* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
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The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.Please note that this cross reference is based on TOSHIBA's estimate of compatibility with other manufacturers' products, based on other manufacturers' published data, at the time the data was collected.TOSHIBA is not responsible for any incorrect or incomplete information. Information is subject to change at any time without notice.
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扇出系数是一个通用逻辑输出可驱动的通用逻辑输入的数量。
因此,扇出系数等于驱动IC的输出电流除以被驱动IC的输入电流:
扇出系数=IOH / IIH or IOL / IIL
该计算对于CMOS逻辑IC出现之前常用的TTL逻辑IC具有重要意义。然而,由于目前的CMOS逻辑IC的直流输入电流为微安量级,输入电流不会对扇出系数造成主要限制。
对于CMOS逻辑IC,被驱动的IC的电容是一个限制因素。通常,不建议将大电容刻意连接至CMOS逻辑IC的输出端。 一般情况下,CMOS逻辑IC的输入电容约为10 pF量级。(具体取决于产品系列。详见数据表。)可连接CMOS逻辑IC输出的电容总和可高达500 pF。
请参阅以下FAQ:
通用逻辑IC输出端子上的电容器的容量有什么规定吗?
因此,最多可将50个CMOS逻辑IC连接至CMOS逻辑IC的输出。但应注意以下几点:
信号波形的上升斜率变缓,传输延迟时间增加。
(数据表中显示的传输延迟时间是在输出电容为50pF时测定的。)
负载电容(即被驱动IC的输入电容的总和)增加,会由于充电和放电而导致耗电量增加。
请参阅以下FAQ:
如何计算通用逻辑IC的功耗?
因此,请提前进行电路板评估,以确保CMOS逻辑IC能正常工作。
以下文档也包含相关信息。