BQ25890: BQ25890

This circuit is a battery power monitoring and power control circuit used as a monitoring teaching pant for semiconductor process control equipment.
I've been designing and developing this chip for six months, but I haven't solved one problem yet.
We couldn't solve the symptoms of not being recharged when the battery was discharged.

So I added a circuit that cuts the battery at 3.2V to prevent it from being discharged. Of course, the microcontroller checked the battery voltage value and chose the method of hardware off the battery and battery charging IC.
It is designed to work like a smartphone.

Please check where the problem is.

I sent the circuit I designed to your email, but there is a message saying that I can't send it, how can I send my development data?

Hello, 

Firstly, I sent an email to the emails you listed in your initial post. You should be able to reply to the email to send me your circuit schematics. 

I also have a few comments on the charge settings you provided.

Change REG00 --> 7F. Bit 7, enable HIZ, is 1 and should be 0 to allow the device to charge. 

On REG06 what is the purpose of setting VREG to 4.53 V? You mention above that you are charging a 4.2V battery, so this value seems high. Based on the input sources you provided, +5V/2.6A, +9V/1.65A, the device will not be able to charge at 5A charge current set on REG04 because required Pout > provided Pin during fast charge.

Finally, when you are unable to recharge the discharged battery what is seen on the device? Is the BQ25890 providing any current to the battery? What is the charge status (REG0B) and is there a fault (REG0C)?

When the battery is below 3V the device should be in the precharge phase of the charge cycle. The IC should provide 1024 mA (the precharge setting on REG05) to the battery until battery voltage rises above 3 V.

Regards,

Garrett

Thanks for your assistance

First question : The reason why we set ut to 4.35V in REG06 it has a different between the voltage when we try to charge Battery as USB chaging
The difference is 200 to 350mV. so we set up to 4.35V in order to charge real battery Voltage.
So we set the charging mode voltage to 4.35V in order for the actual battery voltage to be charged to 4.2V, We want to charge up to 4.2V to increase battery usage time

When the battery discharge, and recharge again, The battery Voltage is 0 ~ 0.7V to PIN_14_15 BAT, The current is 0mA, or 200 ~ 500mA
I try to send you the value of REG_0B, REG_0C

Hi, 

HIZ is the high impedance mode. The REGN LDO is off and switching on Q2 and Q3 FETs stop. In HIZ the battery powers the system load until it is discharged or HIZ mode is disabled. Refer to section 9.2.3.1 of the datasheet linked here: BQ25890 Datasheet to see the input conditions required to turn on the REGN LDO and enter normal operation. HIZ can also be enabled/disabled by writing to REG00 via I2C. 

From the REG values you provided above you have REG06 = AF --> VREG = 4.53V, To set VREG to ~4.35V REG06 = 83.

Refer to figure 13 in the datasheet linked above for a plot of the charging cycle. When the battery is deeply discharged (below 2V) the charge current is only 100mA until battery voltage rises above 2V. Then the charge current will be at your Pre-charge value set on REG05 until the battery voltage rises above 3 V. Your discharged battery should never be at voltages as low as 0.7V.

To address your initial question,

HA TEASHIK said:

when the battery is fully charged and the remaining battery volume falls below 2.7V when using the system, when I try to charge to connecting USB C-type charger.  charging is not good from this point on

The expected operation of the BQ25890 is to lower the charge current when battery voltage is below 3V.

Regards,

Garrett

Thank you for your a respone. 

When the battery is discharged and the voltages of PIN14 and PIN13 of BQ25890 are 0.7V or less, power is not supplied to BQ25890. At this time, will the value set in the register of BQ25890 be cleared? When the battery is discharged, it is read as REG 0B: CF, REG 0C:00 when the value of BQ25890 is read without using the power from the battery to the bypass circuit.

In the case of charge monitoring of BQ25890, we perform battery charge control by connecting I2C from raspberry pie. However, after the battery is discharged, a value state of the BQ25980 cannot be read because the pins of the PIN_13, PIN_14, and the pins of the BQ25890 are 0.7V. In this case, the raspberry pie is also turned off, so that it is impossible to communicate the state value set value of BQ25890 in the raspberry pie. In this case, the USB power supply terminal of the raspberry pie is connected instead of the power supply through the battery.
The state value of BQ25980 was read by booting the raspberry.

I sent it by e-mail to send you our circuit, but it keeps being returned. How can I send my design circuit diagram?

Hello, 

I am not sure why your email reply is not getting through. An alternative method to share your circuit is that you can insert a pdf file of your schematic on a reply to this thread.

When in battery only mode, the battery monitor is only active when Vbat > SYS_Min, which is set in REG03. With your setting of SYS_Min = 3V the battery monitor will not be active whenever your battery is discharged below 3V. Furthermore when no Vbus is connected the minimum battery voltage for active I2C communications is V_BAT(UVLOZ) (2.3V). When in battery only mode the battery must be at or above 2.3V to maintain I2C communication with the raspberry pie. 

If you wish to maintain I2C communication between the device and the host an input power supply or Vbat > 2.3V must be present. 

Regards,

Garrett 

Dear Garrett 

Now I'm starting to understand this chip.
Now, I'm going to control the battery so that it's not below 3.1V. Then, I don't think there will be any problem.
But there is one thing I want to know.
If the battery voltage is in a low state and bq25890 is shut down, there is a method of preventing a value stored in bq25890 by i2c from resetting to the default mode.

If it falls below 2.4V due to a battery problem, the battery protection circuit operates to hold the battery power. In this case, since power is not supplied to the bq25890, the value of the register of the bq25890 chip returns to default.
And when charging again, if it go to default mode, the battery seems to be charged very slowly. It seems to be charging slowly at 200 mA.
In this case, should let  to  leave it to charge slowly?  Or even if the set value becomes power off, I want to know if it can be saved and started in precharge mode.