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11 page 
Transmitter Outputs when Exiting Shutdown Figure 7 shows a transmitter output when exiting shut- down mode. The transmitter is loaded with 3kΩ in par- allel with 1000pF. The transmitter output displays no ringing or undesirable transients as it comes out of shutdown, and is enabled only when the magnitude of V- exceeds approximately -3V. High Data Rates The MAX3228E/AE and MAX3229E/AE 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 250kbps. For Figure 9, the transmitter was driven at 120kbps into an RS-232 load in parallel with 1000pF. For Figure 10, a single transmitter was driven at 250kbps, and loaded with an RS-232 receiver in parallel with 1000pF. Figure 8. Transmitter Loopback Test Circuit MAX3229E/AE 5k Ω R1IN R1OUT C2- C2+ C1- C1+ V- V+ VCC VCC C4 C3 C1 C2 0.1 μF 0.1 μF FORCEOFF FORCEON INVALID T1OUT T1IN GND VL TO POWER- MANAGEMENT UNIT 1000pF VL VL VL VL Figure 9. Loopback Test Result at 120kbps 0 R_OUT T_OUT T_IN -5V 5V 0 5V 5V 0 4 μs/div Figure 10. Loopback Test Result at 250kbps 0 -5V 5V 0 5V 5V 0 R_OUT T_OUT T_IN 4 μs/div Figure 7. Transmitter Outputs Exiting Shutdown or Powering Up FORCEON = FORCEOFF TOUT 4 μs/div 0 2V/div 0 5V/div ±15kV ESD-Protected +2.5V to +5.5V RS-232 Transceivers in UCSP and WLP ______________________________________________________________________________________ 11 |
