ATA5756/ATA5757
UHF ASK/FSK Transmitter
DATASHEET
Features
●
PLL transmitter IC with single-ended output
●
High output power (6dBm) at 8.1mA (315MHz) and 8.5mA (433MHz) typical values
●
Divide by 24 (Atmel
®
ATA5756) and 32 (Atmel ATA5757) blocks for 13MHz crystal
●
●
●
●
●
●
●
●
●
frequencies and for Low XTO start-up times
Modulation scheme ASK/FSK with internal FSK switch
Up to 20kBaud manchester coding, up to 40kBaud 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 0.6ms
Supply voltage 2.0V to 3.6V in operation temperature range of –40°C to +125°C
ESD protection at all pins (4kV HBM)
Small package TSSOP10
Benefits
●
Low parasitic FSK switch integrated
●
Very short and reproducible time to transmit typically < 0.85ms
●
13.125MHz/13.56MHz
crystals give opportunity for small package sizes
4702L-RKE-03/14
1.
Description
The Atmel
®
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 20kBaud Manchester coding and 40kBaud NRZ coding. The transmitting frequency
range is 313MHz to 317MHz (Atmel ATA5756) and 432MHz to 448MHz (Atmel ATA5757), respectively. It can be used in
both FSK and ASK systems. Due to its shorten crystal oscillator settling 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
1 Li cell
UHF ASK/FSK
Remote control receiver
U3741B/
U3745B/
T5743/
T5744
ATA5756/
ATA5757
Encoder
ATARx9x
1 to 3
Demod
Control
Micro-
controller
PLL
Antenna
XTO
VCO
Antenna
PLL
XTO
Keys
Power
amp.
LNA
VCO
2
ATA5756/ATA5757 [DATASHEET]
4702L–RKE–03/14
2.
Pin Configuration
Figure 2-1. Pinning TSSOP10
CLK
1
10
ENABLE
ASK
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
VS
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.
100Ω
CLK
100Ω
200kΩ
2
ASK
Switches on the power amplifier for
ASK modulation and enables the
PLL and XTO if the ENABLE pin is
open
ASK
50kΩ
V
Ref
= 1.1V
200kΩ
20µA
FSK
200kΩ
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
200kΩ
5µA
ATA5756/ATA5757 [DATASHEET]
4702L–RKE–03/14
3
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
210µA
6
XTO2
Diode switch, used for FSK
modulation
(FSK < 0.25V)
and
(ENABLE > 1.7V)
XTO2
VS
VS
1.5kΩ
1.2kΩ
7
XTO1
Connection for crystal
XTO1
182µA
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
30µA
10
ENABLE
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.
(FSK > 1.7V)
or
(ASK > 1.7V)
ENABLE
150kΩ
250kΩ
4
ATA5756/ATA5757 [DATASHEET]
4702L–RKE–03/14
Figure 2-2. Block Diagram
ATA5756/
ATA5757
Power up/down
CLK
1
f
8
EN
ENABLE
10
f
ASK
2
24/
32
GND
9
OR
FSK
3
PDF
VS
8
CP
Ampl. OK
ANT2
4
LF
EN
ANT1
5
PA
PLL
VCO
XTO
XTO1
7
XTO2
6
3.
General Description
This fully integrated PLL transmitter allows the design of simple, low-cost RF miniature transmitters for TPM and RKE
applications. The VCO is locked to 24
×
f
XTAL
/32
×
f
XTAL
for Atmel
®
ATA5756/ATA5757. Thus, a 13.125MHz/13.56MHz
crystal is needed for a 315MHz/433.92MHz 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 connected 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 1.64/1.69MHz CLK output. As a result, the first period of the CLK output is always a full
period. The PLL is then locked <250µs after CLK output activation. This means an additional wait time of
≥
250µs is
necessary before the PA can be switched on and the data transmission can start. This results in a significantly lower time of
about 0.85ms between enabling the Atmel ATA5756/ATA5757 and the beginning of the data transmission which saves
battery power especially in tire pressure monitoring systems.
The power amplifier is an open-collector output delivering a current pulse which is nearly independent 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 50Ω. A high power efficiency for the power
amplifier results if an optimized load impedance of Z
Load, opt
= 380Ω + j340Ω (Atmel ATA5756) at 315MHz and
Z
Load, opt
= 280Ω + j310Ω (Atmel ATA5757) at 433.92MHz is used at the 3-V supply voltage.
ATA5756/ATA5757 [DATASHEET]
4702L–RKE–03/14
5
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