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MAX1472AKA+T Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX1472AKA+T Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 9 page 300MHz-to-450MHz Low-Power, Crystal-Based ASK Transmitter 6 Detailed Description The MAX1472 is a highly integrated OOK/ASK transmit- ter operating over the 300MHz to 450MHz frequency range. The IC includes a complete PLL and a highly efficient PA. The device can also be easily placed into a 5nA low-power shutdown mode. Shutdown Mode The ENABLE pin is internally pulled down with a 15µA current source. If the pin is left unconnected or pulled low, the MAX1472 goes into shutdown mode, where the supply current drops to less than 5nA. When ENABLE is high, the IC is enabled and is ready for transmission after 220µs (frequency settles to within 50kHz). The 220µs turn-on time of the MAX1472 is mostly domi- nated by the crystal oscillator startup time. Once the oscillator is running, the 1.6MHz PLL loop bandwidth allows fast-frequency recovery during power-amplifier toggling. Phase-Locked Loop The PLL block contains a phase detector, charge pump, integrated loop filter, VCO, 32X clock divider, and crystal oscillator. This PLL requires no external components, other than a crystal. The relationship between the carrier and crystal frequency is given by: fXTAL = fRF / 32 The lock-detect circuit prevents the PA from transmit- ting until the PLL is locked. In addition, the device shuts down the PA if the reference frequency is lost. Power Amplifier (PA) The PA of the MAX1472 is a high-efficiency, open-drain, switch-mode amplifier. With proper output matching net- work, the PA can drive a wide range of impedances, including the small-loop PC board trace antenna and any 50 Ω antenna. The output-matching network for a 50 Ω antenna is shown in the Typical Application Circuit. The output-matching network suppresses the carrier har- monics and transforms the antenna impedance to an optimal impedance at PAOUT (pin 4), which is between 100 Ω and 150Ω for a 2.7V supply. When the output matching network is properly tuned, the PA transmits power with high efficiency. The Typical Application Circuit delivers 10.3dBm at 2.7V supply with 9.1mA of supply current. Thus, the overall efficiency is 44%. The efficiency of the PA itself is more than 52%. Applications Information Output Power Adjustment It is possible to adjust the output power down to -10dBm with the addition of a resistor. The addition of the power-adjust resistor also reduces power con- sumption. See the Supply Current and Output Power vs. External Resistor and Supply Current vs. Output Power graphs in the Typical Operating Characteristics section. It is imperative to add both a low-frequency and a high-frequency decoupling capacitor as shown in the Typical Application Circuit. Pin Description PIN NAME FUNCTION 1 XTAL1 1st Crystal Input. fRF = 32 x fXTAL. 2 GND Ground. Connect to system ground. 3 PAGND Ground for the Power Amplifier (PA). Connect to system ground. 4 PAOUT Power-Amplifier Output. This output requires a pullup inductor to the supply voltage, which may be part of the output-matching network to a 50 Ω antenna. 5 ENABLE Standby/Power-Up Input. A logic low on ENABLE places the device in standby mode. 6 DATA OOK Data Input. Power amplifier is ON when DATA is high. 7VDD Supply Voltage. Bypass to GND with capacitor as close to the pin as possible. 8 XTAL2 2nd Crystal Input. fRF = 32 x fXTAL. |
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Similar Description - MAX1472AKA+T |
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