Rainbow Electronics MAX7057 - Manual (Page 8)

MAX7057
300MHz to 450MHz Frequency-Programmable
ASK/FSK Transmitter
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Pin Description
PIN NAME FUNCTION
1 CS Serial Interface Active-Low Chip Select. Internally pulled up to DVDD.
2 SDI Serial Interface Data Input. Internally pulled down to GND.
3 SCLK Serial Interface Clock Input. Internally pulled down to GND.
4 PAGND Power Amplifier Ground
5 PAOUT
Power Amplifier Output. Requires a pullup inductor to the supply voltage or ROUT. The pullup inductor can
be part of the output-matching network.
6 ROUT
Envelope-Shaping Output. ROUT controls the power amplifier envelope’s rise and fall times. Connect
ROUT to the PA pullup inductor or to an optional power-adjust resistor. Bypass the inductor to GND as
close as possible to the inductor with 680pF and 220pF capacitors.
7 PAVDD
Power Amplifier Supply Voltage. Bypass to ground with 0.01μF and 220pF capacitors placed as close as
possible to the pin.
8 AVDD
Analog Positive Supply Voltage. Bypass to ground with 0.1μF and 0.01μF capacitors placed as close as
possible to the pin.
9 XTAL2 Crystal Input 2. XTAL2 can be driven from an AC-coupled external reference.
10 XTAL1 Crystal Input 1. Bypass to ground if XTAL2 is driven from an AC-coupled external reference.
11 AGND Analog Ground
12 ENABLE
Enable Pin. Drive high for normal operation; drive low or leave unconnected to put the device in standby
mode. Internally pulled down to GND.
13 DIN
ASK/FSK Data Input. Use the control register (address: 0x00) to select the type of modulation. Internally
pulled down to GND.
14 DGND Digital Ground
15 GPO
General-Purpose Output. Can be configured to output various digital signals (SPI serial data output—SDO,
CLKOUT—reference oscillator frequency divided by 1, 2, 4, or 8 for microprocessor clock, etc).
16 DVDD
Digital positive supply voltage. Bypass to ground with 0.1μF and 0.01μF capacitors placed as close as
possible to the pin.
Detailed Description
The MAX7057 is frequency programmable from 300MHz
to 450MHz, by using a fractional-N phase-locked loop
(PLL), and transmits data using either ASK or FSK mod-
ulation. The MAX7057 has integrated tuning capacitors
at the output of the power amplifier (PA) to ensure high-
power efficiency at various programmable frequencies
with a single-matching network.
The crystal-based architecture of the MAX7057 elimi-
nates many of the common problems with SAW trans-
mitters by providing greater modulation depth, faster
frequency settling, tighter transmit frequency tolerance,
and reduced temperature dependence. In particular,
the tighter transmit frequency tolerance means that a
superheterodyne receiver with a narrower IF bandwidth
(therefore lower noise bandwidth) can be used. The
payoff is better overall receiver performance when using
a superheterodyne receiver such as the MAX1471,
MAX1473, MAX7033, MAX7034, or MAX7042.
Frequency Programming
The MAX7057 is a crystal-referenced phased-locked
loop (PLL) VHF/UHF transmitter that transmits data over
the frequency range of 300MHz to 450MHz in ASK or
FSK mode. The transmit frequency is set by the crystal
frequency and the programmable divider in the PLL;
the programmable-divide ratios can be set anywhere
from 19 to 28, which means that with a crystal frequen-
cy of 16MHz, the output frequency range can be from
304MHz to 448MHz.
The fractional-N architecture of the PLL in the MAX7057
allows the FSK signal to be programmed for exact fre-
quency deviations and rapid, transient-free frequency
settling time. This modulation method completely elimi-