PIC18F97J94 Design Issues, Internal Voltage Regulator and External Crystal

Hello

I am starting with new project and would like to use PIC18F97J94 (100pin TQFP). Device will be used for communication with PC over USB or BLUETOOTH.

Device will be powered from USB power supply (+5V) or alternative battery supply (voltage from 4V to 9V). I will step-down any input voltage to 3.3V with LDO fixed linear voltage regulator, because all components (MCU, bluetooth module, led drivers, shift registers) works with 3.3V power supply.

I dont know what should I do with internal voltage regulator in my case? Do I need it or not? Since I already use external voltage regulator to deliver stable 3.3V power supply? How should I connect Vcap/Vddcore pin in this case (enable/disable internal voltage regulator)?

PIC18F97J94 also offers crystal-free setup and guarantee USB communication to work without external crystal. Since I dont want to use external crystal, what should I do with pins #61 (OSC1/CLKI/RP10/RA7) and #62 (OSC2/CLKO/RP6/RA6). Can those 2 pins be used as I/O pins instead?

- PIC18F97J94
- LDO voltage regulator Micrel MIC39100
- Bluetooth module WT12

I really hope someone can reply and answer all my questions
Thank you

Read the datasheet!

Vdd must not be supplied with a voltage larger than 3.3V, the on-chip regulator must be enabled for 3.3V Vdd. Means the LDO is needed in bus-powered operation, too.

Thank you for super fast reply!

I had been reading the datasheet for more than a week, but please understand I am not an expert so reading and understanding datasheet is not so easy for all people.

Vdd must not be supplied with a voltage larger than 3.3V

Click to expand...

Vdd for this PIC can be between 2.0V - 3.6V (according to datasheet), I am right? Like I said, I will be using external voltage regulator to step-down any input voltage down to 3.3V

So PIC will be powered with stable 3.3V and now I am confused why should I need internal PIC regulator and how to connect Vcap/Vddcore properly?

With 3.3V Vdd, you wire everything according to the "Regulator Enabled" scheme, see datasheet section 24.3 On-Chip Voltage Regulator.

Section 24.3? Operation During Sleep

Im sorry, in my datasheet, there is no schematic under section 24.3

https://www.farnell.com/datasheets/1701036.pdf

Sorry, I was referring to a different document. The respective explanations are in section 2.1-2.4.

The internal voltage regulator is always enabled, connecting a bypass capacitor according to the specifications is all you need to do.

Okay thank you. How about Vbat pin? Should it be connected to GND or Vdd or left floating?

Strange enough that the datasheet has no explicit connection suggestion for Vbat. I presume all three options are equally valid.