300MHz to 450MHz Frequency-Programmable

ASK/FSK Transmitter

8

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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.

6ROUT

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-