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19-2872; Rev 1; 4/05
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter
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 50 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
2.1V to 3.6V Single-Supply Operation Low 5.3mA Operating Supply Current* Supports ASK with 90dB Modulation Depth Output Power Adjustable to More than +10dBm Uses Small Low-Cost Crystal Small 3mm 3mm 8-Pin SOT23 Package Fast-On Oscillator 220µs Startup Time
MAX1472
*At 50% duty cycle (315MHz, 2.7V supply, +10dBm output power)
Applications
Remote Keyless Entry RF Remote Controls Tire Pressure Monitoring Security Systems Radio-Controlled Toys Wireless Game Consoles Wireless Computer Peripherals Wireless Sensors
PART MAX1472AKA-T
Ordering Information
TEMP RANGE -40°C to +125°C PINPACKAGE 8 SOT23-8 TOP MARK AEKS
Typical Application Circuit
TOP VIEW
1 XTAL1 XTAL2 8 3.0V
Pin Configuration
*
2 GND MAX1472 VDD 7 50 ANTENNA 220pF 680pF
XTAL1 1 GND 2
8 7
XTAL2 VDD DATA ENABLE
3 PAGND
DATA 6 DATA INPUT
MAX1472
PAGND 3 6 5 PAOUT 4
STANDBY OR POWER-UP
4 PAOUT
ENABLE 5
SOT23
*Optional power adjust resistor. ________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter MAX1472
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
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 50, 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 SYSTEM PERFORMANCE Supply Voltage VDD VENABLE = VDD (Note 2) fRF = 315MHz VENABLE = VDD, VDATA = VDD VENABLE = VDD, VDATA = 0V VENABLE = VDD (Note 2) fRF = 433MHz VENABLE = VDD, VDATA = VDD VENABLE = VDD, VDATA = 0V Standby Current Frequency Range Data Rate Modulation Depth Output Power POUT ISTDBY fRF VENABLE < VIL, TA < +85°C (Note 3) VENABLE < VIL TA < +125°C (Note 3) (Note 1) (Note 3) ON to OFF POUT ratio (Note 4) TA = +25°C, VDD = 2.7V (Notes 8, 9) TA = +125°C, VDD = 2.1V (Notes 8, 9) TA = -40°C, VDD = 3.6V (Notes 8, 9) Turn-On Time Transmit Efficiency with CW Transmit Efficiency at 50% Duty Cycle tON To fOFFSET < 50kHz (Note 5) To fOFFSET < 5kHz (Note 5) fRF = 315MHz (Note 6) fRF = 433MHz (Note 6) fRF = 315MHz (Note 7) fRF = 433MHz (Note 7) 7.3 3.3 300 0 90 10.3 6.0 13.7 220 450 43.6 41.3 37.6 35.1 16.2 µs % % 12.8 dBm 2.1 5.3 9.1 1.5 5.7 9.6 1.7 5 2.5 350 1.7 450 100 nA µA MHz kbps dB 3.6 9.2 16.4 2.1 mA V SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Current
IDD
2
_______________________________________________________________________________________
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter
ELECTRICAL CHARACTERISTICS (continued)
(Typical Application Circuit, output power is referenced to 50, 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 VCO Gain fRF = 315MHz Phase Noise fRF = 433MHz Maximum Carrier Harmonics Reference Spur Loop Bandwidth Crystal Frequency Oscillator Input Impedance Frequency Pushing by VDD Maximum Crystal Inductance DIGITAL INPUTS Data Input High Data Input Low Maximum Input Current Pulldown Current VIH VIL 2 25 VDD - 0.25 0.25 V V nA µA fXTAL From each XTAL pin to GND fRF = 315MHz fRF = 433MHz fRF = 315MHz fRF = 433MHz fOFFSET =100kHz fOFFSET = 1MHz fOFFSET =100kHz fOFFSET = 1MHz SYMBOL CONDITIONS MIN TYP 330 -84 -91 -82 -89 -50 -50 -75 -81 1.6 fRF / 32 6.2 3 50 dBc dBc MHz MHz pF ppm/V nH dBc/Hz MAX UNITS MHz/V
MAX1472
PHASE-LOCKED LOOP PERFORMANCE
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. 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). Output power can be adjusted with external resistor. Guaranteed by design and characterization at fRF = 315MHz.
_______________________________________________________________________________________
3
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter MAX1472
Typical Operating Characteristics
(Typical Application Circuit, VDD = 2.7V, TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1472 toc01
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1472 toc02
SUPPLY CURRENT vs. SUPPLY VOLTAGE
12 SUPPLY CURRENT (mA) 11 10 9 8 7 6 5 +125°C VENABLE = VIH, VDATA = VIH, fRF = 433MHz -40°C +25°C +85°C
MAX1472 toc03
13 12 SUPPLY CURRENT (mA) 11 10 9 8 7 6 5
VENABLE = VIH, VDATA = VIH, fRF = 315MHz -40°C
1.9 1.8 SUPPLY CURRENT (mA) 1.7 1.6 1.5 1.4 1.3 1.2 1.1 +25°C -40°C VENABLE = VIH, VDATA = VIL, fRF = 315MHz +85°C +125°C
13
+25°C
+125°C +85°C
2.0
2.4
2.8
3.2
3.6
2.0
2.4
2.8
3.2
3.6
2.0
2.4
2.8
3.2
3.6
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1472 toc04
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX1472 toc05
OUTPUT POWER vs. SUPPLY VOLTAGE
13 OUTPUT POWER (dBm) 12 11 10 9 8 7 6 +85°C -40°C +125°C VENABLE = VIH, VDATA = VIH, fRF = 433MHz
MAX1472 toc06
2.2 VENABLE = VIH, VDATA = VIL, fRF = 433MHz +85°C
+125°C
14 13 OUTPUT POWER (dBm) 12 11 10 9
14
2.0 SUPPLY CURRENT (mA)
VENABLE = VIH, VDATA = VIH, fRF = 315MHz -40°C
-25°C
+25°C
1.8
+125°C +85°C
1.6 +25°C 1.4
-40°C
8 7 6
1.2 2.0 2.4 2.8 3.2 3.6 SUPPLY VOLTAGE (V)
5 2.0 2.4 2.8 3.2 3.6 SUPPLY VOLTAGE (V)
2.0
2.4
2.8
3.2
3.6
SUPPLY VOLTAGE (V)
REFERENCE SPUR MAGNITUDE vs. SUPPLY VOLTAGE
MAX1472 toc07
FREQUENCY STABILITY vs. SUPPLY VOLTAGE
MAX1472 toc08
TRANSMIT POWER EFFICIENCY vs. SUPPLY VOLTAGE
MAX1472 toc09
-65 -67 -69 REFERENCE SPUR (dBc) -71 -73 -75 -77 -79 -81 -83 -85 2.0 2.4 2.8 3.2 433MHz 315MHz
2 1 OFFSET FREQUENCY (ppm) 0 -1 -2 -3 -4 315MHz 433MHz
55 50 EFFICIENCY (%) 45 40 35 +85°C 30 25 +125°C CW OUTPUT fRF = 315MHz 2.0 2.4 2.8 3.2 -40°C +25°C
3.6
2.0
2.4
2.8
3.2
3.6
3.6
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
4
_______________________________________________________________________________________
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter
Typical Operating Characteristics (continued)
(Typical Application Circuit, VDD = 2.7V, TA = +25°C, unless otherwise noted.)
TRANSMIT POWER EFFICIENCY vs. SUPPLY VOLTAGE
MAX1472 toc10
MAX1472
TRANSMIT POWER EFFICIENCY vs. SUPPLY VOLTAGE
MAX1472 toc11
TRANSMIT POWER EFFICIENCY vs. SUPPLY VOLTAGE
MAX1472 toc12
50 -40°C +25°C
50 45 EFFICIENCY (%) 40 35 30 25 20 +85°C -40°C +25°C
45
45 EFFICIENCY (%)
40 -40°C EFFICIENCY (%) 35
+25°C
40 +125°C 35 +85°C
30 +85°C 25
+125°C
+125°C OOK OUTPUT AT 50% DUTY CYCLE fRF = 315MHz 2.8 3.2 3.6
30
CW OUTPUT fRF = 433MHz 2.0 2.4 2.8 3.2 3.6
25 SUPPLY VOLTAGE (V)
20 2.0 2.4 2.8
OOK OUTPUT AT 50% DUTY CYCLE fRF = 433MHz 3.2 3.6
2.0
2.4
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
PHASE NOISE vs. OFFSET FREQUENCY
MAX1472 toc13
SUPPLY CURRENT AND OUTPUT POWER vs. EXTERNAL RESISTOR
12 10 OUTPUT POWER (dBm) 8 6 4 2 0 POWER
MAX1472 toc14
SUPPLY CURRENT vs. OUTPUT POWER
fRF = 315MHz 9 SUPPLY CURRENT (mA) 8 7 CW 6 5 4 3 2 0 2 4 6 8 10 OUTPUT POWER (dBm) 50% DUTY CYCLE SUPPLY CURRENT (mA)
MAX1472 toc15
-40 -50 -60 PHASE NOISE (dBc/Hz) -70 -80 -90 -100 -110 -120 -130 -140 10 100 1k 10k fOFFSET (Hz) 100k 1M
fRF = 315MHz
12 10 8 6 4 2
10
CURRENT
10M
0.1
1
10
100
0 1000
EXTERNAL RESISTOR ()
FREQUENCY SETTLING TIME
MAX1472 toc16
AM DEMODULATION OF PA OUTPUT
MAX1472 toc17
25kHz/div
ENABLE TRANSITION FROM LOW TO HIGH START: 0s 1ms ENABLE TRANSITION FROM LOW TO HIGH START: 0s 1ms START: 0s 15%/div
DATA RATE = 100kHz
2.5kHz/div
STOP: 20µs
_______________________________________________________________________________________
5
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter MAX1472
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME XTAL1 GND PAGND PAOUT ENABLE DATA VDD XTAL2 1st Crystal Input. fRF = 32 x fXTAL. Ground. Connect to system ground. Ground for the Power Amplifier (PA). Connect to system ground. Power-Amplifier Output. This output requires a pullup inductor to the supply voltage, which may be part of the output-matching network to a 50 antenna. Standby/Power-Up Input. A logic low on ENABLE places the device in standby mode. 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. FUNCTION
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.
Power Amplifier
The PA of the MAX1472 is a high-efficiency, open-drain, class-C 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 50 antenna. The output-matching network for a 50 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 250 . 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%.
Shutdown Mode
The ENABLE pin is internally pulled down with a 15µA current source. If the pin is left floating 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.
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.
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
_______________________________________________________________________________________
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter
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: fp = Cm 2 1 1 6 - × 10 Ccase + Cload Ccase + Cspec
Output Matching to 50
When matched to a 50 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 50 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.
MAX1472
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 0.5, the lossy impedance is less than 0.7, 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 50 network; thus, the harmonics are lower.
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.
_______________________________________________________________________________________
7
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter 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 /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 AND GATE VDD
MAX1472
PA PAOUT
PAGND LOCK DETECT 32 x PLL GND XTAL1 XTAL2 CRYSTALOSCILLATOR DRIVER
Chip Information
TRANSISTOR COUNT: 1430 PROCESS: CMOS
8
_______________________________________________________________________________________
300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
MAX1472
SEE DETAIL "A" b e
C L
SYMBOL A A1 A2 b C D E E1 L L2 e e1
MIN 0.90 0.00 0.90 0.28 0.09 2.80 2.60 1.50 0.30
MAX 1.45 0.15 1.30 0.45 0.20 3.00 3.00 1.75 0.60 0.25 BSC.
C L
E
C L
E1
PIN 1 I.D. DOT (SEE NOTE 6) e1 D C
C L
0
0.65 BSC. 1.95 REF. 8 0
L2 A A2 A1
SEATING PLANE C
GAUGE PLANE
NOTE:
1. ALL DIMENSIONS ARE IN MILLIMETERS. 2. FOOT LENGTH MEASURED FROM LEAD TIP TO UPPER RADIUS OF HEEL OF THE LEAD PARALLEL TO SEATING PLANE C. 3. PACKAGE OUTLINE EXCLUSIVE OF MOLD FLASH & METAL BURR. 4. PACKAGE OUTLINE INCLUSIVE OF SOLDER PLATING. 5. COPLANARITY 4 MILS. MAX. 6. PIN 1 I.D. DOT IS 0.3 MM ÿ MIN. LOCATED ABOVE PIN 1. 7. SOLDER THICKNESS MEASURED AT FLAT SECTION OF LEAD BETWEEN 0.08mm AND 0.15mm FROM LEAD TIP. 8. MEETS JEDEC MO178.
L
0
DETAIL "A"
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, SOT-23, 8L BODY
APPROVAL DOCUMENT CONTROL NO. REV.
21-0078
D
1 1
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 © 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
SOT23, 8L .EPS