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MAX3228EEBV Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX3228EEBV Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 15 page ±15kV ESD-Protected +2.5V to +5.5V RS-232 Transceivers in UCSP 6 _______________________________________________________________________________________ Detailed Description Dual-Mode Regulated Charge-Pump Voltage Converter The MAX3228E/MAX3229E internal power supply con- sists of a dual-mode regulated charge pump. For sup- ply voltages above +3.7V, the charge pump will generate +5.5V at V+ and -5.5V at V-. 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. For supply voltages below +2.85V, the charge pump will generate +4.0V at V+ and -4.0V at V-. The charge pumps operate in a discontinuous mode. If the output voltages are less than ±4.0V, the charge pumps are enabled, if the output voltages exceed ±4.0V, 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- supply voltages. Voltage Generation in the Switchover Region The MAX3228E/MAX3229E include a switchover circuit between these two modes that have approximately 400mV of hysteresis around the switchover point. The hysteresis is shown in Figure 1. This large hysteresis eliminates mode changes due to power-supply bounce. For example, a three-cell NiMh battery system starts at VCC = +3.6V, and the charge pump will generate an output voltage of ±5.5V. As the battery discharges, the PIN MAX3228E MAX3229E NAME FUNCTION C5 C5 FORCEOFF FORCEOFF Input, Active-Low. Drive FORCEOFF low to shut down transmitters, receivers, and on-board charge pump. This overrides all automatic circuitry and FORCEON. Pulls itself high internally if not connected. C6, D6 C6 R_OUT Receiver Output(s) D1 D1 C1- Negative Terminal of Positive Regulated Charge-Pump Capacitor E1 E1 GND Ground E2 E2 INVALID Output of Valid Signal Detector. INVALID is enabled low if no valid RS-232 level is present on any receiver input. E3, E4 E3 T_OUT RS-232 Transmitter Output(s) E5, E6 E5 R_IN RS-232 Receiver Input(s) Pin Description (continued) SYSTEM SUPPLY (V) VCC (V) VL (V) RS-232 MODE 1 Li+ Cell +2.4 to +4.2 Regulated System Voltage Compliant/Compatible 3 NiCad/NiMh Cells +2.4 to +3.8 Regulated System Voltage Compliant/Compatible Regulated Voltage Only (VCC falling) +3.0 to +5.5 +3.0 to +5.5 Compliant Regulated Voltage Only (VCC falling) +2.5 to +3.0 +2.5 to +3.0 Compatible Table 1. Operating Supply Options Figure 1. V+ Switchover for Changing VCC 0 6V 4V 0 20ms/div VCC V+ |
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