Best settings for used and unused pins in sleep mode with battery

XBee & XBee Gateway XBee - Hardware
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1

Hi, i’m developping a new design with Zigbee Xbee3 in MMT profile.

I’m currently coding pin settings with MicroPython, and i’m confused about how configure used and unused pins in sleep mode to achieve ultra low power consumption.

Digi Xbee3 documentation is not clear for me.

  1. How configure all NC pins ? Doc says digital output low but sometimes …
  2. Is it better or not to set NC pin as input with internal pull-down ?
  3. What is exact electricaly differences between “as input” and “disabled” with/without internal pull-up/down resistor?
  4. I control dynamicaly one mosfet P to power 1 or 2 sensors. This mosfet has a physical 100k pull-up resistor on gate for power down by default. What setting for this pin ?
  5. What best settings about ON/SLEEP output, ASSOC output, RSSI output, Commissionning input, and RST input pins ?

And finally … I have a FT230XS chip to communicate with Xbee3 and host via USB. This one is hardware connected with Rx, Tx, CTS and RTS and FT230XS is completly off without Vbus and USB cable.

How configure these 4 xbee lines when Xbee3 go to sleeping if Rx input of FT230 is floating and probably diodes protection present ?

Sorry for theses questions, hope you will help me :wink:

Best regards,

Syl

2

It is best to follow the manual. As indicated, set them NC pins as output low.

I am not sure I understand your 2nd question (3). You should not be using a NC pin as an Input.

What pin are you controlling your Mosfet? I would expect it to be an output high or low state to turn on and off your mosfef.

This lines should be set for output low.

3

Hi @mvut,

Ok for the NC pins, i wil follow the Digi docs, with digital output low.

For my other question, I thought that an NC pin or any other pins can’t draws current if I set as input high impedance and internal pull-down resistor.

The mosfet is a channel P and has 100k pull-up resistor between gate and Vcc, controled by DIO4. So I turn on this mosfet to power sensors by setting Xbee3 output to low. Turn off is the default state during xbee sleeping. What will happens if i put this output to high ?

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4

It will drive the line to a high state (3V).

5

Ok so, in this case what is the best for consumption during sleeping mode and let MOSFET off :

  • set DIO4 as Digital Output Hight to drive PWR_ON High
  • set DIO4 as Input floating with R9 pullup ?
6

No, set the DIO line as output low to power off the device.

7

Sorry but, if i want to turn off +3V3_on/off (on my graphic), i must to put PWR_ON from DIO4 to high during all sleeping time.

PS : it’s a mosfet channel P

8

I may have the direction off but the process is the same. You set the pin for output high or output low.

9

I have a PCB that I can get down to 90uA in sleep. I would suggest taking all pins that dont need to do something during sleep, like hold a FET off, to inputs. This lowers the current. Try a pull down or pull up resistor for pins that must stay outputs during sleep. I have 2 FETs on my PCB

10

Hi Jexx,

Can you explain more your application please ?

90uA the entire PCP, not xbee3 only ?

How do you manage your gate FET during sleep excacly ?

11

Yes, 90uA for the entire PCB during Sleep_Now(). Prior to going to sleep, I change the output pin for the FET to an input with pull up. I also have a 10K pullup resistor on the gate.

12

Ok !

And why put the internal pullup resistor if you have a phisically 10k pullup resistor ?

I suppose you tested 3 possibilities :

  • Input pin with or without pullup ?
  • Output digital high ?
13

I agree the internal pullup is not needed since I have a pullup resistor on the board. Output digital high has a higher sleep current.