmable output power level
Alternative OOK support
The integrated power amplifier of the transmitter has an open-collector
differential output that directly drive a loop antenna with programmable
output level. No additional matching network is required. An automatic
antenna tuning circuit is built in to avoid costly trimming procedures and
de-tuning due to the “hand effect”.
For low-power applications, the device supports automatic activation from
sleep mode. Active mode can be initiated by several wake-up events (on-
chip timer timeout, low supply voltage detection, or activation of any of the
four push-button inputs).
EEPROM mode supported
The Si4021’s on-chip digital interface supports both a microcontroller
mode and an EEPROM mode. The latter allows complete data transmitter
operation without a microcontroller (both control commands and data are
read from the EEPROM). Any wake-up event can start a transmission of the
corresponding data stored in the EEPROM.
SPI bus for applications with microcontroller
Clock output for microcontroller
Integrated programmable crystal load capacitor
Multiple event handling options for wake-up activation
Push-button event handling with switch de-bounce
Wake-up timer
Low battery detection
2.2 to 5.4 V supply voltage
FUNCTIONAL BLOCK DIAGRAM
Low power consumption
Low standby current (0.3 µA)
Compact 16-pin TSSOP package
Transmit bit synchronization
RFP
REFERENCE
CRYSTAL
OSCILLATOR
XTL
SYNTHESIZER
RFN
CLOCK
FREQUENCY
TYPICAL APPLICATIONS
Remote control
Home security and alarm
Wireless keyboard/mouse and other PC peripherals
Toy control
Remote keyless entry
Tire pressure monitoring
Telemetry
LOAD CAP
LEVEL
OOK
MOD
nIRQ/nLBD
CLK/SDO
SDI
LOW BAT
LOW
BATTERY
DETECT
TRESHOLD
CONTROLLER
SCK
TIMEOUT
PERIOD
nSEL
VDD
VSS
WAKE-UP
TIMER
FSK
Personal/patient data logging
Remote automatic meter reading
PB1 PB2 PB3 PB4
1
Si4021-DS Rev 2.3r 0408
www.silabs.com/integration
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