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 programmed for match-
ing 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 50Ω load is
+10dBm. The MAX7058 operates 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 oper-
ation by selecting synthesizer-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
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
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
PART TEMP RANGE PIN-PACKAGE
MAX7058ATG+ -40°C to +125°C 24 Thin QFN-EP*
(4mm x 4mm)
5
6
4
3
14
13
15
CAP3
PAOUT
ROUT
N.C.
16
N.C.
N.C.
ENABLE
TOGGLE
N.C.
N.C.
7 8
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
7 8 9 10
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*
MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
19-3206; Rev 1; 7/14
Functional Block DiagramPin Conguration
Ordering Information
EVALUATION KIT AVAILABLE
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
(Typical Operating Circuit, 50Ω system impedance, VAVDD = VDVDD = VPAVDD = +2.1V to +3.6V, fRF = 315MHz or 390MHz,
TA = -40°C to +125°C, unless otherwise noted. Typical values are at VAVDD = VDVDD = VPAVDD = +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
Supply Voltage VDD
PAVDD, AVDD, and DVDD connected to
power supply, VDD
2.1 2.7 3.6 V
Supply Current IDD
PA off, VDIN at 0% duty
cycle
fRF = 315MHz 3.4 5.4
mA
fRF = 390MHz 3.8 6.3
VDIN at 50%, duty cycle
(Notes 1, 2, 3)
fRF = 315MHz 8.0 13.7
fRF = 390MHz 8.3 14.2
VDIN at 100%, duty cycle
(Note 1)
fRF = 315MHz 12.6 21.9
fRF = 390MHz 12.9 22.1
Standby Current ISTDBY
VENABLE < VIL TA = +25°C 0.8
µA(Note 3) TA < +85°C 1.0 4.0
TA < +125°C 6.2 16.1
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
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
DC Electrical Characteristics
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.
Absolute Maximum Ratings
(Typical Operating Circuit, 50Ω system impedance, VAVDD = VDVDD = VPAVDD = +2.1V to +3.6V, fRF = 315MHz or 390MHz,
TA = -40°C to +125°C, unless otherwise noted. Typical values are at VAVDD = VDVDD = VPAVDD = +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
GENERAL CHARACTERISTICS
Frequency Range 300 315/390 450 MHz
Power-On Time tON
ENABLE transition low-to-high, frequency
settled to within 50kHz of the desired carrier 110
µs
ENABLE transition low-to-high, frequency
settled to within 5kHz of the desired carrier 250
Maximum Data Rate Manchester encoded 50 kbps
Nonreturn to zero (NRZ) 100
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
PLL Phase Noise
fRF = 315MHz 10kHz offset -87
dBc/Hz
1MHz offset -98
fRF = 390MHz 10kHz offset -84
1MHz offset -98
Loop Bandwidth 600 kHz
Reference Frequency Input Level 500 mVP-P
Frequency-Divider Range 21 26
CRYSTAL OSCILLATOR
Crystal Frequency fXTAL 15 MHz
Frequency Pulling by VDD 4 ppm/V
Crystal Load Capacitance (Note 4) 10 pF
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
AC Electrical Characteristics
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.
(Typical Operating Circuit, 50Ω system impedance, VAVDD = VDVDD = VPAVDD = +2.1V to +3.6V, fRF = 315MHz or 390MHz,
TA = -40°C to +125°C, unless otherwise noted. Typical values are at VAVDD = VDVDD = VPAVDD = +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
Output Power (Note 1) POUT
TA = +25°C (Note 3) 4.2 10 15.5
dBm
TA = +125°C, VPAVDD = VAVDD = VDVDD =
+2.1V 3.0 5.9
TA = -40°C, VPAVDD = VAVDD = VDVDD =
+3.6V (Note 3) 13.3 16.4
Modulation Depth 80 dB
Maximum Carrier Harmonics With output matching
network
fRF = 315MHz -28 dBc
fRF = 390MHz -32
Reference Spur -48 dBc
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
AC Electrical Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
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
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
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
SUPPLY CURRENT
vs. OUTPUT POWER
MAX7058 toc06
OUTPUT POWER (dBm)
SUPPLY CURRENT (mA)
200 10-10-20-30
2
4
6
8
10
12
14
0
-40
ON
50% PA
315MHz
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. 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
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 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 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
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
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
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 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 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
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
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
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
Typical Operating Characteristics (continued)
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.
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
Pin Description
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 frequency.
The crystal-based architecture of the MAX7058 eliminates
many of the common problems with surface acoustic
wave (SAW) transmitters, by providing greater modulation
depth, faster frequency settling, tighter transmit frequen-
cy tolerance, and reduced temperature dependence. In
particular, the tighter transmit frequency tolerance means
that a super-heterodyne receiver with a narrower IF band-
width (therefore lower noise bandwidth) can be used. The
payoff is improved overall receiver performance when
using a super-heterodyne 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 ref-
erence 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 different crys-
tal frequencies. The two operating frequencies 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 corresponds
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 50Ω load.
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 log-
ic-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.
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
Operating Mode
TOGGLE and FSEL are two pins available for controlling
the state of the toggle mode and the operating frequency.
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 Denition
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 50Ω antenna. The output-matching network sup-
presses the carrier harmonics and transforms the
antenna impedance to optimal impedance at PAOUT,
which is from 125Ω to 250Ω.
When the output-matching network is properly tuned, the
PA transmits +10dBm (typ), with a high overall efficiency.
The efficiency of the PA itself is more than 40%. The out-
put 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 modulat-
ed 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 capacit-
ors 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.
Figure 1. Power-Up Waveform with DIN/ENABLE for MAX7058
Table 1. Toggle Pin Operation for MAX7058
TOGGLE
PIN
FSEL
PIN OPERATING STATE
0 0 Continuous fixed-frequency operation at
390MHz
0 1 Continuous fixed-frequency operation at
315MHz
1 0 Five packets toggle operation between
315MHz and 390MHz
1 1 100 packets toggle operation between
315MHz and 390MHz
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)
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
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 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 pull-
ing is given by:
6
m
pcase load case spec
C
11
ü§ü 2CCCC


= −×

++

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
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.
Table 2. Variable Capacitor Values and
Control Input Pins
CAPACITOR
CONTROL PIN STATE
(CAP4–CAP1)
ADDED SHUNT CAPACITANCE
IN pF
315MHz (÷21) 390MHz (÷26)
0000 0
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
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
Applications Information
Output Matching to 50Ω
When matched to a 50Ω system, 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 transistor,
which has internal selectable shunt tuning capacitors for
impedance matching (see the Variable Capacitor section).
It is connected to VDD through a pullup inductor for proper
biasing. The internal selectable 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, providing 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 attenua-
tion 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
terminated to ground). In a typical application,
the inductance 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 5Ω or 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 λ is
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
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11
MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
PACKAGE
TYPE
PACKAGE
CODE
DOCUMENT
NO.
LAND
PATTERN NO.
24 TQFN-EP T2444+3 21-0139 90-0021
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MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
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
0.01F
C9
0.01F
C8
0.1F
XTAL
C12
0.01F
C13
0.1F
RFOUT
L2
18nH
L1
22nH
R1
0
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
Typical Operating Circuit
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.
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 1/08 Initial Release —
1 7/14 Removed automotive reference from data sheet 1
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 specications 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.
MAX7058 315MHz/390MHz Dual-Frequency ASK Transmitter
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2014 Maxim Integrated Products, Inc.
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Revision History
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