RFB433B Micrel Inc, RFB433B Datasheet - Page 6

• Manufacturer Part Number: RFB433B
• Manufacturer: Micrel Inc

Specifications of RFB433B

• Operating Frequency (max): 434000kHz
• Operating Temperature (min): -20C
• Operating Temperature Classification: Commercial
• Modulation Type: FSK
• Operating Supply Voltage (typ): 3V
• Lead Free Status / Rohs Status: Not Compliant

Application notes
Hovfaret 17B, N-0275 Oslo, Norway. Tel: [phone] Fax: [phone] E-mail:
DATA
Bi-directional RX / TX data. Modulation is applied to
the VCO and therefore the modulation cannot have
any DC component. Some kind of coding is needed
to ensure that the modulation is DC free, e.g.
Manchester code or block code. With Manchester
code the bit rate is half the baud rate, but with 3B4B
block code the bit rate is ¾ of the baud rate.
Connection to a Microcontroller capture/ compare
I/O pin allows use of the clock recovery and bit sync
routines in the supplied software. The I/O pin should
be set as an input for 6ms after programming the
RF block in TX mode, prior to starting transmission
of data. This gives the fastest set up times for
transmit. The 6 ms is for the settling time of the PLL
and the P.A. stage ramp up. The I/O line should be
set as an input after completion of keying of TX
data, prior to loading a new control word in the RF
block.
DIGVDD It is recommended that DIGVDD is divided
from IFVDD and RFVDD and joined at a common
VDD point.
LD The RF Block has a lock detector feature that
indicates whether the PLL is in lock or not. A logic
high on pin LD means that the PLL is in lock. See
reference manual for BCC418.
RSSI (Received Signal Strength Indicator ) The
RSSI provides a DC output voltage proportional to
the strength of the RF input signal. Impedance is
approximate 50k. See reference manual for
BCC418.
PUEXT The PUEXT pin should be connected to an
I/O line.After power on, the pin should be held low
while loading in the control word for the first time.
An alternative, if no I/O lines are available, is to
connect the PUEXT pin to VDD via resistor and a
capacitor to GND. After power is applied, a control
word should be clocked in during the time the
PUEXT pin is at logic 0 levels (30% of VDD). The
time constant should be chosen to match the data
clock in rate from the Microcontroller. Further
loading in of control words can be done in a normal
manner.
PCB layout
Keep ground plane areas as large as possible.
Keep the track to the RF connector/ antenna as
short as possible. The best is a 50 ohm strip line
solution. VDD must be "clean" for good
performance. If a RS232 converter IC is used , run
it on its own voltage regulator as they introduce
spikes on VDD. Avoid switch mode power supplies
if possible or use a linear regulator after them. For
a final type approval of a complete product, there
must be detection of a low voltage condition so that
the microcontroller places the RF block in standby,
otherwise the VCO can get out of lock at below
2.4V and there could be unintentional radiation of
RF outside the intended band.
[e-mail]
Orgnr. NO 929 510 909 www.bluechip.no