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ATL431LI: Using ALT431Li to make UV lockout circuit for UCC5350

Ted Dager
Prodigy 60 points
Part Number: ATL431LI
Other Parts Discussed in Thread: UCC5350, ATL431

Hi 

I am using UCC5350 in 3 phase bridge circuit , sadly i decided later in the project to use isolated Bipolar dc/dc converter (+15/-9) for gate drive supply 15 connected to VDD and -9 to VEE and Switch-node will connect to 0v pin of the DC/DC converter. Now the problem is that this gate driver is not optimized for bipolar supply and UVLO is too low. Since I bought a large quantity and i cannot change the gate driver , I have to implement UVLO externally especially for turn On voltage (+15v) or for the total voltage (15+9=24v).

1. Do you have any suggestion on a simple circuit other than using ATL431 and its derivatives?

2. What would be better , using ATL431 to control p-channel mosfet to turn off Gate driver supply OR using ATL431 to control an opto coupler which controls a buffer or AND gate to disable PWM inputs ?

3. What would be better monitoring the Total output of dc/dc converter , or just the positive voltage ? I am worried that switch node undershoot and noise could cause false triggering ATL431. 

4. Can I add Capacitor and is there a limit on maximum value near Feedback/Ref pin of ATL431 ? the goal is to filter the switching noise and prevent false triggering . 

thanks

  • +1
    TI__Expert 7090 points

    Hello,

    1. Could a simple voltage supervisor device such as the TPS3808EG01DBVR be used instead? The reset threshold voltage can be set with a resistor divider on the sense pin.

    2. It would be simpler for the ATL431 to directly control the mosfet instead of using an optocoupler unless isolation is necessary.

    3. Monitoring just the positive voltage would be simpler.

    4. Please do not place a capacitor between the ATL431 Ref pin and ground as this could cause the device to become unstable.

    Best,

    Walter