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BQ25180: Issue pulling current from VSYS when running from battery

Angus Thomson
Prodigy 30 points
Part Number: BQ25180
Other Parts Discussed in Thread: TPS61252

I'm using the BQ25180 with a small LiPo battery to power a reasonably large load (90mA). When I power the system from a USB source everything works fine, but when powered from a fully charged battery (VBATT = 3.8V) the voltage at VSYS drops periodically. The attached wafeform shows the voltage on VSYS - the period of the signal is around 32ms.

I have verified that the circuit runs fine with the battery connected directly to the VSYS net, and have left the registers at their defauilt values.

Note that the system works fine with a smaller load (~10mA) - it is only when enabling the larger load that the issue occurs.

  • 0
    TI__Mastermind 23350 points

    Hi Angus,

    Are you able to communicate with the device still when this happens? Is this when you plug in a battery? What is connected to your SYS pin besides the capacitor? 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 30 points

    Hi Anthony

    Thanks for the response.

    Yes - it appears I can communicate with the device over I2C whilst in this state.

    The issue occurs only when running from the battery. If a USB source is connected (to VIN) it runs fine.

    VSYS powers several other devices, but the one which causes the issue to occur is an SGX Sensortech MICS-6814 gas sensor, which uses small heating elements. The device is powered by a 5.5V boost converter (TPS61252) which provides ~90mA.

    Please note that as per my original message, I have checked that the battery alone is capable of powering the circuit ok (i.e. connecting the battery directly to VSYS).

    I have also done a test with a variable load on VSYS, and as soon as I pull over 90mA, the issue occurs (VSYS drops as per the original post). If I remove the load whilst in this state the issue goes away.

    Thanks

    Angus

  • 0 in reply to Angus Thomson
    Prodigy 30 points

    My apologies - I have just done another quick test and I think the issue is elsewhere! the battery over-current discharge protection was kicking in, causing the problem. Sorry!