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ADM3202ARN-REEL Arkusz danych(PDF) 8 Page - Analog Devices |
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ADM3202ARN-REEL Arkusz danych(HTML) 8 Page - Analog Devices |
8 / 16 page ADM3202/ADM3222/ADM1385 Rev. E | Page 8 of 16 GENERAL DESCRIPTION The ADM3202/ADM3222/ADM1385 are RS-232 line drivers/ receivers. Step-up voltage converters coupled with level-shifting transmitters and receivers allow RS-232 levels to be developed while operating from a single 3.3 V supply. CMOS technology is used to keep the power dissipation to an absolute minimum, allowing maximum battery life in portable applications. The ADM3202/ADM3222/ADM1385 are modifications, enhancements, and improvements of the AD230 to AD241 family and derivatives. They are essentially plug-in compatible and do not have any materially different applications. CIRCUIT DESCRIPTION The internal circuitry consists of these main sections: • A charge pump voltage converter • 3.3 V logic to EIA-232 transmitters • EIA-232 to 5 V logic receivers Charge Pump DC to DC Voltage Converter The charge pump voltage converter consists of a 200 kHz oscillator and a switching matrix. The converter generates a ±6.6 V supply from the input 3.3 V level. This is done in two stages by using a switched capacitor technique as illustrated in Figure 18 and Figure 19. First, the 3.3 V input supply is doubled to 6.6 V by using Capacitor C1 as the charge storage element. The +6.6 V level is then inverted to generate −6.6 V using C2 as the storage element. C3 is shown connected between V+ and VCC but is equally effective if connected between V+ and GND. Capacitors C3 and C4 are used to reduce the output ripple. Their values are not critical and can be increased, if desired. Capacitor C3 is shown connected between V+ and VCC. It is also acceptable to connect this capacitor between V+ and GND. If desired, larger capacitors (up to 10 μF) can be used for Capacitors C1 to C4. C1+ C2+ C1– C2– VCC V– V+ T1IN T1OUT T2IN T2OUT R1OUT R1IN R2OUT R2IN CMOS INPUTS EIA/TIA-232 OUTPUTS CMOS OUTPUTS EIA/TIA-232 INPUTS* T1 T2 R1 R2 + + 0.1µF 10V 0.1µF 10V GND ADM3202 C3 0.1µF 6.3V +3.3V INPUT +3.3V TO +6.6V VOLTAGE DOUBLER +6.6V TO –6.6V VOLTAGE INVERTER C5 0.1µF C4 0.1µF 10V *INTERNAL 5kΩ PULL-DOWN RESISTOR ON EACH RS-232 INPUT Figure 15. ADM3202 Typical Operating Circuit C1+ C2+ C1– C2– VCC V– V+ T1IN T1OUT T2IN T2OUT R1OUT R1IN R2OUT EN R2IN SD CMOS INPUTS EIA/TIA-232 OUTPUTS CMOS OUTPUTS EIA/TIA-232 INPUTS* T1 T2 R1 R2 + + 0.1µF 10V 0.1µF 10V GND ADM3222 C3 0.1µF 6.3V +3.3V INPUT +3.3V TO +6.6V VOLTAGE DOUBLER +6.6V TO –6.6V VOLTAGE INVERTER C5 0.1µF C4 0.1µF 10V *INTERNAL 5kΩ PULL-DOWN RESISTOR ON EACH RS-232 INPUT Figure 16. ADM3222 Typical Operating Circuit C1+ C2+ C1– C2– VCC V– V+ T1IN T1OUT T2IN T2OUT R1OUT R1IN R2OUT DD R2IN SD CMOS INPUTS EIA/TIA-232 OUTPUTS CMOS OUTPUTS EIA/TIA-232 INPUTS* T1 T2 R1 R2 + + 0.1µF 10V 0.1µF 10V GND ADM1385 +3.3V INPUT +3.3V TO +6.6V VOLTAGE DOUBLER +6.6V TO –6.6V VOLTAGE INVERTER C5 0.1µF *INTERNAL 5kΩ PULL-DOWN RESISTOR ON EACH RS-232 INPUT C3 0.1µF 10V C4 0.1µF 10V Figure 17. ADM1385 Typical Operating Circuit C1 + C3 + S3 S4 S1 S2 INTERNAL OSCILLATOR VCC GND VCC V+ = 2VCC Figure 18. Charge Pump Voltage Doubler C2 + C4 + S3 S4 S1 S2 INTERNAL OSCILLATOR V+ GND V– = –(V+) GND FROM VOLTAGE DOUBLER Figure 19. Charge Pump Voltage Inverter |
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