为何I2C 的连接数， 用400pF 限制？

Quantum_

1. 如题 ："The number of ICs that can be connected to the same bus is limited only by a maximum bus capacitance of 400 pF."---THE I2C-BUS SPECIFICATION
# Y' S7 u' W8 P* }- q1 R7 W2. 如何用电容来定义。
3. 这个400pF 是如何推导/计算 得来的？
( r8 X6 E2 T5 A* q9 W7 e4 f0 k* ?
  V' f5 \' j5 v: G6 T" d4 U; W/ f谢谢！

Aubrey

IIC线上电平从低到变化时, 电源通过上拉电阻RP对线上负载电容CL充电, 这需要一定的时间, 即上升时间, 端口信号的上升时间t可近似用充电时间常数RPCL乘积表示,
如果RC 充电时间常数过大, 将使得信号上升沿变化缓慢, 达不到传输要求.  

超級狗

嗯插屁（NXP）I2C-Bus Specification and User Manual Revision 6.0
  v; J" Y. t0 `6 q9 f/ l' W$ eThe switched pull-up circuit in Figure 44 is for a supply voltage of VDD = 5 V ± 10 % and a maximum capacitive load of 400 pF. Since it is controlled by the bus levels, it needs no additional switching control signals. During the rising/falling edges, the bilateral switch in the HCT4066 switches pull-up resistor Rp2 on/off at bus levels between 0.8 V and 2.0 V. Combined resistors Rp1 and Rp2 can pull up the bus line within the maximum specified rise time (tr) of 300 ns.

gdutchen

谢谢，受教了。

沙漠风铃10

太大，信号质量就不好了

ruanyj228

谢谢，受教了。

soswelcome

谢谢，受教了。

傻大个牌纯碱

学习了。

wjy870825

受教了

tomatogua

根据时序要求，上升时间来定了，负载电容大了上升时间会变慢，时序会变差

林少230

受教了