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BQ28Z610: Shutdown Mode - Voltage to PACK pin to wake up?

Xavier Bernard
Prodigy 200 points
Part Number: BQ28Z610

Hi all,

I recently bought the BQ28Z610EVM-532 eval kit and I am trying it right now. I watched the Youtube video: 

It runs through the basics of the EVM and BQ Studio. One of the manipulation that the guy says to do is to apply a voltage at the PACK pin, or press the S1 switch (with batteries connected) in order to wake the IC up from shutdown. Is it the only way to wake the IC up? There is not much about the state of the IC when it boots from scratch in the TDS.

I am designing a wireless product that will eventually be stored and transported. The user will not have access to the batteries, so they are always connected. It is a 2S LiFePO4 configuration that can be charged via a charger. That said, I want to make sure the battery will not discharge in the fuel gauge when the product is stored or transported, so I implemented a magnetic switch to toggle between the operational and storing modes. So with that switch, I would like to connect the PACK+ to the load, as well as waking up the fuel gauge from shutdown.

What would you recommend to do?

Thanks,

Xavier

  • 0
    Prodigy 200 points

    Hi again,

    Here is a schematic of what I tought would work:



    I don't need the OV protection since my charger takes care of that. Also my batteries have integrated OV and UV protections. So the CT52AN is the magnetic switch that latches when a magnet comes near (putting the product in operation mode). The PACK pin is connected to VC2 pin through the 5 ohm resistor so that the BQ wakes up. When the user swipes the magnet again, the switch latches off and the BQ goes back to shutdown. My question is: is it a problem to have a voltage on VC1 when the IC is in shutdown? Will there be a lot of leakage through VC1?

    Please tell me if yo see somwthing wrong with this circuit.

    Regards,

    Xavier

  • 0 in reply to Xavier Bernard
    TI__Mastermind 42535 points

    Your question has been assigned to me. I will answer it within the next 48 hours.

  • 0
    TI__Mastermind 42535 points
    Yes, a voltage at PACK is needed to wake up the gauge from shutdown. A switch as implemented by you will also wake up the gauge. Schematic is NOT OK. The 5Ohm is a balancing resistor. You need to connect the PACK after the DSG fet. In this case it's before it. If you have voltage at VC1, it will definitely have a lot of leakage through the gauge.
  • 0 in reply to Batt
    Prodigy 200 points

    Thanks Batt.

    I did some measurements with our Otii measurement source from Qoitech to check the consumption and leakage of the IC in different situations.

    When the chip is in shutdown mode and VC1 is at 3.2V (VC2 not connected), i get less than 1uA going inside. So thats OK with me. That is the state I want to be in when I am in shipping and storing mode. So I basically disconnect the 2P port of the battery pack and after there is only 1P connected to VC1. I also noticed that if VC2 is connected to PACK at this point, current will leak from VC1 to PACK from the internal mosfet's body diode. That current is over 500uA, so I need to avoid that. I need to disconnect VC2 from PACK when shpping and storing the product. I'll look after that.

    When I put 3.2V on VC1 and short VC1, VC2 and PACK together in order to wake up the fuel gauge, I get into a mode that draws about 870uA.

    When I remove the jumper between VC2 and PACK, it goes down to 220uA. This is the state I would like to get in for operation. So it means I need a circuit that will just send a pulse to PACK in order to wake up the fuel gauge. Thats a bit of a hassle, so that is why I wanted to know if there was any other HW and passive way of waking up the device.

    I dont want to have the charger to provide a voltage in order to wake up the fuel gauge. I want the battery to wake the fuel gauge via my switch. For that I need PACK to be connected to the battery, but if PACK is connected after the DSG FET, I short them and they are of no use. That is why I only want to use PACK as a wake up pin. I also need to find a way to disconnect PACK from VC2 at some point, since I found out that it drwas a lot more current.

    Do you understand the issue?

    Thanks,

    Xavier

  • 0 in reply to Xavier Bernard
    TI__Mastermind 42535 points
    No, there is no other way to wake up the device except pack. Your fets should be before the PACK pin input, the reason for this is we use the fet to break the circuit in case of an overvoltage or undervoltage condition. In your case VC2 is between the dsg fet and chg fet. So even if the dsg fet turns off your leakage path through the chg fet which will be ON for charging purposes will drain the battery. Unfortunately I don't see your PACK working this way.