MAX7031 データシートの表示（PDF） - Maxim Integrated

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MAX7031

Low-Cost, 308MHz, 315MHz, and 433.92MHz FSK Transceiver with Fractional-N PLL

Maxim Integrated 

Low-Cost, 308MHz, 315MHz, and 433.92MHz

FSK Transceiver with Fractional-N PLL

Bypass T/R, ENABLE, DATA, AGC0-1, and AUTOCAL

with 10pF capacitors to GND. Place all bypass capaci-

tors as close to the respective pins as possible.

Transmit/Receive Antenna Switch

The MAX7031 features an internal SPST RF switch that,

when combined with a few external components, allows

the transmit and receive pins to share a common anten-

na (see the Typical Application Circuit). In receive

mode, the switch is open and the power amplifier is

shut down, presenting a high impedance to minimize

the loading of the LNA. In transmit mode, the switch

closes to complete a resonant tank circuit at the PA out-

put and forms an RF short at the input to the LNA. In

this mode, the external passive components couple the

output of the PA to the antenna to protect the LNA input

from strong transmitted signals.

The switch state is controlled by the T/R pin (pin 22).

Drive T/R high to put the device in transmit mode; drive

T/R low to put the device in receive mode.

Crystal Oscillator (XTAL)

The XTAL oscillator in the MAX7031 is designed to pre-

sent a capacitance of approximately 3pF between the

XTAL1 and XTAL2 pins. In most cases, this corre-

sponds to a 4.5pF load capacitance applied to the

external crystal when typical PCB parasitics are added.

It is very important to use a crystal with a load

capacitance that is equal to the capacitance of the

MAX7031 crystal oscillator plus PCB parasitics. If a

crystal designed to oscillate with a different load

capacitance is used, the crystal is pulled away from its

stated operating frequency, introducing an error in the

reference frequency. Crystals designed to operate with

higher differential load capacitance always pull the ref-

erence frequency higher.

In actuality, the oscillator pulls every crystal. The crys-

tal’s natural frequency is really below its specified fre-

quency, but when loaded with the specified load

capacitance, the crystal is pulled and oscillates at its

specified frequency. This pulling is already accounted

for in the specification of the load capacitance.

Additional pulling can be calculated if the electrical

parameters of the crystal are known. The frequency

pulling is given by:

fP

= Cm

2

⎛

⎝⎜ CCASE

1

+ CLOAD

−

CCASE

1

+

⎞

CSPEC ⎠⎟

x 106

where:

fP is the amount the crystal frequency is pulled in ppm.

Cm is the motional capacitance of the crystal.

CCASE is the case capacitance.

CSPEC is the specified load capacitance.

CLOAD is the actual load capacitance.

When the crystal is loaded as specified, i.e., CLOAD =

CSPEC, the frequency pulling equals zero.

PROCESS: CMOS

Chip Information

TOP VIEW

Pin Configuration

24 23 22 21 20 19 18 17

N.C. 25

DVDD 26

HVIN 27

AUTOCAL 28

AGC1 29

MAX7031

AGC0 30

XTAL1 31

XTAL2 32

+1 2 3 4 5 6 7 8

16 PDMAX

15 PDMIN

14 IFIN+

13 IFIN-

12 MIXOUT

11 MIXIN-

10 MIXIN+

9 LNAOUT

THIN QFN

______________________________________________________________________________________ 15

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