BQ2970: doesn't work as expected

Vincenzo Pizzolante

Part Number: BQ2970
Other Parts Discussed in Thread: PMP4496,

hi all,

We have a question about bq2970 battery protection IC in our project. We are using CSD83325 Dual N-Channel MOS as external power FET. We are using the same application as shown in IC’s datasheet in Figure 26 and same schematic as shown in TI application number PMP4496 (USB-C DRP Power Bank With Fast Charger Input R). Pin PACK- is connected to ground (or charger ground when it is connected).

While testing circuit in “test condition” showed in 8.2, we saw correct reaction from overcharge and over-discharge protection logic. We used schematics showed in Figure 20 and Figure 21.

Problem appear when battery is attached. Without charger (external voltage on PACK+), the bq2970 appear in fault state and close the D FET which prevent battery to work on load. When charger is connected it should bring back the normal state as we can see in caution note, but in our case, it closes the C FET which don’t allow battery to charge. Battery voltage is always 3.5 V, so no fault conditions should appear. Connecting V- and VSS for voltage equality helps only sometimes, but it neglects all protection anyway and useless in the real-life circuit design.

any advice is more than welcome

Vincenzo

over 6 years ago

0 Vish Nadarajah over 6 years ago

TI__Expert 6085 points

Hi Vincenzo,
Please check the integrity of the resistor that is hooked btween the V- node to the PAC-. This is importan to provide isolation for V- and PACk - transients. Also may be affecting the Vshort threshold

0 Vincenzo Pizzolante over 6 years ago in reply to Vish Nadarajah

TI__Mastermind 22756 points

hi Vish Nadarajah,

I sent an EVM to customer, so we can remove all the variables related to customer's design...
It is working fine, but there is an open point: when battery is taken out and getting back again, IC doesn’t enable discharging circuit and doesn’t allow battery to connect to the system. According to datasheet info, it can be fixed by adding the charger or shorting V- pin to the VSS pin.
But this creates some difficulties for mobile use, in case battery need to be removed.
Can we do something to avoid this IC state?

thanks a lot in advance
KR
Vincenzo

0 Vincenzo Pizzolante over 6 years ago in reply to Vincenzo Pizzolante

TI__Mastermind 22756 points

Hi Vish / all,

Any comment on this?

Vincenzo

0 Miguel Angel Rios over 6 years ago in reply to Vincenzo Pizzolante

TI__Expert 4640 points

Hi Vincenzo,

This is because the battery protector is meant to be always on and attached to the bare cell. If you are removing the cell away from the protector each time then you will have to either add a charger or short those pins. Where is the bq2970 placed in the system in reference to the battery pack? and Why?

Thanks

Miguel

Power management

Power management forum

BQ2970: doesn't work as expected