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MAX3238CAI Datasheet(PDF) 5 Page - Maxim Integrated Products |
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MAX3238CAI Datasheet(HTML) 5 Page - Maxim Integrated Products |
5 / 12 page +3.0V to +5.5V, 1µA, up to 250kbps, True RS-232 Transceiver with AutoShutdown Plus™ _______________________________________________________________________________________ 5 _______________Detailed Description Dual Charge-Pump Voltage Converter The MAX3238’s internal power supply consists of a reg- ulated dual charge pump that provides output voltages of +5.5V (doubling charge pump) and -5.5V (inverting charge pump), regardless of the input voltage (VCC) over the 3.0V to 5.5V range. The charge pumps operate in a discontinuous mode: if the output voltages are less than 5.5V, the charge pumps are enabled; if the output voltages exceed 5.5V, the charge pumps are disabled. Each charge pump requires a flying capacitor (C1, C2) and a reservoir capacitor (C3, C4) to generate the V+ and V- supplies. RS-232 Transmitters The transmitters are inverting level translators that con- vert CMOS-logic levels to 5.0V EIA/TIA-232 levels. The MAX3238 transmitters guarantee a 250kbps data rate with worst-case loads of 3k Ω in parallel with 1000pF, providing compatibility with PC-to-PC communication software (such as LapLink™). Transmitters can be par- alleled to drive multiple receivers. Figure 1 shows a complete system connection. LapLink is a trademark of Traveling Software. When FORCEOFF is driven to ground, the transmitters and receivers are disabled and the outputs go high impedance, except for R1OUTB. When the Auto- Shutdown Plus circuitry senses that all receiver and transmitter inputs are inactive for more than 30sec, the transmitters are disabled and the outputs go into a high-impedance state, but the receivers remain active. When the power is off, the MAX3238 permits the out- puts to be driven up to ±12V. The transmitter inputs do not have pull-up resistors. Connect unused inputs to GND or VCC. RS-232 Receivers The receivers convert RS-232 signals to CMOS-logic output levels. All receivers have inverting three-state outputs and are inactive in shutdown ( FORCEOFF) (Table 1). The MAX3238 also features an extra, always- active noninverting output, R1OUTB. This extra output monitors receiver activity while the other receivers are high impedance, allowing Ring Indicator to be moni- tored without forward biasing other devices connected to the receiver outputs. This is ideal for systems where VCC is set to 0V in shutdown to accommodate peripher- als, such as UARTs (Figure 2). Table 1. Output Control Truth Table FORCEON FORCEOFF AUTOSHUTDOWN PLUS* OPERATION STATUS T_OUT R_OUT R1OUTB X 0 X Shutdown (Forced Off) High-Z High-Z Active 1 1 X Normal Operation (Forced On) Active Active Active 0 1 <30sec* Normal Operation (AutoShutdown Plus) Active Active Active 0 1 >30sec* Shutdown (AutoShutdown Plus) High-Z Active Active X = Don’t Care * Time since last receiver or transmitter input transition. |
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