Analog-Devices-Inc–Maxim-Integrated-MAX7044AKA-T

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EVALUATION KIT AVAILABLE

MAX7044

300MHz to 450MHz High-Efficiency,

Crystal-Based +13dBm ASK Transmitter

General Description

Features

The MAX7044 crystal-referenced phase-locked-loop

(PLL) VHF/UHF transmitter is designed to transmit

OOK/ASK data in the 300MHz to 450MHz frequency

range. The MAX7044 supports data rates up to 100kbps,

and provides output power up to +13dBm into a 50Ω load

while only drawing 7.7mA at 2.7V.

●

+2.1V to +3.6V Single-Supply Operation

●

OOK/ASK Transmit Data Format

●

Up to 100kbps Data Rate

● +13dBm

Output Power into 50Ω Load

●

Low 7.7mA (typ) Operating Supply Current*

●

Uses Small, Low-Cost Crystal

The crystal-based architecture of the MAX7044 eliminates

many of the common problems with SAW-based transmitters

by providing greater modulation depth, faster frequency

settling, higher tolerance of the transmit frequency, and

reduced temperature dependence. The MAX7044 also

features a low supply voltage of +2.1V to +3.6

hese

improvements enable better overall receiver performance

when using the MAX7044 together with a superheterodyne

receiver such as the MAX1470 or MAX1473.

●

Small 3mm x 3mm 8-Pin SOT23 Package

● Fast-On

Oscillator: 250μs Startup Time

Applications

●

Remote Keyless Entry (RKE)

●

Tire-Pressure Monitoring (TPM)

●

Security Systems

●

Garage Door Openers

●

RF Remote Controls

●

Wireless Game Consoles

●

Wireless Computer Peripherals

●

Wireless Sensors

A simple, single-input data interface and a buffered

clock-out signal at 1/16th the crystal frequency make the

MAX7044 compatible with almost any microcontroller or

code-hopping generator.

The MAX7044 is available in an 8-pin SOT23 package

and is specified over the -40°C to +125°C automotive

temperature range.

Ordering Information

PIN-

PACKAGE

TOP

MARK

PART

TEMP RANGE

MAX7044AKA+T -40°C

to +125°C

8 SOT23

AEJW

*At 50% duty cycle (315MHz, 2.7V supply, +13dBm output power).

Denotes a lead(Pb)-free/RoHS-compliant package.

T =

pe and reel.

Typical Application Circuit

Pin Conﬁguration

TOP VIEW

XTAL

3.0V

XTAL2

XTAL1

GND

XTAL2

220pF

100nF

680pF

100nF

GND

MAX7044

SOT23

MAX7044

PAGND

PAOUT

DATA

DATA INPUT

ANTENNA

DATA

PAGND

PAOUT

CLOCK

CLKOUT

OUTPUT

CLKOUT

f /16)

XTAL

19-3221; Rev 5; 4/17

MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

Absolute Maximum Ratings

to GND …………………………………………………-0.3V to +4.0V

Storage

mperature Rang

……………………… -60°C to +150°C

Junction

mperatur

…………………………………………….

150°C

Lead

mperature (soldering, 10s) …………………………..

300°C

Soldering

mperature (reflow

)

……………………………….

260°C

All Other Pins to GN

……………………….. -0.3V to (V

+ 0.3V)

Continuous Power Dissipation (T

= +70°C)

8-Pin SOT23 (derate 8.9mW/°C above +70°C) ……….714mW

Operating

mperature Range……………………. -40°C to +125°C

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these

or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect

device reliability.

Electrical Characteristics

(

Typical Application Circuit

, all RF inputs and outputs are referenced to 50Ω, V

= +2.1V to +3.6

, T

–

40°C to +125°C, unless

otherwise noted. Typical values are at V

= +2.7

, T

25°C, unless otherwise noted.) (Note 1)

PARAMETER

SYSTEM PERFORMANCE

Supply Voltage

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

2.1

3.6

at 50% duty

DATA

7.7

14.1

cycle (Notes 3, 4)

PA on (Note 5)

PA off (Note 6)

= 315MHz

13.8

1.7

25.4

2.8

Supply Current

(Note 2)

at 50% duty

DATA

8.0

14.4

cycle (Notes 3, 4)

PA on (Note 5)

PA off (Note 6)

= 433MHz

< V

for

more than WAIT

time (Notes 4, 7)

14.0

1.9

25.7

3.1

< +25°C

130

DATA

Standby Current

STDBY

< +125°C

550

2900

Frequency Range (Note 4)

Data Rate (Note 4)

300

450

100

MHz

kbps

Modulation Depth (Note 8)

ON to OFF P

ratio

OUT

= +25°C,

9.6

5.9

12.5

15.4

12.0

18.5

= +2.7V

Output Power, PA On

(Notes 4, 5)

= 300MHz to

T =

+125°C,

9.0

dBm

OUT

450MHz

= +2.1V

= -40°C,

13.1

15.8

= +3.6V

Oscillator settled to within 50kHz

Oscillator settled to within 5kHz

220

450

Turn-On Time

µs

= 315MHz

= 433MHz

= 315MHz

= 433MHz

Transmit Efﬁciency with CW

(Notes 5, 9)

Transmit Efﬁciency with 50% OOK

(Notes 3, 9)

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MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

Electrical Characteristics (continued)

(

Typical Application Circuit

, all RF inputs and outputs are referenced to 50Ω, V

= +2.1V to +3.6

, T

–

40°C to +125°C, unless

otherwise noted. Typical values are at V

= +2.7

, T

25°C, unless otherwise noted.) (Note 1)

PARAMETER

PHASE-LOCKED LOOP (PLL)

VCO Gain

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

330

-84

-91

-82

-89

-50

-74

-80

1.6

MHz/V

= 100kHz

= 1MHz

OFFSET

= 315MHz

= 433MHz

Phase Noise

dBc/Hz

= 100kHz

= 1MHz

= 315MHz

= 433MHz

= 315MHz

= 433MHz

Maximum Carrier Harmonics

Reference Spur

dBc

Loop Bandwidth

MHz

ppm/V

Crystal Frequency

/32

XTAL

Frequency Pulling by V

Crystal Load Capacitance

DATA INPUT

0.25

–

Data Input High

Data Input Low

0.25

Maximum Input Current

Pulldown Current

CLKOUT OUTPUT

Output Voltage Low

µA

= 650µA (Note 4)

0.25

SINK

0.25

–

Output Voltage High

= 350µA (Note 4)

SOURCE

Load Capacitance

CLKOUT Frequency

(Note 4)

LOAD

/16

XTAL

Note 1:

Supply current, output power, and efficiency are greatly dependent on board layout and PAOUT match.

Note 2:

Production tested at T

= +25°C with f

= 300MHz and 450MHz. Guaranteed by design and characterization over tem-

perature and frequency.

Note 3:

50% duty cycle at 10kbps with Manchester coding.

Note 4:

Guaranteed by design and characterization, not production tested.

Note 5:

PA output is turned on in test mode by V

Note 6:

PA output is turned off in test mode by V

= V

/2 + 100m

DATA

= V

/2 – 100m

Note 7:

Wait time: t

= (216 x 32)/f

WAIT

Note 8:

Generally limited by PCB layout.

Note 9:

V =

V .

Efficiency = P

/(V

x I

DATA

OUT DD

Maxim Integrated

│

www.maximintegrated.com

MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

Typical Operating Characteristics

(

Typical Application Circuit

, V

= +2.7

, T

25°C, unless otherwise noted.) (Note 1)

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

= 315MHz

= 433MHz

PA ON

PA 50% DUTY CYCLE AT 10kHz

PA ON

= -40°C

= +25°C

= -40°C

= +85°C

= +125°C

3.0

= +125°C

3.0

= +125°C

3.0

2.1

2.4

2.7

3.3

3.6

2.1

2.4

2.7

3.3

3.6

2.1

2.4

2.7

3.3

3.6

SUPPLY VOLTAGE (V)

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

OUTPUT POWER

vs. SUPPLY VOLTAGE

OUTPUT POWER

vs. SUPPLY VOLTAGE

= 433MHz

= 315MHz

= 433MHz

PA 50% DUTY CYCLE AT 10kHz

PA ON

= -40°C

= +25°C

= +85°C

T =

+125°C

= +125°C

3.0

= +125°C

2.7

2.1

2.4

2.7

3.3

2.4

2.7

3.0

3.3

2.4

3.0

3.3

3.6

SUPPLY VOLTAGE (V)

REFERENCE SPUR MAGNITUDE

vs. SUPPLY VOLTAGE

TRANSMIT POWER EFFICIENCY

vs. SUPPLY VOLTAGE

FREQUENCY STABILITY

vs. SUPPLY VOLTAGE

-70

-72

-74

-76

-78

-80

f =

315MHz

REFERENCE SPUR = f

RF XTAL

PA ON

= 433MHz

T =

-40°C

= +25°C

= 433MHz

= 315MHz

-1

-2

-3

= +85°C

3.3

= 315MHz

2.4

= +125°C

2.4

2.7

3.0

3.3

2.1

2.7

3.0

3.3

2.4

2.7

3.0

3.6

SUPPLY VOLTAGE (V)

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MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

Typical Operating Characteristics (continued)

(

Typical Application Circuit

, V

= +2.7

, T

25°C, unless otherwise noted.) (Note 1)

TRANSMIT POWER EFFICIENCY

vs. SUPPLY VOLTAGE

TRANSMIT POWER EFFICIENCY

vs. SUPPLY VOLTAGE

TRANSMIT POWER EFFICIENCY

vs. SUPPLY VOLTAGE

= 315MHz

= 433MHz

= +25°C

PA 50% DUTY CYCLE AT 10kHz

PA ON

PA 50% DUTY CYCLE AT 10kHz

= -40°C

= +25°C

= -40°C

= +25°C

= -40°C

= +85°C

= +125°C

2.7

= +125°C

2.7

= +125°C

2.7

2.1

2.4

3.0

3.3

3.6

2.1

2.4

3.0

3.3

3.6

2.1

2.4

3.0

3.3

3.6

SUPPLY VOLTAGE (V)

SUPPLY CURRENT AND OUTPUT POWER

PHASE NOISE vs. OFFSET FREQUENCY

vs. EXTERNAL RESISTOR

SUPPLY CURRENT vs. OUTPUT POWER

MAX7044 toc14

-40

-50

= 315MHz

POWER

-60

-70

-80

CURRENT

PA ON

-90

-100

-110

-120

-130

-140

-4

-8

-12

-16

= 315MHz

PA ON

50% DUTY CYCLE

100

1000 10,000

-10

-6

-2

0.01

0.1

100

EXTERNAL RESISTOR (

Ω

)

OUTPUT POWER (dBm)

OFFSET FREQUENCY (kHz)

AM DEMODULATION OF PA OUTPUT

DATA RATE = 100kHz

OUTPUT SPECTRUM

FREQUENCY SETTLING TIME

0dB

= 315MHz

5dB/

div

10dB/

div

50kHz/

div

25µs/div

3.2µs/div

100MHz/div

Maxim Integrated

│

www.maximintegrated.com

MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

Typical Operating Characteristics (continued)

(

Typical Application Circuit

, V

= +2.7

, T

25°C, unless otherwise noted.) (Note 1)

CLKOUT SPUR MAGNITUDE

vs. SUPPLY VOLTAGE

-40

= 315MHz

-43

-46

-49

-52

-55

2.1

2.4

2.7

3.0

3.3

3.6

SUPPLY VOLTAGE (V)

Pin Description

NAME

XTAL1

GND

FUNCTION

1st Crystal Input. f

= fRF/32.

XTAL

Ground. Connect to system ground.

PAGND

Ground for the Power Ampliﬁer (PA). Connect to system ground.

Power-Ampliﬁer Output. The PA output requires a pullup inductor to the supply voltage, which can be

part of the output-matching network to an antenna.

PAOUT

CLKOUT Buffered

Clock Output. The frequency of CLKOUT is f

/16.

XTAL

DATA

OOK Data Input. DATA also controls the power-up state. See the

Shutdown Mode

section.

Supply Voltage. Bypass to GND with a 100nF capacitor as close as possible to the pin.

XTAL2

2nd Crystal Input. f

= f

/32.

XTAL RF

Functional Diagram

Detailed Description

The MAX7044 is a highly integrated ASK transmitter

operating over the 300MHz to 450MHz frequency band.

The IC requires only a few external components to

complete a transmit solution. The MAX7044 includes a

complete PLL and a highly efficient power amplifier. The

device is automatically placed into a low-power shutdown

mode and powers up when data is detected on the data

DATA

MAX7044

DATA

ACTIVITY

DETECTOR

GND

PAOUT

input. Once power is supplied to V

, the DATA pin must

PAGND

LOCK DETECT

32x PLL

receive at least one logic pulse (low-high-low transition) in

order to properly initialize the device.

CRYSTAL-

OSCILLATOR

DRIVER

XTAL1

XTAL2

Shutdown Mode

/16

CLKOUT

The MAX7044 has an automatic shutdown mode that

places the device in low-power mode if the DATA input

has not toggled for a specific amount of time (wait time).

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MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

The wait time is equal to 2

clock cycles of the crystal.

This equates to a wait time of approximately 6.66ms for

a 315MHz RF frequency and 4.84ms for a 433MHz RF

frequency. For other frequencies, calculate the wait time

with the following equation:

When the output matching network is properly tuned, the

power amplifier transmits power with high efficiency.

The

Typical Application Circuit

delivers +13dBm at +2.7V

supply with 7.7mA of supply current. Thus, the overall

efficiency is 48% with the efficiency of the power amplifier

itself greater than 54%.

x 32

WAIT

Buffered Clock Output

The MAX7044 provides a buffered clock output (CLKOUT)

for easy interface to a microcontroller or frequency-hop-

ping generator. The frequency of CLKOUT is 1/16 the

crystal frequency. For a 315MHz RF transmit frequency,

a crystal of 9.84375MHz is used, giving a clock output of

615.2kHz. For a 433.92MHz RF frequency, a crystal of

13.56MHz is used for a clock output of 847.5kHz.

The clock output is inactive when the device is in shut-

down mode. The device is placed in shutdown mode

by the internal data activity detector (see the

Shutdown

Mode

section). Once data is detected on the data input,

the clock output is stable after approximately 220μs.

where t

RF transmit frequency.

is the wait time to shutdown and f

is the

WAIT

When the device is in shutdown, a rising edge on DATA

initiates the warm up of the crystal and PLL. The crystal

and PLL must have 220μs settling time before data can

be transmitted. The 220μs turn-on time of the MAX7044

is dominated by the crystal oscillator startup time. Once

the oscillator is running, the 1.6MHz PLL loop bandwidth

allows fast frequency recovery during power amplifier

toggling.

When the device is operating, each edge on the data line

resets an internal counter to zero and it begins to count

again. If no edges are detected on the data line, the

Applications Information

Output Power Adjustment

counter reaches the end-of-count (2

clock cycles) and

It is possible to adjust the output power down to -15dBm

places the device in shutdown mode. If there is an edge

on the data line before the counter hits the end of count,

the counter is reset and the process starts over. It may

be necessary to keep the power amplifier on steadily for

testing and debugging purposes.

o this, set the DATA

with the addition of a resistor (see R

Figure 1

PWRADJ

The addition of the power adjust resistor also reduces

power consumption. See the Supply Current and Output

Power vs. External Resistor and Supply Current vs. Output

Power graphs in the

Typical Operating Characteristics

section. It is imperative to add both a low-frequency and a

high-frequency decoupling capacitor as shown in Figure 1.

pin voltage slightly above the midpoint between V

and

ground (V

/2 + 100mV).

Phase-Locked Loop

Crystal Oscillator

The PLL block contains a phase detector, charge pump,

integrated loop filter, VCO, asynchronous 32x clock

divider, and crystal oscillator. This PLL requires no external

components. The relationship between the carrier and

crystal frequency is given by:

The crystal oscillator in the MAX7044 is designed to

present a capacitance of approximately 3pF between the

XTAL1 and XTAL2 pins. If a crystal designed to oscillate

= f

/32

XTAL

The lock-detect circuit prevents the power amplifier from

transmitting until the PLL is locked. In addition, the device

shuts down the power amplifier if the reference frequency

is lost.

3.0V

XTAL

3.0V

100nF

XTAL2

XTAL1

PWRADJ

Power Ampliﬁer (PA)

100nF

The PA of the MAX7044 is a high-efficiency, open-drain,

switch-mode amplifier. With a proper output matching

network, the PA can drive a wide range of impedances,

including the small-loop PCB trace antenna and any 50Ω

antenna. The output-matching network for an antenna

with a characteristic impedance of 50Ω is shown in the

Typical Application Circuit

. The output matching network

suppresses the carrier harmonics and transforms the

antenna impedance to an optimal impedance at PAOU

which is about 125Ω.

GND

220pF

680pF

MAX7044

DATA INPUT

ANTENNA

DATA

PAGND

PAOUT

CLOCK

OUTPUT

CLKOUT

/16)

XTAL

Figure 1. Output Power Adjustment Circuit

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MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

with a different load capacitance is used, the crystal is

pulled away from its intended operating frequency, thus

introducing an error in the reference frequency. Crystals

designed to operate with higher differential load capacitance

always pull the reference frequency higher. For example,

a 9.84375MHz crystal designed to operate with a 10pF

load capacitance oscillates at 9.84688MHz with the

MAX7044, causing the transmitter to be transmitting

at 315.1MHz rather than 315.0MHz, an error of about

100kHz, or 320ppm.

Output Matching to

PCB Loop Antenna

In some applications, the MAX7044 power amplifier output

has to be impedance matched to a small-loop antenna.

The antenna is usually fabricated out of a copper trace on

a PCB in a rectangular, circular, or square pattern. The

antenna will have an impedance that consists of a lossy

component and a radiative component.

chieve high

radiating efficiency, the radiative component should be as

high as possible, while minimizing the lossy component.

In addition, the loop antenna will have an inherent loop

inductance associated with it (assuming the antenna

is terminated to ground). For example, in a typical

application, the radiative impedance is less than 0.5Ω, the

lossy impedance is less than 0.7Ω, and the inductance is

approximately 50nH to 100nH.

In actuality, the oscillator pulls every crystal. The crystal’s

natural frequency is really below its specified frequency,

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:

The objective of the matching network is to match the

power amplifier output to the small-loop antenna. The

matching components thus transform the low radiative

and resistive parts of the antenna into the much higher

value of the PA output. This gives higher efficiency. The

low radiative and lossy components of the small-loop

antenna result in a higher Q matching network than the

50Ω network; thus, the harmonics are lower.













−

case

spec

load

where:

f is

the amount the crystal frequency is pulled in ppm.

is the motional capacitance of the crystal.

Layout Considerations

(or C ) is the vendor-specified case capacitance

case

A properly designed PCB is an essential part of any

RF/microwave circuit. At the power amplifier output,

use controlled-impedance lines and keep them as short

as possible to minimize losses and radiation. At high

frequencies, trace lengths that are approximately 1/20 the

wavelength or longer become antennas. For example, a

2in trace at 315MHz can act as an antenna.

of the crystal.

is the specified load capacitance.

is the actual load capacitance.

spec

load

When the crystal is loaded as specified (i.e., C

the frequency pulling equals zero.

= C

)

load

spec

Output Matching to 50Ω

When matched to a 50Ω system, the MAX7044 PA is

capable of delivering up to +13dBm of output power

Keeping the traces short also reduces parasitic

inductance. Generally, 1in of PCB trace adds about 20nH

of parasitic inductance. The parasitic inductance can

have a dramatic effect on the effective inductance. For

example, a 0.5in trace connecting a 100nH inductor adds

an extra 10nH of inductance, or 10%.

at V

= 2.7

he output of the PA is an open-drain

transistor that requires external impedance matching

and pullup inductance for proper biasing. The pullup

inductance from PA to V

serves three main purposes:

it resonates the capacitance of the PA output, provides

biasing for the PA, and becomes a high-frequency choke

educe the parasitic inductance, use wider traces and a

solid ground or power plane below the signal traces. Using

a solid ground plane can reduce the parasitic inductance

from approximately 20nH/in to 7nH/in. Also, use low-

inductance connections to ground on all GND pins, and

to reduce the RF energy coupling into V

. The recom-

mended output-matching network topology is shown in

the

Typical Application Circuit

. The matching network

transforms the 50Ω load to approximately 125Ω at the

output of the PA in addition to forming a bandpass filter

that provides attenuation for the higher order harmonics.

place decoupling capacitors close to all V

connections.

Maxim Integrated

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www.maximintegrated.com

MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

Chip Information

PROCESS: CMOS

Package Information

For the latest package outline information and land patterns

(footprints), go to

www.maximintegrated.com/packages

. Note

that a “+”, “#”, or “-” in the package code indicates RoHS status

only. Package drawings may show a different suffix character, but

the drawing pertains to the package regardless of RoHS status.

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

8 SOT23

K8SN+1

21-0078

90-0176

Maxim Integrated

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MAX7044

300MHz to 450MHz High-Efﬁciency,

Crystal-Based +13dBm ASK Transmitter

Revision History

REVISION REVISION

PAGES

CHANGED

DESCRIPTION

NUMBER

DATE

Changed part number in Ordering Information to lead-free and made a correction

in the Power Ampliﬁer (PA) section

6/09

1, 7

Deleted Maximum Crystal Inductance spec and Note 9 from the Electrical

Characteristics table and updated the Absolute Maximum Ratings, Shutdown

Mode, and Crystal Oscillator sections

2/11

5/17

2, 3, 7, 8

Updated Detailed Description section

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses

are implied. Maxim Integrated reserves the right to change the circuitry and speciﬁcations without notice at any time. The parametric values (min and max limits)

shown in the Electrical Characteristics table are guaranteed.

Other parametric values quoted in this data sheet are provided for guidance.

Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.

2017 Maxim Integrated Products, Inc.

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Analog-Devices-Inc–Maxim-Integrated-MAX7044AKA-T

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