BQ24161 STAT output pin

Hi Sergio,

Thanks again for your quick response. I am still seeing the charging LED lighted when the charger is disconnected from the device, and the device is powered from the battery.  I have attempted to address all of your comments and questions below:

1. I have rewired the circuit so that the charging LED is wired between the STAT pin and the DRV pin via a 120 ohm resister.  

2. I am not sure how to determine the VBATREG setting.  The BQ24161 is connected to a BQ27530-g1 which I communicate with via its I2C bus. The BQ27530 is reporting that the battery is 74% full and has a voltage of 3.942 volts.

3. I took a look at Figure 16 of the datasheet and compared the waveforms to the SYS and BAT pins on the BQ24161 when the issue is exhibited.  The SYS pin looks about the same as the signal shown in Figure 16.  The BAT pin waveform looks almost identical to the SYS pin waveform, except that it may be slightly lower voltage in places (maybe a few 10s of millivolts).

4. One other observation: the issue only exhibits when the battery is under higher loads (>400mA).

Is there any other information I can provide that might shed light on the cause of this issue?

With thanks, Andy.

Hi Andrew,

I would highly recommend to go through the section 9.3.16.5 of the datasheet. It is pretty well explained why and what happens when the reverse boost prevention circuit is working.

Let me know if you have further questions.

Sergio

Sergio,

Issue: When the charger is disconnected but the device is powered on (by which I mean that power is being drawn from the battery by a load, and the battery is not being charged) the charging LED is still lighted - STAT is still active.  The charging LED is placed between the STAT pin and the DRV pin via a 120 ohm resister.

VBATREG is set at 4.2 volts (inc. offset).  The battery voltage can be as low as 3.7 volts yet the issue will still occur.  It only occurs at higher loads, and the load is pulsatile.    Section section 9.3.16.5 says the "The reverse current protection is only active when VBOVP > VBAT > VBATREG - VRCH."

As VBAT is not greater than VBATREG, I don't think this should be the issue.  Also, although I see some dipping in the VSYS waveform, it is not 100 mV at a 1msec interval. It is at about 250 usec intervals.

Therefore, from the description in section 9.3.16.5 of the datasheet, it seems unlikely that the Reverse Boost (Boost Back) Prevention Circuit is being activated.

I'm still looking for some direction on resolving this issue, and look forward to hearing back from you.

Andy

Hi Andrew,

I see your point. Actually I might need to check in the lab.

I will let you know as soon as I have something.

In the meantime if you can send me the register setup and give me some information on the load (voltage and current) so that I can have the same set-up as you in the lab.

Thanks.

Sergio

Hi Sergio,

The load is very high at about 5A peak triangular pulses from a baseline of about 100mA.  One cycle is 100mA for 130uS then a ramp up to 5A over 50uS, then a ramp down to 100mA over 100msecs.

When I unplud (disconnect) the charger, the STAT pin stays active.

I have included a zip file with:

1. A copy of the programming file for the battery management circuit.  This programs the bq27530 which controls the bq24161.

2. A snippet of the circuit showing the bq24161 and bq27530.

Thanks again for your help.

Regards, AndybattZip.zip

6562.ScreenShots.zipHi Sergio,

I use TI GaugeStudio. I have attached screen shots from that (files b15 to b23).  I also have BQ Gas Guage Evaluation Software.  I have attached a screenshot from this (file b24).

Regards, Andy

Hi Steve,
I am not sure I fully understand what you are suggesting. But first to answer your question and respond to your comments:

Your question: you using the gauge to control the charger, correct?
My answer: Yes. As per the Texas Instruments document SLUUA09A titled "bq27530EVM with bq27530 Battery Management Unit Impedance Track™ Fuel Gauge and bq24161 2.5-A, DualInput, Switch-Mode Battery Charger for Single-Cell Applications"

Your comment: The gauge likely disables auto termination by the charger and disables charge when the battery voltage reaches regulation. When termination is disabled, the STAT pin does not turn off because the charger terminates
My response: Why would it work differently when a small load is applied as opposed to the larger load. Surely if this were the problem, it would be a problem whatever the load. As you know, this is only an issue when the high load (5A pulses) is applied. Also, why would TI recommend a configuration that doesn't fully support the STAT function? Perhaps I am missing your point. Please help me to understand.

Your comment: Also, 120 ohm resistor is too small for STAT pull up. Abs max current into STAT pin is 10mA.
My response: Good catch Sergio. I am changing that to 470 ohms. But I doubt that is the cause of this issue.

Just to reiterate (I know you already know the problem, but just for completeness):
1. The problem is that the charging LED stays ON when the charger has been disconnected, and the load is being supplied by the battery.
2. This is NOT a problem if the load is light, but is a problem at the heavier loads (5A pulses - see earlier comments)

Sergio - How did your bench testing go?

Steve and Sergio - I look forward to your continued help.

Andy

Thanks Sergio.  I look forward to your response. Regards, Andy

Sergio,

Do you have an idea when you might be able to respond to this query?

Thanks, Andy

Sergio,

I confirm that it is wired correctly and that DRV is not low when the voltage to the IN pin is removed, when the load is as specified in earlier posts.  The schematic that was sent, was before the change to the wiring of the LED charging LED (please review earlier posts).

I thought that you were going to preform the test with the SAME load and the SAME register settings.  It acts as you say when a lower or non-pulsitile load is applied.

Andy

To confirm, DRV output is not available when the IC is powered from battery only so there is no voltage to turn on the LED, pulled up through resistor to DRV, when battery only is applied.

I am telling you that under the register configuration and the specific load described, there is a voltage at that pin.