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!