串行数据接口芯片供应双极电压-Serial-Data Int
some of the interface ics currently available for serial-data transmission not only operate from low vcc levels (5v or 3.3v); they also generate bipolar dc voltages (±6.5v to ±10v) to support the minimum driver-output levels as specified by eia/tia-232. with care, you can steal useful amounts of power from these voltage rails without interfering with the ic's operation.
in figure 1, the ic's switch-mode controller operates with an external inductor, two diodes, and two capacitors to produce ±6.5v. fets q1 and q2 ensure start-up for the circuit by disconnecting the load until these switch-mode supply voltages are present. note that q1 must be a logic-level device.
figure 1. for data rates and driver-output loads less than the maximum allowed, the v+ and v- outputs of this serial interface ic can supply modest amounts of current to an external curcuit.
unlike ics designed to generate supply voltages, an interface ic generally doesn't specify how much current you can draw from its internally generated supply rails. the amount available depends almost entirely on loads connected to the driver outputs. ic1, for example, guarantees that one transmitter can drive a parallel combination of 3kω and 1000pf at 250kbps while the other two maintain dc outputs across 3kω loads. these conditions let you calculate the chip's maximum output current capability, but you can't expect to draw extra current while delivering that maximum.
to calculate the maximum output current available, superimpose the ac and dc components: output current flows alternately from each rail as the nrz output waveform swings between the guaranteed minimum output levels (±5v). assuming the output requires one whole data period (4µs at 250kbps) to slew from -5v to +5v, the ac component equals cload(dv/dt) = 1000pf(10v/4µs) = 2.5ma. for the dc component, ohm's law gives i = e/r = 5v/3kω = 1.67ma from one transmitter, so the three transmitters together represent a dc load of 5ma. adding the ac and dc components together gives a conservative maximum rating of 2.5ma + 5ma = 7.5ma.
the 3kω load is an eia-232 requirement, but the data rate and load capacitance are application-dependent parameters. lower values for these parameters make more current available for external use. a remote-sensing system, for instance, might operate at 2400 bits/sec (2400bps) with a load of 3kω in parallel with 1000pf (50 feet of cable at 20pf/ft). the dc load for three transmitters is 5ma, and the ac load for one transmitter (72µa) is almost negligible in this low-data-rate application. so, the available current in this case is calculated as 7.5ma - (5ma + 72µa) = 2.428ma.
the above calculation is conservative: with vcc = 2.7v and the three transmitters loaded with 3kω||1000pf, a circuit transmitting valid eia-232 levels at 2400bps will actually deliver 6.7ma to an external load (even more for vcc = 3v and up). as mentioned, q1 and q2 enable the circuit to start under these conditions. if you disconnect the transmitter loads, the maximum external load current that allows start-up is 11.5ma. with q1 and q2 removed, the maximum is only 5.7ma.
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in figure 1, the ic's switch-mode controller operates with an external inductor, two diodes, and two capacitors to produce ±6.5v. fets q1 and q2 ensure start-up for the circuit by disconnecting the load until these switch-mode supply voltages are present. note that q1 must be a logic-level device.
figure 1. for data rates and driver-output loads less than the maximum allowed, the v+ and v- outputs of this serial interface ic can supply modest amounts of current to an external curcuit.
unlike ics designed to generate supply voltages, an interface ic generally doesn't specify how much current you can draw from its internally generated supply rails. the amount available depends almost entirely on loads connected to the driver outputs. ic1, for example, guarantees that one transmitter can drive a parallel combination of 3kω and 1000pf at 250kbps while the other two maintain dc outputs across 3kω loads. these conditions let you calculate the chip's maximum output current capability, but you can't expect to draw extra current while delivering that maximum.
to calculate the maximum output current available, superimpose the ac and dc components: output current flows alternately from each rail as the nrz output waveform swings between the guaranteed minimum output levels (±5v). assuming the output requires one whole data period (4µs at 250kbps) to slew from -5v to +5v, the ac component equals cload(dv/dt) = 1000pf(10v/4µs) = 2.5ma. for the dc component, ohm's law gives i = e/r = 5v/3kω = 1.67ma from one transmitter, so the three transmitters together represent a dc load of 5ma. adding the ac and dc components together gives a conservative maximum rating of 2.5ma + 5ma = 7.5ma.
the 3kω load is an eia-232 requirement, but the data rate and load capacitance are application-dependent parameters. lower values for these parameters make more current available for external use. a remote-sensing system, for instance, might operate at 2400 bits/sec (2400bps) with a load of 3kω in parallel with 1000pf (50 feet of cable at 20pf/ft). the dc load for three transmitters is 5ma, and the ac load for one transmitter (72µa) is almost negligible in this low-data-rate application. so, the available current in this case is calculated as 7.5ma - (5ma + 72µa) = 2.428ma.
the above calculation is conservative: with vcc = 2.7v and the three transmitters loaded with 3kω||1000pf, a circuit transmitting valid eia-232 levels at 2400bps will actually deliver 6.7ma to an external load (even more for vcc = 3v and up). as mentioned, q1 and q2 enable the circuit to start under these conditions. if you disconnect the transmitter loads, the maximum external load current that allows start-up is 11.5ma. with q1 and q2 removed, the maximum is only 5.7ma.
摩托罗拉(谷歌)召开发布会 推新机主打LTE与电池
安全性是智能家电应用的关键
PLC可编程逻辑控制器的常见错误类型以及修复方法
揭秘雪铁龙SUV天逸如何保证优越的质量保障和优秀的NVH
介绍一个很棒的Markdown编辑器UltraEdit
串行数据接口芯片供应双极电压-Serial-Data Int
10.3.1 金刚石(Diamond)∈《集成电路产业全书》
Unified SID助力SRv6应用发展
智能镜子显示屏是什么，它的一面是镜一面是屏
VR巨幕，把IMAX影院带回家！基于传统视频和直播打造巨幕式体验
基于VHDL语言对高速A/D器件TLC5510控制的实现
更新MIUI新版本后小米6重启有效解决，实测没毛病！
如何使用泰克示波器检测维修焊机？
滤波器设计软件介绍
低价的智能音箱物有所值吗？人工智能靠“补贴”能否有效落地？
朱老师邀请你免费参加LeaTech全球CTO领导力峰会
云、安全性以及如何保护基础架构
高交会：新一代5G+AIoT如何赋能高科技企业 干货满满
师吉姆·苏瓦：预估苹果会宣布把股东回报计划的规模提高1000亿美元
2022软件安全年终大考成绩公布：95%软件都有漏洞，你是那5%吗？