RFD21733 Datasheet, PDF (21/76 Pages) List of Unclassifed Manufacturers – Compliance Approved 2.4 GHz RF Transceiver Modules with Built-In RFDP8 Application Protocol

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7/10/2011 1:40 AM
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RFD21733 • FCC • IC
RFD21743 • FCC
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RFDP8
RF Module
RFD21733
RFD21735
RFD21737
RFD21738
RFD21739
RFDP8
RFDANT
RFD21742
RFD21743
RFD21772
RFD21773
KEYFOBs
RF Modules and RFDANTs run on 3V Logic Levels (1.9V to 3.6V)
The RFD21733, RFD21735, RFD21742 and RFD21743 all run on a supply of 1.9V to 3.6V. They have an
internal voltage regulator which is set to 1.8V and it is an LDO so you only need about 100mV of overhead to
keep it in regulation. Most circuits which will interface with these devices will be 3V or 3.3V typical, so we will use
those voltages for reference in this section. If your circuit runs on 2.5V, 3V or 3.3V, then no problem, you can
directly apply supply voltage of 2.5V, 3V or 3.3V to the Module or RFDANT and all your logic signals will be at
2.5V, 3V or 3.3V for a direct interface with your hardware. However if your circuit is running at a higher voltage
such as 5V, then you need to use a level shifter IC or a circuit which will translate the Module or RFDANT signals
from 3V to 5V for your circuit, and also the 5V from your circuit to the 3V for the Module or RFDANT. Of course
you will also need a regulator to drop from 5V down to 3V for the Module or RFDANT.
Simple 5V to 3V Logic Level Shifter for prototyping ONLY.
If you want a quick an dirty, temporary solution to interface the 3V RF Module or RFDANT to your 5V logic circuit,
then you can use a simple resistive divider to get your prototype up and running quickly with just a couple
resistors. First, you must supply a regulated 3V or 3.3V to the RF Module or RFDANT using a voltage regulator.
Now regarding the logic signals, you can connect a 47k pull down resistor to the logic lines on the following 6
signals, Mode Select 1, Mode Select 2, Learn / Status, IN1 / OUT 1 / LOGIC IO, IN2 / OUT2 / RXD, IN3 / OUT3 /
TXD. The RESET has an internal 3.3K pull up and does not apply to this option, and the Mode Select 0, at power
up has an internally switched 13k resistor and also does not apply to this option. After connecting the 47k pull
down resistor on the Module or RFDANT pins, then use a 22k series resistor to connect the six Module or
RFDANT logic pins mentioned above to your 5V device. That will create a 2/3 voltage divider from your 5V
device to the 3V RF Module or RFDANT when the 5V device is driving 3V device. When the 3V device is driving
the 5V device, there is no divider in that direction, only a 22k series resistor into a high-Z input on the 5V side, so
the 5V side will see the full 3V logic, and that is in most cases, just enough to cause a logic high for a 5V logic
input. Note this is not a production solution, its just a quick-and-dirty way to get a 5V logic circuit to work with a
5V logic circuit for prototyping. Of course once you have hooked this up and if it does not work for you, do
measure the logic levels using a scope on both 5V and 3V nodes to make sure they are actually at sufficient
levels to meet the minimums for logic levels for the specific device. Note if you do not have a high-Z input on the
5V side, this will not work. At first chance, when possible, use a proper level shifter capable of sinking and
sourcing current and able to do fast switching as this circuit is very limited with its scope of value and use. The
Eval Boards have a 47k pull down resistor mounted on the above six referenced pins, so if you are using an Eval
Board then all you need is the series 22K resistor (don’t add an additional 47k resistor or it will not work), but if
you are using the RF Module or the RFDANT WITHOUT the Eval Board, then you will need to add the 47k
resistors.
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