MAXIM MAX1472 Technical data

General Description

The MAX1472 is a crystal-referenced phase-locked
loop (PLL) VHF/UHF transmitter designed to transmit
OOK/ASK data in the 300MHz to 450MHz frequency
range. The MAX1472 supports data rates up to
100kbps, and adjustable output power to more than
+10dBm into a 50Ω load. The crystal-based architec­ture of the MAX1472 eliminates many of the common
problems with SAW transmitters by providing greater
modulation depth, faster frequency settling, higher
tolerance of the transmit frequency, and reduced
temperature dependence. Combined, these improve­ments enable better overall receiver performance when
using a superheterodyne receiver such as the MAX1470
or MAX1473.

The MAX1472 is available in a 3mm x 3mm 8-pin
SOT23 package and is specified for the automotive
(-40°C to +125°C) temperature range. An evaluation kit
is available. Contact Maxim Integrated Products for
more information.

Applications

Remote Keyless Entry

RF Remote Controls

Tire Pressure Monitoring

Security Systems

Radio-Controlled Toys

Wireless Game Consoles

Wireless Computer Peripherals

Wireless Sensors

Features

o 2.1V to 3.6V Single-Supply Operation

o Low 5.3mA Operating Supply Current*

o Supports ASK with 90dB Modulation Depth

o Output Power Adjustable to More than +10dBm

o Uses Small Low-Cost Crystal

o Small 3mm

 3mm 8-Pin SOT23 Package

o Fast-On Oscillator 220µs Startup Time

MAX1472

300MHz-to-450MHz Low-Power,

Crystal-Based ASK Transmitter

________________________________________________________________

Maxim Integrated Products

1

Pin Configuration

Ordering Information

8

7

6

5

1

+

2

3

4

DATA

ENABLE

PAOUT

XTAL2

V

DD

GND

PAGND

XTAL1

MAX1472

3.0V

DATA INPUT

STANDBY OR

POWER-UP

*

680pF220pF

50Ω

ANTENNA

Typical Application Circuit

19-2872; Rev 3; 10/10

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

EVALUATION KIT

AVAILABLE

*

Optional power adjust resistor.

+

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

T = Tape and reel.

*

At 50% duty cycle (315MHz, 2.7V supply, +10dBm output

power)

PART

MAX1472AKA+T -40°C to +125°C 8 SOT23 AEKS

TEMP

RANGE

PIN­PACKAGE

TOP

MARK

TOP VIEW

1

XTAL1

2

GND

3

PAGND

4

+

87XTAL2

V

MAX1472

SOT23

DD

DATA

6

ENABLEPAOUT

5

MAX1472

300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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.

VDDto GND ..........................................................-0.3V to +4.0V

All Other Pins to GND ................................-0.3V to (V

DD

+ 0.3V)

Continuous Power Dissipation (T

A

= +70°C)

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

Operating Temperature Range .........................-40°C to +125°C

Storage Temperature Range .............................-60°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

Soldering Temperature (reflow) .......................................+260°C

ELECTRICAL CHARACTERISTICS

(

Typical Application Circuit

, output power is referenced to 50Ω, VDD= 2.1V to 3.6V, V

ENABLE

= VDD, TA= -40°C to +125°C, unless

otherwise noted. Typical values are at V

DD

= 2.7V, TA= +25°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

SYSTEM PERFORMANCE

Supply Voltage V

Supply Current I

Standby Current I

Frequency Range f

Data Rate (Note 3) 0 100 kbps

Modulation Depth ON to OFF P

Output Power P

Turn-On Time t

Transmit Efficiency with CW

Transmit Efficiency at 50%
Duty Cycle

DD

V

ENABLE

= V

DD

(Note 2)

DD

V
V

V
V

V

ENABLE

= V

DATA

ENABLE

= 0V

DATA

ENABLE

= VDD,

DD

= VDD,

= V

DD

(Note 2)

STDBY

RF

fRF = 433MHz

V
V

V
V

V

V

< VIL, TA < +85°C (Note 3) 5 350 nA

ENABLE

< V

ENABLE

TA < +125°C (Note 3) 1.7 µA

IL

(Note 1) 300 450 MHz

ratio (Note 4) 90 dB

OUT

ENABLE

= V

DATA

ENABLE

= 0V

DATA

= VDD,

DD

= VDD,

TA = +25°C, VDD = 2.7V (Notes 5, 6) 7.3 10.3 12.8

OUT

TA = + 125° C , V

= 2.1V ( N otes 5, 6) 3.3 6.0

D D

TA = -40°C, VDD = 3.6V (Notes 5, 6) 13.7 16.2

ON

To f

To f

f

RF

f

RF

f

RF

f

RF

< 50kHz (Note 7) 220

OFFSET

< 5kHz (Note 7) 450

OFFSET

= 315MHz (Note 8) 43.6

= 433MHz (Note 8) 41.3

= 315MHz (Note 9) 37.6

= 433MHz (Note 9) 35.1

2.1 3.6 V

5.3 9.4

9.1 16.6fRF = 315MHz

1.5 2.3

5.7

9.6

1.7 2.7

mA

dBm

µs

%

%

MAX1472

300MHz-to-450MHz Low-Power,

Crystal-Based ASK Transmitter

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(

Typical Application Circuit

, output power is referenced to 50Ω, VDD= 2.1V to 3.6V, V

ENABLE

= VDD, TA= -40°C to +125°C, unless

otherwise noted. Typical values are at V

DD

= 2.7V, TA= +25°C, unless otherwise noted.) (Note 1)

Note 1: 100% tested at TA= +25°C. Guaranteed by design and characterization over temperature.
Note 2: 50% duty cycle at 10kHz data.
Note 3: Guaranteed by design and characterization, not production tested.
Note 4: Generally limited by PC board layout.
Note 5: Output power can be adjusted with external resistor.
Note 6: Guaranteed by design and characterization at f

RF

= 315MHz.

Note 7: V

ENABLE

< VILto V

ENABLE

> VIH. f

OFFSET

is defined as the frequency deviation from the desired carrier frequency.

Note 8: V

ENABLE

> VIH, V

DATA

> VIH, Efficiency = P

OUT

/(VDDx IDD).

Note 9: V

ENABLE

> VIH, DATA toggled from VILto VIH, 10kHz, 50% duty cycle, Efficiency = P

OUT

/(VDDx IDD).

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

PHASE-LOCKED LOOP PERFORMANCE

VCO Gain 330 MHz/V

=100kHz -84

f

OFFSET

f

= 1MHz -91

OFFSET

f

=100kHz -82

OFFSET

= 1MHz -89

f

OFFSET

dBc/Hz

dBc

dBc

Phase Noise

Maximum Carrier Harmonics

Reference Spur

= 315MHz

f

RF

f

= 433MHz

RF

f

= 315MHz -50

RF

= 433MHz -50

f

RF

f

= 315MHz -75

RF

= 433MHz -81

f

RF

Loop Bandwidth 1.6 MHz

Crystal Frequency f

XTAL

/ 32 MHz

f

RF

Oscillator Input Impedance From each XTAL pin to GND 6.2 pF

Frequency Pushing by V

DD

3 ppm/V

DIGITAL INPUTS

Data Input High V

Data Input Low V

IH

IL

V

- 0.25 V

D D

0.25 V

Maximum Input Current 2nA

Pulldown Current 25 µA

MAX1472

300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter

4 _______________________________________________________________________________________

Typical Operating Characteristics

(Typical Application Circuit

, VDD= 2.7V, TA= +25°C, unless otherwise noted.)

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX1472 toc01

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

3.22.4 2.8

6

7

8

9

10

11

12

13

5

2.0 3.6

V

ENABLE

= VIH,

V

DATA

= VIH,

f

RF

= 315MHz

-40°C

+25°C

+85°C

+125°C

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX1472 toc02

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

3.22.82.4

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0 3.6

+85°C

+125°C

-40°C

+25°C

V

ENABLE

= VIH,

V

DATA

= VIL,

f

RF

= 315MHz

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX1472 toc03

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

3.22.82.4

7

8

9

10

11

12

13

6

5

2.0 3.6

V

ENABLE

= VIH,

V

DATA

= VIH,

f

RF

= 433MHz

+25°C

-40°C

+125°C

+85°C

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX1472 toc04

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

3.22.82.4

1.2

1.4

1.6

1.8

2.0

2.2

2.0 3.6

+125°C

-40°C

V

ENABLE

= VIH,

V

DATA

= VIL,

f

RF

= 433MHz

+85°C

+25°C

OUTPUT POWER vs. SUPPLY VOLTAGE

MAX1472 toc05

SUPPLY VOLTAGE (V)

OUTPUT POWER (dBm)

3.22.4 2.8

6

7

8

9

10

11

12

13

14

5

2.0 3.6

V

ENABLE

= VIH,

V

DATA

= VIH,

f

RF

= 315MHz

-40°C

-25°C

+85°C

+125°C

OUTPUT POWER vs. SUPPLY VOLTAGE

MAX1472 toc06

SUPPLY VOLTAGE (V)

OUTPUT POWER (dBm)

3.22.4 2.8

6

7

8

9

10

11

12

13

14

2.0 3.6

V

ENABLE

= VIH,

V

DATA

= VIH,

f

RF

= 433MHz

-40°C

+25°C

+85°C

+125°C

REFERENCE SPUR MAGNITUDE

vs. SUPPLY VOLTAGE

MAX1472 toc07

SUPPLY VOLTAGE (V)

REFERENCE SPUR (dBc)

3.22.82.4

-83

-81

-79

-77

-75

-73

-71

-69

-67

-65

-85

2.0 3.6

315MHz

433MHz

FREQUENCY STABILITY

vs. SUPPLY VOLTAGE

MAX1472 toc08

SUPPLY VOLTAGE (V)

OFFSET FREQUENCY (ppm)

3.22.82.4

-3

-2

-1

0

1

2

-4

2.0 3.6

433MHz

315MHz

TRANSMIT POWER EFFICIENCY

vs. SUPPLY VOLTAGE

MAX1472 toc09

SUPPLY VOLTAGE (V)

EFFICIENCY (%)

3.22.82.4

30

35

40

45

50

55

25

2.0 3.6

+25°C

+85°C

+125°C

-40°C

CW OUTPUT
f

RF

= 315MHz

MAX1472

300MHz-to-450MHz Low-Power,

Crystal-Based ASK Transmitter

_______________________________________________________________________________________

5

Typical Operating Characteristics (continued)

(

Typical Application Circuit

, VDD= 2.7V, TA= +25°C, unless otherwise noted.)

TRANSMIT POWER EFFICIENCY

vs. SUPPLY VOLTAGE

50

+25°C

45

40

35

EFFICIENCY (%)

30

25

-40°C

+85°C

2.0 3.6
SUPPLY VOLTAGE (V)

PHASE NOISE vs. OFFSET FREQUENCY

-40

-50

-60

-70

-80

-90

-100

PHASE NOISE (dBc/Hz)

-110

-120

-130

-140
10 10M

f

(Hz)

OFFSET

TRANSMIT POWER EFFICIENCY

vs. SUPPLY VOLTAGE

-40°C

+25°C

+85°C

SUPPLY VOLTAGE (V)

+125°C

OOK OUTPUT AT
50% DUTY CYCLE

= 315MHz

f

RF

3.22.82.4

SUPPLY CURRENT AND OUTPUT POWER

vs. EXTERNAL RESISTOR

POWER

CURRENT

EXTERNAL RESISTOR (Ω)

fRF = 315MHz

100101

+125°C

CW OUTPUT

= 433MHz

f

RF

3.22.82.4

1M100k10k1k100

MAX1472 toc10

EFFICIENCY (%)

MAX1472 toc13

50

45

40

35

30

25

20

2.0 3.6

12

10

8

6

4

OUTPUT POWER (dBm)

2

0

0.1 1000

MAX1472 toc14

45

MAX1472 toc11

12

10

8

6

4

2

0

40

35

30

EFFICIENCY (%)

25

20

10

9

SUPPLY CURRENT (mA)

8

7

6

5

SUPPLY CURRENT (mA)

4

3

2

TRANSMIT POWER EFFICIENCY

vs. SUPPLY VOLTAGE

+25°C

-40°C

+125°C

+85°C

OOK OUTPUT AT
50% DUTY CYCLE

= 433MHz

f

RF

2.0 3.6
SUPPLY VOLTAGE (V)

3.22.4 2.8

SUPPLY CURRENT vs. OUTPUT POWER

fRF = 315MHz

CW

50% DUTY CYCLE

010

OUTPUT POWER (dBm)

862 4

MAX1472 toc12

MAX1472 toc15

25kHz/div

2.5kHz/div

FREQUENCY SETTLING TIME

START: 0s

START: 0s

MAX1472 toc16

1ms

1ms

ENABLE
TRANSITION
FROM LOW
TO HIGH

ENABLE
TRANSITION
FROM LOW
TO HIGH

15%/div

AM DEMODULATION OF PA OUTPUT

START: 0s STOP: 20µs

MAX1472 toc17

DATA RATE
= 100kHz

MAX1472

300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter

6 _______________________________________________________________________________________

Detailed Description

The MAX1472 is a highly integrated OOK/ASK transmit­ter operating over the 300MHz to 450MHz frequency
range. The IC includes a complete PLL and a highly
efficient PA. The device can also be easily placed into
a 5nA low-power shutdown mode.

Shutdown Mode

The ENABLE pin is internally pulled down with a 15µA
current source. If the pin is left unconnected or pulled
low, the MAX1472 goes into shutdown mode, where the
supply current drops to less than 5nA. When ENABLE
is high, the IC is enabled and is ready for transmission
after 220µs (frequency settles to within 50kHz).

The 220µs turn-on time of the MAX1472 is mostly 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.

Phase-Locked Loop

The PLL block contains a phase detector, charge
pump, integrated loop filter, VCO, 32X clock divider,
and crystal oscillator. This PLL requires no external
components, other than a crystal. The relationship
between the carrier and crystal frequency is given by:

f

XTAL

= fRF/ 32

The lock-detect circuit prevents the PA from transmit­ting until the PLL is locked. In addition, the device shuts
down the PA if the reference frequency is lost.

Power Amplifier (PA)

The PA of the MAX1472 is a high-efficiency, open-drain,
switch-mode amplifier. With proper output matching net­work, the PA can drive a wide range of impedances,
including the small-loop PC board trace antenna and
any 50Ω antenna. The output-matching network for a
50Ω antenna 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 PAOUT (pin 4), which is about
250Ω .

When the output matching network is properly tuned,
the PA transmits power with high efficiency. The

Typical

Application Circuit

delivers 10.3dBm at 2.7V supply with

9.1mA of supply current. Thus, the overall efficiency is
44%. The efficiency of the PA itself is more than 52%.

Applications Information

Output Power Adjustment

It is possible to adjust the output power down to

-10dBm with the addition of a resistor. 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 the

Typical Application Circuit

.

Pin Description

PIN NAME FUNCTION

1 XTAL1 1st Crystal Input. fRF = 32 x f

XTAL

.

2 GND Ground. Connect to system ground.

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

4 PAOUT

Power-Amplifier Output. This output requires a pullup inductor to the supply voltage, which may be part
of the output-matching network to a 50Ω antenna.

5

Standby/Power-Up Input. A logic low on ENABLE places the device in standby mode.

6 DATA OOK Data Input. Power amplifier is ON when DATA is high.

7VDDSupply Voltage. Bypass to GND with capacitor as close to the pin as possible.

8 XTAL2 2nd Crystal Input. fRF = 32 x f

XTAL

.

ENABLE

MAX1472

300MHz-to-450MHz Low-Power,

Crystal-Based ASK Transmitter

_______________________________________________________________________________________ 7

Crystal Oscillator

The crystal oscillator in the MAX1472 is designed to
present a capacitance of approximately 3.1pF between
the XTAL1 and XTAL2 pins. If a crystal designed to
oscillate 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 MAX1472, causing
the transmitter to be transmitting at 315.1MHz rather
than 315.0MHz, an error of about 100kHz, or 320ppm.

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:

where:

f

p

is the amount the crystal frequency is pulled in ppm.

Cmis the motional capacitance of the crystal.

C

case

is the case capacitance.

C

spec

is the specified load capacitance.

C

load

is the actual load capacitance.

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

load

=

C

spec

, the frequency pulling equals zero.

Output Matching to 50

ΩΩ

When matched to a 50Ω system, the MAX1472 PA is
capable of delivering more than +10dBm of output
power at VDD= 2.7V. The output of the PA is an open­drain transistor that requires external impedance
matching and pullup inductance for proper biasing.
The pullup inductance from PA to VDDserves three
main purposes: It resonates the capacitance of the PA
output, provides biasing for the PA, and becomes a
high-frequency choke to reduce the RF energy cou­pling into V

DD

. The recommended output-matching net-

work topology is shown in the

Typical Application

Circuit

. The matching network transforms the 50Ω load
to a higher impedance at the output of the PA in addi­tion to forming a bandpass filter that provides attenua­tion for the higher order harmonics.

Output Matching to PC Board Loop

Antenna

In most applications, the MAX1472 PA output has to be
impedance matched to a small-loop antenna. The
antenna is usually fabricated out of a copper trace on a
PC board in a rectangular, circular, or square pattern.
The antenna has an impedance that consists of a lossy
component and a radiative component. To achieve
high radiating efficiency, the radiative component
should be as high as possible, while minimizing the
lossy component. In addition, the loop antenna has 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.

The objective of the matching network is to match the
PA 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, which 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.

f

C

CCCC

p

m

case load case spec

=

+

−
+

⎛

⎝

⎜

⎞

⎠

⎟

×

2

11

10

6

MAX1472

Layout Considerations

A properly designed PC board is an essential part of
any RF/microwave circuit. On the PA output, use con­trolled-impedance lines and keep them as short as
possible to minimize losses and radiation. At high fre­quencies, trace lengths that are on the order of λ/10 or
longer can act as antennas.

Keeping the traces short also reduces parasitic induc­tance. Generally, 1in of PC board 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%.

To reduce 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 place decoupling capacitors close to all
V

DD

connections.

300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter

8 _______________________________________________________________________________________

Functional Diagram

Chip Information

PROCESS: CMOS

Package Information

For the latest package outline information and land patterns,
go to www.maxim-ic.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

DATA

ENABLE

XTAL1

XTAL2

LOCK DETECT

MAX1472

OSCILLATOR

AND

GATE

32 x PLL

CRYSTAL-

DRIVER

V

DD

PA

PAOUT

PAGND

GND

MAX1472

300MHz-to-450MHz Low-Power,

Crystal-Based ASK Transmitter

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________

9

© 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

Revision History

REVISION

NUMBER

1 4/05 — —

2 6/09

3 10/10

REVISION

DATE

DESCRIPTION

Updated EC table Ma x supply currents, added lead-free note, and corrected
Electrical Characteristics notes

Removed Maximum Crystal Inductance spec from Electrical Characteristics
table

PAGES

CHANGED

1, 2, 3, 6, 8

3