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LM74610-DQEVM: OR two devices with offset

Johnd2225
Prodigy 170 points
Part Number: LM74610-DQEVM
Other Parts Discussed in Thread: TPS24740, TPS2660, LM5069

I want to simulate a diode OR configuration combining a main power supply/battery and a small bootstrap battery.  The small battery has two diodes in series while the large supply/battery has a single diode.  During start-up the small battery runs a small load before it enables a contactor to the main supply.  Transfer is seamless but with the associated power loss across the diodes.

We cannot allow the small battery to supply any current once the main contactor is ON because the charger on that small battery will brown out and we could drain the bootstrap battery during normal operation.  But if the BMS drops out the contactor we need the small supply for an orderly shutdown. 

Can a put one or two small signal diodes in series with the sense line to the ANODE pin of the LM74610 to fool it into thinking that the difference between the ANODE and CATHODE is higher and so the device remains switched off.  I'd also have to add a second controlled MOSFET in the opposite direction to block the body diode of the other MOSFET.

Main battery current is up to 15A so normal diodes use a fair amount of power.

  • 0
    TI__Expert 5940 points
    John,

    Sorry for the delay, we will get back to you on this by the end of the week.

    Brian
  • 0 in reply to Brian Daugherty
    TI__Expert 5940 points
    John,

    The body diode needs to see .48v for start up of the charge pump. Adding a diode(s) in the anode leg will adversely affect this. So, no you should not do this.

    Brian
  • 0 in reply to Brian Daugherty
    Prodigy 170 points
    Is there a different ideal diode circuit that can simulate this?
  • 0 in reply to Brian Daugherty
    TI__Expert 5940 points
    John,

    Can you sketch out for a better picture of what you are attempting. I will be OOO for a couple of weeks starting now and another Engr will look into this.

    Brian
  • 0 in reply to Brian Daugherty
    Prodigy 170 points
    V1=24V------Diode|-------------------------------------+----------Target Application.
    V2=24V------Diode|----Diode|-------------------------|

    Only if V1 vanishes do we want V2 to be the supply. We are using Linear Technologies LTC4359s as the ideal diode which we disable and have a circuit to re-enable the V2 circuit automatically if V1 vanishes but it doesn't enable fast enough and we get a momentary brown out. So I'm looking for other options.
  • 0 in reply to Johnd2225
    TI__Genius 12380 points
    Hi John,

    If I understand the application correctly, it sounds like you never want both V1 and V2 to be on at the same time. If that is the case, our team tends to call this a "priority power MUX" application. You have a priority (V1 in this case) and if V1 is present then pass to the output or if V1 is not, then pass V2.

    We have the TPS24740 which can accomplish this but cannot operate at 24V. Nevertheless, feel free to read section 10.3.2 on page 43 of the datasheet if you are interested in the system topology:
    www.ti.com/.../tps24740.pdf

    We do not have a corresponding high voltage, high current solution. Closest option would be TPS2660 which can operate up to 55V, 2A. That may work for V2 but not for V1.

    While you may get by with a 3x chip solution, I understand it may not be a cost effective solution:
    V1: Use LM5069 + LM74610
    V2: Use TPS2660

    Thanks,
    Alex