I used to micom connect ADG451 1,8,9,16(in)pins
but, After turning off the +15v/-15v power, my microcomputer started to heat up. What is the reason?
Do I need a switching circuit (TR/FET) on pins 1,8,9,16?
The ADG451 IN pins have internal esd protection diodes. it is likely that you have violated the max ratings of the ADG451.
The digital inputs must be kept with in 2 volts of the supply.
To prevent this you could consider our overvoltage protection switches such as the ADG5412F.
These devices can stand off voltages up to 48 V on the digital pins, both in the power on and power off condition.