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BQ24259: IC getting exceptionally hot, and not charging Li-Po battery

Alexander Mompoint
Prodigy 10 points
Part Number: BQ24259
Other Parts Discussed in Thread: BQ25628, BQ24296M

Tool/software:

To show initially, these two snippets are of the registers and faults when the battery is NOT connected.

VINDPM- Dynamic Power Management, In Voltage: 4.36V
IINLIM- Input Current Limit: 3.00A
Register reset: 0
I2C Watchdog Timer Reset: Normal
OTG Enabled: OTG Disable
Charge Enabled:: Charge Enable
SYS_MIN - Minimum System Voltage Limit:: 3.10V
Boost_Lim: 1 A
ICHG - FastCharge Current Limit: 2048mA
Set Boost Mode Temperature monitor threshold voltage to disable boost mode: 76%
Force 20PCT: ICHG as Fast Charge Current and IPRECH as Pre Charge Current
Pre-Charge/Termination Current Control Register: 128mA
Iterm - termination current limit: 129mA
VREG - Charge Voltage Limit: 4.21V
Battery Low Voltage: 2.8 V
Battery Recharage Threshold: 300 mV
Fast Charge Timer Setting: 12 hrs
Charging Safety Timer Enable: 1
WATCHDOG: 40s
Charging Termination Enable: 1
Thermal Regulation Threshold: 120 C
Set Boost Mode temperature monitor threshold voltage to disable boost mode Voltage to disable boost mode: 33% of REGN
BOOSTV- Boost Voltage: 5.00V
BATFET turned on
VBUS_STAT: Adapter Port
CHRG_STAT: Pre-Charging
DPM_STAT: VINDPM or IINDPM
PG_STAT: Power Good
ThERM_STAT: Normal
VSYS_STAT: In VSYSMIN regulation (BAT < VSYSMIN)
No Faults

And as well when the battery is connected.

The device is plugged in to a power source and no registers are manually changed in these snippets.

Thermal Shutdown: StatPin:0
VINDPM- Dynamic Power Management, In Voltage: 4.36V
IINLIM- Input Current Limit: 3.00A
Register reset: 0
I2C Watchdog Timer Reset: Normal
OTG Enabled: OTG Disable
Charge Enabled:: Charge Enable
SYS_MIN - Minimum System Voltage Limit:: 3.10V
Boost_Lim: 1 A
ICHG - FastCharge Current Limit: 2048mA
Set Boost Mode Temperature monitor threshold voltage to disable boost mode: 76%
Force 20PCT: ICHG as Fast Charge Current and IPRECH as Pre Charge Current
Pre-Charge/Termination Current Control Register: 128mA
Iterm - termination current limit: 129mA
VREG - Charge Voltage Limit: 4.21V
Battery Low Voltage: 2.8 V
Battery Recharage Threshold: 300 mV
Fast Charge Timer Setting: 12 hrs
Charging Safety Timer Enable: 1
WATCHDOG: 40s
Charging Termination Enable: 1
Thermal Regulation Threshold: 120 C
Set Boost Mode temperature monitor threshold voltage to disable boost mode Voltage to disable boost mode: 33% of REGN
BOOSTV- Boost Voltage: 5.00V
BATFET turned on
VBUS_STAT: Adapter Port
CHRG_STAT: Fast Charging
DPM_STAT: VINDPM or IINDPM
PG_STAT: Power Good
ThERM_STAT: In Thermal Regulation
VSYS_STAT: Not in VSYSMIN regulation (BAT > VSYSMIN)
No Faults

The issue I am having is that I cannot figure out what is causing the BQ24259 to run extremely hot in normal operation. When the battery is solely connected, with no charging the IC is physically getting hot to the touch.

Then when the IC is also being charged by connecting my adapter, the IC gets extremely hot to the touch, to the point of possible burns. As well the BQ is reporting Fast Charging via the registers, but it is pulling less than 200 mA without actively cooling(blowing on the IC). Is this normal behavior for the IC? I do not see any mention of requiring active cooling in order to reach any charging above 200 mA. By simply blowing air onto the IC I was able to reach around 1.4A of charging, which is near my ILIM limit by resistance (1.5A). 

Side question: is there a way to get around the thermistor requirement? I understand I can use a resistor in place to spoof the thermistor, but is there is a register or something along the lines that would be a simple bypass that would be appreciated.

Below is the schematic for reference.

 

  • 0
    TI__Guru** 104030 points

    Hello Alexander,

    We will review your information and provide a response by end of day tomorrow.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    TI__Mastermind 26190 points

    Hi Alexander, 

    Firstly, regarding your question on thermistor requirement there is not a register configuration option to disable the TS pin function. The easiest way to bypass this function is connect TS between two 10kohm resistors from REGN to GND. I will point out that some of our newer buck chargers such as the BQ25628 have the ability to bypass the TS pin function via register setting 'TS_IGNORE'.

    Regarding your issue of the IC heating I have reviewed your schematic and see no major issues. TI does strongly recommend having an input capacitor at VBUS, but missing this cap should not be the reason for IC heating. 

    Alexander Mompoint said:
    As well the BQ is reporting Fast Charging via the registers, but it is pulling less than 200 mA without actively cooling(blowing on the IC). Is this normal behavior for the IC?

    This is not expected behavior. The BQ24259 has been verified to operate with 2A output current without entering into thermal regulation as your board is. The 'extreme' heating you mention is most likely related to layout design. 

    For your reference please ensure you are following our layout guidelines stated on page 40 of the datasheet. Additionally, the board layout shown in the BQ24296M EVM User's Guide (linked here: https://www.ti.com/lit/pdf/sluub62 ) is a helpful reference of a good layout design for this IC. The BQ24259 has the same pinout and thermal performance as the BQ24296M. 

    Best Regards,

    Garrett