Problem with noise in LCA110 chip used in phone line

[eric_yeow]

Chip LCA110

Friends:

I am using LCA110 chip to connect phone line for realizing hook-off function in a system design. The hook-off circuit is included two transistors and few capacitors. One transistor’s emitter has been connected to the ground by 1UF poly capacitor. Pin2 of the LCA110 is set to logic 0 by 8051.
The wired thing is when Pin2 of the LCA110 is set to 0; few seconds later, the noise is coming out.
What are the possible reasons for it?
Thank you for your suggestions. 8O

 

[vfone]

Re: Chip LCA110

Maybe your microcontroller cannot supply the Input Control Current.
For LCA110 the control current (LED) can be between 2mA and 50mA