BQ25622E: On POR, anyway to force charging into battery terminal even if no battery detected?

I cant provide a waveform as I don't have a battery discharged on my workbench. This is a demo product in the field currently. 

I think you may have misunderstood my post. 

In a POR, the charger leaves the battery terminals at 0, until a voltage is introduced externally by a battery.

You say it doesn't have a battery detection function... I'm assuming you mean something that is broken out to the user via a register... But it does indeed detect a battery present...

What I need is a way to trick this into kicking in and forcing a charge cycle (trickle charge) on a battery thats going to present as 0V as its BMS has past its threshold. It will only wake up when theres an external voltage supply is being given...

Its only on POR that the terminals will be 0, once a voltage is present this all wakes up and will charge the dead battery. But we cant physically swap batteries around.

So anyway of trigging it into starting?

Hi Garrett Kreger,

Just to clarify what we see a bit further in hopes you can help:

• If an external supply is connected and the BQ is in charging mode:
  • The battery terminals will continue to receive power as long as a battery has been present at some point.
  • This remains true even if there is no battery currently in the terminal.
• The battery we are using shows 0 volts when its protection mode is enabled.
• If the external supply is not removed and the BQ itself has not lost all power:
  • Inserting a battery that is currently in protection mode into the terminals will wake it up and start charging.
• If the external supply has been removed and the BQ itself has lost all power:
  • Simply reconnecting the external supply will not wake the battery from protection mode as the charging cycle won't start.

Having received the protected cell at my location, I have "fully" discharged the battery and now confirmed that the battery reads 0 as its past its built in BMS threshold. 

The BQ charger is not triggering a charge cycle when external power is applied, and the battery terminals remain zero. 

The goal is to force a charge cycle and get voltage on the terminals. This will wake up the batteries BMS and charging should just work as normal (though be it trickle charge to begin with) 

Ive included a wave. The yellow is the wave off the battery terminals. The currently 0 reading battery is attached. The blue is the external supply, provided by a PSU being powered on. Set to 11V (for some reason reading as 11.2) 

As you can see at no point is any voltage being applied to the battery terminal. And Charge enabled by the register, and CE# is set low.

Hi Simon and Alan, 

Thank you for your replies. Please see my comments below. 

The behavior you show in the provided waveform is not expected. The waveform I provided in my last response shows expected behavior with a depleted battery with all register settings in default configuration. As long as /CE pin is pulled low the device will attempt to start charging. There is no way to "force a charge cycle" beyond pulling /CE pin low and setting EN_CHG = 1b.

Can you please help to double check that /CE pin remains pulled low throughout the duration of your test? 

Can you please help to answer a few additional questions to aid in debug as well. 

-In your waveform is the battery voltage measured at the BQ25622E BAT output or at the actual battery terminals? If you are not doing so already please measure BAT pin voltage before the protection circuit. 

-In your test where charge does not begin can you check if SYS voltage is being regulated to the expected value (i.e. above SYSMIN setting)?

-Can you please provide a single read (i.e. register dump) of all BQ25628E registers during time when external supply is provided, but battery is not charging? 

-Can you please repeat the test with no battery connected rather than a BQ which has lost all power? Expectation is BAT pin output voltage will increase to approx. full charge voltage setting. 

Best Regards,

Garrett

Hi Garrett I can do those tests tomorrow, but in the mean time can you tell me the status of the QON pin in your setup?

In our design QON is left floating as according to the datasheet it was optional and we dont have a user operated on switch. 

Hi Simon, 

QON pin is also floating in my setup. With default I2C configuration QON status will not impact ability to charge. 

Best Regards,

Garrett 

Thank you. Was hoping that was the case.

While ill do the rest of the tests tomorrow I can confirm CE is low by my reading off the oscilloscope. 

Garret, I want to thank you for your time looking into this.... I made the register dump and then did one last couple of tests and reread your post, and made me think to check something.... And I've discovered what the problem is, and it is to do with our design.

We have a reverse polarity protection circuit on the PCB. Separate from the batteries built in protection. I was testing from the battery terminal but not from the charger side of that PCB protection...

Yes indeed the charger is providing a voltage, but with the battery being 0 it wasn't charging the nfet that opened up the reverse polarity protection circuit. 

I hope you don't feel we wasted your time, as your help has been really great and got me to find the real issue. 

Thank you again for your help.

Kind regards

Simon