LM5066 Overcurrent Response Time?

Hi Allen,

The LM5066 has two threshold voltages for overcurrent.

One threshold (the current limit, CL, or ILIM) is selectable between 26mV and 50mV. When this threshold is crossed, the LM5066 has a regulation loop to control the GATE voltage to maintain this threshold. So the gate voltage will reduce, the FET Rds-on will increase until the regulation loop is stabilized. This could put the FET to operate with a large Vds voltage and power dissipation. During this time, a "fault timer" will begin to charge. When the fault time expires, then the device will pull down the GATE with a 4.2mA current source, so it may take a few hundred microseconds to shut off the FET. Overall the fault time is adjustable but must be set longer than the startup time unless a dv/dt circuit is used. To understand what that means, I recommend using this application note as a design guide:

www.ti.com/hotswap --> "Technical Documents" --> "Robust Hot Swap Design"

The second threshold is the "Circuit Breaker" threshold which is selectable around 1.9x or 3.9x the current limit threshold.

So for example, if you use the 26mV CL threshold and 1.9x for CB, then the CB threshold is 48mV.  If a short circuit occurs on the output then the voltage will exceed this threshold and the device will have a response time in microseconds, then begin to pull down the GATE with a strong pull down of around 160mA which should shut off in a couple microseconds.

We have some data for the LM5066I regarding the response time of the circuit breaker. It depends on how much overdrive signal is present. See the document attached below:

LM5066I_Response_Vs_Overdrive.pdf

Thanks!

Alex

Hi Alex,

Thanks for the response.

I guess I am asking how fast is the regulation loop that controls the current/power limit during non-circuit breaker events?

Thanks,
Allen