TH72001
315MHz
FSK Transmitter
Features and Benefits
Fully integrated PLL-stabilized LC VCO
Frequency range of 290MHz to 350MHz
Single-ended RF output
FSK through crystal pulling allows
modulation from DC to 40 kbit/s
High FSK deviation possible for wideband
data transmission
Wide power supply range from 2.1 V to 5.5 V
Very low standby current
On-chip low voltage detector
High over-all frequency accuracy
FSK deviation and center frequency
independently adjustable
Adjustable output power range from
-12 dBm to +11 dBm
Adjustable current consumption from
3.2 mA to 10.3 mA
Conforms to EN 300 220 and similar
standards
8-pin Small Outline Integrated Circuit (SOIC)
Application Examples
General digital data transmission
Tire Pressure Monitoring System (TPMS)
Remote Keyless Entry (RKE)
Low-power telemetry
Alarm and security systems
Garage door openers
Home automation
Pin Description
Ordering information
Product Code
TH72001
TH72001
Legend:
Temperature Code:
Package Code:
Packing Form:
Ordering example:
Temperature Code
K
K
Package Code
DC
DC
Option Code
BAA-000
BAA-000
Packing Form Code
RE
TU
K for Temperature Range -40°C to 125°C
DC for SOIC
RE for Reel, TU for Tube
TH72001KDC-BAA-000
General Description
The TH72001 FSK transmitter IC is designed for applications in the 315 MHz industrial-scientific-medical (ISM) band. It can also be
used for any other system with carrier frequencies at
290 to 350MHz.
The transmitter's carrier frequency f
c
is determined by the frequency of the reference crystal f
ref
. The integrated PLL synthesizer
ensures that the radio frequency (RF) can be achieved by using a crystal with a reference frequency according to: f
ref
= f
c
/N, where
N = 32 is the PLL feedback divider ratio.
REVISION 011 - JUNE 13, 2017
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TH72001
315MHz
FSK Transmitter
Contents
Features and Benefits ................................................................................................................................ 1
Application Examples ................................................................................................................................. 1
Pin Description ........................................................................................................................................... 1
Ordering information ................................................................................................................................. 1
General Description ................................................................................................................................... 1
1. Theory of Operation ............................................................................................................................... 4
1.1. General................................................................................................................................................ 4
1.2. Block Diagram ..................................................................................................................................... 4
2. Functional Description ........................................................................................................................... 5
2.1. Crystal Oscillator................................................................................................................................. 5
2.2. FSK Modulation .................................................................................................................................. 5
2.3. Crystal Pulling ..................................................................................................................................... 5
2.4. Output Power Selection ..................................................................................................................... 6
2.5. Lock Detection .................................................................................................................................... 6
2.6. Low Voltage Detection ....................................................................................................................... 6
2.7. Mode Control Logic ............................................................................................................................ 7
2.8. Timing Diagrams ................................................................................................................................. 7
3. Pin Definition and Description ................................................................................................................ 8
4. Electrical Characteristics ........................................................................................................................ 9
4.1. Absolute Maximum Ratings ............................................................................................................... 9
4.2. Normal Operating Conditions ............................................................................................................ 9
4.3. Crystal Parameters ............................................................................................................................. 9
4.4. DC Characteristics ............................................................................................................................ 10
4.5. AC Characteristics............................................................................................................................. 11
4.6. Output Power Steps ......................................................................................................................... 11
5. Typical Operating Characteristics ......................................................................................................... 12
5.1. DC Characteristics ............................................................................................................................ 12
5.2. AC Characteristics............................................................................................................................. 15
6. Test Circuit ........................................................................................................................................... 19
6.1. Test circuit component list to Fig. 18 .............................................................................................. 19
7. Package Information ............................................................................................................................ 21
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TH72001
315MHz
FSK Transmitter
8. Standard information regarding manufacturability of Melexis products with different
soldering processes ............................................................................................................................. 22
9. ESD Precautions ................................................................................................................................... 22
10. Contact............................................................................................................................................... 23
11. Disclaimer .......................................................................................................................................... 23
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TH72001
315MHz
FSK Transmitter
1. Theory of Operation
1.1. General
As depicted in Fig.1, the TH72001 transmitter consists of a fully integrated voltage-controlled oscillator (VCO), a
divide-by-32 divider (div32), a phase-frequency detector (PFD) and a charge pump (CP). An internal loop filter
determines the dynamic behavior of the PLL and suppresses reference spurious signals. A Colpitts crystal oscillator
(XOSC) is used as the reference oscillator of a phase-locked loop (PLL) synthesizer. The VCO’s output signal feeds the
power amplifier (PA). The RF signal power P
out
can be adjusted in four steps from P
out
= –12 dBm to +11 dBm, either by
changing the value of resistor RPS or by varying the voltage V
PS
at pin PSEL. The open-collector output (OUT) can be
used either to directly drive a loop antenna or to be matched to a 50Ohm load. Bandgap biasing ensures stable
operation of the IC at a power supply range of 2.1 V to 5.5 V.
1.2. Block Diagram
RPS
VCC
PSEL
6
5
PLL
ENTX
4
mode
control
32
PA
7
OUT
antenna
matching
network
ROI
3
PFD
XOSC
XTAL
FSKSW
2
CX2
CX1
XBUF
CP
VCO
low
voltage
detector
1
FSKDTA
8
VEE
Fig. 1: Block diagram with external components
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TH72001
315MHz
FSK Transmitter
2. Functional Description
2.1. Crystal Oscillator
A Colpitts crystal oscillator with integrated functional capacitors is used as the reference oscillator for the PLL
synthesizer. The equivalent input capacitance CRO offered by the crystal oscillator input pin ROI is about 18pF. The
crystal oscillator is provided with an amplitude control loop in order to have a very stable frequency over the specified
supply voltage and temperature range in combination with a short start-up time.
2.2. FSK Modulation
FSK modulation can be achieved by pulling the
crystal oscillator frequency. A CMOS-compatible
data stream applied at the pin FSKDTA digitally
modulates the XOSC via an integrated NMOS
switch. Two external pulling capacitors CX1 and CX2
allow the FSK deviation
f
and the center frequency
f
c
to be adjusted independently. At FSKDTA = 0, CX2
is connected in parallel to CX1 leading to the low-
frequency component of the FSK spectrum (f
min
);
while at FSKDTA = 1, CX2 is deactivated and the
XOSC is set to its high frequency f
max
.
An external reference signal can be directly AC-
coupled to the reference oscillator input pin ROI.
Then the transmitter is used without a crystal. Now
the reference signal sets the carrier frequency and
may also contain the FSK (or FM) modulation.
VCC
Fig. 2: Crystal pulling circuitry
XTAL
ROI
FSKSW
CX2
CX1
VEE
FSKDTA
0
1
Description
f
min
= f
c
-
f
(FSK switch is closed)
f
max
= f
c
+
f
(FSK switch is open)
2.3. Crystal Pulling
A crystal is tuned by the manufacturer to the
required oscillation frequency f
0
at a given load
capacitance CL and within the specified calibration
tolerance. The only way to pull the oscillation
frequency is to vary the effective load capacitance
CL
eff
seen by the crystal.
Figure 3 shows the oscillation frequency of a crystal
as a function of the effective load capacitance. This
capacitance changes in accordance with the logic
level of FSKDTA around the specified load
capacitance. The figure illustrates the relationship
between the external pulling capacitors and the
frequency deviation.
It can also be seen that the pulling sensitivity
increases with the reduction of CL. Therefore,
applications with a high frequency deviation require
a low load capacitance. For narrow band FSK
applications, a higher load capacitance could be
chosen in order to reduce the frequency drift
caused by the tolerances of the chip and the
external pulling capacitors.
f
XTAL
L1
f
max
C1
R1
f
c
C0
CL
eff
f
min
CX1 CRO
CX1+CRO
CL
(CX1+CX2) CRO
CX1+CX2+CRO
CL
eff
Fig. 3: Crystal pulling characteristic
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