BQ24090: Using protected battery causes the part to fail?

Hello
The bq24090 has battery short protection, this is active when the voltage a OUT pin is below 0.8V and the current is limited to 15mA. If system has a load on the OUT pin during this time it may prevent the voltage from increasing to pre-charge level of 2.5V.

What can you tell me about the short protection? Is this resettable, or a one-time fuse-type device?  For the failing devices (we have two of them), it is clear that applying power when the battery is dead and the power drain is <50mA still results in the failure, while our other boards built the same way have reasonable pre-charge voltages.

Due to the nature of the load, there is the possibility that the startup load could be as high as 700mA. My understanding of how we picked the resistors is that this should have been a non-issue.

Since although there are 30 or so of these units in operation, the problem only appeared when we switched from unprotected cells to protected cells, I'm wondering whether the short-detection circuitry can get confused by the protection circuit on the battery? Is this something that has been tested?

Hello
"What can you tell me about the short protection? Is this resettable, or a one-time fuse-type device?" --Bill J -- This is not a fuse or one-time device. The short circuit protection is an active circuit that monitors output voltage and restricts current base on battery voltage.
Battery Voltage 0.8V or less -- Short circuit protection current limited to 15mA
Battery Voltage 0.8V to 2.5V -- Precharge mode current limit set by PRE-TERM pin, typically 20% of fast charge (ISET).
Battery Voltage 2.5V to 4.2V -- Fast charge current set by ISET pin

The device is looking for a voltage on the battery (OUT) if the protector circuit is open no voltage is present and only 15mA will be available. The protector may need a voltage level or current to reset and connect battery to charger. If system load is connected the voltage may not rise enough for protector to reset.

This seems like a pretty fundamental design flaw - is there a known workaround to the part of the circuit that limits the current to 15mA? this was NOT described in the data sheet.

We designed with the pre-charge current that was documented:

"If the battery voltage is below the LOWV threshold, the battery is considered discharged and a preconditioning
cycle begins. The amount of precharge current can be programmed using the PRE-TERM pin which programs a
percent of fast charge current (10 to 100%) as the precharge current. This feature is useful when the system load
is connected across the battery “stealing” the battery current. The precharge current can be set higher to account
for the system loading while allowing the battery to be properly conditioned. The PRE-TERM pin is a dual
function pin which sets the precharge current level and the termination threshold level. The termination "current
threshold" is always half of the precharge programmed current level."

The 15mA limit clearly breaks everything - with a load that at startup might be as high as 750mA, 15mA isn't going to do anything and we'll end up with more bricked devices.

Given that we have over 100 of these already built, what can you suggest, please?

So I left one of the failed units plugged in overnight. The external load is disconnected, so the actual load is <10mA. Measured voltage across the cell is 1.27V. DC current is 55mA. This suggests that the chip is allowing a very very very slow charge - this corresponds to neither your description of the short-detection circuit nor the datasheet's description of the expected pre-charge behavior. Should I try replacing the chip itself?

Try testing the charger with a large capacitor, 1000uF to 100,000uF in place of the battery.  It should go thru the different charge phase stopping at 4.2V.  I set up an EVM with 9.1k pre-term and 576 ISET and charged a 100,000uF capacitor from 0V to 4.2V.  See attached, noted V-BAT should be Current To Capacitor.

I am trying to understand the battery protection circuit do you have any additional info on the protected Panasonic NCR 18650B?
Have you been able to reset the protect circuit and recharge one of the cells?