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PDF PT4455 Data sheet ( Hoja de datos )
| Número de pieza | PT4455 | |
| Descripción | PLL-based OOK/ASK Transmitter IC | |
| Fabricantes | Princeton Technology | |
| Logotipo |  |
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DESCRIPTION
PT4455 is a high performance OOK/ASK
transmitter for the Remote Keyless Entry (RKE)
systems. It consists of a power amplifier, one-shot
circuit and phase-locked loop with internal voltage
controlled oscillator and loop filter. The one-shot
circuit control the phase-locked loop and power
amplifier to have fast start-up time in operation.
APPLICATIONS
Keyless entry systems
Remote control systems
Garage door openers
Alarm systems
Security systems
Wireless sensors
BLOCK DIAGRAM
Preliminary PT4455
PLL-based OOK/ASK Transmitter IC
FEATURES
Highly integrated OOK/ASK transmitter
High output power, 3 V /+11 dBm / 17 mA
Low supply voltage, 2.2 V to 3.6 V operation range
Low external component cost.
PLL-based transmitter with frequency range from
250MHz to 450MHz
On-chip one-shot circuit
60 dB RF on-off ratio for OOK/ASK modulation
SOT23-6 package
Tel: 886-66296288‧Fax: 886-29174598‧ http://www.princeton.com.tw‧2F, 233-1, Baociao Road, Sindian, Taipei 23145, Taiwan
1 page  
PT4455
ONE-SHOT CIRCUIT AND POWER-DOWN CONTROL
During the signal transmission, the crystal oscillator start-up time will limit its wake-up time to work. A one-shoot circuit is
used to solve this problem by turning on/off the power amplifier and PLL circuit separately.
When apply “HIGH” to DIN, will enable the PLL chain and PA. When applied “LOW” to DIN, the PA will be turn-off
immediately, and the PLL chain will be turn-off after one-shot period about 50ms.
To calculate the re-triggerable one-shot delay time, it can be counted as 688128 / fREFOSC . For fREFOSC = 9.844MHz and
13.56MHz, the delay time is about 70ms and 50ms.
ANTENNA DESIGN AND PCB LAYOUT CONSIDERATION
For a λ/4 dipole antenna and operating frequency, f (in MHz), the required antenna length, L (in cm), may be calculated
by using the formula
L 7132
f
For example, if the frequency is 315 MHz, then the length of a λ/4 antenna is 22.6 cm. If the calculated antenna length
is too long for the application, then it may be reduced to λ/8, λ/16, etc. without degrading the input return loss. Usually,
when designing a λ/4 dipole antenna, it is better to use a single conductive wire (diameter about 0.8 mm to 1.6 mm)
rather than a multiple core wire.
If the antenna is printed on the PCB, ensure there is neither any component nor ground plane underneath the antenna
on the backside of PCB. For an FR4 PCB (εr = 4.7) and a strip-width of 30 mil, the length of the antenna, L (in cm), is
calculated by
L c
4 f r
where “c” is the speed of light (3 x1010 cm/s)
Proper PCB layout is extremely critical in achieving good RF performance. At the very least, using a two-layer PCB is
strongly recommended, so that one layer may incorporate a continuous ground plane. A large number of via holes
should connect the ground plane areas between the top and bottom layers.
Careful consideration must also be paid to the supply power and ground at the board level. The larger ground area
plane should be placed as close as possible to all the VSS pins. Grounding the metal case of quartz crystal and isolate
the XIN/XOUT trace to other can suppress the crystal spur signal over PA output.
PRE1.1
5 August 2010
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet PT4455.PDF ] | |
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