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ADM3311EARS-REEL25 Datasheet(PDF) 6 Page - Analog Devices |
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ADM3311EARS-REEL25 Datasheet(HTML) 6 Page - Analog Devices |
6 / 12 page ADM3311E –6– REV. A GENERAL DESCRIPTION The ADM3311E is a ruggedized RS-232 line driver/receiver that operates from a single supply of +2.7 V to +3.6 V. Step-up voltage converters, coupled with level-shifting transmitters and receivers, allow RS-232 levels to be developed while operating from a single supply. Features include low power consumption, Green Idle operation, high transmission rates and compatibility with the EU directive on electromagnetic compatibility. EM compatibility includes protection against radiated and conducted interference including high levels of electrostatic discharge. All RS-232 inputs and outputs contain protection against electrostatic discharges up to ± 15 kV and electrical fast tran- sients up to ± 4 kV. The device is ideally suited for operation in electrically harsh environments or where RS-232 cables are frequently being plugged/unplugged, and is immune to high RF field strengths without special shielding precautions. Emissions are also controlled to within very strict limits. CMOS technology is used to keep the power dissipation to an absolute minimum allowing maximum battery life in portable applications. CIRCUIT DESCRIPTION The internal circuitry consists of three main sections. These are: 1. A charge pump voltage converter. 2. 3.3 V logic to EIA-232 transmitters. 3. EIA-232 to 3 V logic receivers. 4. Transient protection circuit on all I-O lines. Charge Pump DC-DC Voltage Converter The charge pump voltage converter consists of a 180 kHz oscil- lator and a switching matrix. The converter generates a ±9 V supply from the input +3.0 V level. This is done in two stages using a switched capacitor technique as illustrated below. First, the +3.0 V input supply is tripled to +9.0 V using capacitor C4 as the charge storage element. The +9.0 V level is then inverted to generate –9.0 V using C5 as the storage element. However, it should be noted that, unlike other charge-pump dc- dc converters, the charge pump on the ADM3311E does not run open-loop. The output voltage is regulated to ±7.25 V by the Green Idle circuit (as described later) and will never reach ±9 V in practice. This saves power as well as maintaining a more constant output voltage. The tripler operates in two phases. During the oscillator low phase, S1 and S2 are closed and C1 charges rapidly to VCC. S3, S4 and S5 are open. S6 and S7 are closed. During the oscillator high phase, S1 and S2 are open. S3 and S4 are closed, so the voltage at the output of S3 is 2 VCC. This voltage is used to charge C2. In the absence of any discharge current, C2 will charge up to 2 VCC after a several cycles. Dur- ing the oscillator high phase, as previously mentioned, S6 and S7 are closed, so the voltage at the output of S6 will be 3 VCC. This voltage is used to charge C3. + + INTERNAL OSCILLATOR GND C2 C1 S1 S2 S3 S4 VCC + C4 V+ = 3VCC VCC VCC S5 S6 S7 Figure 15. Charge Pump Voltage Tripler The voltage inverter is illustrated in Figure 14. During the oscil- lator high phase S10 and S11 are open, S8 and S9 are closed and (over several cycles) C2 is charged to +3 VCC from the out- put of the voltage tripler. During the oscillator low phase, S8 and S9 are open, while S10 and S11 are closed. C3 is connected across C5, whose positive terminal is grounded and whose nega- tive terminal is the V– output. Over several cycles C5 charges to –3 VCC. + INTERNAL OSCILLATOR GND C3 S8 S9 S11 V+ + C5 V– = –(V+) FROM VOLTAGE TRIPLER S10 GND Figure 16. Charge Pump Voltage Inverter The V+ and V– supplies may also be used to power external circuitry if the current requirements are small. Please refer to Figures 13 and 14 in the Typical Performance section. 1 T [ ] Tek Stop 500kS/s 101 Acqs T T SD 2 Ch1 5.00V Ch2 5.00V M 100 s Ch1 0V V– Figure 13. Charge Pump V– Exiting Shutdown 1 T [ ] Tek Stop 500kS/s 244 Acqs T SD 2 V+ Ch1 5.00V Ch2 5.00V M 100 s Ch1 0V T Figure 14. Charge Pump V+ Exiting Shutdown |
Similar Part No. - ADM3311EARS-REEL25 |
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Similar Description - ADM3311EARS-REEL25 |
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