Thank you in advance for your assistance. Following is a breif description of our application:
This LDO will be part of a circuit we use that will include a PIC Microcontroller (10F202) . We program the PIC serially after the circuit board is fully assembled. During normal operation the PIC supply voltage can be between 2.0 and 5.5 VDC. This fits perfectly with your LP2980 3.3v unit, however… during programming, the PIC Vdd must be at a minimum of 4.5 VDC. We would incorporate a 5-volt regulator in our programming fixture to supply 5 volts to the PIC Vdd and this would also put the 5 volts at the output pin of the LP2980 (only during programming). Our concern is the we need to put a Schottky diode across the output and input pins of the LP2980 as shown on page 11 of the data sheet to protect the LP2980. The input pin of the LP2980 will not be connect to supply voltage during this programming operation, but the LP2980 ground (-DC) pin will be connected to circuit ground. Our plan is to use a BAT54 or BAT750 (lower Vf) for this Schottky diode, but our concern (possible unfounded) is that with the Schottky diode anode on the LP2980 output (at 5-volts) and the cathode at the input, this will allow 5-volts (minus the Vf od the diode) to be at the LP2980 input. As a result this input voltage will cause the LP2980 to act as a regulator and put 3.3-volts on the output (which would already have 5-volts there) We're concerned that forcing the regulator output to a higher voltage than it is designed to provide could damage the regulator. Is this concern valid?
We don't want to have a secondary soldering operation to add a jumper, etc. after the board is assembled and the PIC is programmed.
Again, thank you for your time and any assistance you can provide.
Best regards,
Tim