LTC3894 stops working and heats after short circuit

Question

Hello, 
 I use an LTC3894 as a current limiter. You can find the circuit below. Without load and with low load the output voltage follows the input voltage. The nominal working voltage is 48Vin = Vout. When the load increases the output voltage follows the input voltage minus a voltage drop due to the Rdson of the Pmos, Inductor resistor and shunt . Once the current reaches approx. 1.2A the LTC3894 starts limiting. We can increase gradually the load up to the short circuit and everything works well (1.4A limitation). 
 Problems start when output is suddenly short circuited... 98% of the time, the LTC3894 will work perfectly and limit the current at 1.4A. 
 The other 2%: 
 - During output short circuited: there is no current (normally 1.4A), the switch is not enabled and the LTC3894 starts heating up to 100&deg;C (The rest of circuit elements are cold) 
 - Once the short circuit is removed (no load): the output voltage stays at 2.8V (normally it should jump to 48V), the Mosfet is still not activated, and the LTC3894 is still heating at 100&deg;C... 
 There is no way to jump out of this state, even with other short circuits, even by reducing the input voltage below the undervoltage threshold... the LTC is blocked. 
 The only way is to cut the input voltage and supply 48V again. 
 As I said, the circuit works very well most of the time it also fits the simulations. 
 I hope that you have an Idea to help...

HortaR · Accepted Answer

Hello, 
 Just wanted to let you know that with help of local FAE, a solution has been found! 
 The problem is due to the negative voltage at output right after the short-circuit. You can see this in the previous scopes... 
 Adding a diode in parallel to the output capacitor prevents the output voltage becoming negative. This negative voltage seems to induce a latch-up through SENSE-, SENSE+ or PGOOD pin and disrupt LTC3894. 
 The origin of the negative voltage is due to the LC circuit created by the output capacitor and the output wire (approx. 2m) used to test short-circuit:

A diode with low VF should be used. I tried hundreds of short-circuits and it worked very well. 
 
 Thank you very much for your help!)

HortaR · Answer

Thanks, but I will not try a more complex chip. LTC3894 should do the job, in fact it does, but I think there is an internal issue that occurs during some short-circuits. My application needs to be reliable and I cannot trust this product. Without an explanation of what happen I will leave a side this circuit (and certainly most of Analog regulators).

HortaR · Answer

Hello dkb, 
 Thank you for the suggestion. I just tried it, but the problem still appears sometimes&hellip; 
 I attached captures of scope where you can see that there is no ringing on GATE terminal (the MOSFET is very close). Datasheet do not specify the maximum admissible voltage on GATE pin, but since VIN can go up to 150V, I suppose GATE can handle 150V. I am working at 48V&hellip; 
 
 I do not think the chip is damaged, it just jumps to an undefined blocked/self-heating state. Removing supply and power up again resets the problem, and it works again 98% of the time. 
 We have now an alternative circuit for our application. In case we reconsider LTC3894 in the future we will contact the local FAE.

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LTC3894 stops working and heats after short circuit