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BQ25790: Loop compensation of the buck-boost converter

Part Number: BQ25790

Hello Support Team, I think BQ25790 is very easy to use and smart device.  I want to know how to evaluate the loop compensation of its buck-boost converter. But there are no feedback path from output to internal comparator input, so I can't do measurement of the gain/phase margin using with a Frequency Response Analyzer. Please tell me otherwise methods about that, if you known. Kind Regards.

  • Hi,

    For each loop, you can force a transient event and observe ringing of the loop voltage or current under test.  For example, for the CV or IINDPM loops, you can perform a load transient on SYS that does not enter supplement mode and look at ringing on SYS or VBUS input current, respectively.  For VINDPM loop, you can set IINDPM to highest setting, add a series resistor (~0.5ohm-1ohm) between power supply and VBUS and perform a system load transient, looking at VBUS.  The CC loop is the most difficult but can be done by observing the charge following an I2C register WRITE to change the charge current.  To a first order, the loop response time is the time from the transient event to the voltage or current starts to recover from the transient.  The amount of ringing/settling after the response settles to the correct value is proportional to phase margin, to a first order.   

    Regards,

    Jeff