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The BQ24072T doesn't begin charge. I can't locate the source of the issue.

user4233221
Prodigy 130 points
Other Parts Discussed in Thread: BQ24072T

I made a circuit that contains the part - battery management, which I adopted BQ24072T. But the problem is that, after I soldered some PCB, some worked well, but other didn't begin charge. After I connected the power supply, PGOOD LED lighted up, but the CHG LED didn't.

I configured the TS resistors according the details in datasheet: because I didn't use the Thermal Monitor function, I connected resistors of 200k and 49.9k. 

When I used a oscilloscope to monitor the voltage on pin TS, the voltage was around 850mv.

And I can make sure that I soldered everything correctly.

Here is my schematic and part of PCB. 

Thank your for reading!

Hope someone can help me figure out the problem.

  • 0
    TI__Mastermind 20240 points
    Can you share scope capture on VIN, VOUT, VBAT, and IBAT? Also what is the voltage on /CHG? Can you also show scope capture on /CHG as well?

    On the boards you mentioned is working. can you capture the same waveform?

    RTMR should be between 18k to 72k ohm. It seems like the value on your schematic is out of spec. With the RTMR value on your schematic, if the battery voltage is less than 3V, the charging is going to suspended after 45s when a valid input source is applied.
  • 0 in reply to Jing Zou
    Prodigy 130 points
    Today I tested the circuit again, and I think I have located the problem: I found the voltage on the TS is either 0.626 V (Hot threshold) or 2 V (Cold threshold). If I configure the resistors according to Datasheet, which is 200k (R11) and 49.9k (R13), the voltage on TS is 2.0 V, and if I remove the 200k (R11) resistor, the voltage is still 2.0 V (don't know why it doesn't change); If I connect R13 a 10k resistor and don't connect R11, the voltage would be 0.626 V. But I don't know what causes and how to solve the problem.
  • 0 in reply to user4233221
    Prodigy 30 points

    I'm having the exact same issue.

    200k + 49.9k leads to 2.23V at the TS pin. I haven't tried removing one of them yet, but I have double-measured their values.
    The /CHG pin however stays LOW in my case, independently of the /CE pin, which I toggled in debugging mode with a microcontroller. So I assume the VHOT threshhold of 2V+ is leading to a malfunction. I'll try to tie the port to 1V somehow and post my results.

    Could a TI engineer clarify things up here? The last post is from January this year!

    Edit: I managed to get 1V at the TS pin with a resistor from TS to GND of 14,67k (Resistors parallel: 22k || 75k || 75k), and the battery is being charged. I verified this by measuring a significantly rising voltage (3.71V -> 3.8V). So 15k at TS should do well, without a resistor to Vin.
    However, the /CHG pin stays low, even if I "switch off" charging by setting the /CE high via 3V3 microcontroller.

    My setup:

    Li-Ion Battery 4.2V
    EN1 = high
    EN2 = low
    Power In = USB 5V

  • 0 in reply to Emanuel Leicht65
    Prodigy 30 points

    Quick update on this.

    We've ordered another round of prototype PCBs which were quite expensive. In the meantime, TI has changed the functionality of the chip without giving any notice anywhere, not even in the datasheet or datasheet's changelog. Took me quite some debugging time to find out I haven't done any mistake, the chip just has changed internally.

    As by now, the pin TS has to see a 10k resistor to VSS. The previously necessary 15k as in my previous post lead to a different voltage now and stop the chip from charging the battery. I've written to TI support with a reference to this thread. I'm curious if someone from their engineers will go the long way down to this insignificant and annoying thread and take the burdensome task to clarify things.