E-fuse comparison and recommendation

Sorry, it's TPS24751, not TPS24851

Hi Luiz,

As mentioned in this other thread,
e2e.ti.com/.../1852123

Our apologies and I have also moved this to the Load Switched forum.

Thanks,
Alex

Hi Venkat,

Thanks for you attention. Follow a simplified block diagram of our application. Our concern is about the elements labeled as "E-fuse (3A)" and "E-fuse (3.5A)".

Devices to be connected to the device interfaces are supplied with 12V and can present high current peaks, mainly when inserted. While E-fuse (3A) protects the power rail before it, the storage capacitor provides energy to supply current peaks at 12V rail.

Green power level ranges from 10V to 15V. Especially in battery mode, when it ranges from 10V to 12V, stored energy in capacitor may not be enough to supply current peaks, and buck-boost turns-off in some moments. This leads to 12V shut-down and hence all connected devices to shut-down. Such behavior is undesired.

The e-fuse current limiting phase help the capacitor in supplying energy to the buck-boost. But when it turns-off due to thermal protection, only capacitor supplies energy. We would like that e-fuse remains in limiting mode during a greater time in order to help capacitor to supply power to buck-boost and avoid the undesired behavior of 12V power rail shut-down.

A way to do this is with a bigger e-fuse or maybe a controller with a external fet. Do you have any suggestion or doubt?

The same idea applies to e-fuse (3.5A), but here the undesired effect would be equipment 2 shut-down.

E-fuse (5A) for now are just being used as short-circuit protection.

Thanks.

Hi Luiz,

"Devices to be connected to the device interfaces are supplied with 12V and can present high current peaks, mainly when inserted"

How long do you expect inrush current to flow? If inrush current is due to capacitor charging, E-fuse (5A) can be configured to reduce inrush current to acceptable level of E-fuse(3A). Another idea is to increase E-fuse (3A) current limit by detecting insertion event.

Same idea can be extended to limit inrush current of equipment-2 insertion. Let me know your thoughts on this.

Regards,
Venkat

Hi Venkat,

Time that inrush current flows varies because of different load can be connected. We would like from around 40ms to 100ms of current limiting time before switch is opened. Inrush current may be due to capacitor charging but also due to mistaken power-up management and sequencing in load device, but they are cannot be changed, unless a big fault is detected.

TPS25942A, for a given situation, when e-fuse is limiting current and dissipating around 20W, it remain on for around 10ms, if I'm not wrong. I was studying TPS24751 hoping that it could have the same behavior but with mor dissipation capacity, but I realize that it allows current over the programmed limit and opens switch after a timeout, it does not limit the current, as we desire.

Do you recommend any device with current limiting behavior but that can withstand more time limiting current that TPS25942A? If not an e-fuse with integrated switch, any controller that can produce this behavior?

Thanks.

Hi Luiz,

It seems an external MOSFET solution may be needed.

If active current limit regulation is needed just during startup for inrush current, then TPS24700 may suffice.

If active current limit regulation is needed both during startup and during normal operation, then LM25069 would be recommended.

Each of these devices use an external sense resistor. LM25069 offers a second layer of protection - when the MOSFET has high Vds voltage, there is a separate MOSFET power dissipation regulation loop to keep the MOSFET safe.

If looking to design with either of these devices, I'd recommend reading the app note at "www.ti.com/hotswap" --> "Technical Documents" --> "Robust Hot Swap Design"

Thanks!

Alex