BQ40Z60: Power path configuration

• Hi,
• Could you share your mosfet part number ?
• Have you chnaged the OCC1:Delay and OCC2:Delay time? If the delay time is long, you may see this condition

Hi Terry,

Thanks for your response and help!

I am using TI CSD17573Q5B for the CHG and DSG FETs.

For the HIDRV and LODRV FETs for switching I am using TI CSD17308Q3.

I plan on providing a maximum of 5A from the AC adapter to the system and for charging. But I am using high discharge Li-ion cells that I hope to discharge at up to 20A for short duration.

Damian,

Thanks for the reply and assistance.

Thank you for pointing this out to me. You are correct that I may exceed the max spec for the coulomb counter. Can I reduce the Rsns resistor to ensure that I don't exceed the spec? Will that cause any problems with other parts of the system?

If I do change the value of Rsns, would running a simple current calibration be all that would be needed to make sure current is read properly?

Thanks again for your help.

Hi Chris,

0.005 ohms is the minimum recommended RSNS for bq40z60. You can try using a smaller value, but the risk is gauge current measurement and charger current accuracy.

Thanks Damian,

Another question:

I have an AC adapter that can supply 5A. My Li-Ion cells are recommended to be charged at 2.5A.
When charging, I would like whatever current from the adapter that is not being used to charge the battery to be available to my system. When not charging, the system should draw first from the adapter until the 5A limit of the adapter is reached at this point the battery should supplement the adapter until the discharge limit of both the adapter and battery are reached.

It seems like to do this I would need to set three thresholds. I only know of two. I can set the discharge threshold using AOLD, I can set the charge current under various temperatures using the Advanced Charge Algorithm section. Where do I set the current limit from the AC adapter?

thanks,

Chris

Hi Chris,

What is the voltage of your AC adapter? Can your system run off adapter voltage? There's no place to set the adapter current limit. The requirement is that the adapter can supply the max charge current or more. The switch mode charger in bq40z60 then regulates the battery charge current. If you want an additional 2.5A to be available to the system you may need an 2.5A SMPS connected to the AC adapter and your system. The gauge in the bq40z60 will help with regulating the battery charge/discharge currents.

I'm not aware of a better way to accomplish this with just bq40z60.

Hi Damian,

The AC adapter is a 14VDC adapter. Our system was designed to run off a wide input range so that you can run either off the adapter or the battery. The system should operate over a range of 14-7.5 VDC.

Currently what happens in the circuit is, when the battery is fully charged the Vsys is at the adapter voltage. When I start to draw current from the system the adapter supplies all the current until it reaches the max charge current. At this point it switches over to the battery providing all the current and the adapter is no longer sourcing any current.

From looking at the circuit it seems like the circuit could behave the way we need it to, but it may take a firmware change. There are two locations where current is being monitored. HSRP, HSRN measures the current provided from the switching regulator and SRP. SRN measure current in and out of the battery. It seems that you could set a threshold for current through HSRP,HSRN to be the adapter max current. Then all you would need to know is current in and out of battery. The circuit can already limit the current supplied through the switcher it really just needs to look at the current into the battery (SRP,SRN) instead of the current supplied by the switcher (HSRP, HSRN). The current sensed by HSRP, HSRN should be the max adapter current threshold. Is there a possibility to get a custom firmware build?

Hi Chris,

How about connecting the AC adapter to the charger and system and use a schottky diode to determine when the charger and/or battery kicks in to supplement power?

Hi Damian,

This is an option. I am concerned though that I would need to draw more than the adapters rated current to get the voltage to drop to a point where the battery would start supplementing. If I did this method I would probably add a current limited switching power supply to the adapter side to make sure the adapter was kept in its rated current range.

Is there a way to discuss the possibility of getting a custom firmware build to use the charger switching regulator to do this? We would be willing to pay for any development. As I have searched the E2E forums it looks like this feature has been requested multiple times.

thanks,

Chris Jones

Hi Chris,

The SMPS would be a better option to limits the system current draw, if you don't want the battery to supplement power when the charge is enabled. The firmware change option is a non starter.