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T5750 Datasheet(PDF) 4 Page - ATMEL Corporation |
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T5750 Datasheet(HTML) 4 Page - ATMEL Corporation |
4 / 12 page 4 T5750 [Preliminary] 4546B–RKE–07/04 Functional Description If ENABLE = L and the PA_ENABLE = L, the circuit is in standby mode consuming only a very small amount of current, so that a lithium cell used as power supply can work for several years. With ENABLE = H the XTO, PLL and the CLK driver are switched on. If PA_ENABLE remains L only the PLL and the XTO is running and the CLK signal is delivered to the microcontroller. The VCO locks to 64 times the XTO frequency. With ENABLE = H and PA_ENABLE = H the PLL, XTO, CLK driver and the power amplifier are on. With PA_ENABLE the power amplifier can be switched on and off, which is used to perform the ASK modulation. ASK Transmission The T5750 is activated by ENABLE = H. PA_ENABLE must remain L for t ≥ 4ms, then the CLK signal can be taken to clock the microcontroller and the output power can be modulated by means of Pin PA_ENABLE. After transmission PA_ENABLE is switched to L and the microcontroller switches back to internal clocking. The T5750 is switched back to standby mode with ENABLE = L. FSK Transmission The T5750 is activated by ENABLE = H. PA_ENABLE must remain L for t ≥ 4ms, then the CLK signal can be taken to clock the microcontroller and the power amplifier is switched on with PA_ENABLE = H. The chip is then ready for FSK modulation. The microcontroller starts to switch on and off the capacitor between the XTAL load capaci- tor and GND with an open-drain output port, thus changing the reference frequency of the PLL. If the switch is closed, the output frequency is lower than if the switch is open. After transmission PA_ENABLE is switched to L and the microcontroller switches back to internal clocking. The T5750 is switched back to standby mode with ENABLE = L. The accuracy of the frequency deviation with XTAL pulling method is about ±25% when the following tolerances are considered. Figure 4. Tolerances of Frequency Modulation Using C 4 =9.2 pF ±2%, C5 = 6.8 pF ±5%, a switch port with CSwitch = 3 pF ±10%, stray capacitances on each side of the crystal of C Stray1 =CStray2 = 1 pF ±10%, a parallel capacitance of the crystal of C 0 = 3.2 pF ±10% and a crystal with CM = 13 fF ±10%, an FSK deviation of ±21.5 kHz typical with worst case tolerances of ±16.8 kHz to ±28.0 kHz results. CLK Output An output CLK signal is provided for a connected microcontroller, the delivered signal is CMOS compatible if the load capacitance is lower than 10 pF. Clock Pulse Take-over The clock of the crystal oscillator can be used for clocking the microcontroller. Atmel’s M4xCx9x has the special feature of starting with an integrated RC-oscillator to switch on the T5750 with ENABLE = H, and after 4 ms to assume the clock signal of the transmis- sion IC, so that the message can be sent with crystal accuracy. ~ V S XTAL C Stray1 C M L M R S C 0 C Stray2 C 4 C 5 Crystal equivalent circuit C Switch |
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