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MAX3228EEBV-T Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX3228EEBV-T Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 16 page MAX3228E/AE and MAX3229E/AE maintain the outputs in regulation until the battery voltage drops below +3.1V. Then the output regulation points change to ±4.0V When VCC is rising, the charge pump will generate an output voltage of ±4.0V, while VCC is between +2.5V and +3.5V. When VCC rises above the switchover volt- age of +3.5V, the charge pump switches modes to generate an output of ±5.5V. Table 1 shows different supply schemes and their oper- ating voltage ranges. RS-232 Transmitters The transmitters are inverting level translators that con- vert CMOS-logic levels to RS-232 levels. The MAX3228E/AE and MAX3229E/AE will automatically reduce the RS-232 compliant levels (±5.5V) to RS-232 compatible levels (±4.0V) when VCC falls below approximately +3.1V. The reduced levels also reduce supply current requirements, extending battery life. Built-in hysteresis of approximately 400mV for VCC ensures that the RS-232 output levels do not change if VCC is noisy or has a sudden current draw causing the supply voltage to drop slightly. The outputs will return to RS-232 compliant levels (±5.5V) when VCC rises above approximately +3.5V. The MAX3228E/AE and MAX3229E/AE transmitters guarantee a 250kbps data rate with worst-case loads of 3kΩ in parallel with 1000pF. When FORCEOFF is driven to ground, the transmitters and receivers are disabled and the outputs become high impedance. When the AutoShutdown circuitry senses that all receiver and transmitter inputs are inac- tive for more than 30µs, the transmitters are disabled and the outputs go to a high-impedance state. When the power is off, the MAX3228E/AE and MAX3229E/AE permit the transmitter outputs to be driven up to ±12V. The transmitter inputs do not have pullup resistors. Connect unused inputs to GND or VL. RS-232 Receivers The MAX3228E/AE and MAX3229E/AE receivers con- vert RS-232 signals to logic output levels. All receivers have inverting three-state outputs and can be active or inactive. In shutdown ( FORCEOFF = low) or in AutoShutdown, the MAX3228E/AE and MAX3229E/AE receivers are in a high-impedance state (Table 3). The MAX3228E/AE and MAX3229E/AE feature an INVALID output that is enabled low when no valid RS-232 signal levels have been detected on any receiver inputs. INVALID is functional in any mode (Figures 2 and 3). Figure 2c. MAX322_E AutoShutdown Logic FORCEOFF POWER DOWN INVALID FORCEON INVALID IS AN INTERNALLY GENERATED SIGNAL THAT IS USED BY THE AUTOSHUTDOWN LOGIC AND APPEARS AS AN OUTPUT OF THE DEVICE. POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE OPERATIONAL STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES. VL VL VCC Figure 2a. MAX322_E Entering 1µA Supply Mode via AutoShutdown +0.3V -0.3V INVALID TO MAX322 _E POWER SUPPLY AND TRANSMITTERS R_IN *TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1 μA IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30 μs. 30 μs COUNTER R Figure 2b. MAX322_E with Transmitters Enabled Using AutoShutdown +2.7V -2.7V INVALID TO MAX322 _E POWER SUPPLY R_IN *TRANSMITTERS ARE ENABLED IF: ANY RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V. ANY RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30 μs. 30 μs COUNTER R ±15kV ESD-Protected +2.5V to +5.5V RS-232 Transceivers in UCSP and WLP _______________________________________________________________________________________ 7 |
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