Help identify 3 pin smd element marked A22020

[Gentian]

I am not able to identify this element marked A22020. Some short indexes suggest it is a n-channel mosfet or a pnp transistor. I measured it and it looks to have only a very small capacitance between pins 2 and 3. Any suggestion would be very important. In my experience whatever it should be a dead component. The device is a level radar which looks no current consumption although 12V and 3.3v are ok at MCU and in the circuit but no data transmission?

[stj]

does the pcb have any clues?
like markings or the suspected base pin going to a resistor?

my lookup has several possibility's including:
a 2.2v regulator
a regular mosfet,
and an RF amplifier fet.

[Gentian]

Dear Great Sage thanks for your help. I am attaching a photo of pcb where the 3 pins element is connected. Referring to standard 3 pins smd pin numbering I see that pin 3 goes to Ground and pin 1 and 2 goes to these 2 identical chips above and measuring in the device terminal (RS-485 terminal 2 and 3) pins 1 and 2 of A22020 have a resistance of 9 Ohms each to respective RS-485 terminals so pin 2 and 3 in the output terminal. My Device (RLS hydrologic meter) doesn't transmit data anymore from pin 6 of the terminal but no short circuit anywhere in the circuit although all voltages look ok.

[truclacicr]

The two preceding Bourns devices appear to be this (TBU-CA065-200-WH):

https://docs.rs-online.com/00c6/A700000006416237.pdf

https://ae-pic-a1.aliexpress-media.com/kf/S80d48d2208cf451794d7e96aac63d2a8K.jpg (photo)

It's an over-current protector. Page 3 shows them connected to two overvoltage protectors which are connected to ground. Therefore I expect that the mystery device has one ground pin and two input pins, probably two TVS diodes or two ESD protection diodes in the one package.

Something like this ...

https://www.diodes.com/assets/Datash...SD2CAN2SOQ.pdf

[adam7]

I believe, that it is CDSOT23-SM712 - Surface Mount TVS Diode from Bourns.

[stj]

it looks like it's doing line protection,
but it's very small for such a task - which may explain it's demise

[truclacicr]

https://www.bourns.com/docs/Product-...OT23-SM712.pdf

[truclacicr]

it looks like it's doing line protection,
but it's very small for such a task - which may explain it's demise

It may not be dead. It should normally measure OC on all its pins. In fact, the circuit should work without it.

[adam7]

It may not be dead. It should normally measure OC on all its pins. In fact, the circuit should work without it.

I completely agree.

[Gentian]

Thanks very much for your help. Yes, I think now A22020 is SPD and looks it is not defective as I thought yesterday. I am checking the circuit for any other issue, and I am seeing no signal in the MCU oscillator. Checking it out board and also its 2 small capacitors everything looks ok. Maybe MCU fault but it is another topic.

Thanks again for your help!