data/text/DLP2/891457

TPS62745: TPS62745

Part Number: TPS62745 Hello, We are facing similar situation. Vsel was connected to Vin (design error), powered by batteries higher than 6V and some devices are damaged. Would be possible to share the squematic internally and go deeper on the severity of this problem? Thanks in advance. BRs,

Igor, It is probably difficult at this time. We can only recommend that teh abs max rating be observed. I will contact our design team about internal details. For sure it will require an NDA to share any details.

Igor, These pins connect two to pieces of internal circuitry: 5V ESD clamp, and inputs of 5V CMOS logic gates running on an internal rail. The obvious mechanisms of damage that I can foresee from over-voltage on these pins include: · Damage to pin metallization or ESD clamp due to triggering of ESD cell. This could cause functional issues with the VSEL signaling, as well as other possible issues if reflowed metal shorts to nearby circuitry. This type of failure would be immediate when the overstress occurs. In my estimation the risk of this kind of failure is low if the pin voltage stays below 7V, since the nominal trigger point for the ESD clamp is above 11V. · Damage to the gate oxide of the ESD cell or the CMOS logic gates. This could cause functional issues with the VSEL signaling, as well as other possible issues if the high current flowing through the failed oxide loaded down the internal rail or caused reflowed metal shorts to nearby circuitry. This type of failure has increasing probability of occurring as the time of exposure to over-stress increases. The risk for this failure is also low if the pin voltage stays below 7V. Our model for this kind of failure mechanism predicts less than 1 failed unit per billion after 100k operating hours at the worst case temp of 150C as long as the voltage never exceeds 7V (including transients, ringing, etc). Of course, this assessment should not be taken as any kind of guarantee of results for the customer. I have considered the most apparent mechanisms of failure under this application’s conditions, but this kind of analysis isn’t foolproof. It’s possible that there could be another mechanism or issue that I have not caught, which is why we qualify and specify the components and circuits within a given range. That more rigorous process yielded the abs max specs that are being violated.

Thanks for your complete and so deep reply John. It seems that our board don´t have to face many problems working below 7V (maximum 1 per billion). After your answer, we have tested today 200 boards, just connecting 6,3 V Lithium battery, and 28 units are damaged, so current consumption increases 10-100 times. After changing TPS62745 regulator it works fine returning to the normal current consumption. So, do you think there is another possible problem, maybe on our schematic? Or could be possible to be a batch problem on these regulator, I don´t think so, but do you have any information about it? Thanks in advance.

Igor, There are no lot quality issues that I am aware of.

Hello John, Thanks for your answer. So, if we are working under any probed specifications, there is no explanation for having to replace your regulators on some of our devices in order to work properly. If you are able we can share our schematic with you, maybe there is something wrong that we cannot detect. BRs,

Igor, if you post your schematic, I will review it.

Hello John, Attached you can find schematic referred to TPS62745. Where D1, D2 and T4 are not mounted. So J2-battery power go directly to R2 0 ohm. 6V lithium battery is connected to J2 in normal activity (initially 6,5 V). In parallel 3V3 are applied to Vout from TC1 connector when device is programming. Sometimes could be 3,4 - 3,5 V. Can you see any issue on that schematic? Thanks in advance. BRs,

Igor, If you apply an external 3.3 V to the output of the TPS62745, and the battery is not connected the high side body diode can conduct and you may possibly have enough voltage at the input to allow the device to start switching. Can you check it in that condition?

Hello John, I have checked what you said and there are 0,25 V on the high side body diode along the range of 2-4V applied externally on Vout / SW pins. So, in normal situation, when we apply external 3,3 V at the V output we have 3,05 V at Vin pin. If we apply external 3,4 --> 3,15 V at Vin If we apply external 3,5 --> 3,25 V at Vin So, it could be a problem to damage the chip? Thanks BRs, Igor

Igor, Do you see any switching activity on the SW pin? Is EN tied low?