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MC145406D Folha de dados(PDF) 5 Page - NXP Semiconductors |
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MC145406D Folha de dados(HTML) 5 Page - NXP Semiconductors |
5 / 5 page Philips Semiconductors Linear Products Product specification MC145406 EIA-232-D/V.28 driver/receiver August 31, 1994 471 VDD VCC 1 14 12 10 8 9 7 5 3 16 VSS DI1 DI2 DI3 TX1 TX2 TX3 VIN = +2V ROUT I = VIN Figure 1. Power-Off Source Resistance (Drivers) DRIVERS RECEIVERS 3V 0V +3V 0V 50% 90% 10% 50% 90% 50% 10% DI1-3 TX1-3 VOH VOL tPLH tPHL tF tF VOH VOL tF tF tPLH tPHL DO1-3 RX1-3 Figure 2. Switching Characteristics DRIVERS tSLH TX1-3 3V –3V 3V –3V tSHL –3V –3V 3V – (–3V) OR SLEW RATE (SR) = tSLH tSHL Figure 3. Slew Rate Characteristics APPLICATIONS INFORMATION The MC145406 has been designed to meet the electrical specifications of standards EIA-232-D/CCITT V.28 and as such, defines the electrical and physical interface between Data Communication Equipment (DCE) and Data Terminal Equipment (DTE). A DCE is connected to a DTE using a cable that typically carries up to 25 leads, which allow the transfer of timing, data, control, and test signals. The MC145406 provides the necessary level shifting between the TTL/CMOS logic levels and the high voltage levels of EIA-232-D (ranging from +3 to +25V). DRIVERS As defined by the specification, an EIA-232-D driver presents a voltage of between +5 to +15V into a load of between 3 to 7k Ω. A logic one at the driver input results in a voltage of between -5 to -15V. A logic zero results in a voltage between +5 to +15V. When operating at +7 to +12V, the MC145406 meets this requirement. When operating at +5V, the MC145406 drivers produce less than +5V at the output (when terminated), which does not meet the EIA-232-D specification. However, the output voltages when using a +5V power supply are high enough (around +4V) to permit proper reception by an EIA-232-D receiver, and can be used in applications where strict compliance to EIA-232-D is not required. Another requirement of the MC145406 drivers is that they withstand a short to another driver in the EIA-232-D cable. The worst-case condition that is permitted by EIA-232-D is a +15V source that is current limited to 500mA. The MC145406 drivers can withstand this condition momentarily. In most short circuit conditions the source driver will have a series 300 Ω output impedance needed to satisfy the EIA-232-D driver requirements. This will reduce the short circuit current to under 40mA which is an acceptable level for the MC145406 to withstand. Unlike some other drivers, the MC145406 drivers feature an internally-limited output slew rate that does not exceed 30V/ µs. RECEIVERS The job of an EIA-232-D receiver is to level-shift voltages in the range of -25 to +25V down to TTL/CMOS logic levels (0 to +5V). A voltage of between -3 and -25V on RX1 is defined as a mark and produces a logic one at DO1. A voltage between +3 and +25V is a space and produces a logic zero. While receiving these signals, the RX inputs must present a resistance between 3 and 7k Ω. Nominally, the input resistance of the RX1-3 inputs is 5.0kΩ. The input threshold of the RX1-3 inputs is typically biased at 1.8V above ground (GND) with typically 800mV of hysteresis included to improve noise immunity. The 1.8V bias forces the appropriate DO pin to a logic one when its RX input is open or grounded as called for in EIA-232-D specification. Notice that TTL logic levels can be applied to the RX inputs in lieu of normal EIA-232-D signal levels. This might be helpful in situations where access to the modem or computer through the EIA-232-D connector is necessary with TTL devices. However, it is important not to connect the EIA-232-D outputs (TX1) to TTL inputs since TTL operates off +5V only, and may be damaged by the high output voltage of the MC145406. The DO outputs are to be connected to a TTL or CMOS input (such as an input to a modem chip). These outputs will swing from VCC to ground, allowing the designer to operate the DO and DI pins from the digital power supply. The TX and RX sections are independently powered by VDD and VSS so that one may run logic at +5V and the EIA-232-D signals at +12V. |
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