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ATA5773 Datasheet(PDF) 5 Page - ATMEL Corporation |
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ATA5773 Datasheet(HTML) 5 Page - ATMEL Corporation |
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5 / 287 page  5 9137B–RKE–02/09 ATA5771/ATA5773/ATA5774 3. Functional Description For a typical key fob application 3-4 interconnections between the microcontroller and the trans- mitter are required (see Figure 1-1 on page 2 and Figure 1-2 on page 3). The CLK line is used to 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 th line is necessary to modu- 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 (ATA5773 < 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. Typical Current Consumption in Active Mode at 3.0V and 25°C Type Transmitter Microcontroller (4 MHz Internal RC Oscillator) Total ATA5771 8.5 mA 0.8 mA 9.3 mA ATA5773 9.0 mA 0.8 mA 9.8 mA ATA5774 9.0 mA 0.8 mA 9.8 mA Table 3-2. Current Consumption in Power-down Mode at 3.0V and –40°C to +85°C Type Transmitter Microcontroller (Watchdog Timer Disabled) Total ATA5771 Typ. < 10 nA Max. 350 nA Typ. 200 nA Max. 24 µA(1) Typ. < 210 nA Max. 24.35 µA(1) ATA5773 ATA5774 Note: 1. Maximum value measured in final test at 125°C. Value at 85°C: See Appendix 4, page 196, Figure 23-12 “Power Down Supply Current versus VCC” |
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