Analog telephone circuit and TEA1062 [closed]

Question

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

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

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

4. MCU

Here is MCU circuit diagram. Some keypads and GPIOs.

5. Line (TEA1062AT)!!!

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:

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?

Answer 1

First of all, TEA1062(A) is dead. It's been obsolete for years so you should get rid of it if you plan for serial production. Last time I designed a TEA1062-based circuit was 6 or 7 years ago and the company was trying to find and purchase the last TEA1062(A) chips on Earth! A Taiwan-based company (I'm not gonna give their name) "copied" Philip's original TEA1062(A) chip. I don't know if they still manufacture and sell 1062s, but personally, I wouldn't trust those copy chips to be honest.

Anyway, your line circuitry looks problematic. You can't use a DC voltage directly through a resistor for LN supply of the chip. Here's the circuit I used in my designs:

^{simulate this circuit – Schematic created using CircuitLab}

Build this and use in your design. And everything will be fine.

NOTE: 8V source should be able to supply at least 1A.