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MAX3218CPP Datasheet(PDF) 5 Page - Maxim Integrated Products |
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MAX3218CPP Datasheet(HTML) 5 Page - Maxim Integrated Products |
5 / 12 page _______________Detailed Description The MAX3218 line driver/receiver is intended for bat- tery-powered EIA/TIA-232 and V.28/V.24 communica- tions interfaces that require two drivers and two receivers. The operating voltage extends from 1.8V to 4.25V, yet the device maintains true RS-232 and EIA/TIA-562 transmitter output voltage levels. This wide supply voltage range permits direct operation from a variety of batteries without the need for a voltage regu- lator. For example, the MAX3218 can be run directly from a single lithium cell or a pair of alkaline cells. It can also be run directly from two NiCd or NiMH cells from full-charge voltage down to the normal 0.9V/cell end-of-life point. The 4.25V maximum supply voltage allows the two rechargeable cells to be trickle- or fast- charged while driving the MAX3218. The circuit comprises three sections: power supply, transmitters, and receivers. The power-supply section converts the supplied input voltage to 6.5V, providing the voltages necessary for the drivers to meet true RS-232 levels. External components are small and inexpensive. The transmitters and receivers are guaranteed to oper- ate at 120kbps data rates, providing compatibility with LapLink™ and other high-speed communications soft- ware. The MAX3218 is equipped with Maxim’s new propri- etary AutoShutdown™ circuitry. This achieves a 1µA supply current by shutting down the device when the RS-232 cable is disconnected or when the connected peripheral transmitters are turned off. While shut down, both receivers can remain active or can be disabled under logic control. With this feature, the MAX3218 can be in low-power shutdown mode and still monitor activi- ty on external devices. Three-state drivers are provid- ed on both receiver outputs. Three-state drivers on both receiver outputs are provid- ed so that multiple receivers, generally of different inter- face standards, can be wire-ORed at the UART. Switch-Mode Power Supply The switch-mode power supply uses a single inductor with one diode and three small capacitors to generate ±6.5V from an input voltage in the 1.8V to 4.25V range. Inductor Selection Use a 15µH inductor with a saturation current rating of at least 350mA and less than 1 Ω resistance. Table 1 lists suppliers of inductors that meet the 15µH/350mA/1 Ω specifications. 1µA Supply Current, 1.8V to 4.25V-Powered RS-232 Transceiver with AutoShutdown™ _______________________________________________________________________________________ 5 Receiver Inputs R2IN, R1IN 11, 12 Transmitter Outputs, swing between V+ and V- T2OUT, T1OUT 13, 14 Negative Supply generated on-board V- 15 Terminal for Charge-Pump Capacitor C1-, C1+ 16, 18 Positive Supply generated on-board V+ 19 Ground GND 5, 17, 20 Supply Voltage Input, 1.8V to 4.25V. Bypass to GND with at least 1µF. VCC 6 Transmitter Inputs T1IN, T2IN 7, 8 Receiver Outputs R1OUT, R2OUT 9, 10 Drive low to shut down transmitters and on-board power supply, overriding all automatic circuitry and FORCEON. FORCEOFF 4 Drive high when FORCEOFF = high to override automatic circuitry, keeping transmitters on. FORCEON 3 PIN Output of Invalid Signal Detector. Low if invalid RS-232 levels are present on all receiver inputs, otherwise high. INVALID 2 Inductor/Diode Connection Point LX 1 FUNCTION NAME ______________________________________________________________Pin Description ™ LapLink is a trademark of Traveling Software, Inc. AutoShutdown is a trademark of Maxim Integrated Products. |
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