General Description
The MAX7058 UHF transmitter alternately transmits
ASK/OOK data at 315MHz or 390MHz using a single
crystal. The MAX7058 has internal tuning capacitors at
the output of the power amplifier that can be pro-
grammed for matching to the antenna or load. The
MAX7058 can transmit at a data rate up to 100kbps
NRZ (50kbps Manchester coded). Typical transmitted
power into a 50Ωload is +10dBm. The MAX7058 oper-
ates from +2.1V to +3.6V and draws under 8.0mA of
current. The standby current is less than 1μA at room
temperature. A 15MHz crystal is used as the reference
for 315MHz and 390MHz operation by selecting synthe-
sizer-divide ratios of 21 and 26, respectively.
The MAX7058 is available in a 4mm x 4mm, 24-pin thin
QFN package and is specified to operate in the -40°C
to +125°C automotive temperature range.
Applications
Garage Door Openers
RF Remote Controls
Home Automation
Wireless Sensors
Security Systems
Automotive
Features
Switched 315MHz/390MHz Carrier Frequency
Using One Crystal
+2.1V to +3.6V Single-Supply Operation
ASK/OOK Modulation
Internal Switched Capacitors for Optimum Dual-
Frequency Operation
8.0mA DC Current Drain (50% Duty Cycle OOK)
0.8µA Standby Current
Small 4mm x 4mm, 24-Pin Thin QFN Package
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
________________________________________________________________
Maxim Integrated Products
1
Pin Configuration
Ordering Information
5
6
4
3
14
13
15
CAP3
PAOUT
ROUT
N.C.
16
N.C.
N.C.
ENABLE
TOGGLE
N.C.
N.C.
78
CAP1
10 11 12
2324 22 20 19
CAP2
N.C.
XTAL2
AVDD
PAVDD
N.C.
MAX7058
CAP4 DIN
9
21
FSEL
217 XTAL1
DVDD
118 N.C.
N.C.
DIGITAL
CONTROL
FREQUENCY
÷21 OR ÷26
CRYSTAL
OSCILLATOR
CHARGE
PUMP
PFD
LOOP
FILTER
ENVELOPE
SHAPING
EXPOSED
PADDLE
(GND) VCO
PA
MAX7058
1
2
3
4
78 910
TQFN
11 12
24 23 22 21 20 19
5
6
18
17
16
15
14
13
N.C.
FSEL
DVDD
CAP1
N.C.
N.C.
CAP3
CAP4
PAOUT
ROUT
N.C.
N.C.
N.C.
ENABLE
TOGGLE
N.C.
CAP2
N.C.
XTAL2
XTAL1
AVDD
N.C.
PAVDD
DIN
TOP VIEW
+
*EP = EXPOSED PADDLE.
EP*
Functional Block Diagram
19-3206; Rev 0; 1/08
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.
+
Denotes a lead-free package.
*
EP = Exposed paddle.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE PKG
CODE
MAX7058ATG+ - 40°C to + 125°C 24 Thi n QFN - E P *
( 4m m x 4m m ) T2444+3
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS
(
Typical Operating Circuit
, 50Ωsystem impedance, AVDD = DVDD = PAVDD = +2.1V to +3.6V, fRF = 315MHz or 390MHz, TA=
-40°C to +125°C, unless otherwise noted. Typical values are at AVDD = DVDD = PAVDD = +2.7V, TA= +25°C, unless otherwise
noted. All min and max values are 100% tested at TA= +125°C, and guaranteed by design and characterization over temperature,
unless otherwise noted.)
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.
Supply Voltage, AVDD, DVDD, PAVDD to GND (Exposed
Paddle) ...................................………..……………-0.3V to +4V
All Other Pins ………..…Exposed Paddle - 0.3V to (VDD + 0.3V)
Continuous Power Dissipation (TA= +70°C)
24-Pin TQFN (derate 20.8mW/°C above +70°C) .....1666.7mW
Operating Temperature……………….………….-40°C to +125°C
Storage Temperature………………….……….…-65°C to +150°C
Lead Temperature (soldering, 10s) ......………………..…+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage VDD PAVDD, AVDD, and DVDD connected to
power supply, VDD 2.1 2.7 3.6 V
fRF = 315MHz 3.4 5.4
PA off, VDIN at 0% duty
cycle fRF = 390MHz 3.8 6.3
fRF = 315MHz 8.0 13.7
VDIN at 50%, duty cycle
(Notes 1, 2, 3) fRF = 390MHz 8.3 14.2
fRF = 315MHz 12.6 21.9
Supply Current IDD
VDIN at 100%, duty cycle
(Note 1) fRF = 390MHz 12.9 22.1
mA
VENABLE < VIL TA = +25°C 0.8
(Note 3) TA < +85°C 1.0 4.0Standby Current ISTDBY
TA < +125°C 6.2 16.1
μA
DIGITAL I/O
Input High Threshold VIH 0.9 x
DVDD V
Input Low Threshold VIL 0.1 x
DVDD V
Pulldown Sink Current 13 μA
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
_______________________________________________________________________________________ 3
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GENERAL CHARACTERISTICS
Frequency Range 300 315/390 450 MHz
ENABLE transition low-to-high, frequency
settled to within 50kHz of the desired carrier 110
Power-On Time tON ENABLE transition low-to-high, frequency
settled to within 5kHz of the desired carrier 250
μs
Manchester encoded 50
Maximum Data Rate Nonreturn to zero (NRZ) 100 kbps
Frequency Switching Time
Time from low-to-high or high-to-low
transition of FSEL to frequency settled to
within 5kHz of the desired carrier
30 μs
PHASE-LOCKED LOOP (PLL)
VCO Gain KVCO 320 MHz/V
10kHz offset -87
fRF = 315MHz 1MHz offset -98
10kHz offset -84
PLL Phase Noise
fRF = 390MHz 1MHz offset -98
dBc/Hz
Loop Bandwidth 600 kHz
Reference Frequency Input Level 500 mVP-P
Fr eq uency- D i vi d er Rang e 21 26
CRYSTAL OSCILLATOR
Crystal Frequency fXTAL 15 MHz
Frequency Pulling by VDD 4 ppm/V
C r ystal Load C ap aci tance (Note 4) 10 pF
AC ELECTRICAL CHARACTERISTICS
(
Typical Operating Circuit
, 50Ωsystem impedance, AVDD = DVDD = PAVDD = +2.1V to +3.6V, fRF = 315MHz or 390MHz, TA=
-40°C to +125°C, unless otherwise noted. Typical values are at AVDD = DVDD = PAVDD = +2.7V, TA= +25°C, unless otherwise
noted. All min and max values are 100% tested at TA= +125°C, and guaranteed by design and characterization over temperature,
unless otherwise noted.)
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
4 _______________________________________________________________________________________
AC ELECTRICAL CHARACTERISTICS (continued)
(
Typical Operating Circuit
, 50Ωsystem impedance, AVDD = DVDD = PAVDD = +2.1V to +3.6V, fRF = 315MHz or 390MHz, TA=
-40°C to +125°C, unless otherwise noted. Typical values are at AVDD = DVDD = PAVDD = +2.7V, TA= +25°C, unless otherwise
noted. All min and max values are 100% tested at TA= +125°C, and guaranteed by design and characterization over temperature,
unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
POWER AMPLIFIER
TA = +25°C (Note 3) 4.2 10 15.5
TA = +125°C , P AV DD = AVD D = D VD D = +2.1V 3.0 5.9
Output Power (Note 1) POUT TA = - 40°C , P AV D D = AV D D = D V D D = + 3.6V
( N ote 3) 13.3 16.4
dBm
Modulation Depth 80 dB
fRF = 315MHz -28
Maximum Carrier Harmonics With output matching
network fRF = 390MHz -32 dBc
Reference Spur -48 dBc
Note 1: Supply current and output power are greatly dependent on board layout and PAOUT match.
Note 2: 50% duty cycle at 10kHz ASK data (Manchester coded).
Note 3: Guaranteed by design and characterization, not production tested.
Note 4: Dependent on PCB trace capacitance.
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
_______________________________________________________________________________________
5
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX7058 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
3.53.32.9 3.12.5 2.72.3
10
11
12
13
14
15
16
17
18
9
2.1
TA = -40°C
TA = +25°C
TA = +85°C and +125°C
fRF = 315MHz
PA ON
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX7058 toc02
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
3.63.12.6
2.5
3.0
3.5
4.0
4.5
5.0
2.0
2.1
TA = -40°C
TA = +25°C
TA = +125°CTA = +85°C
fRF = 315MHz
PA OFF
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX7058 toc03
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
3.63.12.6
11
10
12
14
13
16
15
18
17
19
9
2.1
TA = -40°C
TA = +25°C
TA = +125°C
TA = +85°C
fRF = 390MHz
PA ON
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX7058 toc04
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
3.63.12.6
2.5
3.0
3.5
4.0
4.5
5.0
2.0
2.1
TA = -40°C
TA = +25°C
fRF = 390MHz
PA OFF
TA = +85°C and +125°C
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX7058 toc05
SUPPLY VOLTAGE (V)
OUTPUT POWER (dBm)
3.63.12.6
2
4
6
8
10
12
14
0
2.1
315MHz AND 390MHz
SUPPLY CURRENT
vs. OUTPUT POWER
MAX7058 toc06
OUTPUT POWER (dBm)
SUPPLY CURRENT (mA)
20010-10-20-30
2
4
6
8
10
12
14
0
-40
ON
50% PA
315MHz
SUPPLY CURRENT
vs. OUTPUT POWER
MAX7058 toc07
OUTPUT POWER (dBm)
SUPPLY CURRENT (mA)
20100-10-20
2
4
6
8
10
12
14
0
-30
ON
50% PA
390MHz
PHASE NOISE
vs. OFFSET FREQUENCY
MAX7058 toc08
OFFSET FREQUENCY (Hz)
PHASE NOISE (dBc/Hz)
10M1M100k10k1k
-120
-110
-90
-100
-80
-70
-60
-50
-130
100
315MHz
PHASE NOISE
vs. OFFSET FREQUENCY
MAX7058 toc09
OFFSET FREQUENCY (Hz)
PHASE NOISE (dBc/Hz)
10M1M100k10k1k
-120
-110
-90
-100
-80
-70
-60
-50
-130
100
390MHz
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
REFERENCE SPUR MAGNITUDE
vs. SUPPLY VOLTAGE
MAX7058 toc10
SUPPLY VOLTAGE (V)
REFERENCE SPUR MAGNITUDE (dBc)
3.63.12.6
-49.5
-49.0
-48.0
-48.5
-47.5
-47.0
-46.5
-46.0
-45.5
-50.0
2.1
390MHz
315MHz
FREQUENCY STABILITY
vs. SUPPLY VOLTAGE
MAX7058 toc11
SUPPLY VOLTAGE (V)
FREQUENCY STABILITY (ppm)
3.63.12.6
-3
-2
-1
0
1
2
3
4
-4
2.1
390MHz
315MHz
EFFICIENCY
vs. SUPPLY VOLTAGE
MAX7058 toc12
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
3.63.0 3.32.4 2.7
14
12
16
18
22
20
24
28
26
30
10
2.1
TA = -40°CTA = +25°C
315MHz
50% DUTY CYCLE
TA = +125°C
TA = +85°C
EFFICIENCY
vs. SUPPLY VOLTAGE
MAX7058 toc13
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
3.63.0 3.32.4 2.7
20
25
30
35
40
15
2.1
TA = -40°C
TA = +25°C
315MHz
PA ON
TA = +125°C
TA = +85°C
EFFICIENCY
vs. SUPPLY VOLTAGE
MAX7058 toc14
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
3.63.0 3.32.4 2.7
14
12
16
18
22
20
24
26
10
2.1
TA = +25°C
390MHz
50% DUTY CYCLE
TA = +125°C
TA = +85°C
TA = -40°C
EFFICIENCY
vs. SUPPLY VOLTAGE
MAX7058 toc15
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
3.63.0 3.32.4 2.7
19
17
23
21
25
29
27
31
33
15
2.1
TA = +25°C
390MHz
PA ON
TA = +125°C
TA = +85°C
TA = -40°C
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
_______________________________________________________________________________________
7
_______________________________________________________________________________________
7
Pin Description
PIN NAME FUNCTION
1, 6, 7, 12,
13, 18, 19,
24
N.C. No Connection. Internally not connected.
2 DVDD Digital Positive Supply Voltage. Bypass to GND with 0.1μF and 0.01μF capacitors placed as close to
the pin as possible.
3 FSEL
Frequency Select. Internally pulled down to GND when the part is not in standby mode. Set FSEL =
0/TOGGLE = 0 to select continuous 390MHz, and FSEL = 1/TOGGLE = 0 to select continuous
315MHz. See Table 1 for detailed mode description.
4 CAP1
Output Capacitance Adjustment 1. Logic pin to control the capacitance on PAOUT (see Table 2). Set
CAP1 = 1 to add 0.5pF shunt capacitance at PAOUT when at 315MHz. Internally pulled down to GND
when the part is not in standby mode.
5 CAP2
Output Capacitance Adjustment 2. Logic pin to control the capacitance on PAOUT (see Table 2). Set
CAP2 = 1 to add 1pF shunt capacitance at PAOUT when at 315MHz. Internally pulled down to GND
when the part is not in standby mode.
8 CAP3
Output Capacitance Adjustment 3. Logic pin to control the capacitance on PAOUT (see Table 2). Set
CAP3 = 1 to add 2pF shunt capacitance at PAOUT when at 315MHz. Internally pulled down to GND
when the part is not in standby mode.
9 CAP4
Output Capacitance Adjustment 4. Logic pin to control the capacitance on PAOUT (see Table 2). Set
CAP4 = 1 to add 4pF shunt capacitance at PAOUT when at 315MHz. Internally pulled down to GND
when the part is not in standby mode.
10 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.
11 ROUT
Envelope-Shaping Output. ROUT controls the power amplifier envelope’s rise and fall times. Connect
ROUT to PA pullup inductor or optional power-adjust resistor. Bypass the inductor to GND as close to
the inductor as possible with 680pF and 220pF capacitors.
14 PAVDD Power Amplifier Supply Voltage. Bypass to GND with 0.01μF and 220pF capacitors placed as close
to the pin as possible.
15 AVDD Analog Positive Supply Voltage. Bypass AVDD to GND with 0.1μF and 0.01μF capacitors placed as
close to the pin as possible.
16 XTAL2 Crystal Input 2. XTAL2 can be driven from an AC-coupled external reference.
17 XTAL1 Crystal Input 1. Bypass to GND if XTAL2 is driven from an AC-coupled external reference.
20 TOGGLE Toggle Pin. Set TOGGLE = 1 to enable toggle operation (see the Detailed Description section and
Table 1 for operating mode). Internally pulled down to GND when the part is not in standby mode.
21 ENABLE Enable Pin. Drive high for normal operation, and drive low or leave unconnected to put the device in
standby mode. Internally pulled down to GND.
22 DIN ASK Data Input. Internally pulled down to GND. Auto power-up occurs upon activity (see the Detailed
Description section.)
23 N.C. No connection. Must remain unconnected.
EP (GND)
Exposed Paddle. Internally connected to ground (the only ground for the MAX7058.) Requires low-
inductance path (e.g., one or more vias) to solid ground plane. Solder evenly to the board’s ground
plane for proper operation.
MAX7058
Detailed Description
The MAX7058 alternately transmits OOK/ASK data at
315MHz or 390MHz using a single crystal. The device
has integrated tuning capacitors at the output of the
power amplifier to ensure high efficiency at each fre-
quency.
The crystal-based architecture of the MAX7058 elimi-
nates many of the common problems with surface
acoustic wave (SAW) transmitters, by providing greater
modulation depth, faster frequency settling, tighter
transmit frequency tolerance, and reduced temperature
dependence. In particular, the tighter transmit frequen-
cy tolerance means that a super-heterodyne receiver
with a narrower IF bandwidth (therefore lower noise
bandwidth) can be used. The payoff is improved over-
all receiver performance when using a super-hetero-
dyne receiver such as the MAX1471, MAX1473,
MAX7033, MAX7034, or MAX7042.
Dual Frequency
The MAX7058 is a crystal-referenced PLL VHF/UHF
transmitter that transmits OOK/ASK data at 315MHz or
390MHz. Two fixed synthesizer-divide ratios of 21 and
26 can be selected, and a 15MHz crystal is used as the
reference for 315MHz/390MHz operation. The FSEL pin
is used to select the divide ratio. The MAX7058 can
operate over a 300MHz to 450MHz range by using dif-
ferent crystal frequencies. The two operating frequen-
cies are always related by a 26:21 ratio.
An internal variable shunt capacitor is connected at the
PA output. This capacitor is controlled by four external
logic bits (CAP1–CAP4) to maintain highly efficient
transmission at either 315MHz or 390MHz. This means
that it is possible to change the frequency and retune
the antenna to the new frequency in a very short time.
The combination of rapid-antenna tuning ability with
rapid-synthesizer tuning makes the MAX7058 a true fre-
quency-agile transmitter. The tuning capacitor has a
resolution of 0.5pF. When the MAX7058 operates at
315MHz, the capacitance added at PAOUT corre-
sponds to the setting at CAP1–CAP4, as seen in Table
2. When the MAX7058 operates at 390MHz, the
MAX7058 does not add any internal shunt capacitance
at PAOUT.
The MAX7058 supports ASK data rates up to 100kbps
NRZ and features adjustable output power through an
external resistor to more than +10dBm into a 50Ωload.
Power-Up and Standby Modes
The MAX7058 can be placed in either an enabled state
(all circuit blocks necessary for transmission powered
up) or a disabled state (low-current standby). The state
selection can be controlled either by ENABLE (ENABLE
method) or by activity on DIN (auto-power-up method).
In either method, the MAX7058 can begin transmission
within 250μs after being enabled. Either method can be
used with any TOGGLE/FSEL operating mode.
In the ENABLE method, setting ENABLE to a logic-high
state enables the MAX7058 and setting it to a logic-low
state disables the MAX7058. To avoid conflict with the
auto-power-up method, DIN must be set to a logic-low
state before ENABLE is set to a logic-low state, and
remains low until after ENABLE is set to a logic-
high state.
In the auto-power-up method, ENABLE can be hard-
wired to a logic-low state and a rising edge on DIN
will enable the MAX7058. The MAX7058 will remain
enabled until DIN is placed in a steady logic-low
state for 222 cycles of the reference clock (279.62ms
with a 15MHz crystal), at which time the MAX7058 will
be disabled.
When the MAX7058 is enabled, the active pulldowns at
CAP1–CAP4, FSEL, and TOGGLE will be turned on.
When the MAX7058 is disabled, these active pulldowns
will be turned off. The active pulldowns at ENABLE and
DIN are always turned on.
315MHz/390MHz Dual-Frequency
ASK Transmitter
8 _______________________________________________________________________________________
Operating Mode
TOGGLE and FSEL are two pins available for control-
ling the state of the toggle mode and the operating fre-
quency. The following truth table defines the pin logic
for the four possible operating states.
The internal variable shunt capacitor control pins
(CAP1–CAP4) are used whenever the frequency setting
is 315MHz, in either continuous (TOGGLE = 0, FSEL =
1) or toggle (TOGGLE = 1) mode.
Toggle Definition
With TOGGLE/FSEL set to state 10, the MAX7058 is in
5-packet toggle mode; with TOGGLE/FSEL set to state
11, the MAX7058 is in 100-packet toggle mode. Upon
power-up, the MAX7058 begins transmission at
315MHz within 250μs. Packet termination is defined as
the time duration of greater than 218 crystal oscillator ref-
erence clock cycles (17.49ms) with DIN continuously at
logic 0. The frequency of operation toggles every five or
100 packets based on the logic level of FSEL.
Power Amplifier (PA)
The power amplifier (PA) of the MAX7058 is a high-
efficiency, open-drain, switching-mode amplifier. In a
switching-mode amplifier, the gate of the final-stage
FET is driven with a very sharp 25% duty-cycle square
wave at the transmit frequency. This square wave is
derived from the synthesizer circuit. When the matching
network is tuned correctly, the output FET resonates the
attached tank circuit with a minimum amount of power
dissipated in the FET. With a proper output-matching
network, the PA can drive a wide range of antenna
impedances, which include a small-loop PCB trace and
a 50Ωantenna. The output-matching network sup-
presses the carrier harmonics and transforms the
antenna impedance to optimal impedance at PAOUT,
which is from 125Ωto 250Ω.
When the output-matching network is properly tuned,
the PA transmits +10dBm (typ), with a high overall effi-
ciency. The efficiency of the PA itself is more than 40%.
The output power can be adjusted by changing the
impedance seen by the PA or by adjusting the value of
an external resistor at PAOUT.
Envelope Shaping
The MAX7058 features an internal envelope-shaping
resistor, which connects between PAVDD and ROUT.
When connected to the PA pullup inductor, the enve-
lope-shaping resistor slows the turn-on/turn-off time of
the PA and results in a smaller spectral width of the
modulated PA output signal.
Variable Capacitor
The MAX7058 has a set of selectable internal shunt
capacitors that can be switched in and out to present
different capacitor values at the PA output. The capaci-
tors are connected from the PA output to ground. This
allows changing the tuning network, along with the syn-
thesizer-divide ratio each time the transmitted frequen-
cy changes, making it possible to maintain maximum
transmitter power while moving rapidly from one fre-
quency to another.
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
_______________________________________________________________________________________ 9
Table 1. Toggle Pin Operation for MAX7058
TOGGLE
PIN
FSEL
PIN OPERATING STATE
00
Continuous fixed-frequency operation at
390MHz
01
Continuous fixed-frequency operation at
315MHz
10
Five packets toggle operation between
315MHz and 390MHz
11
100 packets toggle operation between
315MHz and 390MHz
Figure 1. Power-Up Waveform with DIN/ENABLE for MAX7058
DIN
ENABLE
POWER-UP
(INTERNAL)
DIN
ENABLE
POWER-UP
(INTERNAL)
CASE 1: DIN PIN ONLY USED TO POWER UP THE MAX7058
CASE 2: ENABLE PIN ONLY USED TO POWER UP THE MAX7058
FALLING EDGE OF ENABLE MUST COME AFTER
LAST DIN FALLING EDGE
279.62ms
(WITH 15MHz
REFERENCE)
MAX7058
When the particular capacitance control input pin is
high, then the corresponding amount of capacitance is
added at PAOUT; this capacitance tuning works only at
315MHz. The 16 capacitor values are selected by set-
ting CAP1–CAP4; the capacitance resolution is 0.5pF.
The total capacitance varies from 0 to 7.5pF. For exam-
ple, if CAP1 and CAP3 are high and CAP4 and CAP2
are low when operating at 315MHz, then this circuit will
add 2.5pF at PAOUT.
Phase-Locked Loop
The MAX7058 utilizes a fully integrated, programmable
PLL for its frequency synthesizer. All PLL components
including the loop filter are included on-chip. The divide
ratio is set at one of two fixed values: 21 (FSEL is set to
high) or 26 (FSEL is set to low).
Crystal (XTAL) Oscillator
The crystal (XTAL) oscillator in the MAX7058 is
designed to present a capacitance of approximately
6pF between XTAL1 and XTAL2. In most cases, this
corresponds to an 8pF load capacitance applied to the
external crystal when typical PCB parasitics are added.
The MAX7058 is designed to operate with a typical
10pF load capacitance crystal. It is very important to
use a crystal with a load capacitance equal to the
capacitance of the MAX7058 crystal oscillator plus
PCB parasitics. If a crystal designed to oscillate with a
different load capacitance is used, the crystal is pulled
away from its stated operating frequency, introducing
an error in the reference frequency. A crystal designed
to operate at a higher load capacitance than the value
specified for the oscillator will always be pulled higher
in frequency. Adding capacitance to increase the load
capacitance on the crystal will increase the startup time
and may prevent oscillation altogether.
In actuality, the oscillator pulls every crystal. The crys-
tal’s natural frequency is really below its specified fre-
quency, 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:
fpis the amount the crystal frequency is pulled in ppm
Cmis the motional capacitance of the crystal
Ccase is the case capacitance
Cload is the actual load capacitance
Cspec is the specified load capacitance
When the crystal is loaded as specified (i.e., Cload =
Cspec), the frequency pulling equals zero.
fC
CCCC
pm
case load case spec
=++
×
2
11
1006
315MHz/390MHz Dual-Frequency
ASK Transmitter
10 ______________________________________________________________________________________
Table 2. Variable Capacitor Values and
Control Input Pins
ADDED SHUNT CAPACITANCE
IN pF
CAPACITOR
CONTROL PIN STATE
(CAP4CAP1) 315MHz (÷21) 390MHz (÷26)
0000 0
0001 0.5
0010 1.0
0011 1.5
0100 2.0
0101 2.5
0110 3.0
0111 3.5
1000 4.0
1001 4.5
1010 5.0
1011 5.5
1100 6.0
1101 6.5
1110 7.0
1111 7.5
0
Applications Information
Output Matching to 50
Ω
Ω
When matched to a 50Ωsystem, the MAX7058’s PA is
capable of delivering +10dBm of output power at VDD
= +2.7V. The output of the PA is an open-drain transis-
tor, which has internal selectable shunt tuning capaci-
tors for impedance matching (see the
Variable
Capacitor
section). It is connected to VDD through a
pullup inductor for proper biasing. The internal selec-
table shunt capacitors make it easy for tuning when
changing the output frequency. The pullup inductance
from the PAOUT to VDD or ROUT serves three main
purposes: resonating the capacitive PA output, provid-
ing biasing for the PA, and acting as a high-frequency
choke to prevent RF energy from coupling into VDD.
The pi network between the PA output and the antenna
also forms a lowpass filter that provides attenuation for
the higher-order harmonics.
Output Matching to PCB Loop Antenna
In many applications, the MAX7058 must be imped-
ance-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
has impedance that consists of a lossy component and
a radiative component. To achieve high radiating effi-
ciency, the radiative component should be as high as
possible, while minimizing the lossy component. In
addition, the loop antenna has an inherent loop induc-
tance associated with it (assuming the antenna is termi-
nated to ground). In a typical application, the induc-
tance of the loop antenna is approximately 50nH to
100nH. The radiative and lossy impedances may be
anywhere from a few tenths of an ohm to 5Ωor 10Ω.
Layout Considerations
A properly designed PCB is an essential part of any
RF/microwave circuit. At high-frequency inputs and
outputs, use controlled-impedance lines and keep
them as short as possible to minimize losses and radi-
ation. At high frequencies, trace lengths that are on
the order of λ/10 or longer act as antennas, where λis
the wavelength.
Keeping the traces short also reduces parasitic induc-
tance. Generally, one inch of PCB trace adds about
20nH of parasitic inductance. The parasitic inductance
can have a dramatic effect on the effective inductance
of a passive component. For example, a 0.5in trace
connecting to a 100nH inductor adds an extra 10nH of
inductance, or 10%.
To reduce 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 the ground plane
and place decoupling capacitors as close as possible
to all VDD pins.
Chip Information
PROCESS: CMOS
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
______________________________________________________________________________________ 11
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
12 ______________________________________________________________________________________
Typical Operating Circuit
MAX7058
8CAP3
9CAP4
10 PAOUT
11 ROUT
14 PAVDD
2
DVDD
17
XTAL1
15
AVDD
16
XTAL2
5
CAP2
4
CAP1
3
FSEL
C4
220pF
C10
100pF
C11
100pF
C2
10pF
C3
10pF
VDD
VDD
C7
220pF
C6
0.01μF
C9
0.01μF
C8
0.1μF
XTAL
C12
0.01μF
C13
0.1μF
RFOUT
L2
18nH
L1
22nH
R1
0Ω
EXPOSED PADDLE
C1
8.2pF
C5
680pF
FSEL
CAP1
CAP2
CAP3
CAP4
VDD
DIN
22
DIN
TOGGLE
20
TOGGLE
ENABLE
21
ENABLE
C13
3.9pF
C12
3.9pF
MAX7058
315MHz/390MHz Dual-Frequency
ASK Transmitter
______________________________________________________________________________________ 13
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.)
24L QFN THIN.EPS
MAX7058
315MHz/390MHz Dual-Frequency
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.
14
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(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.)