I am currently working on an analog telephone project.

I have some questions. 

ICs and Central are below:

 1. Central: KX-NS500 (gives 28VDC)
 2. DTMF receiver: MT8870
 3. DTMF generator: HT9200B
 4. MCU: STM32WB10CCU5
 5. Line Mng. IC:  TEA1062AT
 6. Power IC: 3V3 fixed SMPS

Below is my circuit diagram with some details;

2. DTMF receiver

[![enter image description here][1]][1]

Here is the DTMF receiver with MT8870 IC. I built the transistor circuits because the datasheet says the IC's typical Vdd = 5.0V however it works fine with 3V3.

3. DTMF generator  

[![enter image description here][2]][2] 

Here is the tone generator circuit. It works in parallel mode. 

4. MCU

[![enter image description here][3]][3]

Here is MCU circuit diagram. Some keypads and GPIOs.

5. Line (TEA1062AT)!!!

[![enter image description here][4]][4]

Here are the TEA1062AT and line connection. J2 stands for "Hook Switch" and J3 for "Line Input".

Here I have some problems. 

First of all, when I supply all other ICs (receiver, generator, MCU) with 3V3 from the power supply (isolated from the TEA1062AT's Vcc) all of them work fine. I can send and receive DTMF tones. 

When I try to supply using the TEA1062At VCC pin (the datasheet says you can use this pin to supply peripherals,) the current from this pin is not being enough. 

When I upload empty code to MCU, I have stable 3.32V @VCC from TEA. (VCC_Line net) but when I try to send and receive some data from the MCU to the generator and receiver, that 3.32V oscillates. I tried to increase the current capability by lowering R114 and by increasing R93. It did not work. 

Then I tried get fixed fixed 3V3 voltage by using the circuit below:
 
[![enter image description here][5]][5]  
 
I take supply for this circuit from after R87 (voltage drop here is approximately 9V,) It works. This time I could not get the DTMF tone from TEA1062 line pin. 

Ok. 
- Is there any way to supply all peripherals without/with TEA1062AT?
- How can I interface with Central - TEA1062 IC?
- What is wrong in these circuits? 




 


  [1]: https://i.sstatic.net/EHF50.png
  [2]: https://i.sstatic.net/1PQD7.png
  [3]: https://i.sstatic.net/vW3Wf.png
  [4]: https://i.sstatic.net/lKgCE.png
  [5]: https://i.sstatic.net/oBz44.png