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MAX3243EWI Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX3243EWI Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 16 page 1µA Supply-Current, True +3V to +5.5V RS-232 Transceivers with AutoShutdown _______________________________________________________________________________________ 9 Power-Supply Decoupling In most circumstances a 0.1µF bypass capacitor is adequate. In applications that are sensitive to power- supply noise, decouple VCC to ground with a capacitor of the same value as the charge-pump capacitor C1. Connect bypass capacitors as close to the IC as possible. Transmitter Outputs when Exiting Shutdown Figure 6 shows two transmitter outputs when exiting shutdown mode. As they become active, the two trans- mitter outputs are shown going to opposite RS-232 levels. Each transmitter is loaded with 3k Ω in parallel with 2500pF. The transmitter outputs display no ringing or undesirable transients as they come out of shut- down. Note that the transmitters are enabled only when the magnitude of V- exceeds approximately 3V. Figure 7a shows the MAX3243’s transmitter output voltage vs. current per transmitter. Figure 7b is a mouse driver test circuit. Mouse Driveability (MAX3243) The MAX3243 has been specifically designed to power serial mice while operating from low-voltage power sup- plies. It has been tested with samples of ten major mouse models from six manufacturers including the leading three: Logitech (5 models), Mouse Systems, and Microsoft. The MAX3243 successfully drove all serial mice and met their respective current and voltage requirements. Figure 7a shows the transmitter outputs under increasing load current. The MAX3243’s switching regulator ensures the transmitters will supply at least ±5V during worst-case conditions. The AutoShutdown feature does not work with a mouse, so FORCEOFF and FORCEON should be connected to VCC. High Data Rates The MAX3221/MAX3223/MAX3243 maintain the RS-232 ±5.0V minimum transmitter output voltage even at high data rates. Figure 8 shows a transmitter loopback test circuit. Figure 9 shows a loopback test result at 120kbps, and Figure 10 shows the same test at 235kbps. For Figure 9, all three transmitters were driv- en simultaneously at 120kbps into RS-232 loads in par- allel with 1000pF. For Figure 10, a single transmitter was driven at 235kbps, but all three transmitters were loaded with an RS-232 receiver in parallel with 1000pF. Interconnection with 3V and 5V Logic The MAX3221/MAX3223/MAX3243 can directly inter- face with various 5V logic families, including ACT and HCT CMOS. See Table 4 for more information on possi- ble combinations of interconnections. -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 01 23 45 67 LOAD CURRENT PER TRANSMITTER (mA) VOUT+ VCC = 3.0V VOUT- VOUT+ VCC VOUT- T1 T2 T3 Figure 7a. MAX3243 Transmitter Output Voltage vs. Load Current per Transmitter 5V/div VCC = +3.3V C1–C4 = 0.1 µF 2V/div T2 50 µs/div T1 Figure 6. Transmitter Outputs when Exiting Shutdown or Powering Up |
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