TPS2121: tps2121 will restart under surging test

Hi Sammi,

Welcome to E2E!

The TPS2121 has a couple protective features besides the OVP that could potentially restart the device during transients like a surge test.

The first one I'd like to mention is over current protection. With the RILIM resistor you have set up you are setting your current limit threshold at about 2.25A. If the surge has a current above 2.4*ILIM= 2.4*2.25= 5.4A then the device will shutdown for 25ms and then will restart with the soft start feature.

The second one is OTP(over temperature protection). The TPS2121 has two over temperature protection features. It has relative thermal temperature protection and absolute thermal temperature protection. The relative thermal protection will be enable when the temperature of one of the FETS, IN1 or IN2 channel, rises 60 degrees Celsius above the rest of the die. If the TPS2121 is presented with a surge and the temperature of the FET rises 60 degrees Celsius above the temperature of the rest of the board the device will shutdown for 25ms and then will restart with the soft start feature. Absolute thermal protection is when the temperature of the whole die exceeds the absolute maximum specification. The device will shutdown for 25ms and then will restart with the soft start feature.

Does the customer know the amount of current and voltage that the device is being exposed to during this surge test?

tSET is configured internally and cannot be externally programmed by the user. What is the customers concern with tSET?

Best regards,

Andy Robles

This is the surge waveform, at the input of TPS2121, the waveform measured by oscilloscope, will TPS2121 be at the zero of the waveform, because the voltage is low to zero, TPS2121 has no output.Then, the above mentioned TPD2121 is the protection caused by overcurrent or overtemperature, may I ask how the undercurrent and overtemperature are generated, and is the over-temperature of 60 degrees is the protection temperature too low?

Hi,

Over-current and over-temperature occur in transients when the switch is attempting to turn on. Usually there will be an amount of inrush current going through the device to charge the capacitors at the output. Lowering the capacitance at the output can help mitigate the amount of inrush current. If even more current is being applied in the surge test it could also trigger the over current protection of the device. When a high current goes through the device it'll cause the pass FET to heat up. If the pass FET heats up 60C higher than the rest of the board the device is able to notice the difference in temp and shut the device down to avoid damage.

From the waveform it is a little unclear the magnitude of the voltage that is being applied to the TPS2121. Could you help clarify this?

Would they be able to capture a scope shot of the current being applied during the surge test?

By no output do you mean that all the output components shown in the schematic are removed or there is no load attached at the end of 12V0 at the output of the TPS2121?

Best regards,

Andy Robles

I'm having the same problem.  Is there a way to suppress the thermal cut out for troubleshooting? 

Hi Rich,

Over temperature protection of the device is internally programmed in the device and can't be cut out. I would suggest starting a new thread sharing as much information as you have available to that I may assist you in troubleshooting the application of the device.

Best regards,

Andy Robles