外文翻译---MAX232-5V的供电，多通道RS-232接口驱动器接收器.docx

附录AMAX232-5V-Powered,Multichannel RS-232 Drivers/Receivers The MAX232 is a dual driver/receiver that includes a capacitive voltage generator to supply TIA/EIA-232-F voltage levels from a single 5-V supply. Each receiver converts TIA/EIA-232-F inputs to 5-V TTL/CMOS levels. These receivers have a typical threshold of 1.3 V, a typical hysteresis of 0.5 V, and can accept 30-V inputs. Each driver converts TTL/CMOS input levels into TIA/EIA-232-F levels. The driver, receiver, and voltage-generator functions are available as cells in the Texas Instruments LinASIC library.The MAX220MAX249 contain four sections: dual charge-pump DC-DC voltage converters, RS-232 drivers,RS-232 receivers, and receiver and transmitter enable control inputs.Dual Charge-Pump Voltage ConverterThe MAX220MAX249 have two internal charge-pumps that convert +5V to 10V (unloaded) for RS-232 driver operation. The first converter uses capacitor C1 to double the +5V input to +10V on C3 at the V+ output. The second converter uses capacitor C2 to invert +10V to -10V on C4 at the V- output.A small amount of power may be drawn from the +10V (V+) and -10V (V-) outputs to power external circuitry (see the Typical Operating Characteristics section), except on the MAX225 and MAX245MAX247, where these pins are not available. V+ and V- are not regulated, so the output voltage drops with increasing load current. Do not load V+ and V- to a point that violates the minimum 5V EIA/TIA-232E driver output voltage when sourcing current from V+ and V- to external circuitry.When using the shutdown feature in the MAX222,MAX225, MAX230, MAX235, MAX236, MAX240,MAX241, and MAX245MAX249, avoid using V+ and V- to power external circuitry. When these parts are shut down, V- falls to 0V, and V+ falls to +5V. For applications where a +10V external supply is applied to the V+ pin (instead of using the internal charge pump to generate +10V), the C1 capacitor must not be installed and the SHDN pin must be tied to VCC. This is because V+ is internally connected to VCC in shutdown mode.RS-232 DriversThe typical driver output voltage swing is 8V when loaded with a nominal 5k RS-232 receiver and VCC =+5V. Output swing is guaranteed to meet the EIA/TIA-232E and V.28 specification, which calls for 5V minimum driver output levels under worst-case conditions. These include a minimum 3k load, VCC = +4.5V, and maximum operating temperature. Unloaded driver output voltage ranges from (V+ -1.3V) to (V- +0.5V).Input thresholds are both TTL and CMOS compatible.The inputs of unused drivers can be left unconnected since 400k input pull-up resistors to VCC are built in (except for the MAX220). The pull-up resistors force theoutputs of unused drivers low because all drivers invert.The internal input pull-up resistors typically source 12A, except in shutdown mode where the pull-ups are disabled.Driver outputs turn off and enter a high-impedance statewhere leakage current is typically microamperes (maximum 25A)when in shutdown mode, in three-state mode, or when device power is removed. Outputs can be driven to 15V. The power supply current typically drops to 8A in shutdown mode. The MAX220 does not have pull-up resistors to force the outputs of the unused drivers low. Connect unused inputs to GND or VCC.The MAX239 has a receiver three-state control line, and the MAX223, MAX225, MAX235, MAX236, MAX240, and MAX241 have both a receiver three-state controlline and a low-power shutdown control. Table 2 shows the effects of the shutdown control and receiver three state control on the receiver outputs. The receiver TTL/CMOS outputs are in a high-impedance, three-state mode whenever the three-state enable line is high (for the MAX225/MAX235/MAX236/MAX239MAX241), and are also high-impedance whenever the shutdown control line is high.When in low-power shutdown mode, the driver outputs are turned off and their leakage current is less than 1A with the driver output pulled to ground. The driver output leakage remains less than 1A, even if the transmitter output is backdriven between 0V and (VCC + 6V). Below -0.5V, the transmitter is diode clamped to ground with 1k series impedance. The transmitter is also zener clamped to approximately VCC + 6V, with a series impedance of 1k. The driver output slew rate is limited to less than 30V/s as required by the EIA/TIA-232E and V.28 specifications. Typical slew rates are 24V/s unloaded and 10V/s loaded with 3 and 2500pF.RS-232 ReceiversEIA/TIA-232E and V.28 specifications define a voltage level greater than 3V as a logic 0, so all receivers invert. Input thresholds are set at 0.8V and 2.4V, so receiversrespond to TTL level inputs as well as EIA/TIA-232E and V.28 levels. The receiver inputs withstand an input overvoltage up to 25V and provide input terminating resistors with nominal 5k values. The receivers implement Type 1 interpretation of the fault conditions of V.28 and EIA/TIA-232E. The receiver input hysteresis is typically 0.5V with a guaranteed minimum of 0.2V. This produces clear output transitions with slow-moving input signals, even with moderate amounts of noise and ringing. The receiver propagation delay is typically 600ns and is independent of input swing direction.Low-Power Receive ModeThe low-power receive-mode feature of the MAX223, MAX242, and MAX245MAX249 puts the IC into shutdown mode but still allows it to receive information. This is important for applications where systems are periodically awakened to look for activity. Using low-power receive mode, the system can still receive a signal that will activate it on command and prepare it for communication at faster data rates. This operation conserves system power.Receiver and Transmitter EnableThe MAX225 and MAX245MAX249 feature transmitter and receiver enable controls.The receivers have three modes of operation: full-speed receive (normal active) three-state (disabled) and low power receive (enabled receivers continue to functionat lower data rates). The receiver enable inputs control the full-speed receive and three-state modes. The transmitters have two modes of operation: full-speed transmit (normal active) and three-state (disabled). The transmitter enable inputs also control the shutdown mode. The device enters shutdown mode when all transmitters are disabled. Enabled receivers function in the low-power receive mode when in shutdown.ShutdownMAX222MAX242On the MAX222 MAX235 MAX236 MAX240 and MAX241 all receivers are disabled during shutdown. On the MAX223 and MAX242 two receivers continue to operate in a reduced power mode when the chip is in shutdown. Under these conditions the propagation delay increases to about 2.5s for a high-to-low input transition. When in shutdown, the receiver acts as a CMOS inverter with no hysteresis. The MAX223 and MAX242 also have a receiver output enable input (EN for the MAX242 and EN for the MAX223) that allows receiver output control independent of SHDN (SHDN for MAX241). With all other devices SHDN (SHDN for MAX241) also disables the receiver outputs.The MAX225 provides five transmitters and five receivers while the MAX245 provides ten receivers and eight transmitters. Both devices have separate receiver and transmitter-enable controls. The charge pumps turn off and the devices shut down when a logic high is applied to the ENT input. In this state, the supply current drops to less than 25A and the receivers continue to operate in a low-power receive mode. Driver outputs enter a high-impedance state (three-state mode). On the MAX225all five receivers are controlled by the ENR input. On the MAX245 eight of the receiver outputs are controlled by the ENR input while the remaining two receivers (RA5 and RB5) are always active. RA1RA4 and RB1RB4 are put in a three-state mode when ENR is a logic high.The MAX247 provides nine receivers and eight drivers with four control pins. The ENRA and ENRB receiver enable inputs each control four receiver outputs. The ENTA and ENTB transmitter enable inputs each control four drivers. The ninth receiver (RB5) is always active. The device enters shutdown mode with a logic high on both ENTA and ENTB.The MAX248 provides eight receivers and eight drivers with four control pins. The ENRA and ENRB receiver enable inputs each control four receiver outputs. The ENTA and ENTB transmitter enable inputs control four drivers each. This part does not have an always-active receiver. The device enters shutdown mode and transmitters go into a three-state mode with a logic high on both ENTA and ENTB.附录BMAX232-5V的供电，多通道RS-232接口驱动器/接收器 该MAX232是一种双驱动器/接收器，其中包括一个电容式电压发电机，供应TIA/EIA-232-F一个单一的5 V电源。每个接收器转换TIA/EIA-232-F需要工作电压5V的TTL/CMOS。这些接收器有一个典型的阈值为1.3伏，一个典型的滞后为0.5伏，并且可以接受30电压。每个TTL/CMOS驱动转换的输入和TIA/EIA-232-F同一水平。在德州仪器LinASIC库该驱动器，接收器和电压发生器起到了主要作用。 该MAX220-MAX249包含四个部分：双电荷泵型DC-DC电压转换器，RS-232接口的驱动程序，RS-232接口接收器和能控制输入的发射器。双电荷泵电压转换器该MAX220-MAX249有两个内部电荷泵能将RS-232驱动从+5V转换为10V。第一个转换器使用电容器C1将+5V变为+10V在C3上的V+上输出，而第二个转换器使用电容C2将+10V转变为-10V在C4在V-输出。少量的功率可能来自电源外部电路10V(V+）和-10V（V-）的输出（见典型工作特性部分），除非MAX225和MAX245-MAX247，这些引脚不可用。V+和V-不固定，因此，输出电压下降而负载电流就相应的增加。当在外部电路时电源从V+到V-时不要将V+和V-接到一点，违反了EIA/TIA-232E接口的最小输出电压5V。 当在MAX222，MAX225，MAX230，MAX235，MAX236，MAX240，MAX241和MAX245，MAX249中使用停机功能，应避免在电源外部电路使用V+和V-。当这部分被关闭时，V-下降到0V，V+下降到+5V，10V的外部电源应接到V+引脚上（而不是使用内部电荷泵产生的10V），C1电容不需要接并且SHDN引脚必须接到VCC上。这是因为V+接到VCC是在关断模式状态下。RS-232接口卡 当一个5kRS-232接收器接电源5V时，典型的驱动器输出电压幅值变化为8V。输出幅值保证满足EIA/TIA-232E的要求，在最坏的情况下它要求驱动器输出的电压为5V。这些条件有阻值最小为3k负载，外接电源4.5伏，最高工作温度。卸载驱动器的输出电压范围为1.3V至-0.5V。 TTL和CMOS的输入阀值是相互兼容的。未被使用的驱动器不工作这是因为400k输入上拉电阻接到VCC（除MAX220）。上拉电阻使得未使用的驱动器输出电压变低，因为所有的驱动器倒置了。内部输入上拉电阻电流通常12，除了在关断模式下都不能被使用。驱动器输出端关闭了并且进入了高阻抗状态下泄漏电流通常是微安（最大25A），在停机模式，三态模式，或者设备电源被移除时。驱动电压输出可达到15V。在关断模式电源电流通常降至8A。该MAX220没有上拉电阻使未使用的驱动器输出电压降低。将未使用的输入端连接到GND或Vcc上。 该MAX239接收器有三态控制线，并且MAX223，MAX225，MAX235，MAX236，MAX240，和MAX241都同时拥有三态控制线和一个低功耗的关断控制器。表2说明了关断控制和三态门控制接收器输出的影响。无论三态门使能端是不是接高电平，TTL/CMOS接收器输出端都处于高阻抗，三态模式（为MAX225/MAX235/MAX236/MAX239-MAX241），并且关断控制端是否高电平也同样处于高阻抗模式。 当在低功耗关断模式下，驱动器输出端将被关闭并且漏电流低于1uA，同时驱动器输出端接地。该驱动器输出漏极电流仍然低于1uA，即使发射极输出电压在0V和6V之间（电源电压为+6V）。当低于-0.5V，发射极端的二极管和1k的电阻串联之后接地。发射极与1k的电阻串联之后接到6V的外部电压上。该驱动器输出转换速率是有限的，按EIA/TIA-232E和V.28的规格以低于30V/s的速率转换。通常卸载的转换速率是24V/s，当满载3和2500pF为10V/s。RS-232接口接收器EIA/TIA-232E和V.28的规格为将电压大于3V作为逻辑0，因此，所有接收颠倒。输入阈值定为0.8V和2.4V，所以TTL接收器和EIA/TIA-232E和V.28是相同的。接收器输入端的输入电压高达 25V的输入，并供应5k电阻。接收器解释V.28和EIA/TIA-232E故障的原因 ，该接收器迟滞输入电压通常是0.5V，其中0.2V是最低电压。这明显的表明了转换输出带有缓慢移动的输入信号，即使有适量的噪声和振铃。接收器传输延迟通常是600ns和具有独立的输入摆动方向。低功耗接收模式MAX223，MAX