Features
•
PLL Transmitter IC with Single-ended Output
•
High Output Power (6 dBm) at 8.1 mA (315 MHz) and 8.5 mA (433 MHz) Typical Values
•
Divide by 24 (ATA5756) and 32 (ATA5757) Blocks for 13 MHz Crystal Frequencies and
•
•
•
•
•
•
•
•
•
for Low XTO Start-up Times
Modulation Scheme ASK/FSK with Internal FSK Switch
Up to 20 kBaud Manchester Coding, Up to 40 kBaud NRZ Coding
Power-down Idle and Power-up Modes to Adjust Corresponding Current Consumption
through ASK/FSK/Enable Input Pins
ENABLE Input for Parallel Usage of Controlling Pins in a 3-wire Bus System
CLK Output Switches ON if the Crystal Current Amplitude has Reached 35% to 80% of
its Final Value
Crystal Oscillator Time Until CLK Output is Activated, Typically 0.6 ms
Supply Voltage 2.0 V to 3.6 V in Operation Temperature Range of -40°C to +125°C
ESD Protection at all Pins (4 kV HBM)
Small Package TSSOP10
UHF ASK/FSK
Transmitter
ATA5756
ATA5757
Benefits
•
Low Parasitic FSK Switch Integrated
•
Very Short and Reproducible Time to Transmit Typically < 0.85 ms
•
13.125 MHz/13.56 MHz Crystals Give Opportunity for Small Package Sizes
1. Description
The ATA5756/ATA5757 is a PLL transmitter IC which has been developed for the
demands of RF low-cost transmission systems at data rates up to 20 kBaud Man-
chester coding and 40 kBaud NRZ coding. The transmitting frequency range is
313 MHz to 317 MHz (ATA5756) and 432 MHz to 448 MHz (ATA5757), respectively.
It can be used in both FSK and ASK systems. Due to its shorten crystal oscillator set-
tling time it is well suited for Tire Pressure Monitoring (TPM) and for Passive Entry Go
applications.
Figure 1-1.
System Block Diagram
UHF ASK/FSK
TPM and Remote control
transmitter
UHF ASK/FSK
Remote control receiver
1 Li cell
ATA5756/
ATA5757
PLL
Antenna Antenna
XTO
VCO
Keys
Encoder
ATARx9x
U3741B/
U3745B/
T5743/
T5744/
Demod.
Control
1...3
µC
IF Amp
PLL
XTO
Power
amp.
LNA
VCO
4702J–RKE–09/08
2. Pin Configuration
Figure 2-1.
Pinning TSSOP10
10
CLK
ASK
1
ENABLE
2
ATA5756
ATA5757
9
GND
FSK
3
8
VS
ANT2
4
7
XTO1
ANT1
5
6
XTO2
Table 2-1.
Pin
Pin Description
Symbol
Function
Configuration
1
CLK
Clock output signal for the
microcontroller.
The clock output frequency is set by the
crystal to f
XTAL
/8.
The CLK output stays Low in
power-down mode and after enabling of
the PLL.
The CLK output switches on if the
oscillation amplitude of the crystal has
reached a certain level.
VS
100
100
200k
CLK
ASK
50k
V
Ref
= 1.1V
2
ASK
Switches on the power amplifier for
ASK modulation and enables the PLL
and XTO if the ENABLE pin is open
200k
20 µA
FSK
200k
V
Ref
= 1.1V
3
FSK
Switches off the FSK switch (switch has
high Z if signal at pin FSK is High) and
enables the PLL and the XTO if the
ENABLE pin is open
5 µA
200k
2
ATA5756/ATA5757
4702J–RKE–09/08
ATA5756/ATA5757
Table 2-1.
Pin
4
Pin Description (Continued)
Symbol
ANT2
Function
Emitter of antenna output stage
ANT1
Configuration
5
ANT1
Open collector antenna output
ANT2
6
XTO2
Diode switch, used for FSK modulation
(FSK < 0.25V)
AND
(ENABLE > 1.7V)
XTO2
210 µA
VS
1.5k
1.2k
VS
7
XTO1
Connection for crystal
XTO1
182 µA
8
9
VS
GND
Supply voltage
Ground
See ESD protection circuitry (see
Figure 4-9 on page 14)
See ESD protection circuitry (see
Figure 4-9 on page 14)
VS
ENABLE input
If ENABLE is connected to GND and
the ASK or FSK pin is High, the device
stays in idle mode.
In normal operation ENABLE is left
open and ASK or FSK is used to enable
the device.
30 µA
(FSK >1.7 V ) OR
(ASK > 1.7 V)
ENABLE
150k
10
ENABLE
250k
3
4702J–RKE–09/08
Figure 2-2.
Block Diagram
ATA5756 /
ATA5757
Power up/down
CLK
EN
f
8
ENABLE
1
10
f
ASK
24/
32
GND
2
OR
FSK
9
PFD
VS
3
CP
Ampl. OK
ANT2
8
XTO1
XTO
LF
4
7
EN
ANT1
XTO2
PA
5
VCO
6
PLL
3. General Description
This fully integrated PLL transmitter allows the design of simple, low-cost RF miniature transmit-
ters for TPM and RKE applications. The VCO is locked to 24
×
f
X T A L
/32
×
f
X T A L
for
ATA 5 7 5 6 / ATA 5 7 5 7 . T h u s , a 1 3 . 1 2 5 M H z / 1 3 . 5 6 M H z c r y s t a l i s n e e d e d f o r a
315 MHz/433.92 MHz transmitter. All other PLL and VCO peripheral elements are integrated.
The XTO is a series resonance (current mode) oscillator. Only one capacitor and a crystal con-
nected in series to GND are needed as external elements in an ASK system. The internal FSK
switch, together with a second capacitor, can be used for FSK modulation. The crystal oscillator
needs typically 0.6 ms until the CLK output is activated if a crystal as defined in the electrical
characteristics is used (e.g., TPM crystal). For most crystals used in RKE systems, a shorter
time will result.
The CLK output is switched on if the amplitude of the current flowing through the crystal has
reached 35% to 80% of its final value. This is synchronized with the 1.64/1.69 MHz CLK output.
As a result, the first period of the CLK output is always a full period. The PLL is then locked
<250 µs after CLK output activation. This means an additional wait time of
≥250
µs is necessary
before the PA can be switched on and the data transmission can start. This results in a signifi-
cantly lower time of about 0.85 ms between enabling the ATA5756/ATA5757 and the beginning
of the data transmission which saves battery power especially in tire pressure monitoring
systems.
4
ATA5756/ATA5757
4702J–RKE–09/08
ATA5756/ATA5757
The power amplifier is an open-collector output delivering a current pulse which is nearly inde-
pendent from the load impedance and can therefore be controlled via the connected load
impedance.
This output configuration enables a simple matching to any kind of antenna or to 50
Ω.
A high
power efficiency for the power amplifier results if an optimized load impedance of
Z
Load, opt
= 380
Ω
+ j340
Ω
(ATA5756) at 315 MHz and Z
Load, opt
= 280
Ω
+ j310
Ω
(ATA5757) at
433.92 MHz is used at the 3-V supply voltage.
4. Functional Description
If ASK = Low, FSK = Low and ENABLE = open or Low, the circuit is in power-down mode con-
suming only a very small amount of current so that a lithium cell used as power supply can work
for many years.
If the ENABLE pin is left open, ENABLE is the logical OR operation of the ASK and FSK input
pins. This means, the IC can be switched on by either the FSK of the ASK input.
If the ENABLE pin is Low and ASK or FSK are High, the IC is in idle mode where the PLL, XTO
and power amplifier are off and the microcontroller ports controlling the ASK and FSK inputs can
be used to control other devices. This can help to save ports on the microcontroller in systems
where other devices with 3-wire interface are used.
With FSK = High and ASK = Low and ENABLE = open or High, the PLL and the XTO are
switched on and the power amplifier is off. When the amplitude of the current through the crystal
has reached 35% to 80% of its final amplitude, the CLK driver is automatically activated. The
CLK output stays Low until the CLK driver has been activated. The driver is activated synchro-
nously with the CLK output frequency, hence, the first pulse on the CLK output is a complete
period. The PLL is then locked within <250 µs after the CLK driver has been activated, and the
transmitter is then ready for data transmission.
With ASK = High the power amplifier is switched on. This is used to perform the ASK modula-
tion. During ASK modulation the IC is enabled with the FSK or the ENABLE pin.
With FSK = Low the switch at pin XTO2 is closed, with FSK = High the switch is open. To
achieve a faster start-up of the crystal oscillator, the FSK pin should be High during start-up of
the XTO because the series resistance of the resonator seen from pin XTO1 is lower if the
switch is off.
The different modes of the ATA5756/ATA5757 are listed in
Table 4-1,
the corresponding current
consumption values can be found in the table
“Electrical Characteristics” on page 15.
Table 4-1.
ASK Pin
Low
Low
Low
High
High
Low/High
High
ATA5756/ATA5757 Modes
FSK Pin
Low
Low
High
Low
High
High
Low/High
ENABLE Pin
Low/open
High
High/open
High/open
High/open
Low
Low
Mode
Power-down mode, FSK switch High Z
Power-up, PA off, FSK switch Low Z
Power-up, PA off, FSK switch High Z
Power-up, PA on, FSK switch Low Z
Power-up, PA on, FSK switch High Z
Idle mode, FSK switch High Z
Idle mode, FSK switch High Z
5
4702J–RKE–09/08
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