# switches electronic model

sir:

ADI do not provide spice model for switch ADG5412. But the "off isolaltion" characteristic of ADG5412 is a main problem that exist in my design. So I want to do some simluation about ADG5412.  I have a few question that need to be answered first before my simulation.

(1) When the switch is in off state,  there are parameters Cd(Off),Cs(Off). What does Cd and Cs stand for? what is the capacitance bewteen

Drain and Source? Is the Cds equal to the sum of Cd and Cs?

(2) What is the electronic model when the switch is in off state? If we assume off resistance is infinite, can we think that the electronic model of the switch is a capacitance with value equal to  Cds?

Thanks！

Regards

Jacky

2012-11-15

• Hello Jacky,

Please find following a tutorial that covers a lot of your questions:

http://www.analog.com/static/imported-files/tutorials/MT-088.pdf

To be specific, Cd(off) and Cs(off) are the drain capacitance and source capacitance to ground when the switch is turned off. Cds(on) is the combined capacitance of the channel when the switch is turned on.

Regards,

Sean

• Sean:

I have carefully learned the 'MT-088 tutorials'. I find that if I want to simulate the ac performance of the switch, I have to know the parameter of Cds. If I want to simulate the corsstalk of two adjenct channel, I have to know the parameter of Css and Cdd. But in the datasheet for ADG5412, I can not find these parameters. Sir, where can I find these parameters?

Thanks

Regards

Jacky

2012-11-16

• Hello Jacky,

We do not usually specify the CSS and CDD, but we have already measured the crosstalk. This can be seen on Figure 17 of the data sheet for the ADG5412.

Regards,

Sean

• Sean:

What about the capacitance of Cds ? It is very important for me to evaluate the switch in the off condition. Where can I find this capacitance Cds?

Thanks

Regards

Jacky

2012-11-17

• Hello Jacky,

We don't measure or specify Cds, but this can usually be approximated by subtracting the Cs(OFF) and Cd(OFF) from the Cds(ON).

These specifications are usually typical values and this method has better results with the ADG12xx series of parts which are given maximum specifications for the capacitances.

Regards,

Sean