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PT4455
PLL-based OOK/ASK Transmitter IC
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
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FEATURES
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Highly integrated OOK/ASK transmitter
High output power, 3V /+11dBm /17mA
Low supply voltage, 2.2V to 3.6V operation range
Low external component cost.
PLL-based transmitter with frequency range from
300MHz to 450MHz
• On-chip one-shot circuit
• 60dB RF on-off ratio for OOK/ASK modulation
• Available in 6-pin, SOT-23 package
Keyless entry systems
Remote control systems
Garage door openers
Alarm systems
Security systems
Wireless sensors
BLOCK DIAGRAM
Tel: 886-66296288‧Fax: 886-29174598‧ http://www.princeton.com.tw‧2F, No. 233-1, Baociao Rd., Sindian Dist., New Taipei City 23145, Taiwan
PT4455
APPLICATION CIRCUIT
BILL OF MATERIALS
Part
X1
R1
R2
R3
R4
R5
C1
C2
C3
C4
C5
C6
C7
L1
L2
Value
315MHz
9.844M
10K
100K
0
0
560K
22p
22p
1μ
220p
8.2p
18p
2.2μ
180n
33n
433.92MHz
13.56M
10K
100K
0
0
560K
18p
18p
1μ
220p
4.7p
10p
2.2μ
180n
27n
Unit
Hz
Ω
Ω
Ω
Ω
Ω
F
F
F
F
F
F
F
H
H
Notes:
1. C1/C2 can be used to trim the transmitted signal frequency for matching the specified value.
2. L2/C5/C6 value will depend on PCB layout.
3. The recommend maximum ESR value of X1 is 40Ω.
4. To populate the R5 over XIN will help to maintain good oscillation in high X1 ESR.
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PT4455
ORDER INFORMATION
Valid Part Number
Package Type
Top Code
PT4455
6-Pin, SOT23
PT4455
PIN CONFIGURATION
PIN DESCRIPTION
V1.1
Pin Name
I/O
Description
XOUT
O
Oscillator output
1
VSS
G
Ground connection
2
PAOUT
O
Power amplifier output
3
DIN
I
Data input
4
VDD
P
Power supply
5
XIN
I
Oscillator input
6
3
Pin No.
January 2013
PT4455
FUNCTION DESCRIPTION
PA OUTPUT MATCHING
The PA output is an open-drain structure. Its output connects a large choke inductor to supply voltage and follows by a
DC block capacitor. After the DC block capacitor, a C-L-C-type matching network is used to tune with the antenna
impedance. The inductor and capacitor values may be different from the suggestion value depending on PCB material,
PCB thickness, ground configuration, and the layout traces length.
For the open-drain structure in PA, the HBM (Human Body Mode) and MM (Machine Mode) ESD strength is 4KV and
400V.
REFERENCE OSCILLATOR
For a quartz crystal to oscillate in the specified frequency, it should work with vendor provided load capacitor value,
called CL . The load capacitor is about 12pF to 18pF in general. In PT4455, the Pierce type crystal oscillator is used, and
the shunt capacitor over XIN and XOUT is in series together equivalently. The shunt capacitor should be placed as 2x CL
to oscillate with specified frequency. The temperature coefficient of quartz crystal will cause the VCO output frequency
drift in high/low temperature range.
With a fixed divided-by-32 PLL, the fREFOSC = fTX / 32. The following table list fREFOSC for some common transmit
frequencies
Transmit Frequency fTX
Reference Oscillator Frequency fREFOSC
315MHz
9.844MHz
340MHz
10.625MHz
390MHz
12.188MHz
433.92MHz
13.56MHz
The recommend maximum ESR value of reference oscillator is 40Ω.
PHASE-LOCKED LOOP (PLL)
The PT4455 own a fixed divided-by-32 PLL to generate the transmitter signal. The PLL consists of the
voltage-controlled oscillator (VCO), crystal oscillator, asynchronous ÷ 32 divider, charge pump, loop filter and
phase-frequency detector (PFD). All these circuits are integrated on-chip. The PFD compares two signals and produces
an error signal which is proportional to the difference between the input phases. The error signal passes through a loop
filter with an approximately 180KHz bandwidth, and is used to control the VCO. A frequency divider placed after the
VCO and it will feedback the divided signal to PFD. In the final the VCO will get locked to reference signal as fVCO =
fREFOSC * 32. The block diagram below shows the basic elements of the PLL.
The PLL chain circuit is supplied by internal voltage regulator to ease the PA pulling and crystal spur issue
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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 315MHz, then the length of a λ/4 antenna is 22.6cm. 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 0.8mm to 1.6mm)
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 30mil, the length of the antenna, L (in cm), is
calculated by
L=
c
4× f × εr
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.
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PT4455
ABSOLUTE MAXIMUM RATINGS
(VSS=0V)
Parameter
Supply Voltage Range
I/O Voltage
Operating Temperature Range
Storage Temperature Range
Symbol
VDD
VI/O
TOPR
TSTG
Min.
-0.3
-0.3
-40
-40
Max.
5
5
+85
+150
Unit
V
V
℃
℃
RECOMMENDED OPERATING CONDITIONS
(VSS=0V)
Parameter
Supply Voltage Range
Operating Temperature Range
Symbol
Min.
Max.
Unit
VDD
TA
-0.3
-40
3.6
+85
V
℃
ELECTRICAL CHARACTERISTICS
Nominal conditions: VDD = 3.0 V, VSS = 0 V, TA = +27℃.
Parameter
Symbol
Conditions
General Characteristics
Supply Voltage
VDD
DIN=High(CW mode);
POUT=12dBm, fRF=315MHz
(Note)
Operating Current
IDD
DIN=High(CW mode);
POUT=10dBm, fRF=434MHz
DIN=Low, TDELAY>50ms
Standby Current
Istandby
RF
Frequency Range
fRF
fRF=315MHz
Power Amplifier Output Power (Note)
Pout
fRF=434MHz
RF Power On / Off Ratio
PEXT
315MHz, 10KHz offset
Phase Noise
PNOISE
(Note)
2x/3x fRF
Harmonics
PHARM
fRF=315MHz
Crystal Spur
PSPUR
fRF=434MHz
Data Input and One-shot
Data Rate
DRATE
CL not connected
Crystal Oscillator Start-up Time
TON
One-shot Delay Time
TDELAY
Min.
Typ.
Max.
Unit
2.2
3.0
3.6
V
-
17
-
mA
-
19
-
mA
-
-
1
μA
300
-
11
10
60
-75
-40
-40
-40
450
-
MHz
dBm
dBm
dB
dBc/Hz
dBc
dBc
dBc
0.5
50
2
1
-
50
-
Kbps
ms
ms
Note: Depend on power amplifier output matching
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PT4455
PACKAGE INFORMATION
6-PIN, SOT23
Symbol
Min.
Nom.
Max
A
-
-
1.45
A1
0.00
-
0.15
A2
0.90
1.15
1.30
b
0.30
-
0.50
c
0.080
0.130
0.200
e
0.95 BSC.
e1
1.90 BSC.
D
2.90 BSC.
E
2.80 BSC.
E1
1.60 BSC.
L
0.30
0.45
0.60
θ
0°
-
8°
Notes;
1. Refer to JEDEC MO-178
2. All dimensions are in millimeter
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PT4455
IMPORTANT NOTICE
Princeton Technology Corporation (PTC) reserves the right to make corrections, modifications, enhancements,
improvements, and other changes to its products and to discontinue any product without notice at any time.
PTC cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a PTC product. No
circuit patent licenses are implied.
Princeton Technology Corp.
2F, 233-1, Baociao Road,
Sindian Dist., New Taipei City 23145, Taiwan
Tel: 886-2-66296288
Fax: 886-2-29174598
http://www.princeton.com.tw
V1.1
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January 2013