According to LT1236 datasheet, NC pin is connected internally. Where NC pin is connected internally ? How much the resistance is between NC and GND ? The customer measured it. One is 1.82kohm another one is only 1.57ohm. What's happened the IC ?
As additional info, there is a capacitor between NC and GND on the pcb because they used MAX6250 on their old version pcb instead of LT1236. Does the capacitor cause any problem ?
We have been reviewing this query for the last few days. We are awaiting some more information from the design team before we can answer. We will have an answer within the next few days for you. Thank you for your patience.
After reviewing LT1236 schematic, these NC pins are internally connected and are used for factory trimming. This means, resistance measurement can vary within NC pins and from part to part.
Capacitance connected to NC pin can affect the trim precision. Therefore, NC pin should be left floating/no connect.
Thank you very much for your support.
The customer continue to use LT1236 with the capacitor over 10 years but the resistance issue occurs recently.
What is difference between recent IC and previous IC ? We have to ask QA division ?
There is not any recent change introduced to LT1236. If there is any change within mask or design, customer will be notified through ADI PCN system.
I would suggest customer to leave NC pins floating/no connect.