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BQ4050: Provide output power at power on

Donovan Sydow
Intellectual 300 points
Part Number: BQ4050

Hello, I'm trying to find out if there is a way I can enable the PACK+ output on the BQ4050 without tying in a "wake" button or FET_EN command, or similar physical button to it, so it will turn on as soon as the battery is connected. I have tried to set the wake voltage as low as possible, enabled FET_EN via Manufacturer Access, among many other settings. Is there a list of options I can program on the firmware that would enable this to always be on? I am hoping I can do this so I don't have to redesign my board (that doesn't have a wake button), with a special circuit that only temporarily fires a short to PACK+ when a battery is connected. 

  • 0
    TI__Mastermind 42535 points
    No, there is no way to wake the device without a voltage on the PACK pin.
  • 0 in reply to Batt
    Intellectual 300 points

    That's odd, because as soon as I plugged in a new battery today, it turned on automatically. Are you sure this can't ben enabled?

  • 0 in reply to Donovan Sydow
    TI__Mastermind 42535 points
    Donovan, what I meant was if your battery is removable and your system present pin isn't grounded (NR in DA configuration set to 0), then your fets won't be turned on. Your fets are enabled for normal operation once you send the FET enable command. If you have auto shutdown enabled, you will need VPACK for the gauge to wake up.
  • 0 in reply to Batt
    Intellectual 300 points
    So are you saying the combination that would work for automatic turn on it to set NR to 1, and FET_EN to 1? Or is there another combination? I turned down the wake voltage all the way, but I think that kept it powered on as it destroyed a battery over the weekend draining it from 16.8V to 1.7v even though the cut off voltage was set to 13v.
  • 0 in reply to Donovan Sydow
    TI__Mastermind 42535 points

    Setting NR=1 means your battery is non removable. What this would do is that if your battery exceeds certain safety thresholds only a drop below the said threshold would result in protective actions being cleared. You will always need to have FET_EN set to 1. There is no reason to manually turn it off using your uc. The gauge will handle all safety conditions to turn off your FET as and when required. For this you need to have the appropriate protections enabled. What is the wake voltage parameter that you are referring to? Is the the charger present voltage? If yes, then the device will wake up only if the voltage threshold is above the charger present threshold. That has nothing to do with destroying your battery.

    Your gauge if separated from the pack (system side gauge) will wake up from a cmd base shutdown if a pack insertion or Vpack is detected. For emergency shutdown a pack insertion is required to turn on the gauge after shutdown.

    This gauge is mostly used pack side (meaning the gauge is with the battery all the time) and can be inserted into the system as and when required.

  • 0 in reply to Batt
    Intellectual 300 points
    Sorry I meant the wake comparator. No, the charger is normally not present when the battery is plugged in. Although if I plug in the charger after the battery is present, then the device battery side will turn on. I swore I was able to get play with the different settings to get it come up after a battery insertion without having the charger present. back flowing voltage to the PACK+ pin. I'm not able to replicate this. Is there any way around this? Even with FET_EN I can't get it to output power without apply PACK+ power. Would this work with PRES grounded, and NR bit set to 0?
  • 0 in reply to Donovan Sydow
    TI__Mastermind 42535 points
    Oh, OK. The gauge will always be in sleep mode when the current is below sleep current. In this state it will take measurements every 20s. In your case I suggest that you set NR=0 and ground the PRES pin to allow PRES bit to be set in the registers. That will detect system present.
  • 0 in reply to Batt
    Intellectual 300 points
    Still not able to replicate a bq4050 to wake when the battery is inserted. I have FET_EN=1 NR=0, PRES grounded. In this configuration if the battery is inserted that BQ4050 stays off, even though powered, and with SDA,SCL connected. Only once I short BAT to PACK will the it turn on, and outputs power.
  • 0 in reply to Donovan Sydow
    TI__Mastermind 42535 points
    Now you have me thoroughly confused. If you want the gauge to wake up from a shutdown event, you need to have a PACK voltage detected. So, there's no way of getting around that without having a PACK V. However, if you want the gauge to wake from sleep on detecting a current, you can toggle the thresholds on the wake comparator. Based on the settings for RSNS0,1,IWAKE and the value of your sense resistor you can change the wake threshold for the gauge to enter active mode from sleep.