Gate signal not coming from LM5050

Dear All,
Kindly need your valuable reply, Customer telling it looks like it happening after they try short circuiting the output.


Aravind.

Hi Aravind,

The LM5050 does not offer short circuit protection. When the output is shorted, current will flow through the FET if its on or otherwise through the FET's body diode.

But if they are doing short circuit testing and have a device which will open (either a fuse or FET), then there could be a fast change in current from high to zero (or a large di/dt). This di/dt will create voltage transients due to trace inductance and V = L * di/dt. These voltage transients could be large enough to exceed the ABS_MAX voltage rating of the LM5050 IC or other surrounding components (such as the FET's Vds rating).

Often in ORing controller and hot swap design, transient protection devices such as a TVS is used to clamp positive voltage spikes and a schottky diode to clamp negative voltage spikes.

If they are shutting off forward current (short circuit is on the output), then a positive voltage transient will occur on the input (and a TVS should be added here to clamp) and a negative voltage transient will occur on the output (and a schottky diode should be added here to clamp).

If they are shutting off negative/reverse current (short circuit is on the input), then everything is reversed. The positive transient will be on the output and the TVS should be there, and a negative transient will be on the input and a schottky should be added there.


If it is not related to transient protection, another topic could be whether there is load current when they are testing. The LM5050 is a linear regulation controller. If there is low current on the output, it will reduce gate drive voltage until the Rds-on of the FET increases and the forward voltage drop is 22mV (typ). So if they are using a 10mohm FET, they should load the output with 2-3A to see if the GATE voltage rises.

I would also recommend obtaining the LM5050 EVM to test functionality.

Finally, if this is a solar application, be sure to check out the SM74611 which is specifically geared towards photovoltaic applications.
www.ti.com/.../SM74611

Thanks!
Alex

Dear Sir,

Thanks. Feedback was very helpful. Once customer tried short circuiting the output, because of reverse current , LM5050 stopped giving gate signal to FET, if the short is removed in output-will LM5050  return back to its normal operation of giving gate signal to FET. customer telling it is not recovering back, once they replace current LM5050 with another LM5050 IC only it is working. kindly need your valuable advise

 

 

Aravind.

Hi Aravind,

The LM5050 does not shut off the MOSFET if the output is shorted. It will shut off the MOSFET if the input is shorted. This is because the LM5050 is an ORing controler, so it only shuts off reverse current, not forward current.

If they need a device that will protect an output short circuit and then recover, then they should consider a hot swap controller such as the LM5069.

For example this TI Design of a LM5050 and LM5069 combo may be of interest:
www.ti.com/.../TIDA-00233

If the circuit is functioning fine except that the IC is breaking from a short circuit test, then they may need transient protection clamp devices such as a TVS on the output and a schottky diode on the input. The size (current/power rating) of these devices depend on the current of their application, and what the Rds-on of the external MOSFET is.

Is the application a bypass diode for photovoltaic panels? If so, then a SM74611 may be a better choice. The SM74611 has a wide operating range and can handle negative transients, so it may not need these clamp devices. This device is very simple: it is "pin-pin" compatible with a standard D2PAK high schottky diode:
www.ti.com/.../sm74611.pdf

Thanks!
Alex

Dear Alex Sir,

Thanks for your feedback - it was useful. I have checked with customer and got complete info as below, please help to advise your inputs.

Customer using LM5050 controller to use MOSFET as diode. They are facing an issue where in the controller gets damaged when the load is short circuited. They have only battery connected. There is no input being fed. Their short circuit protection circuitry continues to work.  There is a FET after this diode D1 which is fine but LM5050 connected to diode  D1 is getting damaged always.  Sometimes even the MOSFET which acts as diode D1 is also getting damaged.

Kindly please advise how to go about resolving it.  Need your valuable inputs sir. Attached handsketch of circuit diagram for your kind reference.

 

Rgds,

Aravind.

Hi Aravind,

Thanks a lot for the diagram, it helps a lot!

If I understand correctly, they have the BAT connected, the load is a short circuit, and they have a short circuit protection switch (fuse/electronic fuse/MOSFET) which opens in that condition?

So the path of discharge is as follows:

And after the fet/fuse/switch opens, the LM5050-1 connected to D1 is getting damaged, sometimes the D1 MOSFET itself?

I will think it through some more and discuss with our team but first want to make sure we understand the setup.

Also, is that device on the BAT line a TVS or a schottky diode? And can you provide the part number?

Thanks!

Alex