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BQ24171 :- 5Volt input charging issues with single cell Li-ion Battery

Other Parts Discussed in Thread: BQ24171, BQ24650


We are working with a battery charging circuit using  bq24171 IC.

The charger input voltage is  5V and the charge current is set to 2A.

Now the issue is that when we power the Board with 5V input, the charging functionality is not working properly.

Our system load will be 800mA.

Case1 :

Input votlage @ 5V/5A , Battery voltage  - 3.6V

Charger current will not go above 200 mA

if we connect the battery around 4 hours the charger current will reduces to 150mA and battery voltage will be  3.8V

Case2 :

Input votlage @ 5.3V 

The charger current will be around 1.6A

From the data sheet it is given that the Bq24171 input voltage range is 4.5 - 17V. The architecture is shown below

Kindly share your inputs 

  • can you share the sch?
  • There are two diodes (D25) connected to AVCC pin which at 5V input will cause AVCC < 4.5V which is out of spec. Please check datasheet Fig 23 for single cell 5V adapter ref design. If power path is needed, recommend to replace Q29 with diode. Q14 and Q28 can also be replaced by diode to reduce the cost.
  • Thanks Ming !!!!

    Will the diode circuit be okay as the TI evaluation board too recommends the MOSFET ??

    Anyway we will test as per your suggestion and share you the modified schematic.

    Please share your thoughts

  • Hi Ming,

    The circuit works with the diode shorted and the battery charging is happening with 5Volt input

    But we have a doubt whether Battery charger is following the Li-ion charging profile
    -------------------------------------------------------------------------------------------------------------------------
    Test case : Input 5V/5A
    ------------------------------------
    Battery used : 3.7 V 11.6Ah

    Battery Condition before connecting to charger- > 3V (Battery cutoff voltage)

    Charge current set to 2A
    --------------------------------------------------------------------------------------------------
    Charge Time Battery Voltage Charge current Status LED
    0 3 V 2.06 ON
    5 minutes 3.1 V 2.05 ON
    10 minutes 3.3 V 1.7 - 1.9 A ON
    1 Hour 3.5 V 1.4 - 1.7 A ON
    2 Hours 3.6V 1.1 - 1.4 A ON
    3 Hours 3.68V 1 -1.2 A ON
    4 Hours 3.8V 0.7 -0.9 A ON
    4.5 Hours 3.88 V 0.4 – 0.7 A ON
    5 Hours 3.9 V 0 – 0.4 A ON
    8 Hours 3.95V 0 – 0.3 A Blinking
    ---------------------------------------------------------------------------------------------------
    And when the battery voltage reaches 3.9V, it stops charging . This is strange since, we expect it to go up to 4.1V

    Are we missing anything in the BQ24171 circuit.

    Thanks in advance.
  • Hi Ming,

    The circuit works with the diode shorted and the battery charging is happening with 5Volt input

    But we have a doubt whether Battery charger is following the Li-ion charging profile
    -------------------------------------------------------------------------------------------------------------------------
    Test case : Input 5V/5A
    ------------------------------------
    Battery used : 3.7 V 11.6Ah

    Battery Condition before connecting to charger- > 3V (Battery cutoff voltage) 

    Charge current set to 2A
    --------------------------------------------------------------------------------------------------

    Charge Time

    Battery Voltage

    Charge current

    Status LED

    0

    3 V

    2.06

    ON

    5 minutes

    3.1 V

    2.05

    ON

    10 minutes

    3.3 V

    1.7 - 1.9 A

    ON

    1 Hour

    3.5 V

    1.4 - 1.7 A

    ON

    2 Hours

    3.6V

    1.1 - 1.4 A

    ON

    3 Hours

    3.68V

    1 -1.2 A

    ON

    4 Hours

    3.8V

    0.7 -0.9 A

    ON

    4.5 Hours

    3.88 V

    0.4 – 0.7 A

    ON

    5 Hours

    3.9 V

    0 – 0.4 A

    ON

    8 Hours

    3.95

    0 – 0.3 A

    Blinking


    ---------------------------------------------------------------------------------------------------
    And when the battery voltage reaches 3.9V, it stops charging . This is strange since, we expect it to go up to 4.1V

    Are we missing anything in the BQ24171 circuit.

    Thanks in advance.

  • please modify the schematic based on fig 23 in the datasheet for 1S applications.
  • can you also try to increase the 5V to 6V to see if the VBAT cab terminate at 4.2V?
  • Hi Ming,

    But our confusion is that the charger is not following the Li-ion charging profile. Especially the constant current case.

    We increased the voltage but the current is fluctuating as indicated in the table (previous post )

    SInce we are working with an evaluation board, we cant replace the MOSFET  with the diodes

    One more clarification, In the TI evaluation board they too follows the MOSFET circuits, does that circuits works well with 5V input ??

    We had experience working BQ24650 this charger IC works perfectly with the LI-ion profile. But the Input voltage is 12V

    We are in a big dilemma !!!

  • Lijo,

    we had some internal discussion yesterday and did not see any major issue on the schematic. couple questions:

    1. how high you have apply the input voltage

    2. what is the FB voltage when stop charging

    3. Also the input voltage may drop too much in the input cable and charger runs into sleep mode during the charge. Can you also use a scope to monitor AVCC and SRN and compare it with sleep comparator spec.

    Ming

  • Hi Ming,

    Thanks for the support.

    Please see the values you have queried, when the battery charger goes into error mode.

    Input Voltage

    6V

    5V

    SRN(V)

    4-3.9V

    3.9-4.02V

    FB(V)

    2.09V

    2-2.1V

    AVCC(V)

    6V

    5V

    Does the TI evaluation board works well with 5V input ?

    Do we need to raise the input voltage more ???

    Regards

    Lijo Thomas

  • Lijo,

    Can you double check R379 and R415 actual value on your board? looks like the output voltage is regulated to 4V. I will check on the EVM as well.

    Ming
  • Ming,

    The resistance values are 100 K only.

    Are you able to test the EVM .

    The issue we are telling is that the charger is not able to follow the Li-ion battery charging profile.

    During charging when the output voltage goes beyond 3.8 V, the voltage will be jumping from 3.9 to 4.2 and the current would be 200mA and 0mA accordingly.

    And when we connect a completely discharged battery the constant current charging is not happening.

    Is it a specific chip problem or the charging issue at 5V.
  • Lijo,

    Maybe I misunderstood your log file. It only went up to 3.9-4.0V. I did not see the jump from 3.9V to 4.2V. current jump from 200mA to 0mA looks like a charging termination event  I will check the EVM. At the mean time, can you check another board of yours to make sure this is not a bad IC.

    Ming

  • Lijo,

    I have checked on our EVM and it terminate properly at 4.2V with CC/CV profile for Li battery charging. Please check if the IC is bad or have another board to run the same test. Voltage level to monitor at:

    AVCC, OVPSET, TS, FB, V(ISET).
  • Ming,

    Nice to hear that the EVM works well with 5V input.

    We are just wondering how we could do the testing as we have procured only one board.

    Will it be possible to share oneTI EVM form a local distributor here and we will return after testing.

    Anyway thanks for the support 

    Will get back if we get some inputs to share !!!

    Thanks & Regards

    Lijo Thomas