Hello TI,
Test setup:
We are using the following TI components on our PCB: LM7812 and LM7912
The LM7812 provides +12V and LM7912 for -12V which are supplied by +15V / -15V.
!! With respect to the used electrical circuit the output of the LM7912 (-15V) is connected to the output of the LM7812 (+12V) by using a diode.
The anode of the diode is connected to -12V. The cathode is connected to +12V.
Test procedure:
Step 1: Switch on -15V input voltage first.
Step 2: Switch on +15V input voltage.
Test result:
Unfortunately our test engineer found out that the +12V power supply drops to 0,8V.
If the diode is removed from the voltage regulators the power supply is stable.
If the test procedure is inverted the +12V power supply is stable, too.
QUESTION TO ST:
Can you explain this behavior ?
Why does the output voltage of the LM7812 depends on the power on sequence ?
Is there any protection mechanism of the device which is responsible for this behavior ?
Thank you !
