moonie223
Newbie level 4
Hello!
I am building a electronic module for use in a car, the main use is data transfer over canbus. The input power is ignition switched 12V, and I have two linear voltage regulators for 5V and 3.3V.
I have assembled my PCB successfully but for some reason I have linear regulators running well outside spec. I am using a NCV5501 for 5V, and a TLV73333 for 3.3V. The NCV5501 is powered by 12V, the TLV7333 is powered by the NCV5501. I also have a separate 20mA 3.3V linear regulator powered by constant 12v battery voltage, only for running "battery" backup for a GPS module.
I am measuring 5.4V from the NCV5501 and 4.0V from the TLV73333. I measure ~250mA of total input power Neither linear regulator gets too hot to touch although the 5V NCV5501 does get warm as expected. I only expected it to use ~2W in normal operation so nothing unmanageable. I measure 3.3V from the 20mA linear regulator as expected!
The GPS module and VR conditioner circuit appear to work properly. The Thermocouple, RS232 and ADC module are untested, I would like to figure out the 3.3V overvoltage before I hook up a microcontroller! I am without ideas for diagnosing why these regulators are running so far outside spec! I have read both datasheets from cover to cover twice. Is it possible I fried them both in reflow? I have a controlled oven and I had ~1:30 in preheat and soak at 150, ~20 in ramp, and ~40 seconds in 180-210C. I can't find specs in the TLV7333 datasheet, but this should be under max conditions according to the NCV5501. I also doubt heat is an issue as the smaller 20mA linear regulator is working fine!
Here is a picture of my schematic and PCB. Please excuse any messiness, my first time doing this!
https://i.imgur.com/v2PZ1BF.png
https://i.imgur.com/EREJTDs.jpg
Thank you in advance for any advise!
I am building a electronic module for use in a car, the main use is data transfer over canbus. The input power is ignition switched 12V, and I have two linear voltage regulators for 5V and 3.3V.
I have assembled my PCB successfully but for some reason I have linear regulators running well outside spec. I am using a NCV5501 for 5V, and a TLV73333 for 3.3V. The NCV5501 is powered by 12V, the TLV7333 is powered by the NCV5501. I also have a separate 20mA 3.3V linear regulator powered by constant 12v battery voltage, only for running "battery" backup for a GPS module.
I am measuring 5.4V from the NCV5501 and 4.0V from the TLV73333. I measure ~250mA of total input power Neither linear regulator gets too hot to touch although the 5V NCV5501 does get warm as expected. I only expected it to use ~2W in normal operation so nothing unmanageable. I measure 3.3V from the 20mA linear regulator as expected!
The GPS module and VR conditioner circuit appear to work properly. The Thermocouple, RS232 and ADC module are untested, I would like to figure out the 3.3V overvoltage before I hook up a microcontroller! I am without ideas for diagnosing why these regulators are running so far outside spec! I have read both datasheets from cover to cover twice. Is it possible I fried them both in reflow? I have a controlled oven and I had ~1:30 in preheat and soak at 150, ~20 in ramp, and ~40 seconds in 180-210C. I can't find specs in the TLV7333 datasheet, but this should be under max conditions according to the NCV5501. I also doubt heat is an issue as the smaller 20mA linear regulator is working fine!
Here is a picture of my schematic and PCB. Please excuse any messiness, my first time doing this!
https://i.imgur.com/v2PZ1BF.png
https://i.imgur.com/EREJTDs.jpg
Thank you in advance for any advise!