Minimum power modes for PIC18LF4620

[duncan303]

Hi BrianT,

I have recently been reading the datasheets on the 18F2420 with regard to power modes and battery power. it is something I have not done before.

I thought I might start experimenting with a lower class of chip with less features to help me understand how the different power features work. but in the back of my mind I keep thinking why should i use the BOD feature in the chip and not implement an external power monitor circuit, and convey the info to the MCU, possibly to prevent writing to the external eeprom.

I am waaay behind you though, just sharing a first few thoughts.


Duncan

[BrianT]

Table 26.2 shows what peripherals draw.

4.6 uA for the Watch Dog Timer,
40 uA for the Brown Out Detector,
40 uA for the High/Low Voltage Detector,
4.5 uA for the Timer1 Oscillator
2 uA for the Analog to Digital Converter.

Every time the battery goes flat the PIC18LF4620 scrambles the code space (and corrupts the bootloader) so I was going to try the BOR or the HLVD but the current draw is unacceptable. My next PCB layout will have ICSP pins so I can try the Code Protect option which I don't think allows a bootloader.

I think I am right in saying the PBP SLEEP command needs the WDT to be active so that sets a minimum current around 4.6 uA unless there is some other way of getting to the fabled 100 nA mentioned in the Microchip literature.

Any thoughts on how to IDLE or SLEEP the PIC18LF4620 at 100 nA, AND still be able to wake from this comatose state, would be most welcome.

Cheers
Brian

[Archangel]

Hey BrianT,
Greetings !
Those are some mighty tiny power figures, is there any chance you might be able to augment your power with a small (pocket calculator type) solar panel? Or maybe use a smaller device to power up that big 18F device as a supervisor circuit?
JS

[skimask]

Every time the battery goes flat the PIC18LF4620 scrambles the code space (and corrupts the bootloader) so I was going to try the BOR or the HLVD but the current draw is unacceptable. My next PCB layout will have ICSP pins so I can try the Code Protect option which I don't think allows a bootloader.

I think I am right in saying the PBP SLEEP command needs the WDT to be active so that sets a minimum current around 4.6 uA unless there is some other way of getting to the fabled 100 nA mentioned in the Microchip literature.

The '4620 has A/D. You could occasionally sense your own Vdd voltage with an extra diode or voltage divider circuit.
As far as the 100nA goes, I know microchip has a couple of really good app notes for that...I can't remember what or where they are though...