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LTC3894 stops working and heats after short circuit

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°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°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...

Parents Reply
  • My application has a large LC filter before Vin = 48V.
    With a fast transient before the filter, Vin becomes slightly negative and the IC blows-up.
    Probably by SENS+, SENS- lines (had no series-resistors) discharging the 220uF output capacitor (Vout = +32V). 
    I'll add anti-parallel diodes on Vin and Vout & redo my tests.
    The freewheel diode on Lout in series with pFET body-diode would also act as anti-parallel of -2V, but the IC-spec = -0,3V.

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