Identify SOT-23 SMD that should work like a bidirectional switch?

Hello,

The SMD mark is A1VV and it is a SOT-23 (3 pin) package. I couldn't find this code anywhere, nor even Google recognizes it. I found a 2011 SMD Codes Catalog and it ain't there either. The only A1 is an SMD with a common anode pair of small signal diodes.

The device was an electronic cigarette battery (closed system, not just the cell). I actually have 3 of them, ALL of them with that SMD shorted. So I can't measure it somehow.

The battery is based on a PIC16F722 uC. When you press a push on button on the battery, a small LCD powers on and shows how many times the button was pushed till last charge (number of puffs), and a battery level indicator. Also a coil is connected on the battery for as long as you keep the button pressed. When you want to charge the battery, you remove the coil and connect the charger through the same contacts the coil was connected.

The 3-pin SOT-23 SMD is connected like this:
1- uC OUT through a 4K7 resistor (normally HI, LOW when button is pressed or battery connected on charger)
2- Vdd
3- Coil or Charger

Now, when 1 is LOW 2 and 3 should be connected. At first I thought it was a PNP transistor but first of all this thing needs to push large amounts of current on the coil (2-3A) through a very small input from the uC (25mA output max) and secondly, when connected to the charger, the current should flow the opposite direction TO the battery! So it should be bidirectional and this probably means it is not a BJT.

With the SMD shorted the uC mistakenly recognizes being connected on a charger forever because the Coil/Charger (3) pin is connected with Vss (2). I guess, without the button being pressed this is recognized as power flowing in from a charger.

Does anyone have a clue what this thing is? Like a solid state relay with a common pin? What else could it be?

Thank you in advance!

A P-channel MOSFET?

babylonx said:

when 1 is LOW 2 and 3 should be connected

Click to expand...

this sounds like P-channel; maybe you meant Vcc instead of Vss?

First of all, thank you all for your answers!

Yes, I mean the Vcc, the + pole of the battery, call it how you want! Vss is how microchip calls it in the datasheets, that's why I used it like this.

I will try a Si2312 and see if it works!

Yes, I mean the Vcc, the + pole of the battery, call it how you want! Vss is how microchip calls it in the datasheets, that's why I used it like this.

Click to expand...

I never saw the positive supply node named Vss in a datasheet. If pin 2 is the positive supply node and pin 1 more negative tahn pin 2, you'll expect a PMOS FET like Si2323.

Check double V maybe is W.

A1W BAW56 High-speed double diode - A1 and W for made in china.

On A1VV nothing.

I already tried this. A1 and A1W are the same BAW56 component. Before checking what was going on with the pins I tried connecting two 1N4148 diodes but of course it didn't work! First of all BAW56 can't carry such currents and secondly it does not make any sense considering the pin configuration! Also I checked the component under a magnifying glass after cleaning it with isopropyl alcohol to remove flux residue and it is definitely A1VV and not W. The V's have enough space between them.

I see now that I was wrong, Vss is Ground. I meant Vdd/Vcc!

babylonx said:

I will try a Si2312 and see if it works![...]I see now that I was wrong, Vss is Ground. I meant Vdd/Vcc!

Click to expand...

Vcc makes sense ... don't waste time with the Si2312, you need a P-channel here!

iI already had success with an Si4835 that I removed from a dead laptop motherboard. It is a P-Channel of course but it is SOIC-8 package. It doesn't even get warm! I already ordered a few Si2307 to test. That was the only one in stock and I know it is a little small but I think it will do. If it doesn't I'll try to find a bigger Si23xx.