TPS2331 Overcurrent Issues

1)  How is CTIMER reset when the current ceases to exceed the overcurrent threshold? 

CTIMER is set by a current source. Comparators in the chip shut down the charging.

 What would this time constant be (approximately) for CTIMER of 5.6nF? 

From the V, I relationship for a capacitor and a 50uA charge rate to 0.5V, I = C dv/dt, so T = C x V / I, T = (5.6nF x .5V)/50uA. = 56uS

2)  In the same application, if I force an inrush of ~30A for ~50us and have a current limit of 30A, I "often, but not all the time" get the situation where the TPS2331 disables the pass FET after the 50us overcurrent timer (CTIMER is 5.6nF) BUT does not latch off.  This conflicts with the behaviour described in datasheet.  Approximately 200-400us later, the FET is re-enabled.  Subsequent over-current conditions as high a 60A for 100us do not cause CTIMER to charge and no fault is found.  Cycling the input power "resets" the TPS2331 and the next overcurrent cycle behaves properly.  Is there anything that could explain this behaviour?

Do you have some decoupling like 0.1uF across the TPS2331? I wonder if voltage spiked down to 2.75V and it stayed in UVLO? Can the power supply hande these high test loads and inrush?

the TPS2331 has been destroyed during a power transient (confirmed in 2 cases to have occurred during loss of input power).  The "crater" in the package occurs nearest the pin 7/8 end of the TSSOP14.

The TPS2331 has a VIN Max of 13V. This isn't much overvoltage in a 12 V system especially a high current system where even small inductance in the input voltage can on either make or break create a voltage spike.

Bob Kando said:

1)  How is CTIMER reset when the current ceases to exceed the overcurrent threshold? 

CTIMER is set by a current source. Comparators in the chip shut down the charging.

 What would this time constant be (approximately) for CTIMER of 5.6nF? 

From the V, I relationship for a capacitor and a 50uA charge rate to 0.5V, I = C dv/dt, so T = C x V / I, T = (5.6nF x .5V)/50uA. = 56uS

JM -- I undertand how CTIMER is charged.  What I am trying to understand is how CTIMER is discharged when the fault is cleared.  It can't be simply "shutting down the charging" as I can clearly see the CTIMER votlage falling to zero much more quickly than the charge time (which is 56us).

2)  In the same application, if I force an inrush of ~30A for ~50us and have a current limit of 30A, I "often, but not all the time" get the situation where the TPS2331 disables the pass FET after the 50us overcurrent timer (CTIMER is 5.6nF) BUT does not latch off.  This conflicts with the behaviour described in datasheet.  Approximately 200-400us later, the FET is re-enabled.  Subsequent over-current conditions as high a 60A for 100us do not cause CTIMER to charge and no fault is found.  Cycling the input power "resets" the TPS2331 and the next overcurrent cycle behaves properly.  Is there anything that could explain this behaviour?

Do you have some decoupling like 0.1uF across the TPS2331? I wonder if voltage spiked down to 2.75V and it stayed in UVLO? Can the power supply hande these high test loads and inrush?

JM -- The TP2331 Vin is decoupled with 0.1uF to GND (I attached my schematic to the original post).  In this particular test I am certain that Vin stayed at 12V (I had it on the scope too).  That wouldn't really explain why the TPS2331 returns to life but ignores subsequent overcurrent conditions.

3) the TPS2331 has been destroyed during a power transient (confirmed in 2 cases to have occurred during loss of input power).  The "crater" in the package occurs nearest the pin 7/8 end of the TSSOP14.

The TPS2331 has a VIN Max of 13V. This isn't much overvoltage in a 12 V system especially a high current system where even small inductance in the input voltage can on either make or break create a voltage spike.

JM -- I can't say with any certainty that the main power supply did not exceed 13V, but I suspect it would not as it is generally well behaved and is spec'd at 12V +/- 5%.  It is capable of source 60A before it folds back.  I am not sure if the position of the crater is any indication as to what on the die overheated.  However, The main power supply is wired through about 12" of qty 24 of 18AWG wires, so there would be some very small input inductance.  I guess it is possible that if the TPS2331 shut down the FET properly (the current would have ceased) that Vin would have spiked above 13V due to the wire inductance flipping the voltage.  I guess that makes sense.