MAX1472

MAX1472
19-2872; Rev 4; 6/12
KIT
ATION
EVALU
E
L
B
A
AVAIL
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
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.
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
*At 50% duty cycle (315MHz, 2.7V supply, +10dBm output
power)
Applications
Ordering Information
Remote Keyless Entry
RF Remote Controls
Tire Pressure Monitoring
Security Systems
PART
TEMP
RANGE
MAX1472AKA+T
-40°C to +125°C
PINPACKAGE
TOP
MARK
8 SOT23
AEKS
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Radio-Controlled Toys
Wireless Game Consoles
Wireless Computer Peripherals
Wireless Sensors
Pin Configuration
Typical Application Circuit
*
TOP VIEW
+
1
XTAL1
XTAL2 8
3.0V
VDD 7
2 GND
50Ω
ANTENNA
MAX1472
220pF 680pF
3 PAGND
8
XTAL2
7
VDD
3
6
DATA
PAOUT 4
5
ENABLE
GND
2
MAX1472
DATA 6
DATA INPUT
4 PAOUT
+
XTAL1 1
ENABLE 5
PAGND
STANDBY OR
POWER-UP
SOT23
*Optional power adjust resistor.
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.
1
MAX1472
General Description
MAX1472
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
ABSOLUTE MAXIMUM RATINGS
VDD to GND ..........................................................-0.3V to +4.0V
All Other Pins to GND ................................-0.3V to (VDD + 0.3V)
Continuous Power Dissipation (TA = +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
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, output power is referenced to 50Ω, VDD = 2.1V to 3.6V, VENABLE = VDD, TA = -40°C to +125°C, unless
otherwise noted. Typical values are at VDD = 2.7V, TA = +25°C, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
3.6
V
SYSTEM PERFORMANCE
Supply Voltage
VDD
2.1
fRF = 315MHz
Supply Current
IDD
fRF = 433MHz
Standby Current
Frequency Range
ISTDBY
5.3
9.4
VENABLE = VDD,
VDATA = VDD
9.1
16.6
VENABLE = VDD,
VDATA = 0V
1.5
2.3
VENABLE = VDD
(Note 2)
5.7
VENABLE = VDD,
VDATA = VDD
9.6
VENABLE = VDD,
VDATA = 0V
1.7
2.7
5
350
nA
1.7
µA
mA
VENABLE < VIL, TA < +85°C (Note 3)
VENABLE < VIL TA < +125°C (Note 3)
(Note 1)
300
450
MHz
Data Rate
(Note 3)
0
100
kbps
Modulation Depth
ON to OFF POUT ratio (Note 4)
Output Power
Turn-On Time
Transmit Efficiency with CW
Transmit Efficiency at 50%
Duty Cycle
2
fRF
VENABLE = VDD
(Note 2)
POUT
tON
90
TA = +25°C, VDD = 2.7V (Notes 5, 6)
7.3
10.3
TA = +125°C, VDD = 2.1V (Notes 5, 6)
3.3
6.0
TA = -40°C, VDD = 3.6V (Notes 5, 6)
13.7
To fOFFSET < 50kHz (Note 7)
220
To fOFFSET < 5kHz (Note 7)
450
fRF = 315MHz (Note 8)
43.6
fRF = 433MHz (Note 8)
41.3
fRF = 315MHz (Note 9)
37.6
fRF = 433MHz (Note 9)
35.1
dB
12.8
dBm
16.2
µs
%
%
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
(Typical Application Circuit, output power is referenced to 50Ω, VDD = 2.1V to 3.6V, VENABLE = VDD, TA = -40°C to +125°C, unless
otherwise noted. Typical values are at VDD = 2.7V, TA = +25°C, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
PHASE-LOCKED LOOP PERFORMANCE
VCO Gain
330
fRF = 315MHz
Phase Noise
fRF = 433MHz
Maximum Carrier Harmonics
Reference Spur
fOFFSET =100kHz
-84
fOFFSET = 1MHz
-91
fOFFSET =100kHz
-82
fOFFSET = 1MHz
-89
fRF = 315MHz
-50
fRF = 433MHz
-50
fRF = 315MHz
-75
fRF = 433MHz
-81
Loop Bandwidth
Crystal Frequency
fXTAL
Oscillator Input Capacitance
From each XTAL pin to GND
Frequency Pushing by VDD
MHz/V
dBc/Hz
dBc
dBc
1.6
MHz
fRF / 32
MHz
6.2
pF
3
ppm/V
DIGITAL INPUTS
Data Input High
VIH
Data Input Low
VIL
VDD - 0.25
V
0.25
V
Maximum Input Current
2
nA
Pulldown Current
25
µA
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
100% tested at TA = +25°C. Guaranteed by design and characterization over temperature.
50% duty cycle at 10kHz data.
Guaranteed by design and characterization, not production tested.
Generally limited by PC board layout.
Output power can be adjusted with external resistor.
Guaranteed by design and characterization at fRF = 315MHz.
VENABLE < VIL to VENABLE > VIH. fOFFSET is defined as the frequency deviation from the desired carrier frequency.
VENABLE > VIH, VDATA > VIH, Efficiency = POUT/(VDD x IDD).
VENABLE > VIH, DATA toggled from VIL to VIH, 10kHz, 50% duty cycle, Efficiency = POUT/(VDD x IDD).
3
MAX1472
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(Typical Application Circuit, VDD = 2.7V, TA = +25°C, unless otherwise noted.)
-40°C
+125°C
9
+85°C
8
1.6
1.5
1.4
7
1.3
6
1.2
5
+85°C
-40°C
+25°C
3.2
3.6
SUPPLY VOLTAGE (V)
+125°C
+85°C
1.8
1.6
13
OUTPUT POWER (dBm)
3.2
-40°C
+25°C
1.4
1.2
2.4
2.8
3.2
12
VENABLE = VIH,
VDATA = VIH,
fRF = 315MHz
-25°C
10
MAX1472 toc03
2.8
14
13
+125°C
9
+85°C
8
VENABLE = VIH,
VDATA = VIH,
fRF = 433MHz
+25°C
11
-40°C
10
+125°C
9
7
8
6
7
+85°C
6
2.0
2.4
2.8
3.2
2.0
3.6
2.4
2.8
SUPPLY VOLTAGE (V)
REFERENCE SPUR MAGNITUDE
vs. SUPPLY VOLTAGE
FREQUENCY STABILITY
vs. SUPPLY VOLTAGE
TRANSMIT POWER EFFICIENCY
vs. SUPPLY VOLTAGE
2
MAX1472 toc07
315MHz
-77
-79
433MHz
55
0
315MHz
-1
433MHz
-2
-40°C
50
EFFICIENCY (%)
-73
1
OFFSET FREQUENCY (ppm)
-71
-81
40
35
+125°C
+85°C
-3
30
-4
-85
2.4
2.8
SUPPLY VOLTAGE (V)
3.2
3.6
CW OUTPUT
fRF = 315MHz
25
2.0
2.4
2.8
SUPPLY VOLTAGE (V)
3.2
3.6
3.6
+25°C
45
-83
4
3.2
SUPPLY VOLTAGE (V)
-69
3.6
12
SUPPLY VOLTAGE (V)
-67
2.0
3.2
OUTPUT POWER vs. SUPPLY VOLTAGE
-40°C
11
3.6
-65
-75
2.4
SUPPLY VOLTAGE (V)
5
2.0
+125°C
2.0
3.6
MAX1472 toc08
SUPPLY CURRENT (mA)
2.0
2.8
OUTPUT POWER vs. SUPPLY VOLTAGE
14
MAX1472 toc04
VENABLE = VIH,
VDATA = VIL,
fRF = 433MHz
8
SUPPLY VOLTAGE (V)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
2.2
+85°C
9
5
2.4
2.0
OUTPUT POWER (dBm)
2.8
-40°C
+25°C
10
6
MAX1472 toc05
2.4
11
7
1.1
2.0
VENABLE = VIH,
VDATA = VIH,
fRF = 433MHz
12
MAX1472 toc09
10
1.7
+125°C
SUPPLY CURRENT (mA)
11
VENABLE = VIH,
VDATA = VIL,
fRF = 315MHz
1.8
13
MAX1472 toc02
+25°C
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
MAX1472 toc01
VENABLE = VIH,
VDATA = VIH,
fRF = 315MHz
12
SUPPLY CURRENT vs. SUPPLY VOLTAGE
SUPPLY CURRENT vs. SUPPLY VOLTAGE
1.9
MAX1472 toc06
SUPPLY CURRENT vs. SUPPLY VOLTAGE
13
REFERENCE SPUR (dBc)
MAX1472
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
2.0
2.4
2.8
SUPPLY VOLTAGE (V)
3.2
3.6
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
TRANSMIT POWER EFFICIENCY
vs. SUPPLY VOLTAGE
-40°C
40
35
+85°C
30
35
30
2.4
2.8
3.2
3.6
2.0
2.4
2.8
3.2
PHASE NOISE vs. OFFSET FREQUENCY
SUPPLY CURRENT AND OUTPUT POWER
vs. EXTERNAL RESISTOR
MAX1472 toc13
-70
-80
-90
-100
-110
-120
fRF = 315MHz
POWER
2.0
8
6
6
4
4
2
2
0
10
100
1k
10k
100k
1M
10M
0.1
fOFFSET (Hz)
1
10
100
3.2
3.6
fRF = 315MHz
9
0
1000
8
7
CW
6
5
4
50% DUTY CYCLE
3
2
0
2
4
6
8
10
OUTPUT POWER (dBm)
EXTERNAL RESISTOR (Ω)
FREQUENCY SETTLING TIME
AM DEMODULATION OF PA OUTPUT
MAX1472 toc16
MAX1472 toc17
DATA RATE
= 100kHz
ENABLE
TRANSITION
FROM LOW
TO HIGH
25kHz/div
START: 0s
2.8
SUPPLY CURRENT vs. OUTPUT POWER
-130
-140
2.4
10
12
10
CURRENT
8
OOK OUTPUT AT
50% DUTY CYCLE
fRF = 433MHz
20
SUPPLY CURRENT (mA)
OUTPUT POWER (dBm)
-60
MAX1472 toc14
12
10
25
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
-50
+85°C
3.6
SUPPLY VOLTAGE (V)
-40
+125°C
30
OOK OUTPUT AT
50% DUTY CYCLE
fRF = 315MHz
20
2.0
35
+125°C
+85°C
25
CW OUTPUT
fRF = 433MHz
25
PHASE NOISE (dBc/Hz)
EFFICIENCY (%)
+125°C
40
SUPPLY CURRENT (mA)
EFFICIENCY (%)
EFFICIENCY (%)
40
+25°C
-40°C
+25°C
MAX1472 toc12
45
45
MAX1472 toc11
+25°C
-40°C
45
50
MAX1472 toc10
50
TRANSMIT POWER EFFICIENCY
vs. SUPPLY VOLTAGE
MAX1472 toc15
TRANSMIT POWER EFFICIENCY
vs. SUPPLY VOLTAGE
1ms
15%/div
ENABLE
TRANSITION
FROM LOW
TO HIGH
2.5kHz/div
START: 0s
1ms
START: 0s
STOP: 20µs
5
MAX1472
Typical Operating Characteristics (continued)
(Typical Application Circuit, VDD = 2.7V, TA = +25°C, unless otherwise noted.)
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
MAX1472
Pin Description
PIN
NAME
FUNCTION
1
XTAL1
2
GND
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
ENABLE
Standby/Power-Up Input. A logic low on ENABLE places the device in standby mode.
6
DATA
7
VDD
8
XTAL2
1st Crystal Input. fRF = 32 x fXTAL.
Ground. Connect to system ground.
OOK Data Input. Power amplifier is ON when DATA is high.
Supply Voltage. Bypass to GND with capacitor as close to the pin as possible.
2nd Crystal Input. fRF = 32 x fXTAL.
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:
fXTAL = 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.
6
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 between
100Ω and 150Ω for a 2.7V supply.
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.
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
Output Matching to 50Ω
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 VDD serves 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 VDD. The recommended output-matching network 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.
fp =
Cm
2
⎛
⎞
1
1
6
−
⎜
⎟ × 10
C
+
C
C
+
C
load
case
spec ⎠
⎝ case
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.
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.
7
MAX1472
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:
MAX1472
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
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
VDD connections.
Functional Diagram
DATA
ENABLE
VDD
MAX1472
8
PA
PAOUT
PAGND
LOCK DETECT
32 x PLL
GND
CRYSTALOSCILLATOR
DRIVER
XTAL1
XTAL2
Package Information
Chip Information
PROCESS: CMOS
AND
GATE
For the latest package outline information and land patterns
(footprints), 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
300MHz-to-450MHz Low-Power,
Crystal-Based ASK Transmitter
REVISION
NUMBER
REVISION
DATE
1
4/05
—
2
6/09
Updated EC table Max supply currents, added lead-free note, and corrected
Electrical Characteristics notes
3
10/10
4
6/12
DESCRIPTION
PAGES
CHANGED
—
Removed Maximum Crystal Inductance spec from Electrical Characteristics table
Updated Electrical Characteristics, updated Power Amplifier (PA) section
1, 2, 3, 6, 8
3
3, 6
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. 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.
9 __________________Maxim Integrated Products, Inc. 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
© 2012 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX1472
Revision History
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