Bq20z65-R1 with Bq24725

Markus

You can connect the bq20z65-R1, bq24725 and host to the same bus. The bq20z65-R1 can be configured to support PEC in the host and charger. There is another applications note on the bq24725 website (SLUA608) that discuss the setup without the host controller, but it should can be used for your setup as well.

Regards
Tom

 Thanks Tom.

I was able to set up the system as I wanted and it works but I have another question about the bq20z65-R1.
I connected the battery stack (4s1p 4000mAh) to the gas gauge and kick started it by applying a voltage higher than 6V to the pack pin. Then I disconnected the battery stack and reconnected it again. Sometimes the device is powered and the battery voltage is measured on the pack pin. Sometimes the device is not powered. Why is this happening? Is it important that the indivual cells ar connected in a specific order (I use a 5pole jack to connect battery, so all cells are plugged at the same time)? Is it important that CHG and DSG FET were on when the battery stack was removed ? Or any other problems?

In my end application. I will implement a 'mechanical switch'  to power and shut down the end-system. This euquals a connection and disconnection of the battery pack. And I'm expecting that the gas gauge is working and powered up by the battery eachtime I reconnect the battery. Unless the battery voltage is below or near the undevoltage protection of course. Then I understand why I have to use the charger to kick-start the gauge again.
Is this scenario supported? And would you recommend using the non-removal mode [NR=1] or the normal mode [NR=0]. And is it neccessary to pull the Pres pin down manually each time the battery stack is inserted in the system, or is there a way that the gas gauge detects this on its own?

Thanks for you help,

Markus

Markus,

If you do not have voltage applied to Pack+ and you remove the batteries, then the device will go into shutdown. You noted that sometimes the device wakes up after you reinstall the batteries and sometimes it does not. You should not count on it waking up. Maybe some residual voltage was present in the capacitors and this keeps the device awake. You should plan on applying voltage to the Pack+ pin after you have installed the batteries to wake-up the device. We recommend attaching the cells from the lowest one in the stack and moving up the stack if they are attached one at a time. You can attach them simultaneously with a switch.

The CHG and DSG FETs do not have to be off when you remove the cells.

The non-removable mode refers to whether the pack can be removed from the system and not whether the batteries are separated from the device. You can set the NR bit to a 1, if you do not want to use the PRES input.

Regards
Tom

Hi Tom,

I understand that the device will go in shutdown if there are no batteries connected. But if the battery is not connected then the device will go in shutdown, whether there is voltage >6V applied to the pack+ or not. First I also thought that the device wakes up after I reconnect the battery because of some residual voltage. But, I also tried the procedure after 10 hours (disconnected battery and 10 hours later I connected it again)  and the device was woken up (I did not apply external voltage to the Pack+ Pin). So this effect is surely not caused by residual voltage of some capacitors. But, when you look at the schematic of the bq20z65 evaluation module it is obvious that the voltage on the Pack+ Pin comes whether from the Pack+ input (external) or if the charge and discharge FETs are on, from the battery stack.

I guess I should try to explain to scenarios I'm interested in:

1) I want some kind of On/Off switch for my whole system. How can I achive this? If I understand right what you explained, this should work by using the removal mode. So when the switch is in 'On' position, the Pres Pin should be pulled low and then the charge and discharge FETs are on and it is possible to charge or discharge the battery stack. If switch is 'Off', the Pres Pin is pulled high by the internal pull-up. Consequently, charging and discharging is disabled. Am I right?
But this also means that the battery stack needs to be connected to the device throughout the whole time? And that the gas gauge is supplied by the battery stack drawing 6mA (I would call this standby). So my question is: when I think of Laptops I also have a 'on-off' switch. And does off then mean that the gas gauge is running drawing current from battery stack.Or that the battery is completely removed so that no current is drawn.

2) Again the laptop example. I can take out the battery and but it in again and the laptop is working  without the need of connecting an adapter. Is it possible to implement this feature with the above mentioned devices (bq20z65 and bq24725). So far I understod that waking up the gas gauge is just possible by applying external voltage to the pack+ pin (from adapter + LDO for example). But why do I need something else than the battery stack to wake up the gas gauge? I understand that I need the adapter for device wake up if my battery stack is discharged to lower threshold, but why before? And if I'd use the battery stack directly to wake up the device (battery + LDO + Diode on the pack+ pin) I will always draw some current even if the battery is in an undervoltage condition what would mean that the batty is destroyed.

Thanks for your answers,

Markus

Tom,

Thank you for your suggestions. I'll try to implement the wanted funcionality using the PRES Pin.

It would be great if you could answer another question concerning the bq20z65. I connected the charger to the Pack+/- Pins of the gas gauge. The charger started charging with the specs given by the gas gauge. So broadcasting and balancing work fine. If I disconnect, the adapter form the charger the load (a 10k) is supplied by the battery stack. So adapter detection switiching between power sources work fine. But if I connect the Pack+/- Pins of the gas gauge to the charger (no adapter present) the gas gauge always reports a short circuit condition in discharge (SCD=1, and CHG and DSG FETs are disabled). Any suggestion why this is happening? And why it is working if I charge first?

Regards,

Markus