ISO 124 isolation amplifier heating problem

Dear Friend

I am using ISO124 Precision Lowest-Cost ISOLATION AMPLIFIER in a data acquisition system. The no of channels for analog inputs is 40 so i am using 40 iso 124 isolators. when i am using upto 15 channels (15 iso 124 on board) the temprature of the iso 124 isolator remains on room tempeature but when i increase the no of isolators i.e. upto 40 the temperature of the chips increases and they started heating.  I am using DC/Dc converters for providing the supply to all 40 isolators.Each power-supply pin is bypassed with 1uF SMD ceramic capacitors located as close to the amplifier as possible.

 The data acuquisition is working fine but my main problem is why these chips are heated when used in bulk.

Can any one suggest about my problem.