LTC4368-1 Bi-direction Current and Voltage Protection Issue

To Analog Technical Support,

Que1 -> We are using LTC4368-1 IC for Bi-directional voltage and current protection voltage ranging from

UV=15V , OV=36V and Current -> -12.5A to +12.5A.

Que-2-> UV=3V , OV=5V and Current -> -500mA to +500mA.

Main issue seems to be that the GATE voltage does not get pulled low enough to turn-off the FETs when a reverse OC occurs. It seems to stay at approx 3V, so the FETs are not completely turned off. What is going on with the GATE voltage? 
Requirement - The main function for this circuit is the bi-directional over-current protection, to handle a short circuit on either side.
Suggest the solution for the same with reference.
Regards,
Pushkarsinh R
India
Parents
  • +1
    •  Analog Employees 
    on Mar 15, 2021 6:38 PM

    Can you provide a schematic and scope-shots?

    Waveforms of interest are:
    VIN
    VOUT
    GATE
    FAULT#
    Load current - using current probe
    VSNS - voltage across sense resistors using differential probe (if no current probe)

    Thanks,
    -Aaron

  • For Application 1: Attached LTSpce Simulation

    VIN: Max 36VDC, UV : 15V , OV : 36V
    VOUT: max 36VDC, I = -12.5A to +12.5A
    GATE-Attached LTSice Ckt
    FAULT#: Attached LTSice Ckt
    Load current - using current probe(LTSpice Simulation)
    VSNS - voltage across sense resistors using differential probe (if no current probe) -> 4mOhm , 1% . 2W for Current : -12.5A to +12.5A

    Ckt. simulation through LTSpice Tool

    Application1-LTSpiceWaveform1

    Application1-LTSpiceCkt

    For Application 2: Attached LTSpice Simulation:

    VIN: Max 5.5VDC, UV : 3V , OV : 5.5V
    VOUT: max 36VDC, I = -500mA to +500mA
    GATE-Attached LTSice Ckt
    FAULT#: Attached LTSice Ckt
    Load current - using current probe(LTSpice Simulation)
    VSNS - voltage across sense resistors using differential probe (if no current probe) -> 4mOhm , 1% . 2W for Current : -500m to 500mA

    Ckt. simulation through LTSpice Tool

    Application2-LTSpiceWaveform

    Application2-LTSpiceCkt

  • 0
    •  Analog Employees 
    on Mar 23, 2021 11:43 PM in reply to jeb78

    Hi Jeb,
    The diode-OR you installed allows the VIN pin to always receive power, whether it is the left or right side.

    However, the diode-OR interferes with the LTC4368’s FET turn-off mechanism.

    The LTC4368 turns off the FETs by connecting the GATE pin to the VIN or VOUT pin, whichever is lower. (See description of GATE pin in datasheet)

    If we use this diode-OR, apply power to the right side, and connect the left side to a passive load, then VIN will be only a diode drop underneath VOUT. There won’t be much of a difference between an ON and OFF condition.

    For proper operation, the input side (with VIN/UV/OV connections) needs to always receive power, and the VOUT pin cannot be shorted to the VIN pin through a diode.

    -Aaron

  • Hi Aaron,

    thank you for the clarification.

    We tried a naive approach (in LTSpice) with the same setup as above, i.e. diode-or for VIN power, but utilizing the FAULT output to pull the GATE to GND on a fault condition (through a N-FET with series resistor). This seems to work well to limit a reverse current as long as voltage supply does not go negative. Our main concern is limiting bi-directional current, not so much reverse polarity.

    Do you see any potential issues with this approach?

  • 0
    •  Analog Employees 
    on Mar 24, 2021 6:49 PM in reply to jeb78

    Ah, so you would add your own gate turn-off circuitry controlled by the fault pin.
    Can you post the circuit you are describing?
    One of my concerns is that this new FET won’t be able to turn either all the way on, or all the way off.

  • Well, like I said it is a naive approach, so we have not put much work into it yet and only used generic components to modify the circuit you provided earlier.

    Below simulates a redundant 10V supply with 40 ohm load on each side of the circuit breaker. At 12s the left side is shorted to ground. GATE is pulled to GND through a 100 ohm resistor by N-FET M3 controlled by the FAULT pin through PNP Q1. The Right side load ride through the short circuit without any significant drop in current or voltage.

    In our application the nominal bus voltage would be approx 30V and maximum bi-directional current approx. 10A.

  • SCH1-CktBreaker-MainBus-09-04-2021-VfrolmRighttoLeft-BiDirectional.ascSCH1-CktBreaker-CRSBus-09-04-2021-VoltfromRighttoLeft-BiDirectional.asc  To Analog Support , Still waiting for response as Jeb has mention above, we are also taking help  from excel point, share some suggestion with some LTSpice simulation, Here I attached my LTSpice files in that PNP added in gate pin suggested by Analog Device Support Consultant. Do the needful for the same. Our main focus on short ckt. current protection bi-direction by using LTC4368-1.  Here above I attached my LTSpice Files with observation, Wait for suggetions - short ckt.current protection bidirectional using LTC4368-1

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