• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 833 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM5066I: LM5066I Controlling 3 DC fans - Current Design Considerations

Jordan Radice
Prodigy 130 points
Part Number: LM5066I

Hi Team,

I am working with a client and they have a couple questions with regards to the LM5066I if you could help provide answers to the following:

We are going to use the LM5066I hot swap controller for 3 DC fans. The maximum current of each fan is 12.5A, the total maximum current for three fans is 37.5A. I’m going to design the hot swap circuit with a maximum current of 50A. What do you think about this? Is 50A is enough for three fans? Do you have any recommendations about the maximum current of the hot swap circuit?

I’ve tested a fan, and I have seen the negative current during the fan start up and turn off the fan:

1)      Negative current during start up: ~3.5A

2)      Negative current when turning off the fan: ~1.7A

I think if I connect three fans in parallel, the negative current is much higher. So when I use the hot swap circuit LM5066I for these three fans, do I need to add the negative voltage/current protection circuit? Do you have any recommendations?

Thank you,

Jordan

  • 0
    TI__Expert 5940 points
    Jordan,

    Be sure max current includes any low duration peak currents. The LM5066I will see and respond to those. If peak current is guaranteed to be < 37A on the fans, Designing CL at 45A looks to be enough margin, but this is a lot of power to use on a single HSC. The LM5066I will have the FET fully enhanced, negative current isn't an issue unless it overcharges the input cap and creates a false CL/CB threshold on the current sense, causing the LM5066I to respond with CL or CB trip. Take into account CB = 1.9x CL so that will be 95A. That is a lot for a 48v system. During a CB event, all of this current, plus additional due to reaction delay of ~ 1usec, can mean up to 100A needs will be dumped into the input TVS and output Schottky. So you will need multiple input SMD TVS's and output SMC Schottkys to protect. Possible you can use a 50 ohm resistor on the Out pin with a small Schottky on OUT and a single large Schottky on the FET Source. Very careful fault current testing is needed for such a high power design. I would recommend you split these into separate rails with individual LM5066I control.

    Brian