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LT8228 Hysteresis when switching from Buck- to Boost mode and Vice Versa

Hello Guys,

I'm designing a Buck/Boost System with the LT8228, for Battery Charging in Buck mode(V2) and Client Power in Boost mode (V1). The Client voltage is 50V and the Battery voltage is varying from 27 Volt to 15V minimum depending on usage time. The Client voltage must be as close to 50V at all times. The client can decide to Increase the voltage with 5V avg. in order to switch over from Boost mode To Buck mode, charging the batteries in this way. But the problem lies here: When the batteries are charging and the client voltage lowers (as the client wants to stop the charging) it takes a voltage drop from 55 to 30V! to return to Boost mode and powering the Client back up to 50V. This hysteresis is to Big.

Can you please help how to make this hysteresis smaller for example 45V.

lots of thanks in Advance

GUDO

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  • Hello Chris,

    Thanks for the Info.

    I Found the damaged components, what i did: Connected 28V on V2 to make sure, the LT8228 goes in Boost Mode,

    I Measured DG2 (Gate 2 Voltage) and it was +9Volt Higher then the connected 28V, so the charge pump for on DG2 was OK.

    On the Other hand, the DG1 Voltage was  26.41V, way to low. Voltage over Gate-source = 0V.

    It could be 2 things, 1) LT8228 could not Charge the Gates to swittch or 2) Gate-Source on V1 side is leaking, or shorted.

    I removed the 2 Fets an replaced them quicly   with a few low current  TO220 type body fets and  DG1 wend to 57V!

    Looking good. So I soldered Fresh Fets on the PCB and it was working well.

    Thats Good I Learned a lot of things again. But now I must reduce The Inrush Current to prevent further damage.

    I keep you informed.

    Best regards

    Gudo

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  • Hello Chris,

    Thanks for the Info.

    I Found the damaged components, what i did: Connected 28V on V2 to make sure, the LT8228 goes in Boost Mode,

    I Measured DG2 (Gate 2 Voltage) and it was +9Volt Higher then the connected 28V, so the charge pump for on DG2 was OK.

    On the Other hand, the DG1 Voltage was  26.41V, way to low. Voltage over Gate-source = 0V.

    It could be 2 things, 1) LT8228 could not Charge the Gates to swittch or 2) Gate-Source on V1 side is leaking, or shorted.

    I removed the 2 Fets an replaced them quicly   with a few low current  TO220 type body fets and  DG1 wend to 57V!

    Looking good. So I soldered Fresh Fets on the PCB and it was working well.

    Thats Good I Learned a lot of things again. But now I must reduce The Inrush Current to prevent further damage.

    I keep you informed.

    Best regards

    Gudo

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