ATA5771 ATMEL Corporation, ATA5771 Datasheet - Page 5

• Manufacturer Part Number: ATA5771
• Manufacturer: ATMEL Corporation

3. Functional Description
9137A–RKE–10/08
For a typical key fob application 3-4 interconnections between the microcontroller and the trans-
mitter are required (see
allow the microcontroller to generate an XTAL-based transmitter signal. The ENABLE line is
used to start the XTO, PLL, and clock output of the transmitter. The PA_ENABLE line is used to
enable the power amplifier in ASK and FSK mode. In FSK mode a 4
late the load capacity of the XTAL. To wake-up the system from standby mode at least one key
input is required. After pressing the key, the microcontroller starts up with the internal RC oscilla-
tor. For TX operation user software must control ENABLE, PA_ENABLE and XTAL load
capacity as described in the following section.
If ENABLE = L and PA_ENABLE = L the transmitter and the microcontroller (MCU) are in
standby mode, reducing the power consumption so that a lithium cell can be used as power sup-
ply for several years.
If ENABLE = H and PA_ENABLE = L, the XTO, PLL and the CLK driver from the transmitter are
activated. The crystal oscillator together with the PLL from the RF transmitter typically requires
< 1 ms (ATA5774 < 3 ms) until the PLL is locked and the clock output (Pin 8) is stable.
If ENABLE = H and PA_ENABLE = H, the XTO, PLL, CLK driver and the Power Amplifier (PA)
are switched on. The ASK modulation is done by switching on/off the power amplifier via
PA_ENABLE. The FSK modulation is done by switching on/off an additional capacitor between
the XTAL load capacitor and GND, thus changing the reference frequency of the PLL. This is
done using a MOS switch controlled by a microcontroller output. The power amplifier is switched
on via PA_ENABLE = H.
The MCU has to wait at least > 1 ms ATA5774 (> 3 ms ATA5773, > 4 ms ATA5771) after setting
ENABLE = H, before the external clock can be used. The external clock is connected via the
timer0 input pin that clocks the USI from the MCU to achieve an accurate data transfer. The fre-
quency of the internal RC oscillator is affected by ambient temperature and operating voltage.
The USI provides 2 two serial synchronous data transfer modes, with different physical I/O ports
for the data output. The two wire mode is used for ASK and the three wire mode is used for FSK.
Table 3-1.
Table 3-2.
ATA5771
ATA5773
ATA5774
ATA5771
ATA5773
ATA5774
Type
Type
Typical Current Consumption in Active Mode at 3.0V and 25°C
Current Consumption in Power-down Mode at 3.0V and –40°C to +85°C
Figure 1-1 on page 2
Max. 350 nA
Typ. < 10 nA
Transmitter
Transmitter
8.5 mA
9.0 mA
9.0 mA
ATA5771/ATA5773/ATA5774
and
Microcontroller (1 MHz
Internal RC Oscillator)
Figure 1-2 on page
(Watchdog Timer
Microcontroller
Max. 1.0 µA
Typ. 150 nA
Disabled)
0.6 mA
0.6 mA
0.6 mA
th
3). The CLK line is used to
line is necessary to modu-
Typ. < 160 nA
Max. 1.35 µA
9.1 mA
9.6 mA
9.6 mA
Total
Total
5