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BQ24035 EVM - Not able to charger fully discharged Battery

HARISHA BS
Intellectual 500 points
Other Parts Discussed in Thread: BQ24035

Hi,

I am using BQ24035 EVM to test 3.7V li-ion battery charging.

When i connect fully discharged battery (2.5V) to EVM, it is not charging (EVM's  VOUT is loaded with 10Ohm Resister and V LDO is open)

When i connect fully discharged battery, EVM is going to short circuit mode and there is no output at VOUT and STAT 1 LED is in Precharge mode (ON) and STAT2 LED is ON.

I am not able to verify, battery is charging or not?

As per EVM when AC Adapter is powered on V Out will give 5.2V and when AC adapter is OFF VOUT will take supply from VBAT and it will power ON the system (with Fully charged battery this condition is working)

Please, suggest the possible way to charge fully discharged battery?

Note:

I am testing with AC power adapter input.

R TMR is set to 50K and RDPPM is set to 31 K also tried with R TMR with 60 K and R DPDPM with 37K ( in both cases it is not working)

Regards,

Harish.

  • 0
    TI__Expert 7730 points
    Harish,
    With 2.5V battery voltage, the IC will be in pre-charge mode and the LED indication is correct. I verified with an EVM, the IC can charge normally with the VBAT down to below 1V. The only condition that I saw no output at VOUT and no charging current is when the OUT pin is shorted. So can you please verify that your OUT pin is not shorted to ground on your board?
    Thanks, Wenjia
  • 0 in reply to Wenjia Liu
    Intellectual 500 points
    Hi,
    Yes the Charger EVM is in pre-charge condition.
    As soon as i connect fully discharged battery (2.5V) VOUT will go to 0V and EVM indicates pre- charge condition.
    VOUT is connected with 10 Ohm load and every time i need to disconnect the load to Reset short circuit mode of operation.

    Let me know following details.
    1. Pre-charge duration for fully discharged battery (2.5V)?
    2. During prepcharge what is the voltage level at VOUT?
    3. Some time after pre charge EVM is going to short suspend mode and again we need to reset the device.
    4. What is the correct setting for RTMR and R DPPM resistor values?

    Regards,
    Harish.
  • 0 in reply to HARISHA BS
    TI__Expert 7730 points

    To Answer your questions:

    1. It is depending on the charging rate. As soon as the voltage is above 3V, the pre-charge will stop and fast charge will start.

    2. As long as the input power is valid, the output will be regulated to whatever it should be, regardless of the battery voltage.

    3. This is definitely not expected behavior. There might be something shorted on the board.

    4. Please refer to section 10.3.2.2.3 Dynamic Power-Path Management on page 15 o the datasheet for RDPPM calculation.

    Please refer to section 10.4.4.6 Charge Timer Operation on page 21 o the datasheet for RTMR calculation.

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Intellectual 500 points

    Hi,

    I disconnected 10Ohm load from VOUT pin and connected 100Ogm load and now it is able to charge battery with 3.1V.

    Still, it is not able to charge battery with 2.5V (fully discharged battery).

    Please, suggest what is the correct VOUT load for charging fully discharged battery (2.5V)?

    what is the resistor value setting for RDPPM and RTMR?

    Regards,

    Harish.

  • 0 in reply to HARISHA BS
    TI__Expert 7730 points

    The VOUT load should not impact the battery voltage at which the IC will start charging. I suggest you check if the input voltage is too low so that the input current is limited. In this case the input cannot provide enough power to the output and the battery voltage is also too low to supplement the output.

    The RDPPM and RTMR is depending on your system needs - At what VOUT level do you want to start limiting the output current and how long do you want the charger to keep charging the battery. Please refer to the relevant sections on the datasheet for the calculation. (mentioned in my last post.)

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Intellectual 500 points

    Hi,

    I have following queries related to BQ24035 Charger.

    1. I tried connecting 3.7V 2600mAh fully charged Battery in reverse polarity to BQ24035 EVM, immediately IC got burnt as soon as i power ON EVM. Please, let me know, why it is failed and what is the protection for reverse polarity battery?

    2. Do we need to add any additional protection circuit for reverse polarity detection?

    Regards,

    Harish.

  • 0 in reply to HARISHA BS
    TI__Expert 7730 points

    Harish,

    The chip only has a protection for the reverse current from BAT to IN when VBAT is higher than VIN. However, it doesn't have the protection against the wrong battery polarity. You do need to add extra protection components such as diodes and transistors. Please refer to the below app note for some recommendations.

    http://www.ti.com/lit/an/slva139/slva139.pdf

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Intellectual 500 points

    Hi,

    Thanks for your support.
    We are planning to use P Channel Mosfet protection circuit in battery line.

    As per the shared pdf Page no 2, Fig 3 connection made.
    1. With the PMOS FET connection, when we connect AC input power adapter and Battery in reverse polarity how the circuit behaves?
    2. Since, Input and output Ground (Battery Ground) of BQ24035 is common, what is the effect of reverse polarity of battery to this ground, will it damage the IC?
    3. Our requirement is as follows - We are connecting VOUT (pin 15,16,17) to our system load and BAT (Pin 5,6) to Li-ion battery through PMOS FET as reverse polarity protection.
    4. With this connection if we place battery in reverse polarity and AC mains input to BQ24015 is ON, what is the affect on internal MOSFET (Q2,Q3) of BQ24035?
    5. Please, suggest how to test this condition?

    Regards,
    Harish.