MAX7058ATG+T - Maxim - Datasheet.Live

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

Pin Configuration

Ordering Information

CAP3

PAOUT

ROUT

N.C.

ENABLE

TOGGLE

N.C.

CAP1

10 11 12

2324 22 20 19

CAP2

N.C.

XTAL2

AVDD

PAVDD

N.C.

MAX7058

CAP4 DIN

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

MAX7058

78 910

TQFN

11 12

24 23 22 21 20 19

N.C.

FSEL

DVDD

CAP1

N.C.

CAP3

CAP4

PAOUT

ROUT

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

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

_______________________________________________________________________________________

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX7058 toc01

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

3.53.32.9 3.12.5 2.72.3

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

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

2.1

315MHz AND 390MHz

SUPPLY CURRENT

vs. OUTPUT POWER

MAX7058 toc06

OUTPUT POWER (dBm)

SUPPLY CURRENT (mA)

20010-10-20-30

-40

50% PA

315MHz

SUPPLY CURRENT

vs. OUTPUT POWER

MAX7058 toc07

OUTPUT POWER (dBm)

SUPPLY CURRENT (mA)

20100-10-20

-30

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

-4

2.1

390MHz

315MHz

EFFICIENCY

vs. SUPPLY VOLTAGE

MAX7058 toc12

SUPPLY VOLTAGE (V)

EFFICIENCY (%)

3.63.0 3.32.4 2.7

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

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

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

2.1

TA = +25°C

390MHz

PA ON

TA = +125°C

TA = +85°C

TA = -40°C

MAX7058

315MHz/390MHz Dual-Frequency

ASK Transmitter

_______________________________________________________________________________________

Pin Description

PIN NAME FUNCTION

1, 6, 7, 12,

13, 18, 19,

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

FSEL

PIN OPERATING STATE

Continuous fixed-frequency operation at

390MHz

Continuous fixed-frequency operation at

315MHz

Five packets toggle operation between

315MHz and 390MHz

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.

CCCC

case load case spec

=+−+

⎛

⎝

⎜⎞

⎠

⎟×

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

(CAP4–CAP1) 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

Applications Information

Output Matching to 50

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

DVDD

XTAL1

AVDD

XTAL2

CAP2

CAP1

FSEL

220pF

C10

100pF

C11

100pF

10pF

VDD

220pF

0.01μF

0.1μF

XTAL

C12

0.01μF

C13

0.1μF

RFOUT

18nH

22nH

0Ω

EXPOSED PADDLE

8.2pF

680pF

FSEL

CAP1

CAP2

CAP3

CAP4

VDD

DIN

TOGGLE

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.

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

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.)