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MAX3318CAP Datasheet(PDF) 10 Page - Maxim Integrated Products |
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MAX3318CAP Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 15 page 2.5V, 1µA, 460kbps, RS-232-Compatible Transceivers 10 ______________________________________________________________________________________ When shut down, the device’s charge pumps turn off, V+ is pulled to VCC, V- is pulled to ground, the transmitter outputs are high impedance, and READY is driven low. The time required to exit shutdown is typically 30µs (Figure 2). By connecting FORCEON to INVALID, the MAX3318/ MAX3319 shut down when no valid receiver level is detected and wake up when a valid receiver level is detected. A system with AutoShutdown Plus may need time to wake up. Figure 5 shows a circuit that forces the trans- mitters on for 100ms, allowing enough time for the other system to realize that the MAX3318/MAX3319 is awake. If the other system outputs valid RS-232 signal transi- tions within that time, the RS-232 ports on both systems remain enabled. Connecting to the PC (MAX3318/MAX3319) If direct software control is desired, use INVALID to indicate DTR or ring indicator (RI) signal. This can be used to connect a hand-held device to a PC. One example is using the hot sync function on a personal digital assistant (PDA). The transmitter and receiver signals (T_OUT and R_IN) are used for communication, while INVALID causes a change of state on RI. The change of state on RI will trigger an interrupt on the PC and allow communication to begin between the device and the PC. This eliminates the need for the PC to poll constantly the receiver or transmitter lines to determine if the device is connected. Applications Information RS-232-Compatible Operation The MAX3316–MAX3319 do not meet EIA-232 require- ments for transmitter output voltage levels. EIA-232 com- pliance specifies transmitter output voltage swings of ±5V when loaded with 3k Ω and 2500pF. The receiver inputs are fully EIA-232 compliant. The MAX3316–MAX3319 will function properly with most modern RS-232 interfaces. This allows RS-232-compati- ble communication in low-voltage systems without the added expense of a voltage tripler or switched-mode power supply. Capacitor Selection The capacitor type used for C1–C4 is not critical for proper operation; polarized or nonpolarized capacitors can be used. The charge pump requires 0.1µF capaci- tors. Increasing the capacitor values (e.g., by a factor of 2) reduces ripple on the transmitter outputs and slightly reduces power consumption. C2, C3, and C4 can be increased without changing C1’s value. However, do not increase C1 without also increasing the values of +0.3V -0.3V INVALID R_IN INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30 µs. 30µs TIMER R Figure 3a. INVALID Functional Diagram, INVALID Low +2.7V -2.7V INVALID R_IN INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V FOR LESS THAN 30 µs. 30µs TIMER R Figure 3b. INVALID Functional Diagram, INVALID High -2.7V -0.3V +2.7V +0.3V 0 INDETERMINATE INVALID HIGH INVALID LOW INVALID HIGH INDETERMINATE Figure 4a. Receiver Positive/Negative Thresholds for INVALID |
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