Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

  • State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 65 subscribers
  • Views 263 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25616: Unexpected Input Current Limit

Matthew Anauo
Prodigy 140 points
Part Number: BQ25616

I am using the BQ25616 to manage charging a single LiPo battery and powering the rest of the system (in my design the BQ25616 is on a separate PCBA from the rest of the assembly). The implementation is straightforward, based from the datasheets/user guides for the part:

  • Charge current: 1.2A
  • Input current: 3A
  • Input: 5V, 3A (USB-C adapter)
  • Charge voltage: 4.2V
  • SYS full load: 1.5A @ 3.7V (obtained by separating PCBAs and directly supplying VSYS with metered power supply).

I am getting an input current limit imposed that I was not expecting. When connected to the

I've tested this circuit on the BQ25616EVM as well and obtained identical behavior - so there is something going on here. The behavior is:

  • Battery charges normally (charging current reaches full 1.2A maximum, battery charges to correct voltage).
  • When a battery is connected, the BQ25616 is correctly directing it to the SYS output and the rest of the system is powered.
  • When 5V voltage is applied through VBUS, input current seems to be clamping at 500mA, and as a result the output on SYS drops to ~2.6V (system is not able to be powered).
    • I am testing this by powering the BQ25616, then waiting a few seconds on startup (or until the PG indicator LED is active) to connect the full load.
  • When I test this with the evaluation board, this current limit does not seem to be imposed, and the system is powered normally.
  • In all of these tests, the USB data lines were floating/disconnected, so I was expecting the current limit to be 3A as set by R5. I also tested shorting D+/D- together (suggested in another forum post somewhere to implement 2.4A limit for DCP) but it made no difference.

I don't see any difference of significance between my schematic and that of the eval module on which it was based (the bootstrap capacitor is mistakenly 4.7nF on my schematic instead of 47nF, but I corrected that on my board and it did not change any behavior) - what could be causing this?

What

  • 0
    TI__Mastermind 35155 points

    Hi,

    Can you clarify if you are seeing the input current limit at 500 mA on TI EVM?

    Can you double check R5 resistor?

    What happens if you disconnect R1 and R2? Are those connected to the USB input somehow?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 140 points

    Hi Mike,

    The 500mA limit is not seen on the EVM - only on my implementation.

    I've done two tests with R1/R2 - removing them (data pins are floating) and using the pads to short pins 3/4, neither test changed the behavior. At any rate the USB data lines are not connected to anything in any of these tests, because the power is being applied to VBUS from a benchtop supply, and power was being jumpered out of the USB board to the main assembly so there was no connection there.

    R5 measured 160.4ohm on my board, and the total resistance on the ILIM pin of the EVM measured 158.4ohm.

  • 0 in reply to Matthew Anauo
    Prodigy 140 points

    Is it possible for the divider on the TS pin to influence this? On the eval  board the divider is 5.23k (I have JP11 closed) with 30.1k // 10k = 7.5k (I have JP16 closed and JP18 open). On my board I have a divider of 2 10k resistors.

  • 0 in reply to Matthew Anauo
    TI__Mastermind 35155 points

    Hello,

    A TS with 50% REGN should be fine. What are the STAT and PG/ LEDs doing in both cases?

    What is your input current when charging at full 1.2 A? I assume it was greater than 500 mA?

    What is physically different between the setups? Have you tried an ABA swap?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 140 points

    PG LED comes on right after startup, and stays on throughout. STAT is solid during charging, and is off otherwise (I have been doing most testing with no battery and charging disabled to focus on the input current limit issue).

    When charging at full 1.2A input current is just under 1A - I've verified that this is obtainable using both an actual battery and a programmable CV load.

    I don't see anything significant that is physically different but I'm clearly overlooking something. In both setups the input is being applied to VAC. Going through my schematic vs. evaluation board:

    • I don't have the OV FET.
    • I placed 4.7nF for the bootstrap cap instead of 47nF, but reworked that and it didn't seem to change anything.
    • I'm using 1.5uH inductor instead of 1.0uH.
    • Different TS divider.

    Haven't tried ABA swap yet, was hoping to avoid that because the swap is going to be challenging and I have limited supplies but that might have to be the next step.

  • 0 in reply to Matthew Anauo
    Prodigy 140 points

    Is it an issue that the eval board component is the JEITA part and the component on my device is the hot/cold part?

  • 0 in reply to Matthew Anauo
    TI__Mastermind 35155 points

    Hello,

    You are within the good TS range for either part, as demonstrated by your full charge current and voltage.

    What happens if you short out L3?

    Regards,

    Mike Emanuel