TPS3307: Stuck in reset at cold temp

Hi Mark,

Is this a new application for the customer?  Have they used this part before and if so, had they seen this issue before?  Is it possible for you to obtain the lot number of the parts that are failing at cold?

It is possible that having the SENSE pins being above VCC+0.3V can be causing the reset pin to be stock low.  Can the customer drive the SENSE pins a little lower in voltage when testing at cold to see if the output can deassert?

Anytime a customer violates a spec, we cannot guarantee the performance of the product especially when the pins are experiencing an overvoltage event.  It is difficult to quantify when the part will eventually damage itself from excessive voltage.

Ben

Hi Ben,

Thanks for the comments. I will try to get answers to your questions on the lot number.

Regarding the overvoltage,  the resistive dividers on Sense1 and Sense 2 input circuits will limit the voltage and current through the clamp diodes under an over voltage condition. Even if we assume the full 48V is seen on the Sense1 input with VCC = 0V, the current will be limited to 0.8 mA, well below the max clamp current of 20 mA. It seems that the device would survive this condition without damage.  More likely, the 60k resistor might be a concern depending on its current rating. Would you agree?

The customer may be able to work around the stuck reset condition, but is worried that if the TPS3307 fails or is damaged, it might damage something else on the circuit board. For example, if the overvoltage leads to a VCC short, this would impact the rest of the circuit. Do we have any idea how an input voltage overstress may manifest itself in a device failure? 

Hi Mark,

Your overvoltage comment is correct regarding the input resistors will limit the current through the clamp diodes (ESD devices) but the high voltage can stress the internal transistors that are connected to the SENSE pins.  Again, going above the abs max ratings is not recommended and may permanently damage the unit.  So, the clamp diodes (ESD devices) may survive but other parts in the IC may be damaged by the high voltage.

Help me understand that if the /RESET pin is stuck low, it may damage something else on the circuit board.  The /RESET pin is low and should prevent any down stream devices from turning, correct? 

Input voltage overstress may create a device failure over time which is hard to determine.  When transistors are voltage over stress, for example, the oxide of the devices become weak over time because of hot-carrier injection.  In time, the device degrades to a point of failure, and it is anyone's guess the type of failure can come from overvoltage stress.  I can imagine that the /RESET pin may be stuck in a logic high or low, maybe a shoot-through current event occurring internally to the IC, or permanent IC damage making the TPS3307 non-functional.

I hope I have answered your questions.

Ben  

Hi Ben,

This is helpful. On the /RESET stuck low concern - there is a SW work around for the TPS3307 reset being stuck. The work around does not use the supervisor's Reset output to actually reset the system, it's used more as a warning. Thus down stream devices are not shut down due the TPS3307 Reset signal. 

Hi Mark,

Keep me updated if there is anything new.  

Ben