Kepserverex 4 rs232 drivers#
Kepserverex 4 rs232 driver#
Kepserverex 4 rs232 series#

Capacitor C1 is used to control the output slew rate so that no frequency compensation components are required to meet the RS232 specification 4V/РћСs to 30V/РћСs.Р”Р‡igure 2. If the output is forced below the negative supply, the Schottky diode reverse biases and prevents eternal current flow into the chip. The device is unaffected by external voltage up to the breakdown voltage of the transistor. If the output voltage is forced above the positive supply the emitter base junction of the PNP transistor reverse biases, and no current flows into the supply. The PNP transistor will swing to within 200mV of the positive supply while the NPN transistor with its associated Schottky diode will swing within about 900mV of the negative supply. Opposed collector NPN and PNP transistors give the widest possible output swings.

Kepserverex 4 rs232 drivers#

The output stage of the bipolar drivers is shown in FigureР’В 2. Using on-chip resistors precludes the use of the optimum ESD protection structures, so CMOS devices may be more sensitive to ESD destruction at their inputs.

These resistors allow very large voltage swings at the input pins and provide ESD protection to the IC.

Kepserverex 4 rs232 series#

The CMOS LTC1045Р’В which is used as an RS232 receiver has been designed to operate with external resistors in series with the input. No IC can withstand that much voltage without external protection.Р”Р„ requirement of the RS232 specification is the ability to withstand РІВвЂ™5V input signals. Bipolar devices are relatively rugged but still can be damaged by ESD, System requirements for ESD may be as high as 20kV. This problem did not usually exist in the past, because the RS232 interfaces were powered by separate РІВвЂ2V supplies.Р”В®SD damage is probably the most frequent cause of failure of interface chips. This problem can even cause latchup if the logic supply is off when external RS232 signals feed voltage into the supply. This forces the power supply to 12V and 15V damaging the 5V logic that is connected to the supplies. External current flows through the 300РћВ© limiting resistor, through the diodes, which are part of the CMOS structure, and into the power supply.

Kepserverex 4 rs232 driver#

CMOS Line Driver Showing Parasitic Diodes to the Power Supplies.Р”Р„ problem occurs when the output of a driver which is powered from the 5V logic supply is connected to an external 12V or 15V source as is allowed by the RS232 specification. (The resistor is similar to the resistors included in older drivers.) It protects the interface chip, but still allows damage to other devices powered by the same supply.Р”Р‡igure 1. With a CMOS output stage this is achieved with the inclusion of a 300РћВ© resistor in series with the output. A requirement of RS232 interfaces is the ability to withstand voltage applied to the output pins. Inherent in the CMOS structure, are diodes between the drain and source of the CMOS devices and the power supplies as is shown in Figure 1. Consideration of some of the problems associated with CMOS decreases its attractiveness for RS232 drivers.

Power supply requirements are low, output voltage swing is high, and higher voltage CMOS technologies are available to allow operation up to РІВвЂ5V. Initial consideration of technologies for implementing RS232 interfacing might include CMOS as a possible technology for this type of application. Of course, current limiting is included to protect against short circuit conditions. The outputs can be driven beyond the power supply voltage without drawing excessive current or forcing current back into the power supplies. A unique output stage was designed that provides large output swings, minimizing power supply voltage requirements, while retaining outstanding overload protection features. The new RS232 drivers are implemented in a monolithic bipolar technology. Further, the new chips are easier to use, requiring fewer external components and may be turned off to a РІР‚СљzeroРІР‚Сњ power supply current condition for use in battery powered systems. The new RS232 interface ICs improve speed, power, voltage supply requirements, and protection over older devices. New RS232 interface chips have been developed that offer significant advantages over older devices such as the 14. Design Note 4: New Developments in RS232 Interface