DS14185: 12V supply current at Startup with 5 V applied to 2 pins and 3 pins

Takashi-san,

It looks like there is a shoot thorough current during power ramps up when Rin is high. Can you check if the current is related to the ramping speed? Can you also provide V- condition, like was it ramping down symmetrically as V+? Since it's an old part, it may take some time to dig out the information. My wild guess is the internal circuitry are in unknown state when V+<9V. I'll try to see if I can duplicate the result in the lab as well. Other option would be to try SN75LP1185, which is pin-to-pin compatible. Thanks, 

Hi Hao-san,

Thanks for your prompt response on this.

I'm just asking them what you want now. Let you know when I get additional information.

According to the customer, they seem to see some voltage at -12V power supply when applying 5V at Pin2 and Pin3. There might be diode pass or something between -12V supply and these pins under no power condition.

Regards,
Takashi Onawa

Hi Hao-san,

I talked with the engineer, and I clarified what we should be clear today. Please forgot the capture I attached at the first. According to the engineer, it seems that leakage from -12V pin causes this unexpected behavior anywhere in their system. So, they want TI to check whether the leakage from -12V pin is an inherent behavior of DS14185 or not.

Can you check that  there is leakage from those pins to -12V supply pin with no power condition  soon?

> According to the customer, they seem to see some voltage at -12V power supply when applying 5V at Pin2 and Pin3.

>There might be diode pass or something between -12V supply and these pins under no power condition.

And let me know how long it takes. They need to tell the schedule to clarify the cause of this issue to their end customer.

Regards,

Takashi Onawa

Takashi-san,

I will get the parts around mid of next week. So the earliest time I can get results would be then. In the meantime, can the customer check their board condition? According this thread, e2e.ti.com/.../493921, some customer used the similar power up sequence, but didn't have problem. Thanks,

Hi Hao-san,

Thanks for taking the data quickly.

Did you measure the data with shorting Pin3 and Pin2 each other? Or measuring each pins to -12V pin?
If you measure the data each pins to -12V pin, could you try same check with shorting Pin3 and Pin2 also?

The customer is expecting the leakage causes short condition somewhere in power block on their board. So it's enough for them to solve this issue if they get the information so far.

Also, I need to hand in a report about the leakage to the customer by the end of this week. The report should contain :
- Experimental setup
- Result( with some captures )
- The leakage from Pin 2 or Pin3 to -12V pin with no power condition
- The leakage from shorting Pin2 and Pin3 to -12V pin with no power condition

Could you tell me your experimental setup and share some captures to write the report?
If you want to share it on offline, please send e-mail to me.

Regards,
Takashi Onawa

We are talking on this on offline and I close this thread.

Regards,
Takashi Onawa