TPSM33625: Output Voltage Drop

Hi Rahil-san,

Thank you for your support.

In the customer's circuit, the output voltage drops by 1.7V during load fluctuation. Does this IC drop by 1.7 V when a load transient occurs? Also, does switching stop or stop during load transient?

I will suggest the rating of the input capacitor to the customer. If there are any other possible causes, please let me know.

When I contacted the voltage probe to the SW pin, the symptom was improved. Am I correct in understanding that we should not add a capacitor to the SW pin?

Best Regards,

Nishie

Hi Nishie,

The voltage drop is not normal. 

It is possible that the part is overheating and the voltage probe is acting like a heatsink. Is the part getting very hot? Can you try adding airflow to see if that 2.5ms drop gets better? 

Regards,

Rahil

Hi Rahil-san,

If this voltage drop is not normal, is it possible that the protection is working?

In terms of temperature, if the heat protection works, does it return to the original voltage within 2.5ms after the voltage drop occurs? In the case of heat protection, we assume that it takes a little more time for the voltage to return to its original state.

Best Regards,

Nishie

Hi Nishie-san,

It might be some kind of protection but the buck returns to normal operation after the drop so not sure what is causing it.

If thermal are improved (with airflow or heatsink) and there recovery takes less than 2.5ms, we can conclude if it is a thermal issue

Regards,

Rahil

Hi Rahil-san,

I changed the breakdown voltage of the I/O capacitor you told me before to 50V. The voltage drop has been improved a little, but it has not been solved yet. Is there anything else you are concerned about in the circuit diagram?

Regarding the countermeasures against heat, the phenomenon is more likely to occur as the temperature of the IC is lower. If the temperature of the IC is about 40°C higher than normal temperature, the occurrence frequency will decrease.

Also, is it possible to use the TPSM33625 ORing? If a voltage drop occurs in one TPSM33625, do you think switching the output to the other TPSM33625 will be a countermeasure?

Best Regards,

Nishie

It is possible to OR it but we should fix the problem.

Did you try swapping the IC? It is possible that just that one IC is defective. 

Regards,

Rahil

Hi Rahil-san,

I found that ORing is possible. I would like to know the measures to solve the problem. If there is anything we should check other than ABA swap, please let us know.

I have not been able to perform proper ABA swap on the customer side, but we have taken the following measures.

・The customer placed the IC mounted on EVM on the circuit board where the voltage drop occurred and checked the operation.

->The voltage drop was suppressed considerably. The customer tried to measure the waveform by supplying power several times, but the IC broke, so they could not measure the waveform.

・The customer mounted the IC mounted on the circuit board where the voltage drop occurred on EVM and checked the operation. The voltage drop did not occur until the load current reached about 3A.

Best Regards,

Nishie

HI Nishie-san,

To clarify... IC had saw voltage drop on customer board. Then the same IC was put on EVM and got damaged?

What  IC was put back on customer board? Damaged or new?  

Regards,

Rahil

Hi Rahil-san,

The IC mounted on the EVM was damaged. When the EVM IC was mounted on the customer's board and checked for operation, this IC was damaged.

The customer's board currently has another IC that is not damaged.

Best Regards,

Nishie

Hi Nishie-san,

It could be a layout related issue. Could you please share the layout?

Regards,

Rahil

Hi Rahil-san,

We are closing this case because we no longer have the resources to devote to customer design. Thank you for your support.

Best Regards,

Nishie