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SP3222EHEA Datasheet(PDF) 11 Page - Sipex Corporation |
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SP3222EHEA Datasheet(HTML) 11 Page - Sipex Corporation |
11 / 19 page Date: 06/22/04 SP3222EH/3232EH 3.3V, 460 Kbps RS-232 Transceivers © Copyright 2004 Sipex Corporation 11 Phase 4: V DD Transfer (Figure 16) The fourth phase of the clock connects the negative terminal of C 2 to GND, and transfers this positive generated voltage across C 2 to C4, the V DD storage capacitor. This voltage is regulated to +5.5V. At this voltage, the internal oscillator is disabled. Simultaneous with the transfer of the voltage to C 4, the positive side of capacitor C 1 is switched to VCC and the negative side is connected to GND, allowing the charge pump cycle to repeat. The charge pump cycle will continue as long as the operational conditions for the internal oscillator are present. Since both V+ and V– are separately generated from V CC; in a no–load condition V + and V– will be symmetrical. Older charge pump approaches that generate V– from V+ will show a decrease in the magnitude of V– compared to V+ due to the inherent inefficiencies in the design. The charge pump clock rate typically operates at 250kHz. The external capacitors can be as low as 0.1 µF with a 16V breakdown voltage rating. ESD Tolerance The SP3222EH/3232EH series incorporates ruggedized ESD cells on all driver output and receiver input pins. The improved ESD tolerance is at least ±15kV without damage or latch-up. Three methods of ESD testing are performed: a) MIL-STD-883, Method 3015.7 b) IEC1000-4-2 Air-Discharge c) IEC1000-4-2 Direct Contact The Human Body Model has been the generally accepted ESD testing method for semiconduc- tors. This method is also specified in MIL-STD- 883, Method 3015.7 for ESD testing. The premise of this ESD test is to simulate the human body’s potential to store electro-static energy and discharge it to an integrated circuit. The simulation is performed by using a test model as shown in Figure 17. This method will test the IC’s capability to withstand an ESD transient during normal handling such as in manufacturing areas where the ICs tend to be handled frequently. The IEC-1000-4-2, formerly IEC801-2, is used for testing ESD on equipment and systems. For system manufacturers, they must guarantee a certain amount of ESD protection since the system itself is exposed to the outside environment and human presence. The premise with IEC1000-4-2 is that the system is required to withstand an amount of static electricity when ESD is applied to points and surfaces of the equipment that are accessible to personnel during normal usage. In many cases, the RS232 transceiver IC receives most of the ESD current when the ESD source is applied to the connector pins. The test circuit for IEC1000-4-2 is shown on Figure 18. There are two methods within IEC1000-4-2, the Air Discharge method and the Contact Discharge method. With the Air Discharge Method, an ESD voltage is applied to the equipment under test (EUT) through air. This simulates an electrically charged person ready to connect a cable onto the rear of the system. The high energy potential on the person discharges through an arcing path to the rear panel of the system before he or she touches the system. This energy, whether discharged directly or through air, is predominantly a function of the discharge current rather than the discharge voltage. Variables with an air discharge such as approach speed of the object carrying the ESD potential to the system and humidity will tend to change the discharge current. For example, the rise time of the discharge current varies with the approach speed. |
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