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RF2905

433/868/915MHZ FM/FSK/ASK/OOK TRANSCEIVER

RF Micro Devices 

RF2905

Pin Function Description

Interface Schematic

27 DEMOD IN This pin is the input to the FM demodulator. This pin is NOT AC cou-

pled. Therefore, a DC blocking capacitor is required on this pin to avoid

shorting the demodulator input with the LC tank. A ceramic discrimina-

tor or DC blocked LC tank resonant at the IF should be connected to

this pin.

VCC

DEMOD IN

10 kΩ

28

IF2 OUT Balanced IF output from the 60dB limiting amplifier strip. This pin is

intended to be connected to pin 27 through a 4pF (suggested) capaci-

tor and an FM discriminator circuit.

IF2 OUT

29

VCC6

This pin is used is supply DC bias to the second IF amplifier, Demodu-

lator and Data Slicer. An IF bypass capacitor should be connected

directly to this pin and returned to ground. A 10nF capacitor is recom-

mended for 10.7MHz IF applications.

30

RESNTR+

This port is used to supply DC voltage to the VCO as well as to tune the

center frequency of the VCO. Equal value inductors should be con-

ESNTR+

nected to this pin and pin 31 although a small imbalance can be used

to tune in the proper frequency range.

31

RESNTR- See RESNTR+ description.

See pin 30.

32

VCC2

This pin is used is supply DC bias to the VCO, prescaler, and PLL. An

RF bypass capacitor should be connected directly to this pin and

returned to ground. A 22pF capacitor is recommended for 915MHz

applications. A 68pF capacitor is recommended for 433MHz applica-

tions.

33

GND4

GND4 is the ground shared on chip by the VCO, prescaler, and PLL

electronics.

34

MOD IN FM analog or digital modulation can be imparted to the VCO through See pin 30.

this pin. The VCO varies in accordance to the voltage level presented

to this pin. To set the deviation to a desired level, a voltage divider refer-

enced to Vcc is the recommended. This deviation is also dependent

upon the overall capacitance of the external resonant circuit.

35

DIV CTRL This pin is used to select the desired prescaler divisor. A logic high

(DIVCTRL>2.0V) selects the 64/65 divisor. A logic low

(DIVCTRL<1.0V) selects the 128/129 divisor.

DIV CTL

RESNTR-

4 kΩ

MOD IN

11

36 MOD CTRL This pin is used to select the prescaler modulus. A logic high (MOD

CTRL>2.0V) selects 64 or 128 for the prescaler divisor. A logic low

(MOD CTRL<1.0V) selects 65 or 129 for the prescaler divisor.

Due to design timing constraints, the prescaler in the divide by 65 or

129 modes has a limited frequency range for accurate operation.

These two modes are not recommended for use from 400MHz to

460 MHz.

MOD CTL

37

OSC SEL A logic high (OSC SEL>2.0V) applied to this pin powers on reference

oscillator 2 and powers down reference oscillator 1. A logic low (OSC

SEL<1.0V) applied to this pin powers on reference oscillator 1 and

powers down reference oscillator 2.

38

OSC B2 This pin is connected directly to the reference oscillator 2 transistor

base. The intended reference oscillator configuration is a modified Col- OSC B1

pitts.

OSC E

OSC B2

Rev B11 010516

11-59

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