ATA5757 ATMEL Corporation, ATA5757 Datasheet - Page 5

• Manufacturer Part Number: ATA5757
• Description: (ATA5756 / ATA5757) UHF ASK/FSK TRANSMITTER
• Manufacturer: ATMEL Corporation

Functional
Description
4702H–RKE–09/04
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 50 Ω. A
high power efficiency for the power amplifier results if an optimized load impedance of
Z
(ATA5757) at 433.92 MHz is used at the 3-V supply voltage.
If ASK = Low, FSK = Low and ENABLE = open or Low, the circuit is in power-down
mode consuming 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 acti-
vated. The driver is activated synchronously 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
modulation. 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 1, the corresponding
current consumption values can be found in the table “Electrical Characteristics” on
page 15.
Table 1. ATA5756/ATA5757 Modes
ASK Pin
Low
Low
Low
High
High
Low/High
High
Load, opt
= 380 Ω + j340 Ω (ATA5756) at 315 MHz and Z
FSK Pin
Low
Low
High
Low
High
High
Low/High
Low/open
High
High/open
High/open
High/open
Low
Low
ENABLE Pin
Power-up, PA off, FSK switch High Z
Mode
Power-down mode, FSK switch High Z
Power-up, PA off, FSK switch Low 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
ATA5756/ATA5757
Load, opt
= 280 Ω + j310 Ω
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