MAX7058 MAXIM [Maxim Integrated Products], MAX7058 Datasheet - Page 8

• Manufacturer Part Number: MAX7058
• Description: 315MHz/390MHz Dual-Frequency ASK Transmitter
• Manufacturer: MAXIM [Maxim Integrated Products]

315MHz/390MHz Dual-Frequency
ASK Transmitter
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.
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
8
_______________________________________________________________________________________
Detailed Description
Dual Frequency
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 50Ω load.
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 2
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.
22
cycles of the reference clock (279.62ms
Power-Up and Standby Modes