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模拟集成电路的低电压系统-Analog ICs for Lo

作者:时间:2012-01-30来源:网络收藏
32 receivers, which have input thresholds of ±3V. The noise margin, however, is only 0.7V. By comparison, the 232 drivers' ±5V minimum swings guarantee a noise margin of 2V.

Table 4. Comparison of 232E and 562 Interface Standards
ParameterEIA-232EEIA-562
Mode of operationSingle endedSingle ended
Allowed number of transmitters and receivers per data line1 Tx, 1 Rx1 Tx, 1 Rx
Maximum cable lengthC 2500pFC 2500pF for data rates 20kb/s,C 1000pF for data rates > 20kb/s
Maximum data rate (kb/s)2064
Driver output voltage, loaded (V)minimum
±5±3.7
maximum
±15±13.2
Maximum driver short-circuit current (mA)50060
Transmitter load impedance (kΩ)3 to 73 to 7
Instantaneous slew rate (V/µs)3030
Receiver input threshold (sensitivity) (V)±3±3
Receiver input resistance (kΩ)3 to 73 to 7
Receiver input range (V)±25±25

Most modern Maxim RS-232 devices with low-voltage supplies employ voltage-increasing charge-pump converters, sometimes requiring external capacitors. Many Maxim RS-232 devices feature automatic shutdown, and draw only 1µA of current until "awakened" by the RS-232 communication signal. The MAX3381E (Figure 13) operates from as low as 2.35V with a guaranteed data rate of 250kbps, and features ±15kV of built-in ESD protection. Its two receivers remain active during the 1µA shutdown mode, enabling the chip to monitor external devices while consuming small amounts of power. The MAX218 (not shown) operates down to +1.8V and uses a switch-mode power converter, which requires an external inductor, a diode, and a few capacitors.

模拟集成电路的低电压系统-Analog ICs for Lo
Figure 13. This low-voltage interface IC includes a charge pump converter that generates the voltages required for RS-232 communications.

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